PHSE 621 PAC

GEVORDERDE CHEMIE VIR ONDERWYS II
STUDIEGIDS VIR
PHSE 621 PAC
*PHSE621PAC*
FAKULTEIT NATUURWETENSKAPPE

Studiegids saamgestel deur:
Dr J Röscher
Bladuitleg deur Justus Röscher, Skool vir Fisiese- en Chemiese Wetenskappe
Hantering van drukwerk en verspreiding deur Departement Logistiek (Verspreidingsentrum)
Gedruk deur Platinum Press (018) 2994226
Kopiereg 2012 uitgawe. Hersieningsdatum 2013
Noordwes-Universiteit, Potchefstroomkampus
Kopiereg voorbehou. Geen gedeelte van hierdie boek mag in enige vorm of op enige manier
sonder skriftelike toestemming van die uitgewer weergegee word nie. Dit sluit in
fotokopiëring van die boek of gedeeltes van die boek.
ii

Inhoud
Inligting oor die module v
1. Inleiding v
2. Module-uitkomste v
3. Inligting oor die dosent vi
4. Studiemateriaal vi
4.1. Voorgeskrewe handboek vi
4.2. Study material included in the study guide vi
5. Aksiewoorde en die aard van nagraadse studie vii
6. Werkswyse viii
Afwesigheid viii
7. Assesseringsinligting viii
7.1. Formatiewe assessering [Kontinue assessering] viii
Deelnamepunt ix
Deelnamebewys ix
7.2. Summatiewe assessering [Eksamen] ix
Modulepunt [finale punt] ix
8. Hoe om hierdie studie aan te pak ix
9. Kurrikulum x
10. Waarskuwing teen plagiaat xi
1. Die omgewing en omgewingsprobleme 1
1.1. Die omgewing 1
1.1.1. Inleiding 1
1.1.2. Studiemateriaal 1
1.1.3. Self-evaluering 1
1.2. Omgewingsprobleme, hul oorsake en volhoudbaarheid 1
1.2.1. Inleiding 1
1.2.2. Study material 2
1.2.3. Self-evaluation 2
1.3. Ekosisteme – wat dit is en hoe dit werk 2
1.3.1. Studiemateriaal 2
1.3.2. Self-evaluering 2
2. Chemie en die omgewing 3
2.1. Waarom chemie omgewingsprobleme veroorsaak 3
2.2. Omgewingschemie 4
2.2.1. Inleiding 4
2.2.2. Studiemateriaal 4
2.2.3. Self-evaluering 4
2.3. Elementêre biochemie en toksikologie 4
2.3.1. Studiemateriaal 5
2.3.2. Self-evaluering 5
2.4. Groen chemie 5
2.4.1. Inleiding 5
2.4.2. Studiemateriaal 5
2.4.3. Self-evaluering 5
3. Chemie en die atmosfeer 7
3.1. Inleiding 7
3.2. Die atmosfeer en lugbesoedeling 7
3.2.1. Studiemateriaal 7
3.2.2. Self-evaluering 8
3.3. Klimaatontwrigting en osoonvernietiging 8
3.3.1. Studiemateriaal 8
3.3.2. Self-evaluering 8
iii

4. Chemie en die hidrosfeer 9
4.1. Inleiding 9
4.2. Waterbesoedeling 9
4.2.1. Studiemateriaal 9
4.2.2. Self-evaluering 9
4.3. Watersuiwering 10
4.3.1. Studiemateriaal 10
4.3.2. Self-evaluering 10
5. Chemie en die litosfeer 11
5.1. Inleiding 11
5.2. Geologie en mineraalbronne 11
5.2.1. Studiemateriaal 11
5.2.2. Self-evaluering 12
5.3. Basiese beginsels van mynbou en die ekstraksie van metale 12
5.3.1. Studiemateriaal 13
5.3.2. Self-evaluering 13
iv

1. Inleiding
Inligting oor die module
Hierdie module is 'n inleiding tot omgewingschemie. Om die belang van hierdie veld te verstaan,
behoort studente 'n basiese begrip van en waardering vir die omgewing te hê. Omgewingschemie is 'n
multidissiplinêre veld wat gebruik maak van agtergrond vanaf ander dissiplines, soos byvoorbeeld
chemie, biochemie, mikrobiologie, toksikologie, geologie, geografie, plantkunde en dierkunde. Waar
moontlik sal Suid-Afrikaanse omgewingsprobleme uitgelig word, insluitende 'n bespreking van die
mynboubedryf in Suid-Afrika. Die module sluit af met 'n toekomsperspektief oor die rol van chemie in
die industrie en gemeenskap. Omgewingschemie verskaf 'n ryk verskeidenheid kontekste en
toepassings van chemie as gevolg van die multidissiplinêre aard van die vakgebied. Kennis en begrip
van omgewingschemie kan grootliks bydra tot die vermoë van die fisiese wetenskappe onderwyser om
die toepassings van teoretiese chemiese beginsels in die "werklikheid" te verstaan.
Omgewingschemie is multidissiplinêr en daar sal dus van die onderwyser verwag word om
verskillende chemiekonsepte met mekaar te skakel en sodoende kognitiewe strukture te bou wat
nodig is vir helder begrip. Die kennis en vaardighede wat in hierdie module verwerf kan word, sal die
fisiese wetenskappe onderwyser in staat stel om chemie teorie in 'n omgewingskonteks te plaas en
sodoende die leerders help om die relevansie en toepasbaarheid van chemie te begryp.
Hierdie module aanvaar dat u 'n basiese agtergrond van chemie in u vorige studiejare verwerf het. Die
kredietwaarde van die module is 16 en daar word dus verwag dat u ongeveer 160 ure benodig om die
studie te voltooi. Hierdie geskatte studietyd sluit voorbereiding, praktiese werk en assesseringstake in.
Ek hoop dat hierdie module u begrip van chemie in konteks merkbaar sal vergroot.
J. Röscher
April 2012
2. Module-uitkomste
Na voltooiing van hierdie module behoort studente die volgende te kan aantoon.
Omvattende kennis en insig oor 'n wye verskeidenheid nuwe asook bekende konsepte, beginsels,
wette, teorieë en modelle wat deel uitmaak van chemie in die skoolkurrikulum of wat die
effektiewe ontwikkeling van hierdie vakgebied ondersteun.
Die vermoë om probleme binne die multidissiplinêre veld van omgewingschemie op te los deur
kennis van uiteenlopende temas binne chemie en ander vakgebiede te integreer.
Die vermoë om leerders se idees oor geselekteerde konsepte wat omgewingschemie onderlê te
analiseer en evalueer en hierdie idees te verfyn deur implementering van konstruktivistiese
onderrig.
Die vermoë om by te dra tot kritiese en sistematiese denke oor die invloed van wetenskap en
tegnologie op die samelewing en die omgewing.
Basiese laboratoriumvaardigheid en die vermoë om effektiewe praktiese aktiwiteite op skoolvlak te
beplan en aan te bied.
v

Inligting oor die module
3. Inligting oor die dosent
vi
Naam van dosent J Röscher
Kantoornommer en gebou Kantoor G16, Gebou G5
Telefoonnommer 018 299 2333
Faksnommer 086 686 4997
E-pos 10091858@nwu.ac.za
4. Studiemateriaal
4.1. Voorgeskrewe handboek
Miller, GT and Spoolman, SE, 2012, Living in the environmental, 17 th ed., Brooks/Cole.
4.2. Studiemateriaal ingesluit by hierdie studiegids
Uittreksels van die volgende boeke is ingesluit in die bylae aan die einde van die studiegids.
Bylaag 1: Manahan, SE, 2003, Toxicological chemistry and biochemistry, CRC Press, Boca
Raton.
Bylaag 2: Clark, JH and Macquarrie, D, 2002, Handbook of Green Chemistry and Technology,
2 nd ed., Blackwell Science: Oxford.
Bylaag 3: Baird, C and Cann, M, 2008, Environmental chemistry, 4 th ed., W. H. Freeman and
Company: New York, NY.
Bylaag 4: Matthews, P, 1992, Advanced chemistry, Cambridge: Chennaice: Oxford.
Bylaag 5: Hill, JW, Petrucci, RH, McCreary, TW and Perry, SS, 2005, General chemistry, 4 th ed.,
Pearson: Upper Saddle River, NY.

5. Aksiewoorde en die aard van nagraadse studie
Inligting oor die module
Volgens Bloom kan kognitiewe vaardighede in 'n hiërargiese stelsel georganiseer word wat strek
vanaf kennis aan die onderpunt tot evaluering aan die bopunt via begrip, toepassing, ontleding en
sintese. In nagraadse studie verskuif die klem van studie na hoërorde kognitiewe vaardighede.
Gevolglik vereis studie-aktiwiteite die geïntegreerde gebruik van meerdere vlakke van kognitiewe
vaardighede deur die student. Die aksiewerkwoorde wat in hierdie module gebruik word, is ‘n
aanduiding van die kognitiewe vlak van die betrokke handeling, soos onder aangedui:
Kognitiewe vlak Aksiewoorde Verduideliking
VLAK 1:
KENNIS
VLAK 2:
INSIG
VLAK 3:
TOEPASSING
Definieer
Beskryf
Lys, Skryf, Gee, Noem
Verduidelik, Bespreek
Illustreer
Onderskei, Vergelyk
Som op
Bepaal
Bereken
Stel meganisme voor
VLAK 4:
ANALISE Analiseer, Bespreek
VLAK 5:
SINTESE
VLAK 6:
EVALUERING
Bereken
Bewys
Dui verband aan
Som op of konstrueer
Kritiseer, Evaluering
Gee 'n akkurate, kort beskrywing van 'n begrip sodat die
betekenis daarvan duidelik blyk.
Eienskappe, feite of resultate word op ’n logiese, goed
geformuleerde wyse weergegee. Geen bespreking of
verduideliking is nodig nie.
Gee die antwoord (feite) puntsgewys. Geen bespreking
of verduideliking is nodig nie.
Gee redes op ’n logiese, goed gestruktureerde wyse
vanuit illustrasies, modelle, wette en wiskundige
vergelykings.
Beskryf 'n begrip met behulp van voorbeelde of 'n skets
of diagram met of sonder byskrifte.
Feite, gebeure of probleme word teenoor mekaar gestel
en ooreenkomste en verskille word na vore gebring.
Om die wesenlike inligting op 'n beknopte en
sistematiese manier weer te gee.
Pas bestaande kennis en metodes (strategieë) toe op 'n
nuwe probleem of situasie.
Enkele wiskundige metodes word toegepas om 'n
numeriese antwoord te kry.
Gee ’n meganisme, d.w.s. reaksieverloop, met
pyltjienotasie en tussenstappe.
Verdeel 'n probleem, stelling of idee in die
samestellende dele. Verduidelik die belang van elke
deel en dui die onderlinge verwantskap tussen dele
aan.
Meerdere wiskundige metodes word toegepas om 'n
numeriese antwoord te kry.
Stellings word deur logiese aanvoer van aanvaarbare
feite gestaaf.
Vind en verduidelik die verwantskap tussen verskillende
stellings.
'n Groot massa kennis word opgesom en logies en
sistematies georganiseer terwyl die essensie van die
saak behou word.
Bepaal die waarde van 'n stelling, kwessie of argument
deur te verduidelik of jy daarmee saamstem of verskil.
Gee redes vir jou opinies. Analiseer die probleem en
bepaal die waarde van elke komponent. Die resultaat
word opgesom (sintese) om 'n omvattende en
doelgerigte waardebeoordeling te lewer.
vii

Inligting oor die module
6. Werkswyse
Omvattende selfstudie word van nagraadse studente verwag. Die kontaktyd sal primêr gebruik word
om inleidende raamwerke vir die module-inhoude te konstrueer wat later as deel van verdere studie
gebruik kan gebruik. Tyd sal ook afgestaan word aan klasbesprekings en om oefeninge te voltooi. Die
tema van hierdie module is breed en dit is nie moontlik om al die inhoude in die klas te "behandel" nie.
Daarom is dit belangrik dat u voorbereid klas toe kom en selfstudie doen as dit van u verwag word.
Oopboekbenadering
Praktiese werk
Velduitstappie
viii
Die dosent sal u inlig of 'n oopboekbenadering in hierdie module gevolg
word. Lees asseblief die afdeling "Hoe om hierdie studie aan te pak" vir
meer inligting oor hierdie benadering.
Verpligte praktiese werk vorm deel van hierdie module. Die rooster vir
praktiese werk sal aan die begin van die semester beskikbaar gestel word.
'n Verpligte velduitstappie kan moontlik as deel van die module
georganiseer word. Inligting sal vroegtydig aan studente deurgegee word.
Kontak tussen studente en tussen studente en die dosent dra beduidend by tot die betekenisvolle leer
van chemie en fisika. U word aangemoedig en daar word van u verwag om al die kontaksessies by te
woon. Raadpleeg asseblief die prospektus vir verdere inligting oor die kontakgeleenthede in 2009.
Afwesigheid
Indien u nie 'n toets kon skryf nie, moet u so gou as moontlik 'n mediese sertifikaat of ander amptelike
stawende dokumentasie aan die dosent verskaf. Geen verskoning word aangeteken indien die
nodige dokumentasie nie voorsien is nie. In die geval van afwesigheid moet u die moontlikheid van
'n alternatiewe assesseringsgeleentheid of ingeedatum met die dosent bespreek. Geen alternatiewe
rëelings kan in die geval van praktiese werk of velduitstappies getref word nie.
7. Assesseringsinligting
7.1. Formatiewe assessering [Kontinue assessering]
Assesseringsgeleenthede wat bydra tot die deelnamepunt word in die tabel gelys.
Assessering Beskrywing
Klastoetse
Praktiese verslae
Opdragte
Klastoetse word geskryf om u kennis en insig aangaande
die huidige inhoud en die onderliggende chemie teorie
(wat u in vorige chemiemodules moes bemeester het) te
toets. Die datums vir klastoetse sal in die klas bekend
gemaak word.
Praktiese verslaggewing kan aspekte soos die invul van
verslagblaaie, saamstel van 'n omvattende verslag (soos
byvoorbeeld oor 'n velduitstappie) of die ontwikkeling van
'n praktiese aktiwiteit vir gebruik op 'n sekere skoolvlak
behels. Ingeedatums sal in die klas bekend gemaak word.
Opdragte wat daarop gemik is om u te help om spesifieke
vaardighede te bemeester, sal somtyds gegee word.
Ingeedatums sal in die klas bekend gemaak word.
Bydrae tot
deelnamepunt
40%
30%
30%

Deelnamepunt
Die deelnamepunt word as volg saamgestel:
Deelnamepunt = toetse (40%) + praktiese verlae (30%) + opdragte (30%)
Deelnamebewys
Inligting oor die module
Om toelating tot die eksamen te verkry, moet u 'n deelnamebewys verwerf. 'n Deelnamebewys sal
toegeken word indien u deelnamepunt van minstens 40% behaal het.
7.2. Summatiewe assessering [Eksamen]
'n Vraestel van 100 punte en 3 ure word aan die einde van die semester afgelê. 'n Subminimum van
40% moet in die eksamen behaal word ongeag die finale punt wat in die module behaal word.
Modulepunt [finale punt]
Die modulepunt word as volg saamgestel:
Modulepunt = deelnamepunt ( 1 /2) + eksamenpunt ( 1 /2).
'n Modulepunt van ten minste 50% moet verwerf word om die module te slaag.
8. Hoe om hierdie studie aan te pak
Die volgende drie basiese riglyne kan jou help om hierdie module suksesvolle te voltooi.
1. Basiese kennis. Hierdie module bou op die fondament wat tydens u voorgraadse
chemiemodules gelê is. U moet dus reeds 'n basiese begrip van die belangrikste temas in die
vakgebied ontwikkel het.
2. Effektiewe tydsbestuur. Maak seker dat u genoeg geleenthede het om te studeer en dat hierdie
geleenthede goed versprei en lank genoeg is. Tydsbestuur is veral belangrik tydens deeltydse
studie.
ix

Inligting oor die module
3. Korrekte studiemetodes. Die hoeveelheid studiemateriaal in hierdie module is aansienlik.
Omdat dit nie moontlik is om alles te leer nie, is effektiewe studiestrategieë noodsaaklik.
Dit is belangrik om die belangrikste dele van elke afdeling te kan identifiseer sodat die meeste
studietyd daaraan gewy kan word. In hierdie module is toepassing, interpretasie en die
identifikasie van die verwantskappe tussen temas belangriker as blote feite.
Goeie, sistematiese opsommings is baie handig aangesien dit help om groot volumes werk te
hanteer. Gebruik tabelle en diagramme om die logiese samehang tussen verskillende dele van die
studiemateriaal aan te toon. Logiese studiemateriaal leer makliker!
Net soos op skool is oefening en herhaling die beste metodes om te leer. Daar is talle probleme
met antwoorde aan die einde van elke leereenheid in die voorgeskrewe handboek. U moet
besonder versigtig wees as 'n oopboekbenadering in hierdie module gevolg word. Die effektiewe
gebruik van hierdie benadering is 'n vaardigheid wat aangeleer en geslyp moet word deur
voldoende en gereelde oefening. 'n Oopboekbenadering beteken definitief nie dat u nie hoef te
leer nie.
4. Stiptelikheid en toewyding aan studies. Woon alle kontakgeleenthede by en skryf al die toetse.
Voltooi en handig oefeninge, verslae en opdragte betyds in. Statistiek toon duidelik dat
toegewyde studente 'n verbeterde kans het om hul studies suksesvol te voltooi.
9. Kurrikulum
Kurrikulumstruktuur vir Fisiese Wetenskappe Onderwys (Deeltyds)
JAAR 1
Semester 1 Semester 2
x
Module
kode
FOER 611
TLAS 612
PHSE 612
Module name Krediete
Grondslae van
onderrignavorsing
Onderrig, leer en
assessering
Gevorderde chemie
vir onderwys I
Module
kode
16 PHSE 622
16
8
Module name Krediete
Gevorderde fisika
vir onderwys II
Totaal 40 Totaal 16
JAAR 2
Semester 3 Semester 4
Module
kode
Module name Krediete
Module
kode
16
Module name Krediete
RSPR 671* Navorsingsprojek 16 RSPR 671* Navorsingsprojek 16
CUDE 611 Kurrikumontwikkeling 16 PHSE 621
PHSE 611
Gevorderde fisika
vir onderwys I
8
Gevorderde chemie
vir onderwys II
Totaal 40 Totaal 32
* 32-krediet module aangebied oor drie semesters
TOTAAL 128
16

Kurrikulumstruktuur vir Fisiese Wetenskappe Onderwys (Voltyds)
JAAR 1
Semester 1 Semester 2
Module
kode
FOER 611
TLAS 612
Module name Krediete
Grondslae van
onderrignavorsing
Onderrig, leer en
assessering
Module
kode
Inligting oor die module
Module name Krediete
16 RSPR 671 Navorsingsprojek 32
16 PHSE 621
CUDE 611 Kurrikumontwikkeling 16 PHSE 622
PHSE 611
PHSE 612
Gevorderde fisika
vir onderwys I
Gevorderde chemie
vir onderwys I
8
8
Gevorderde chemie
vir onderwys II
Gevorderde fisika
vir onderwys II
Totaal 72 Totaal 56
TOTAAL 128
10. Waarskuwing teen plagiaat
Werkstukke is individuele take en nie groepaktiwiteite nie (tensy dit uitdruklik aangedui word
as 'n groepaktiwiteit)
Kopiëring van teks van ander leerders of uit ander bronne (byvoorbeeld die studiegids, voorgeskrewe
studiemateriaal of direk vanaf die internet) is ontoelaatbaar – net kort aanhalings is toelaatbaar en
slegs indien dit as sodanig aangedui word.
U moet bestaande teks herformuleer en u eie woorde gebruik om te verduidelik wat u gelees het. Dit
is nie aanvaarbaar om bestaande teks/stof/inligting bloot oor te tik en die bron in 'n voetnoot te erken
nie – u behoort in staat te wees om die idee of begrip/konsep weer te gee sonder om die
oorspronklike skrywer woordeliks te herhaal.
Die doel van die opdragte is nie die blote weergee van bestaande materiaal/stof nie, maar om vas te
stel of u oor die vermoë beskik om bestaande tekste te integreer, om u eie interpretasie en/of kritiese
beoordeling te formuleer en om 'n kreatiewe oplossing vir bestaande probleme te bied.
WEES GEWAARSKU: Studente wat gekopieerde teks indien sal 'n nulpunt vir die opdrag
ontvang en dissiplinêre stappe mag deur die Fakulteit en/of die Universiteit teen sodanige
studente geneem word. Dit is ook onaanvaarbaar om iemand anders se werk vir hulle te doen
of iemand anders in staat te stel om u werk te kopieer – moet dus nie u werk uitleen of
beskikbaar stel aan ander nie!
16
16
xi

1. Die omgewing en omgewingsprobleme
TYD BENODIG Dit sal ongeveer 32 ure neem om hierdie leereenheid te voltooi.
UITKOMSTE Gee 'n oorsig van die oorsprong en ontwikkeling van die aarde.
Definieer die term "volhoubaarheid".
Verduidelik die beginsels van volhoubaarheid.
Bespreek die begrip "ekologiese voetspoor".
Verduidelik die "tragedy of the commons" en illustreer die idee met
voorbeelde.
Beskryf en bespreek die IPAT omgewingsinpakmodel.
Bespreek die redes vir ons omgewingsprobleme.
1.1. Die omgewing
1.1.1. Inleiding
"There is a sufficiency in the world for man’s need but not for man’s greed."
Mahatma Gandhi (1869–1948)
Ons lewe in 'n besondere komplekse omgewing wat in staat is om lewe te onderhou. In hierdie
afdeling word studente met min of geen agtergrond van die omgewingswetenskappe begelei tot 'n
basiese begrip van die ontwikkeling van die aarde en 'n waardering vir die interafhanklikheid van alle
elemente van die omgewing.
1.1.2. Studiemateriaal
(a) DVD: How the earth was made.
(b) Verdere notas mag moontlik in die klas verskaf word.
1.1.3. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
1.2. Omgewingsprobleme, hul oorsake en volhoubaarheid
1.2.1. Inleiding
Omgewingswetenskap is 'n multidissiplinêre vakgebied wat handel oor hoe die aarde werk, hoe ons
met die aarde omgaan en hoe ons omgewingsprobleme kan hanteer. Omgewingsvraagstukke
1

Die omgewing en omgewingsprobleme
beïnvloed elke deel van ons lewens en daarom is die inhoud van die voorgeskrewe handboek en
hierdie kursus uiters relevant vir elke student. Die skrywers van die handboek beskou
omgewingswetenskap as die belangrikste kursus in 'n student se opvoeding. Hulle voer aan dat min
sake so belangrik kan wees as om te leer hoe die aarde werk en van die mens se invloed op die
aarde se vermoë om ons te onderhou. Omgewingswetenskap bied ook voorstelle aan oor hoe ons
omgewingsinpak kan verminder. Ons lewe in 'n uitdagende era en dit is duidelik dat ons in hierdie eeu
ingrypende kultuurveranderings sal moet maak om meer volhoubaar te lewe.
1.2.2. Study material
(a) Environmental problems, their causes, and sustainability, [Living in the environment], p. 5 – 30.
1.2.3. Self-evaluation
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
1.3. Ekosisteme – wat dit is en hoe dit werk
1.3.1. Studiemateriaal
(a) Ecosystems: what are they and how do they work? [Living in the environment], p. 54 – 79.
1.3.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
2

2. Chemie en die omgewing
TYD BENODIG Dit sal ongeveer 32 ure neem om hierdie leereenheid te voltooi.
UITKOMSTE Verduidelik waarom die manier waarop die mens chemie aanwend (en
misbruik) uiteindelik tot omgewingsprobleme aanleiding sal gee.
Definieer die term "omgewingchemie".
Gee 'n oorsig van basiese biochemie.
Beskryf van die kategorieë waarin toksisiteit verdeel kan word.
Vergelyk ou en nuwe maniere om oor chemie te dink.
Gee redes waarom groen chemie belangrik is vir die samelewing en industrie.
Lys die beginsels van groen chemie.
Verduidelik die beginsel van atoomekonomie en bespreek die bruikbaarheid
daarvan.
Berekening van die atoomekonomie van gegewe reaksies.
Gee voorbeelde van industriële vervaardigingsmetodes wat meer "groen"
gemaak is.
2.1. Waarom chemie omgewingsprobleme veroorsaak
'n Fundamentele oorsaak van ons groterwordende omgewingsprobleme is dat mense chemie
anders bedryf as bestaande natuurlike prosesse.
For eons, biochemical processes have evolved by drawing primarily on elements that are abundant
and close at hand – such as carbon, hydrogen, oxygen, nitrogen, sulphur, calcium and iron – to create
everything from paramecia to redwoods, clown fish to humans. Our industries, in contrast, gather
elements from nearly every corner of the planet and distribute them in ways natural processes never
could. Lead, for example, used to be found mostly in deposits so isolated and remote that nature
never folded it into living organisms. But now lead is everywhere, primarily because our paints, cars
and computers have spread it around. When it finds its way into children, even at minuscule doses, it
is severely toxic. The same can be said for arsenic, cadmium, mercury, uranium and plutonium. These
elements are persistent pollutants – they do not degrade in animal bodies or in the surrounding
environment – so there is a pressing need to find safer alternatives. Some of the new synthetic
molecules in medicines, plastics and pesticides are so different from the products of natural chemistry
that it is as though they dropped in from an alien world. Many of these molecules do not degrade
easily, and even some biodegradable compounds have become omnipresent because we use them
so copiously.
Recent research indicates that some of these substances can interfere with the normal expression of
genes involved in the development of the male reproductive system. Scientists have known for several
years that prenatal exposure to phthalates (compounds used in plastics and beauty products) can
alter the reproductive tract of new-born male rodents and in 2005 similar effects were reported in male
infants. Another study found that men with low sperm counts living in a rural farming area of Missouri
had elevated levels of herbicides (such as alachlor and atrazine) in their urine. Starting from our
factories, farms and sewers, persistent pollutants can journey intact by air, water and up the food
chain, often right back to us.
[Aangepas vanuit: Environmental chemistry]
3

Chemie en die omgewing
2.2. Omgewingschemie
2.2.1. Inleiding
Chemie is die studie van materie. Daarom het dit te make met die lug wat ons inasem, die water wat
ons drink en die grond waarin ons graan verbou. Mense, plante en diere bevat 'n ongelooflike
hoeveelheid chemiese stowwe wat verwant is deur 'n groot aantal komplekse chemiese reaksies.
Daar is vandag groot besorgdheid oor die gebruik en misbruik van chemie en die invloed wat hierdie
aktiwiteite op die omgewing het. Verskeie gebeure in die geskiedenis van die mensdom herinner ons
aan die gevaar wat die mens vir die omgewing inhou – van individuele blootstelling aan skadelike
stowwe tot verskynsels op 'n globale skaal wat moontlike katastrofiese gevolge kan hê.
Gedurende die 20 ste eeu was die publiek nie werklik bewus van die omgewingasprobleme wat besig
was om te onstaan nie. Die sentiment van die publiek het egter verander aan die begin van die 21 ste
eeu deurdat wetenskaplikes en omgewingsorganisasies die boodskap begin versprei het dat
omgewingsprobleme die volhoubaarheid van die aarde in gedrang bring. Vandag is weinig mense nie
bewus van die gevare wat die kwaliteit van ons lug, water en grond bedreig nie. Kennis bring die
verantwoordelikheid om oplossings te vind vir die probleme wat deur die groeiende menslike bevolking
veroorsaak word. Om omgewingsprobleme te verstaan en oplossings te vind vereis kennis van
omgewingschemie en natuurlik ook ander omgewingswetenskappe. Omgewingschemie is die
afdeling van chemie wat die oorsprong, transport, reaksies, effek en uiteinde van chemiese stowwe in
die lug, water grond en lewende sisteme bestudeer, insluitende die invloed van menslike aktiwiteite
hierop. 'n Verwante dissipline is toksikologiese chemie wat die chemie van gifstowwe bestudeer met
die klem op die interaksie van gifstowwe met biologiese weefsel en lewende sisteme.
2.2.2. Studiemateriaal
(a) [Toxicological chemistry and biochemistry], p. 39 – 75. Sien Bylaag 1.
2.2.3. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
2.3. Elementêre biochemie en toksikologie
GEVALLESTUDIE: DDT in moedersmelk in KZN
Fokusvrae
1. Wat is die oorsprong van die DDT in die moedersmelk?
2. Waarom verbied ons nie bloot die gebruik van DDT nie? Waarom is die verbanning van DDT 'n
emosionele saak?
3. Waarom kom die DDT spesifiek in moedersmelk voor? In watter ander deel of dele van die
liggaam kan DDT ook verwag word?
4. Wat is bioamplifikasie?
5. Waarom is DDT giftig vir mense?
4

2.3.1. Studiemateriaal
(a) [Toxicological chemistry and biochemistry], p. 39 – 75. See Bylaag 1.
(b) Environmental hazards and human health, [Living in the environment], p. 436 – 464.
(c) Verdere notas mag moontlik in die klas verskaf word.
2.3.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
2.4. Groen chemie
2.4.1. Inleiding
Chemie en die omgewing
Chemie het dit tans maar moeilik. Die samelewing verlang groter hoeveelhede van toenemend meer
komplekse chemiese stowwe, maar bejeën ook die industrieë wat hierdie produkte lewer met meer en
meer vrees en agterdog. Die idees van groen chemie kan moontlik oplossings verskaf wat alle partye
tevrede stel. Hierdie afdeling verduidelik die beginsels van groen chemie en gee voorbeelde van die
toepassing daarvan.
2.4.2. Studiemateriaal
(a) [Handbook of Green Chemistry and Technology], p. 1 – 28. See Bylaag 2.
2.4.3. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
5

3. Chemie en die atmosfeer
TYD BENODIG Dit sal ongeveer 32 ure neem om hierdie leereenheid te voltooi.
UITKOMSTE Beskryf die samestelling van die atmosfeer.
Bespreek die belangrikste buitenshuise lugbesoedelingsprobleme.
3.1. Inleiding
Bespreek van die belangrikste binnenshuise lugbesoedelingsprobleme.
Bespreek die effek van lugbesoedeling op gesondheid.
Verduidelik die funksie van osoon in die atmosfeer, die meganisme van
osoonvernietiging en stappe wat geneem is om die probleem op te los.
Bespreek die aardverwarmingsprobleem.
Bespreek die suurreënprobleem.
Stel wyses voor om lugbesoedeling aan te spreek.
Die atmosfeer van die aarde bestaan skynbaar uit konsentriese lae waarvan die eienskappe merkbaar
verskil. Die atmosfeer is die kleinste van die reservoirs op aarde en is daarom mees vatbaar vir
besoedeling. In hierdie afdeling word die struktuur en eienskappe van die atmosfeer beskryf. Die
inligting behoort die nodige agtergrond te verskaf vir 'n latere bespreking van die chemiese prosesse
in die atmosfeer.
GEVALLESTUDIE: Aardverwarming
Fokusvrae
1. Wat is die kweekhuiseffek en wat is aardverwarming?
2. Wat is die meganisme van aardverwarming?
3. Watter getuienis is daar vir aardverwarming?
4. Wat kan moontlike gevolge van aardverwarming wees?
3.2. Die atmosfeer en lugbesoedeling
3.2.1. Studiemateriaal
(a) Air pollution, [Living in the environment], p. 467 – 490.
(b) Verdere notas mag moontlik in die klas verskaf word.
7

Chemie en die atmosfeer
3.2.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
3.3. Klimaatontwrigting en osoonvernietiging
3.3.1. Studiemateriaal
(a) DVD: An inconvenient truth.
(b) Climate disruption and ozone depletion, [Living in the environment], p. 491 – 527.
3.3.2. Self-evaluering
(a) Groepsbespreking oor die film "An inconvenient truth".
(b) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
8

4. Chemie en die hidrosfeer
TYD BENODIG Dit sal ongeveer 32 ure neem om hierdie leereenheid te voltooi.
UITKOMSTE Beskryf die oorsake en gevolge van waterbesoedeling.
Lys en beskryf kortliks die mees algemene siektes wat deur gekontamineerde
water aan die mens oorgedra word.
Bespreek die aard en oorsake van eutrofikasie.
Bespreek hardnekkige organiese besoedelstowwe (persistent organic
pollutants, POPs) in verhouding tot die hidrosfeer. (Hierdie verbindings is
reeds bespreek in die toksikologie afdeling.)
Bespreek die basiese metodes van watersuiwering en rioolverwerking.
Bespreek die vorming en gevolge van suurmynwater.
Stel wyses voor om waterbesoedeling aan te spreek.
4.1. Inleiding
Water is essensieel vir alle lewe op aarde. Toename in die bevolking van die aarde plaas groot druk
op die beskikbare waterbronne en is besig om in 'n waterkrisis te ontaard. Daar is 'n groeiende
konsensus dat die huidige watergebruikspatroon tot 'n waterskaarste asook 'n afname in waterkwaliteit
sal lei. Hierdie faktore sal uiteindelik bepalend en beperkend wees vir toekomstige ekonomiese
ontwikkeling, uitbreiding van kosproduksie en die verskaffing van basiese gesondheidsdienste en
sanitêre dienste aan miljoene mense in ontwikkelende lande.
4.2. Waterbesoedeling
GEVALLESTUDIE: Die Carolina waterkrisis
Fokusvrae
1. Wat is die bron van die suur in Carolina se watertoevoer?
2. Wat is die chemiese oorsprong van suurmynwater (AMD)?
3. Wat is van die omgewingsprobleme wat deur suurmynwater veroorsaak word?
4.2.1. Studiemateriaal
(a) Water pollution, [Living in the environment], p. 528 – 556.
4.2.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
9

Chemie en hidrosfeer
4.3. Watersuiwering
4.3.1. Studiemateriaal
(a) VELDUITSTAPPIE: Daar word van studente vereis om deel te neem aan 'n velduitstappie na 'n
watersuiweringsaanleg.
(b) [Environmental chemistry], p. 601 – 660. Sien Bylaag 3.
4.3.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
10

5. Chemie en die litosfeer
TYD BENODIG Dit sal ongeveer 32 ure neem om hierdie leereenheid te voltooi.
UITKOMSTE Verduidelik die terme "mineraal" en "gesteente" en verduidelik hoe hierdie
entiteite deur middel van die rotssiklus verband hou.
Onderskei tussen stollings-, sedimentêre- en metamorfiese gesteentes.
Gee 'n oorsig van die Suid-Afrikaanse mynbedryf.
Beskryf hoe ekonomies-lewensvatbare erts neerslae op aarde gevorm het.
Illustreer en beskryf die algemene prosedure wat gebruik word om metale te
ekstraheer.
Beskryf die algemene chemiese beginsels wat gebruik word wanneer metale
geëkstraheer word.
Beskryf die basiese ekstraksieprosesse wat gebruik word tydens die
ekstraksie van geselekteerde metale wat van belang is in die Suid-Afrikaanse
konteks.
Bespreek die voorkoms en gevolge van swaarmetaalbesoedeling.
Stel wyses voor om besoedeling van die litosfeer aan te spreek.
GEVALLESTUDIE: Die Sabierivier in 1922
Fokusvrae
1. Wat was die toestand van die Sabierivier in 1922?
2. Hoe dra mynbou by tot omgewingsprobleme?
3. Wat is die gevare van onwettige mynbou?
5.1. Inleiding
Hierdie afdeling bespreek aspekte van algemene geologie en mynbou met die klem op die Suid-
Afrikaanse mynbedryf. Suid-Afrika is een van die belangrikste mynboulande in Afrika en in die wêreld
gebaseer op die verskeidenheid en howeveelheid minerale wat gemyn word. Ons lang beskik oor die
grootste reserwes van chroom, goud, vanadium, mangaan en PGMs in die wêreld. Die mynbou
industrie kan verdeel word in vyf breë kategorieë – goud, PGMs, diamante, steenkool en vanadium. In
totaal dra hierdie sektore ongeveer 6,5% bygedra tot die BBP in 2000. Die studiemateriaal behoort die
student toe te rus met genoegsame agtergrondkennis om van die omgewingsuitdagings te begryp wat
met mynbou geassosieer word. 'n Paar van hierdie probleme sal later in die studiemateriaal aandag
kry.
5.2. Geologie en mineraalbronne
5.2.1. Studiemateriaal
(a) Geology and non-renewable mineral resources, [Living in the environment], p. 346 – 369.
11

Chemie en die litosfeer
5.2.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
5.3. Basiese beginsels van mynbou en die ekstraksie van metale
12

5.3.1. Studiemateriaal
(a) Verslae van die Departement van Minerale en Energie (DME).
(b) [Advanced Chemistry], p. 291 – 303, 518 – 524. Sien Bylaag 4.
(c) [General chemistry], p. 996 – 1003. Sien Bylaag 5.
5.3.2. Self-evaluering
(a) Geselekteerde vrae gebaseer op die studiemateriaal sal in die klas verskaf word.
Chemie en die litosfeer
13

BYLAAG 1
Manahan, SE, 2003, Toxicological chemistry and biochemistry, CRC Press, Boca Raton, p. 59 – 95.
14

3.1 BIOCHEMISTRY
CHAPTER 3
Biochemistry
Most people have had the experience of looking through a microscope at a single cell. It may
have been an amoeba, alive and oozing about like a blob of jelly on the microscope slide, or a cell
of bacteria, stained with a dye to make it show up more plainly. Or it may have been a beautiful
cell of algae with its bright green chlorophyll. Even the simplest of these cells is capable of carrying
out a thousand or more chemical reactions. These life processes fall under the heading of biochemistry,
the branch of chemistry that deals with the chemical properties, composition, and
biologically mediated processes of complex substances in living systems.
Biochemical phenomena that occur in living organisms are extremely sophisticated. In the
human body, complex metabolic processes break down a variety of food materials to simpler
chemicals, yielding energy and the raw materials to build body constituents, such as muscle, blood,
and brain tissue. Impressive as this may be, consider a humble microscopic cell of photosynthetic
cyanobacteria only about a micrometer in size, which requires only a few simple inorganic chemicals
and sunlight for its existence. This cell uses sunlight energy to convert carbon from CO2, hydrogen
– 2– and oxygen from H2O, nitrogen from NO3, sulfur from SO4 , and phosphorus from inorganic
phosphate into all the proteins, nucleic acids, carbohydrates, and other materials that it requires to
exist and reproduce. Such a simple cell accomplishes what could not be done by human endeavors
even in a vast chemical factory costing billions of dollars.
Ultimately, most environmental pollutants and hazardous substances are of concern because of
their effects on living organisms. The study of the adverse effects of substances on life processes
requires some basic knowledge of biochemistry. Biochemistry is discussed in this chapter, with an
emphasis on the aspects that are especially pertinent to environmentally hazardous and toxic
substances, including cell membranes, deoxyribonucleic acid (DNA), and enzymes.
Biochemical processes not only are profoundly influenced by chemical species in the environment,
but they largely determine the nature of these species, their degradation, and even their
syntheses, particularly in the aquatic and soil environments. The study of such phenomena forms
the basis of environmental biochemistry. 1
3.1.1 Biomolecules
The biomolecules that constitute matter in living organisms are often polymers with molecular
masses of the order of a million or even larger. As discussed later in this chapter, these biomolecules
may be divided into the categories of carbohydrates, proteins, lipids, and nucleic acids. Proteins
and nucleic acids consist of macromolecules, lipids are usually relatively small molecules, and
carbohydrates range from relatively small sugar molecules to high-molecular-mass macromolecules,
such as those in cellulose.
15
59

60 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Vacuole
Ribosome
Figure 3.1 Some major features of the eukaryotic cell in animals (left) and plants (right).
The behavior of a substance in a biological system depends to a large extent upon whether the
substance is hydrophilic (water-loving) or hydrophobic (water-hating). Some important toxic substances
are hydrophobic, a characteristic that enables them to traverse cell membranes readily. Part
of the detoxification process carried on by living organisms is to render such molecules hydrophilic,
therefore water soluble and readily eliminated from the body.
3.2 BIOCHEMISTRY AND THE CELL
The focal point of biochemistry and biochemical aspects of toxicants is the cell, the basic
building block of living systems where most life processes are carried. Bacteria, yeasts, and some
algae consist of single cells. However, most living things are made up of many cells. In a more
complicated organism the cells have different functions. Liver cells, muscle cells, brain cells, and
skin cells in the human body are quite different from each other and do different things. Cells are
divided into two major categories depending upon whether or not they have a nucleus: eukaryotic
cells have a nucleus, and prokaryotic cells do not. Prokaryotic cells are found in single-celled
bacteria. Eukaryotic cells compose organisms other than bacteria.
3.2.1 Major Cell Features
Golgi body
Cell membrane
Mitochondria
Nucleus
Lysosome
Starch grain
Mitochondria
Chloroplast
Cell wall
Vacuole
Figure 3.1 shows the major features of the eukaryotic cell, which is the basic structure in which
biochemical processes occur in multicelled organisms. These features are as follows:
• Cell membrane, which encloses the cell and regulates the passage of ions, nutrients, lipid-soluble
(fat-soluble) substances, metabolic products, toxicants, and toxicant metabolites into and out of
the cell interior because of its varying permeability for different substances. The cell membrane
protects the contents of the cell from undesirable outside influences. Cell membranes are composed
in part of phospholipids that are arranged with their hydrophilic (water-seeking) heads on the cell
membrane surfaces and their hydrophobic (water-repelling) tails inside the membrane. Cell membranes
contain bodies of proteins that are involved in the transport of some substances through
the membrane. One reason the cell membrane is very important in toxicology and environmental
biochemistry is because it regulates the passage of toxicants and their products into and out of the
cell interior. Furthermore, when its membrane is damaged by toxic substances, a cell may not
function properly and the organism may be harmed.
• Cell nucleus, which acts as a sort of “control center” of the cell. It contains the genetic directions
the cell needs to reproduce itself. The key substance in the nucleus is DNA. Chromosomes in the
16

BIOCHEMISTRY 61
cell nucleus are made up of combinations of DNA and proteins. Each chromosome stores a separate
quantity of genetic information. Human cells contain 46 chromosomes. When DNA in the nucleus
is damaged by foreign substances, various toxic effects, including mutations, cancer, birth defects,
and defective immune system function may occur.
• Cytoplasm, which fills the interior of the cell not occupied by the nucleus. Cytoplasm is further
divided into a water-soluble proteinaceous filler called cytosol, in which are suspended bodies
called cellular organelles, such as mitochondria or, in photosynthetic organisms, chloroplasts.
• Mitochondria, “powerhouses” that mediate energy conversion and utilization in the cell. Mitochondria
are sites in which food materials — carbohydrates, proteins, and fats — are broken down
to yield carbon dioxide, water, and energy, which is then used by the cell for its energy needs.
The best example of this is the oxidation of the sugar glucose, C 6H 12O 6:
C 6H 12O 6 + 6O 2 → 6CO 2 + 6H 2O + energy
This kind of process is called cellular respiration.
• Ribosomes, which participate in protein synthesis.
• Endoplasmic reticulum, which is involved in the metabolism of some toxicants by enzymatic
processes.
• Lysosome, a type of organelle that contains potent substances capable of digesting liquid food
material. Such material enters the cell through a “dent” in the cell wall, which eventually becomes
surrounded by cell material. This surrounded material is called a food vacuole. The vacuole merges
with a lysosome, and the substances in the lysosome bring about digestion of the food material.
The digestion process consists largely of hydrolysis reactions in which large, complicated food
molecules are broken down into smaller units by the addition of water.
• Golgi bodies, which occur in some types of cells. These are flattened bodies of material that serve
to hold and release substances produced by the cells.
• Cell walls of plant cells. These are strong structures that provide stiffness and strength. Cell walls
are composed mostly of cellulose, which will be discussed later in this chapter.
• Vacuoles inside plant cells that often contain materials dissolved in water.
• Chloroplasts in plant cells that are involved in photosynthesis (the chemical process that uses energy
from sunlight to convert carbon dioxide and water to organic matter). Photosynthesis occurs in these
bodies. Food produced by photosynthesis is stored in the chloroplasts in the form of starch grains.
3.3 PROTEINS
Proteins are nitrogen-containing organic compounds that are the basic units of life systems.
Cytoplasm, the jelly-like liquid filling the interior of cells, is made up largely of protein. Enzymes,
which act as catalysts of life reactions, are made of proteins; they are discussed later in the chapter.
Proteins are composed of amino acids (Figure 3.2) joined together in huge chains. Amino acids are
organic compounds that contain the carboxylic acid group, – CO 2H, and the amino group, – NH 2. They
are sort of a hybrid of carboxylic acids and amines (see Sections 1.8.1 and 1.8.2). Proteins are polymers,
or macromolecules, of amino acids containing from approximately 40 to several thousand amino acid
groups joined by peptide linkages. Smaller molecule amino acid polymers, containing only about 10
to about 40 amino acids per molecule, are called polypeptides. A portion of the amino acid left after
the elimination of H 2O during polymerization is called a residue. The amino acid sequence of these
residues is designated by a series of three-letter abbreviations for the amino acid.
Natural amino acids all have the following chemical group:
H H
N O
R C
H
C
17
OH

62 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
H O
H H O
H H O
H C C OH HO C C C OH H3C C C C OH
NH2 H NH2 Glycine (gly) Serine (ser)
OH NH2 H H O
C C C OH
H NH2 CH3 H H O
H C C C C OH
H H H O
CH3 H
H
NH 3C C C C C OH
2
H CH3 NH2 Isoleucine (ile)*
H H O
O H H H O
HS C C C OH
H NH H3C 2
S
H
C
H
H
C
H
H O H2N C C C C C OH
C C OH H H NH2 NH2 Methionine (met)*
H
H O
3C H
H H H H H O
H
C C C OH
3N C C C C C C OH
H3C H
NH
H H H NH2 2
O H H O
H2N C C C C OH
H NH2 +
H H O
C C C OH
H O
H N NH
NH2 H3C C C OH
NH
Phenylalanine (phe)*
2
Alanine (ala)
H H
H C C H O
H C C C OH
N
H H
H
Cysteine (cys) Glutamine (gin)
H H O
HO C C C OH
Valine (val)* H NH2 Lysine (lys)*
H H O Tyrosine (tyr)
C C C OH
O H H O
H NH
HO C C C C OH
N
2
H NH2 H
Tryptophan (try)*
+
Threonine (thr)*
H
Histidine (his)
Leucine (leu)*
Proline (pro)
Aspartic acid (asp)
Asparagine (asn)
O H H H O
H H H H H O
HO C C
H
C
H
C C OH
NH2 H2N C N
+
NH2 C
H
C
H
C
H
C C OH
NH2 Glutamic acid (glu)
Arginine (arg)
Figure 3.2 Amino acids that occur in proteins. Those marked with an asterisk cannot be synthesized by the
human body and must come from dietary sources.
In this structure the –NH 2 group is always bonded to the carbon next to the –CO 2H group. This is
called the “alpha” location, so natural amino acids are alpha-amino acids. Other groups, designated as
R, are attached to the basic alpha-amino acid structure. The R groups may be as simple as an atom of
H found in glycine, or they may be as complicated as the structure of the R group in tryptophan:
H H
N O
H C C
H
OH
Zwitterion
form
Glycine
18
H
H
+
N H O
H C
H
C
O –

BIOCHEMISTRY 63
Alanine
Figure 3.3 Condensation of alanine, leucine, and tyrosine to form a tripeptide consisting of three amino acids
joined by peptide linkages (outlined by dashed lines).
Table 3.1 Major Types of Proteins
H
H2N C C
CH 3
O
OH
H
H2N C C
CH 3
+ H2N C C OH +
H3C C CH3 Leucine H
O
H2N C C
Tyrosine
Type of Protein Example Function and Characteristics
H
Nutrient Casein (milk protein) Food source; people must have an adequate supply
of nutrient protein with the right balance of amino
acids for adequate nutrition
Storage Ferritin Storage of iron in animal tissues
Structural Collagen (tendons), keratin (hair) Structural and protective components in organisms
Contractile Actin, myosin in muscle tissue Strong, fibrous proteins that can contract and cause
movement to occur
Transport Hemoglobin Transport inorganic and organic species across cell
membranes, in blood, between organs
Defense — Antibodies against foreign agents such as viruses
produced by the immune system
Regulatory Insulin, human growth hormone Regulate biochemical processes such as sugar
metabolism or growth by binding to sites inside cells
or on cell membranes
Enzymes Acetylcholine esterase Catalysts of biochemical reactions (see Section 3.6)
As shown in Figure 3.2, there are 20 common amino acids in proteins. These are shown with
uncharged – NH 2 and – CO 2H groups. Actually, these functional groups exist in the charged zwitterion
form, as shown for glycine above.
Amino acids in proteins are joined together in a specific way. These bonds constitute the peptide
linkage. The formation of peptide linkages is a condensation process involving the loss of water.
For example, consider the condensation of alanine, leucine, and tyrosine shown in Figure 3.3. When
these three amino acids join together, two water molecules are eliminated. The product is a tripeptide
since there are three amino acids involved. The amino acids in proteins are linked as shown for
this tripeptide, except that many more monomeric amino acid groups are involved.
Proteins may be divided into several major types that have widely varying functions. These are
listed in Table 3.1.
O
H C H
H
N C
H C
H 3C
H O
C
H
19
C
H
CH 3
H
N
H
O
C C
H C H
OH
H
O
H C H
OH
OH
OH

64 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
3.3.1 Protein Structure
The order of amino acids in protein molecules, and the resulting three-dimensional structures
that form, provide an enormous variety of possibilities for protein structure. This is what makes
life so diverse. Proteins have primary, secondary, tertiary, and quaternary structures. The structures
of protein molecules determine the behavior of proteins in crucial areas such as the processes by
which the body’s immune system recognizes substances that are foreign to the body. Proteinaceous
enzymes depend on their structures for the very specific functions of the enzymes.
The order of amino acids in the protein molecule determines its primary structure. Secondary
protein structures result from the folding of polypeptide protein chains to produce a maximum
number of hydrogen bonds between peptide linkages:
Hydrogen bonds
C O H N Illustration of hydrogen bonds between
N and O atoms in peptide linkages, which
N H O C
constitutes protein secondary structures
Hydrogen bonds
Further folding of the protein molecules held in place by attractive forces between amino acid side
chains gives proteins a secondary structure, which is determined by the nature of the amino acid
R groups. Small R groups enable protein molecules to be hydrogen-bonded together in a parallel
arrangement, whereas large R groups produce a spiral form known as an alpha-helix.
Tertiary structures are formed by the twisting of alpha-helices into specific shapes. They are
produced and held in place by the interactions of amino side chains on the amino acid residues
constituting the protein macromolecules. Tertiary protein structure is very important in the processes
by which enzymes identify specific proteins and other molecules upon which they act. It is also
involved with the action of antibodies in blood, which recognize foreign proteins by their shape
and react to them. This is what happens in the phenomenon of disease immunity, where antibodies
in blood recognize specific proteins from viruses or bacteria and reject them.
Two or more protein molecules consisting of separate polypeptide chains may be further
attracted to each other to produce a quaternary structure.
Some proteins are fibrous proteins, which occur in skin, hair, wool, feathers, silk, and tendons.
The molecules in these proteins are long and threadlike and are laid out parallel in bundles. Fibrous
proteins are quite tough and do not dissolve in water.
An interesting fibrous protein is keratin, which is found in hair. The cross-linking bonds between
protein molecules in keratin are –S–S– bonds formed from two HS– groups in two molecules of
the amino acid cysteine. These bonds largely hold hair in place, thus keeping it curly or straight.
A “permanent” consists of breaking the bonds chemically, setting the hair as desired, and then
reforming the cross-links to hold the desired shape.
Aside from fibrous protein, the other major type of protein form is the globular protein. These
proteins are in the shape of balls and oblongs. Globular proteins are relatively soluble in water. A
typical globular protein is hemoglobin, the oxygen-carrying protein in red blood cells. Enzymes
are generally globular proteins.
20

BIOCHEMISTRY 65
3.3.2 Denaturation of Proteins
Secondary, tertiary, and quaternary protein structures are easily changed by a process called
denaturation. These changes can be quite damaging. Heating, exposure to acids or bases, and even
violent physical action can cause denaturation to occur. The albumin protein in egg white is
denatured by heating so that it forms a semisolid mass. Almost the same thing is accomplished by
the violent physical action of an egg beater in the preparation of meringue. Heavy metal poisons
such as lead and cadmium change the structures of proteins by binding to functional groups on the
protein surface.
3.4 CARBOHYDRATES
Carbohydrates have the approximate simple formula CH 2O and include a diverse range of
substances composed of simple sugars such as glucose:
CH2OH H
C
HO
C
H
OH
C
O
H
C
H
C
OH
H OH
Glucose molecule
High-molecular-mass polysaccharides, such as starch and glycogen (animal starch), are biopolymers
of simple sugars.
Photosynthesis in a plant cell converts the energy from sunlight to chemical energy in a
carbohydrate, C 6H 12O 6. This carbohydrate may be transferred to some other part of the plant for
use as an energy source. It may be converted to a water-insoluble carbohydrate for storage until it
is needed for energy. Or it may be transformed to cell wall material and become part of the structure
of the plant. If the plant is eaten by an animal, the carbohydrate is used for energy by the animal.
The simplest carbohydrates are the monosaccharides. These are also called simple sugars.
Because they have six carbon atoms, simple sugars are sometimes called hexoses. Glucose (formula
shown above) is the most common simple sugar involved in cell processes. Other simple sugars
with the same formula but somewhat different structures are fructose, mannose, and galactose.
These must be changed to glucose before they can be used in a cell. Because of its use for energy
in body processes, glucose is found in the blood. Normal levels are from 65 to 110 mg of glucose
per 100 ml of blood. Higher levels may indicate diabetes.
Units of two monosaccharides make up several very important sugars known as disaccharides.
When two molecules of monosaccharides join together to form a disaccharide,
C 6H 12O 6 + C 6H 12O 6 → C 12H 22O 11 + H 2O (3.4.1)
a molecule of water is lost. Recall that proteins are also formed from smaller amino acid molecules
by condensation reactions involving the loss of water molecules. Disaccharides include sucrose (cane
sugar used as a sweetener), lactose (milk sugar), and maltose (a product of the breakdown of starch).
Polysaccharides consist of many simple sugar units hooked together. One of the most important
polysaccharides is starch, which is produced by plants for food storage. Animals produce a related
material called glycogen. The chemical formula of starch is (C 6H 10O 5) n, where n may represent a
number as high as several hundred. What this means is that the very large starch molecule consists
21

66 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
CH2OH CH2OH CH2OH H
C
O
C
H
OH
C
O
H
C
H H
C C
O
C
H
OH
C
O
H
C
H H
C C
O
C
H
OH
C
O
H
C
H
C
O
H OH H OH H OH
Figure 3.4 Part of a starch molecule showing units of C 6H 10O 5 condensed together.
CH2OH H OH
H
C
O
C
H
OH
C
O
H
C
O
C C
H H
C
OH
H
C
C
H
O
H
C
O
H OH CH2OH Figure 3.5 Part of the structure of cellulose.
of many units of C 6H 10O 5 joined together. For example, if n is 100, there are 6 times 100 carbon
atoms, 10 times 100 hydrogen atoms, and 5 times 100 oxygen atoms in the molecule. Its chemical
formula is C 600H 1000O 500. The atoms in a starch molecule are actually present as linked rings,
represented by the structure shown in Figure 3.4. Starch occurs in many foods, such as bread and
cereals. It is readily digested by animals, including humans.
Cellulose is a polysaccharide that is also made up of C 6H 10O 5 units. Molecules of cellulose are
huge, with molecular weights of around 400,000. The cellulose structure (Figure 3.5) is similar to
that of starch. Cellulose is produced by plants and forms the structural material of plant cell walls.
Wood is about 60% cellulose, and cotton contains over 90% of this material. Fibers of cellulose
are extracted from wood and pressed together to make paper.
Humans and most other animals cannot digest cellulose. Ruminant animals (cattle, sheep, goats,
moose) have bacteria in their stomachs that break down cellulose into products that can be used
by the animal. Chemical processes are available to convert cellulose to simple sugars by the reaction
(C 6H 10O 5) n + nH 2O → nC 6H 12O 6
cellulose glucose
(3.4.2)
where n may be 2000 to 3000. This involves breaking the linkages between units of C 6H 10O 5 by
adding a molecule of H 2O at each linkage, a hydrolysis reaction. Large amounts of cellulose from
wood, sugar cane, and agricultural products go to waste each year. The hydrolysis of cellulose
enables these products to be converted to sugars, which can be fed to animals.
Carbohydrate groups are attached to protein molecules in a special class of materials called
glycoproteins. Collagen is a crucial glycoprotein that provides structural integrity to body parts.
It is a major constituent of skin, bones, tendons, and cartilage.
3.5 LIPIDS
Lipids are substances that can be extracted from plant or animal matter by organic solvents,
such as chloroform, diethyl ether, or toluene (Figure 3.6). Whereas carbohydrates and proteins are
22
H
C
CH2OH C O
H
OH
C
H
C
O
C
H
H OH

BIOCHEMISTRY 67
Cooling
water in
Rising solvent vapor
Porous thimble
containing sample
Condenser
Boiling solvent
Cooling
water out
Condensed solvent
Siphon back to
solvent reservoir
Heating mantle
Figure 3.6 Lipids are extracted from some biological materials with a soxhelet extractor (above). The solvent
is vaporized in the distillation flask by the heating mantle, rises through one of the exterior tubes
to the condenser, and is cooled to form a liquid. The liquid drops onto the porous thimble containing
the sample. Siphon action periodically drains the solvent back into the distillation flask. The extracted
lipid collects as a solution in the solvent in the flask.
characterized predominately by the monomers (monosaccharides and amino acids) from which
they are composed, lipids are defined essentially by their physical characteristic of organophilicity.
The most common lipids are fats and oils composed of triglycerides formed from alcohol glycerol,
CH 2(OH)CH(OH)CH 2(OH), and a long-chain fatty acid such as stearic acid, CH 3(CH 2) 16C(O)OH
(Figure 3.7). Numerous other biological materials, including waxes, cholesterol, and some vitamins
and hormones, are classified as lipids. Common foods, such as butter and salad oils, are lipids.
Long-chain fatty acids, such as stearic acid, are also organic soluble and are classified as lipids.
Lipids are toxicologically important for several reasons. Some toxic substances interfere with
lipid metabolism, leading to detrimental accumulation of lipids. Many toxic organic compounds
are poorly soluble in water, but are lipid soluble, so that bodies of lipids in organisms serve to
dissolve and store toxicants.
An important class of lipids consists of phosphoglycerides (glycerophosphatides). These compounds
may be regarded as triglycerides in which one of the acids bonded to glycerol is ortho-
23

68 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Figure 3.7 General formula of triglycerides, which make up fats and oils. The R group is from a fatty acid and
is a hydrocarbon chain, such as –(CH 2) 16CH 3.
phosphoric acid. These lipids are especially important because they are essential constituents of
cell membranes. These membranes consist of bilayers in which the hydrophilic phosphate ends of
the molecules are on the outside of the membrane and the hydrophobic “tails” of the molecules
are on the inside.
Waxes are also esters of fatty acids. However, the alcohol in a wax is not glycerol; it is often
a very long chain alcohol. For example, one of the main compounds in beeswax is myricyl palmitate,
H O
(C30H61 ) C O
H
C
(C 15 H 31 )
Alcohol portion Fatty acid portion
of ester of ester
in which the alcohol portion of the ester has a very large hydrocarbon chain. Waxes are produced
by both plants and animals, largely as protective coatings. Waxes are found in a number of common
products. Lanolin is one of these. It is the “grease” in sheep’s wool. When mixed with oils and
water, it forms stable colloidal emulsions consisting of extremely small oil droplets suspended in
water. This makes lanolin useful for skin creams and pharmaceutical ointments. Carnauba wax
occurs as a coating on the leaves of some Brazilian palm trees. Spermaceti wax is composed largely
of cetyl palmitate,
(C 15 H 31 )
H O
C O C
H
(C 15 H 31 )
Cetyl palmitate
which is extracted from the blubber of the sperm whale. It is very useful in some cosmetics and
pharmaceutical preparations.
Steroids are lipids found in living systems that all have the ring system shown in Figure 3.8
for cholesterol. Steroids occur in bile salts, which are produced by the liver and then secreted into
the intestines. Their breakdown products give feces its characteristic color. Bile salts act on fats in
the intestine. They suspend very tiny fat droplets in the form of colloidal emulsions. This enables
the fats to be broken down chemically and digested.
Some steroids are hormones. Hormones act as “messengers” from one part of the body to
another. As such, they start and stop a number of body functions. Male and female sex hormones
are examples of steroid hormones. Hormones are given off by glands in the body called endocrine
glands. The locations of the important endocrine glands are shown in Figure 3.9.
24

BIOCHEMISTRY 69
HO
H 3 C
H 3 C
H 3 C
Figure 3.8 Steroids are characterized by the ring structure shown above for cholesterol.
H
C
Pituitary
Parathyroid
Ovaries
(female)
Figure 3.9 Locations of important endocrine glands.
CH 2 CH 2 CH 2 C H
3.6 ENZYMES
Catalysts are substances that speed up a chemical reaction without themselves being consumed
in the reaction. The most sophisticated catalysts of all are those found in living systems. They bring
about reactions that could not be performed at all, or only with great difficulty, outside a living
organism. These catalysts are called enzymes. In addition to speeding up reactions by as much as
10- to a 100 million-fold, enzymes are extremely selective in the reactions they promote.
Enzymes are proteinaceous substances with highly specific structures that interact with particular
substances or classes of substances called substrates. Enzymes act as catalysts to enable
biochemical reactions to occur, after which they are regenerated intact to take part in additional
reactions. The extremely high specificity with which enzymes interact with substrates results from
their “lock and key” action, based on the unique shapes of enzymes, as illustrated in Figure 3.10.
This illustration shows that an enzyme “recognizes” a particular substrate by its molecular
structure and binds to it to produce an enzyme–substrate complex. This complex then breaks apart
to form one or more products different from the original enzyme, regenerating the unchanged
enzyme, which is then available to catalyze additional reactions. The basic process for an enzyme
reaction is, therefore,
CH 3
CH 3
Cholesterol, a typical steroid
Thymus
Adrenal
25
Thyroid
Testes
(male)

70 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Enzyme
+
Substrate
+
Enzyme-substrate complex
Products Regenerated enzyme
Figure 3.10 Representation of the “lock and key” mode of enzyme action, which enables the very high specificity
of enzyme-catalyzed reactions.
enzyme + substrate ⎯→ ⎯⎯←⎯
enzyme–substrate complex ⎯→ ⎯⎯←⎯
enzyme + product (3.6.1)
Several important things should be noted about this reaction. As shown in Figure 3.10, an enzyme
acts on a specific substrate to form an enzyme–substrate complex because of the fit between their
structures. As a result, something happens to the substrate molecule. For example, it might be split
in two at a particular location. Then the enzyme–substrate complex comes apart, yielding the
enzyme and products. The enzyme is not changed in the reaction and is now free to react again.
Note that the arrows in the formula for enzyme reaction point both ways. This means that the
reaction is reversible. An enzyme–substrate complex can simply go back to the enzyme and the
substrate. The products of an enzymatic reaction can react with the enzyme to form the enzyme–substrate
complex again. It, in turn, may again form the enzyme and the substrate. Therefore, the same
enzyme may act to cause a reaction to go either way.
Some enzymes cannot function by themselves. In order to work, they must first be attached to
coenzymes. Coenzymes normally are not protein materials. Some of the vitamins are important
coenzymes.
Enzymes are named for what they do. For example, the enzyme given off by the stomach,
which splits proteins as part of the digestion process, is called gastric proteinase. The “gastric”
part of the name refers to the enzyme’s origin in the stomach. “Proteinase” denotes that it splits
up protein molecules. The common name for this enzyme is pepsin. Similarly, the enzyme produced
by the pancreas that breaks down fats (lipids) is called pancreatic lipase. Its common name is
26

BIOCHEMISTRY 71
steapsin. In general, lipase enzymes cause lipid triglycerides to dissociate and form glycerol and
fatty acids.
The enzymes mentioned above are hydrolyzing enzymes, which bring about the breakdown
of high-molecular-weight biological compounds by the addition of water. This is one of the most
important reactions involved in digestion. The three main classes of energy-yielding foods that
animals eat are carbohydrates, proteins, and fats. Recall that the higher carbohydrates that humans
eat are largely disaccharides (sucrose, or table sugar) and polysaccharides (starch). These are formed
by the joining together of units of simple sugars, C 6H 12O 6, with the elimination of an H 2O molecule
at the linkage where they join. Proteins are formed by the condensation of amino acids, again with
the elimination of a water molecule at each linkage. Fats are esters that are produced when glycerol
and fatty acids link together. A water molecule is lost for each of these linkages when a protein,
fat, or carbohydrate is synthesized. In order for these substances to be used as a food source, the
reverse process must occur to break down large, complicated molecules of protein, fat, or carbohydrate
to simple, soluble substances that can penetrate a cell membrane and take part in chemical
processes in the cell. This reverse process is accomplished by hydrolyzing enzymes.
Biological compounds with long chains of carbon atoms are broken down into molecules with
shorter chains by the breaking of carbon–carbon bonds. This commonly occurs by the elimination
of –CO 2H groups from carboxylic acids. For example, pyruvic decarboxylase enzyme acts upon
pyruvic acid,
H
H O O
H O
C C C OH
Pyruvate
decarboxylase H C C H + CO2
H
H
Pyruvic acid Acetaldehyde
(3.6.2)
to split off CO 2 and produce a compound with one less carbon. It is by such carbon-by-carbon
breakdown reactions that long-chain compounds are eventually degraded to CO 2 in the body, or
that long-chain hydrocarbons undergo biodegradation by the action of spill bacteria on spilled
petroleum. Oxidation and reduction are the major reactions for the exchange of energy in living
systems. Cellular respiration, discussed in Section 3.2, is an oxidation reaction in which a carbohydrate,
C 6H 12O 6, is broken down to carbon dioxide and water with the release of energy:
C 6H 12O 6 + 6O 2 → 6CO 2 + 6H 2O + energy (3.6.3)
Actually, such an overall reaction occurs in living systems by a complicated series of individual
steps. Some of these steps involve oxidation. The enzymes that bring about oxidation in the presence
of free O 2 are called oxidases. In general, biological oxidation–reduction reactions are catalyzed
by oxidoreductase enzymes.
In addition to the types of enzymes discussed above, there are many enzymes that perform
miscellaneous duties in living systems. Typical of these are isomerases, which form isomers of
particular compounds. For example, there are several simple sugars with the formula C 6H 12O 6.
However, only glucose can be used directly for cell processes. The other isomers are converted to
glucose by the action of isomerases. Transferase enzymes move chemical groups from one
molecule to another, lyase enzymes remove chemical groups without hydrolysis and participate in
the formation of C=C bonds or addition of species to such bonds, and ligase enzymes work in
conjunction with adenosine triphosphate (ATP), a high-energy molecule that plays a crucial role
in energy-yielding, glucose-oxidizing metabolic processes, to link molecules together with the
formation of bonds such as carbon–carbon or carbon–sulfur bonds.
27

72 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Enzyme action may be affected by many different things. Enzymes require a certain hydrogen
ion concentration to function best. For example, gastric proteinase requires the acid environment
of the stomach to work well. When it passes into the much less acidic intestines, it stops working.
This prevents damage to the intestine walls, which would occur if the enzyme tried to digest them.
Temperature is critical. Not surprisingly, the enzymes in the human body work best at around
98.6°F (37°C), which is the normal body temperature. Heating these enzymes to around 140°F
permanently destroys them. Some bacteria that thrive in hot springs have enzymes that work best
at relatively high temperatures. Other “cold-seeking” bacteria have enzymes adapted to near the
freezing point of water.
One of the greatest concerns regarding the effects of surroundings on enzymes is the influence
of toxic substances. A major mechanism of toxicity is the alteration or destruction of enzymes by
agents such as cyanide, heavy metals, or organic compounds, such as insecticidal parathion. An
enzyme that has been destroyed obviously cannot perform its designated function, whereas one
that has been altered either may not function at all or may act improperly. Toxicants can affect
enzymes in several ways. Parathion, for example, bonds covalently to the nerve enzyme acetylcholinesterase,
which can then no longer serve to stop nerve impulses. Heavy metals tend to bind to
sulfur atoms in enzymes (such as sulfur from the amino acid cysteine, shown in Figure 3.2), thereby
altering the shape and function of the enzyme. Enzymes are denatured by some poisons, causing
them to “unravel” so that the enzyme no longer has its crucial specific shape.
3.7 NUCLEIC ACIDS
The essence of life is contained in deoxyribonucleic acid (DNA), which stays in the cell
nucleus, and ribonucleic acid (RNA), which functions in the cell cytoplasm. These substances,
which are known collectively as nucleic acids, store and pass on essential genetic information that
controls reproduction and protein synthesis.
The structural formulas of the monomeric constituents of nucleic acids are given in Figure 3.11.
These are pyrimidine or purine nitrogen-containing bases, two sugars, and phosphate. DNA molecules
are made up of the nitrogen-containing bases adenine, guanine, cytosine, and thymine;
phosphoric acid (H 3PO 4); and the simple sugar 2-deoxy-β-D-ribofuranose (commonly called deoxyribose).
RNA molecules are composed of the nitrogen-containing bases adenine, guanine, cytosine,
and uracil; phosphoric acid (H 3PO 4); and the simple sugar β-D-ribofuranose (ribose).
The formation of nucleic acid polymers from their monomeric constituents may be viewed as
the following steps.
• Monosaccharide (simple sugar) + cyclic nitrogenous base yields nucleoside:
HO
NH2 H
N
C
C
H
O
C C
N H
CH2 C
H
C C
C
H
O
H
H
Deoxyctidine formed by the
dimerization of cytosine and
deoxyribose with the elimination
of a molecule of H2 O.
HO H
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BIOCHEMISTRY 73
HO
H
O
N
O
C
C
C N C
H
Thymine (T)
Occur only in DNA
CH 3
H
CH2 C
H
C C
C
H
O OH
H
H
HO H
2-Deoxy-β-Dribofuranose
NH2 H
N
C
C
H
O
C C
N H
N C
NH2 H
N
C
C
C
N
N
C H
H
N C
O
H
H2N N
C
C
C
N
N
C H
H
P
O- O- - H
Cytosine (C)
Adenine (A)
Guanine(G)
O
O Phosphate
Occur in both DNA
and RNA
Figure 3.11 Constituents of DNA (enclosed by ----) and of RNA (enclosed by |||||).
• Nucleoside + phosphate yields phosphate ester nucleotide.
- O
P
O -
O
O
NH 2
HO
H
O
N
O
C
C
C N C
H
Uracil (U)
Occur only in RNA
H
H
CH2 C
H
C C
C
H
O OH
H
H
HO OH
β-D-Ribofuranose
H
N
C
C
H
O
C C
N H
CH2 C
H
C C
C Nucleotide formed by the
bonding of a phosphate
group to deoxyctidine
H
O O
H
H
HO H
29

74 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
• Polymerized nucleotide yields nucleic acid, as shown by the structure below. In the nucleic acid
the phosphate negative charges are neutralized by metal cations (such as Mg 2+ ) or positively charged
proteins (histones).
O
P
O -
O
O
CH 2
NH 2
H
N
C
C
H
O
C C
N H
O
C
H
C C
C
H H
H
O H
P
O -
N
H C
O O CH2 C
H
H
C
O
H
C
N
C
H
O H
Segment of the DNA polymer
showing linkage of two nucleotides
Molecules of DNA are huge, with molecular weights of greater than 1 billion. Molecules of
RNA are also quite large. The structure of DNA is that of the famed double helix. It was figured
out in 1953 by James D. Watson, an American scientist, and Francis Crick, a British scientist. They
received the Nobel Prize for this scientific milestone in 1962. This model visualizes DNA as a socalled
double α-helix structure of oppositely wound polymeric strands held together by hydrogen
bonds between opposing pyrimidine and purine groups. As a result, DNA has both a primary and
a secondary structure; the former is due to the sequence of nucleotides in the individual strands of
DNA, and the latter results from the α-helix interaction of the two strands. In the secondary structure
of DNA, only cytosine can be opposite guanine and only thymine can be opposite adenine and
vice versa. Basically, the structure of DNA is that of two spiral ribbons “counterwound” around
each other, as illustrated in Figure 3.12. The two strands of DNA are complementary. This means
that a particular portion of one strand fits like a key in a lock with the corresponding portion of
another strand. If the two strands are pulled apart, each manufactures a new complementary strand,
so that two copies of the original double helix result. This occurs during cell reproduction.
The molecule of DNA is like a coded message. This “message,” the genetic information
contained in and transmitted by nucleic acids, depends on the sequence of bases from which they
are composed. It is somewhat like the message sent by telegraph, which consists only of dots,
dashes, and spaces in between. The key aspect of DNA structure that enables storage and replication
of this information is the famed double helix structure of DNA mentioned above.
Portions of the DNA double helix may unravel, and one of the strands of DNA may produce
a strand of RNA. This substance then goes from the cell nucleus out into the cell and regulates the
synthesis of new protein. In this way, DNA regulates the function of the cell and acts to control
life processes.
30
C
C
NH 2
N C
C
N
H

BIOCHEMISTRY 75
3.7.1 Nucleic Acids in Protein Synthesis
When a new cell is formed, the DNA in its nucleus must be accurately reproduced from the
parent cell. Life processes are absolutely dependent upon accurate protein synthesis, as regulated
by cell DNA. The DNA in a single cell must be capable of directing the synthesis of up to 3000
or even more different proteins. The directions for the synthesis of a single protein are contained
in a segment of DNA called a gene. The process of transmitting information from DNA to a newly
synthesized protein involves the following steps:
• The DNA undergoes replication. This process involves separation of a segment of the double
helix into separate single strands, which then replicate such that guanine is opposite cytosine (and
vice versa) and adenine is opposite thymine (and vice versa). This process continues until a
complete copy of the DNA molecule has been produced.
• The newly replicated DNA produces messenger RNA (mRNA), a complement of the single strand
of DNA, by a process called transcription.
• A new protein is synthesized using mRNA as a template to determine the order of amino acids in
a process called translation.
3.7.2 Modified DNA
A T
C G
T A
C G
G
A
G
Figure 3.12 Representation of the double helix structure of DNA showing the allowed base pairs held together
by hydrogen bonding between the phosphate–sugar polymer “backbones” of the two strands of
DNA. The letters stand for adenine (A), cytosine (C), guanine (G), and thymine (T). The dashed
lines represent hydrogen bonds.
DNA molecules may be modified by the unintentional addition or deletion of nucleotides or
by substituting one nucleotide for another. The result is a mutation that is transmittable to offspring.
Mutations can be induced by chemical substances. This is a major concern from a toxicological
viewpoint because of the detrimental effects of many mutations and because substances that cause
mutations often cause cancer as well. DNA malfunction may result in birth defects, and the failure
to control cell reproduction results in cancer. Radiation from x-rays and radioactivity also disrupts
DNA and may cause mutation.
C
T
C
T A
C G
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76 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
3.8 RECOMBINANT DNA AND GENETIC ENGINEERING
As noted above, segments of DNA contain information for the specific syntheses of particular
proteins. Within the last two decades it has become possible to transfer this information between
organisms by means of recombinant DNA technology, which has resulted in a new industry based
on genetic engineering. Most often the recipient organisms are bacteria, which can be reproduced
(cloned) over many orders of magnitude from a cell that has acquired the desired qualities.
Therefore, to synthesize a particular substance, such as human insulin or growth hormone, the
required genetic information can be transferred from a human source to bacterial cells, which then
produce the substance as part of their metabolic processes.
The first step in recombinant DNA gene manipulation is to lyze (open up) a donor cell to
remove needed DNA material by using enzyme action to cut the sought-after genes from the donor
DNA chain. These are next spliced into small DNA molecules. These molecules, called cloning
vehicles, are capable of penetrating the host cell and becoming incorporated into its genetic material.
The modified host cell is then reproduced many times and carries out the desired biosynthesis.
Early concerns about the potential of genetic engineering to produce “monster organisms” or
new and horrible diseases have been largely allayed, although caution is still required with this
technology. In the environmental area, genetic engineering offers some hope for the production of
bacteria engineered to safely destroy troublesome wastes and to produce biological substitutes for
environmentally damaging synthetic pesticides.
3.9 METABOLIC PROCESSES
Biochemical processes that involve the alteration of biomolecules fall under the category of
metabolism. Metabolic processes may be divided into the two major categories of anabolism
(synthesis) and catabolism (degradation of substances). An organism may use metabolic processes
to yield energy or to modify the constituents of biomolecules.
3.9.1 Energy-Yielding Processes
Organisms can gain energy by the following three processes:
• Respiration, in which organic compounds undergo catabolism that requires molecular oxygen
(aerobic respiration) or that occurs in the absence of molecular oxygen (anaerobic respiration).
Aerobic respiration uses the Krebs cycle to obtain energy from the following reaction:
C 6H 12O 6 + 6O 2 → 6CO 2 + 6H 2O + energy
• About half of the energy released is converted to short-term stored chemical energy, particularly
through the synthesis of ATP nucleoside. For longer-term energy storage, glycogen or starch
polysaccharides are synthesized, and for still longer term energy storage, lipids (fats) are generated
and retained by the organism.
• Fermentation, which differs from respiration in not having an electron transport chain. Yeasts
produce ethanol from sugars by fermentation:
C 6H 12O 6 → 2CO 2 + 2C 2H 5OH
• Photosynthesis, in which light energy captured by plant and algal chloroplasts are used to synthesize
sugars from carbon dioxide and water:
32

BIOCHEMISTRY 77
6CO 2 + 6H 2O + hν → C 6H 12O 6 + 6O 2
Plants cannot always get the energy that they need from sunlight. During the dark they must
use stored food. Plant cells, like animal cells, contain mitochondria in which stored food is converted
to energy by cellular respiration.
Plant cells, which use sunlight for energy and CO 2 for carbon, are said to be autotrophic. In
contrast, animal cells must depend on organic material manufactured by plants for their food. These
are called heterotrophic cells. They act as “middlemen” in the chemical reaction between oxygen
and food material, using the energy from the reaction to carry out their life processes.
SUPPLEMENTARY REFERENCES
Bettelheim, F.A. and March, J., Introduction to Organic and Biochemistry, Saunders College Publishing, Fort
Worth, TX, 1998.
Chesworth, J.M., Stuchbury, T., and Scaife, J.R., An Introduction to Agricultural Biochemistry, Chapman &
Hall, London, 1998.
Garrett, R.H. and Grisham, C.M., Biochemistry, Saunders College Publishing, Philadelphia, 1998.
Gilbert, H.F., Ed., Basic Concepts in Biochemistry, McGraw-Hill, Health Professions Division, New York,
2000.
Kuchel, P.W., Ed., Schaum’s Outline of Theory and Problems of Biochemistry, McGraw-Hill, New York, 1998.
Lea, P.J. and Leegood, R.C., Eds., Plant Biochemistry and Molecular Biology, 2nd ed., John Wiley & Sons,
New York, 1999.
Marks, D.B., Biochemistry, Williams & Wilkins, Baltimore, 1999.
Meisenberg, G. and Simmons, W.H., Principles of Medical Biochemistry, Mosby, St. Louis, 1998.
Switzer, R.L. and Garrity, L.F., Experimental Biochemistry, W.H. Freeman and Co., New York, 1999.
Voet, D., Voet, J.G., and Pratt, C., Fundamentals of Biochemistry, John Wiley & Sons, New York, 1998.
Vrana, K.E., Biochemistry, Lippincott Williams & Wilkins, Philadelphia, 1999.
Wilson, K. and Walker, J.M., Principles and Techniques of Practical Biochemistry, Cambridge University
Press, New York, 1999.
QUESTIONS AND PROBLEMS
1. What is the toxicological importance of lipids? How do lipids relate to hydrophobic (waterdisliking)
pollutants and toxicants?
2. What is the function of a hydrolase enzyme?
3. Match the cell structure on the left with its function on the right:
A. Mitochondria 1. Toxicant metabolism
B. Endoplasmic reticulum 2. Fills the cell
C. Cell membrane 3. DNA
D. Cytoplasm 4. Mediate energy conversion and utilization
E. Cell nucleus 5. Encloses the cell and regulates the passage of materials into and out
of the cell interior
4. The formula of simple sugars is C 6H 12O 6. The simple formula of higher carbohydrates is C 6H 10O 5.
Of course, many of these units are required to make a molecule of starch or cellulose. If higher
carbohydrates are formed by joining together molecules of simple sugars, why is there a difference
in the ratios of C, H, and O atoms in the higher carbohydrates, compared to the simple sugars?
5. Why does wood contain so much cellulose?
6. What would be the chemical formula of a trisaccharide made by the bonding together of three
simple sugar molecules?
33

78 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
7. The general formula of cellulose may be represented as (C 6H 10O 5) x. If the molecular weight of a
molecule of cellulose is 400,000, what is the estimated value of x?
8. During 1 month, a factory for the production of simple sugars, C 6H 12O 6, by the hydrolysis of
cellulose processes 1 million kg of cellulose. The percentage of cellulose that undergoes the
hydrolysis reaction is 40%. How many kilograms of water are consumed in the hydrolysis of
cellulose each month?
9. What is the structure of the largest group of atoms common to all amino acid molecules?
10. Glycine and phenylalanine can join together to form two different dipeptides. What are the
structures of these two dipeptides?
11. One of the ways in which two parallel protein chains are joined together, or cross-linked, is by
way of an –S–S– link. What amino acid to you think might be most likely to be involved in such
a link? Explain your choice.
12. Fungi, which break down wood, straw, and other plant material, have what are called “exoenzymes.”
Fungi have no teeth and cannot break up plant material physically by force. Knowing this, what
do you suppose an exoenzyme is? Explain how you think it might operate in the process by which
fungi break down something as tough as wood.
13. Many fatty acids of lower molecular weight have a bad odor. Speculate as to the reasons why
rancid butter has a bad odor. What chemical compound is produced that has a bad odor? What
sort of chemical reaction is involved in its production?
14. The long-chain alcohol with ten carbons is called decanol. What do you think would be the formula
of decyl stearate? To what class of compounds would it belong?
15. Write an equation for the chemical reaction between sodium hydroxide and cetyl stearate. What
are the products?
16. What are two endocrine glands that are found only in females? Which of these glands is found
only in males?
17. The action of bile salts is a little like that of soap. What function do bile salts perform in the
intestine? Look up the action of soaps, and explain how you think bile salts may function somewhat
like soap.
18. If the structure of an enzyme is illustrated as
how should the structure of its substrate be represented?
19. Look up the structures of ribose and deoxyribose. Explain where the “deoxy” came from in the
name deoxyribose.
20. In what respect are an enzyme and its substrate like two opposite strands of DNA?
21. For what discovery are Watson and Crick noted?
22. Why does an enzyme no longer work if it is denatured?
34

CHAPTER 4
Metabolic Processes
4.1 METABOLISM IN ENVIRONMENTAL BIOCHEMISTRY
The biochemical changes that substances undergo in a living organism are called metabolism.
Metabolism describes the catabolic reactions by which chemical species are broken down by
enzymatic action in an organism to produce energy and components for the synthesis of biomolecules
required for life processes. It also describes the anabolic reactions in which energy is used
to assemble small molecules into larger biomolecules. Metabolism is an essential process for any
organism because it provides the two things essential for life — energy and raw materials.
Metabolism is especially important in toxicological chemistry for two reasons: (1) interference
with metabolism is a major mode of toxic action, and (2) toxic substances are transformed by
metabolic processes to other materials that are usually, though not invariably, less toxic and more
readily eliminated from the organism. This chapter introduces the topic of metabolism in general.
Specific aspects of the metabolism of toxic substances are discussed in Chapter 7.
4.1.1 Metabolism Occurs in Cells
Metabolic processes occur in cells in organisms. Figure 3.1 shows the general structure of
eukaryotic cells in organisms such as animals and fungi. A cell is contained within a cell membrane
composed of a lipid bilayer that separates the contents of the cell from the aqueous medium around
it. Other than the cell nucleus, the material inside the cell is referred to as the cell cytoplasm, the
fluid part of which is the cytosol. The cytosol is an aqueous solution of electrolytes that also contains
enzymes that catalyze some important cell functions, including some metabolic processes. Within
the cytoplasm are specialized organelles that carry out various metabolic functions. Of these,
mitochondria are of particular importance in metabolism because of their role in synthesizing
energetic adenosine triphosphate (ATP) using energy-yielding reactions. Ribosomes are sites of
protein synthesis from mRNA templates (Chapter 8).
4.1.2 Pathways of Substances and Their Metabolites in the Body
In considering metabolic processes, it is important to keep in mind the pathways of nutrients
and xenobiotics in organisms. For humans and other vertebrate animals, materials enter into the
gastrointestinal tract, in which substances are broken down and absorbed into the bloodstream.
Most substances enter the bloodstream through the intestinal walls and are transported first to the
liver, which is the main organ for metabolic processes in the human body. The other raw material
essential for metabolic processes, oxygen from air, enters blood through the lungs. Volatile toxic
substances can enter the bloodstream through the lungs, a major pathway for environmental and
35
79

80 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Liver
Gallbladder
Large intestine
(colon)
Figure 4.1 Major organs involved in digestion.
occupational exposure to xenobiotics. Toxic substances can also be absorbed through the skin.
Undigested food residues and wastes excreted from the liver in bile leave the body through the
intestinal tract as feces. The other major pathway for elimination of waste products from metabolic
processes consists of the kidneys, which remove such materials from blood, and the bladder and
urinary tract through which urine leaves the body. Waste carbon dioxide from the oxidation of food
nutrients is eliminated through the lungs.
4.2 DIGESTION
Stomach
Pancreas
Small intestine
Anus
For most food substances and for a very limited number of toxicants, digestion is necessary
for sorption into the body. Digestion is an enzymatic hydrolysis process by which polymeric
macromolecules are broken down with the addition of water into units that can be absorbed from
the gastrointestinal tract into blood in the circulatory system; material that cannot be absorbed is
excreted as waste, usually after it has been subjected to the action of intestinal bacteria. The digestive
tract and organs associated with it are shown in Figure 4.1. A coating of mucus protects the internal
surface of the digestive tract from the action of the enzymes that operate in it.
Various enzymes perform digestion by acting on materials in the digestive tract. Carbohydrase,
protease, peptidase, lipase, and nuclease enzymes hydrolyze carbohydrates, proteins, peptides,
lipids, and nucleic acids, respectively. Digestion begins in the mouth through the action of amylase
enzyme, which is secreted with saliva and hydrolyzes starch molecules to glucose sugar. The major
enzyme that acts in the stomach is pepsin, a protein-hydrolyzing enzyme secreted into the stomach
as an inactive form (a zymogen) that is activated by a low pH of 1 to 3 in the stomach, resulting
from hydrochloric acid secreted into the stomach. In the small intestine, the digestion of carbohydrates
and proteins is finished, the digestion of fats is initiated, and the absorption of hydrolysis
product nutrients occurs. The first part of the small intestine, the duodenum, is where most digestion
occurs, whereas nutrient absorption occurs in the lower jejunum and ileum. The small intestine
produces a number of enzymes, including aminopeptidase, which converts peptides to other peptides
and amino acids; nuclease; and lactase, which converts lactose (milk sugar) to glactose and glucose.
The liver and the pancreas are not part of the digestive tract as such, but they provide enzymes
and secretions required for digestion to occur in the small intestine. The pancreas secretes amylase,
lipase, and nuclease enzymes, as well as several enzymes involved in breaking down proteins and
peptides. As discussed below with digestion of fats, the liver secretes a substance called bile that
is stored in the gallbladder and then secreted into the duodenum when needed for digestion of fats.
36

METABOLIC PROCESSES 81
By the time that ingested food mass reaches the large intestine or colon, most of the nutrients
have been absorbed. Water and ions are absorbed from the mass of material in the colon, concentrating
it and converting it to a semisolid state. Much of the material in the colon is converted to
bacterial biomass by the action of bacteria, especially Escherichia coli, that metabolize food residues
not digested by humans or animals. These bacteria produce beneficial vitamins, such as Vitamin
K and biotin, that are absorbed through the colon walls and are important in nutrition. The reducing
environment maintained by the bacteria in the colon can reduce some xenobiotics (see the discussion
of metabolic reductions in Section 7.3). One such product is toxic hydrogen sulfide, H 2S, which
is detoxified by special enzymes produced in intestinal wall mucus membranes.
4.2.1 Carbohydrate Digestion
A very simple example of a digestion process is the hydrolysis of sucrose (common table sugar),
H
C
HO
CH 2 OH
C O
H
OH H
C C
H OH
H
C
HO
O
HOCH2 H
C C
O H HO
C C
H
H2O C
CH2OH HO H
Sucrose
CH2OH C O
H
H
C
HOCH2 C
O
OH
C
OH
C
H
C
OH H
H
C
HO
C
CH2OH H OH
HO H
Glucose Fructose
(4.2.1)
to produce glucose and fructose monosaccharides that can be absorbed through intestine walls to
undergo metabolism in the body. Each digestive hydrolysis reaction of carbohydrates has its own
enzyme. Sucrase enzyme carries out the reaction above, whereas amylase enzyme converts starch
to a disaccharide with two glucose molecules called maltose, and maltose in turn is hydrolyzed to
glucose by the action of maltase enzyme. A third important disaccharide is lactose or “milk sugar,”
each molecule of which is hydrolyzed by digestive processes to give a molecule of glucose and
one of galactose.
HO
C
H
CH2OH C
H
OH
C
O
H
C
OH
C
H
H OH
37
Galactose

82 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
O H
CH3 (CH2 ) 16C O C H
O
O H C C C(CH2 ) 16CH3 CH3 (CH2 ) 16C O C H
Triglyceride
(fat)
Lipase
enzyme
H
O H
CH3 (CH2 ) 16C O C H
Fatty
acids
Figure 4.2 Illustration of digestion of fats (triglycerides).
Digestion can be a limiting factor in the ability of organisms to utilize saccharides. Many adults
lack the lactase enzyme required to hydrolyze lactose. When these individuals consume milk
products, the lactose remains undigested in the intestine, where it is acted upon by bacteria. These
bacteria produce gas and intestinal pain, and diarrhea may result. The lack of a digestive enzyme
for cellulose in humans and virtually all other animals means that these animals cannot metabolize
cellulose. The cellulosic plant material eaten by ruminant animals such as cattle is actually digested
by the action of enzymes produced by specialized rumen bacteria in the stomachs of such animals.
4.2.2 Digestion of Fats
Fats and oils are the most common lipids that are digested. Digestion breaks fats down from
triglycerides to di- and monoglycerides, fatty acids and their salts (soaps) and glycerol, which pass
through the intestine wall, where they are resynthesized to triglycerides and transported to the blood
through the lymphatic system (see Figure 4.2).
A special consideration in the digestion of fats is that they are not water soluble and cannot be
placed in aqueous solution along with the water-soluble lipase digestive enzymes. However, intimate
contact is obtained by emulsification of fats through the action of bile salts from glycocholic and
taurocholic acids produced from cholesterol in the liver:
HO
H C OH
H C OH H C
O
O
CH3 (CH2 ) 16C O
Diglyceride
C
H
H CH3 (CH2 ) 16C Monoglyceride
O C
H
H HO
Glycerol
C
H
+ + +
{
O
CH3 (CH2 ) 16C OH
O
CH3 (CH2 ) 16C Reassembly of fat
digestion products
38
HO
OH
O
C
H
C
H
O
CH3 (CH2 ) 16C O - Na +
H
C
Triglycerides
H
OH
H
OH
Representation of a bile salt
showing steroid skeleton
from cholesterol
}

METABOLIC PROCESSES 83
H
H
N +
H
H
H
C
CH 3
N + H H O
H
C C
CH 3
Figure 4.3 Illustration of the enzymatic hydrolysis of a tetrapeptide such as occurs in the digestion of protein.
4.2.3 Digestion of Proteins
O H H O H H O H H O
C N C C N C C N C C
H H C H H C H
H C
S
H
O -
Digestion of proteins occurs by enzymatic hydrolysis in the small intestine (Figure 4.3). The
digestion of protein produces single amino acids. These can enter the bloodstream through the
small intestine walls. The amino acids circulate in the bloodstream until further metabolized or
used for protein synthesis; there is not a “storage depot” for amino acids as there is for lipids,
which are stored in “fat depots” in adipose tissue. However, the body does break down protein
tissue (muscle) to provide amino acids in the bloodstream.
4.3 METABOLISM OF CARBOHYDRATES, FATS, AND PROTEINS
In the preceding section the digestion of carbohydrates, fats, and proteins by the enzymatic
hydrolysis of their molecules was discussed. Digestion enables these materials to enter the bloodstream
as relatively small molecules. Once in the bloodstream, these small molecules undergo
further metabolic reactions to enable their use for energy production and tissue synthesis. These
metabolic processes are all rather complex and beyond the scope of this chapter. However, the main
points are covered below.
4.3.1 An Overview of Catabolism
+ 3H 2 O
The overall process by which energy-yielding nutrients are broken down to provide the energy
required for muscle movement, protein synthesis, nerve function, maintenance of body heat, and
other energy-consuming functions is illustrated in Figure 4.4. The approximate empirical formula
of the biomolecules from which energy is obtained in catabolism can be represented as {CH 2O}.
The overall energy-yielding catabolic process is the following:
{CH 2O} + O 2 → CO 2 + H 2O + energy (4.3.1)
Figure 4.4 as summarized in Reaction 4.3.1 represents oxidative respiration, in which glucose,
other nutrients that can be converted to glucose, and the intermediates that glucose generates are
oxidized completely to carbon dioxide and water, yielding large amounts of energy. Oxidative
CH 3
O -
+ N C C + +
+
H O -
H H O
N C C
H H C H
+
H O -
H H O
H
H
39
N + H H O
C C
H
H C H
H C
S
H
CH 3
O -

84 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Glycolysis: degradation and partial oxidation
Fatty acids and
glycerol from digestion
of triglycerides
Fatty acids
Oxidation of nutrients to CO 2 and H 2 O
Electron transport
chain
ATP
Glycerol
CO 2
Glucose, fructose, and
galactose from digestion
of polysaccarides
Glucose ATP
Pyruvate
Amino acids
from digestion
of proteins
Acetyl = CoA Transamination
Citric acid
cycle
NADH FADH 2
Figure 4.4 Overview of catabolic metabolism, the process by which nutrients are broken down to provide
energy.
respiration is in fact a very complicated process involving many steps, numerous enzymes, and a
variety of intermediate species. Discussed in more detail in Section 4.4, oxidative respiration in
eukaryotic organisms begins with the conversion of glucose to pyruvic acid, a step that does not
require oxygen. The second stage of oxidative respiration is the conversion of pyruvic acid to acetyl
coenzyme A (acetyl-CoA). In the third stage, the acetyl-CoA goes through the citric acid cycle, in
which chemical bond energy harvested in the oxidation of the biomolecules metabolized is converted
primarily to a species designated as NADH. In the last stage of oxidative respiration, NADH
ATP
O 2 H 2 O ADP
40
NH 4 + , urea

METABOLIC PROCESSES 85
transfers electrons to molecular O 2 and generates high-energy species (ATP) that are utilized for
metabolic needs.
4.3.2 Carbohydrate Metabolism
As discussed in the preceding section, starch and the major disaccharides are broken down by
digestive processes to glucose, fructose, and galactose monosaccharrides. Fructose and galactose
are readily converted by enzyme action to glucose. Glucose is converted to the glucose 1-phosphate
species:
H
C
HO
From the glucose 1-phosphate form, glucose may be incorporated into macromolecular (polymeric)
glycogen for storage in the animal’s body and to provide energy-producing glucose on
demand. For the production of energy, the glucose 1-phosphate enters the catabolic process through
glycolysis, discussed in Section 4.4.
4.3.3 Metabolism of Fats
Fats are stored and circulated through the body as triglycerides, which must undergo hydrolysis
to glycerol and fatty acids before they are further metabolized. Glycerol is broken down via the
glycolysis pathway discussed above for carbohydrate metabolism. The fatty acids are broken down
in the fatty acid cycle, in which a long-chain fatty acid goes through a number of sequential steps
to be shortened by two carbon fragments, producing CO 2, H 2O, and energy.
4.3.4 Metabolism of Proteins
O -
A central feature of protein metabolism is the amino acid pool, consisting of amino acids in
the bloodstream. Figure 4.5 illustrates the metabolic relationship of the amino acid pool to protein
breakdown, synthesis, and storage.
Proteins are synthesized from amino acids in the amino acid pool as discussed in Section 3.3.
This occurs through the joining of H3N + –
– and –CO2 groups at peptide bonds, with the elimination
of H2O for each peptide bond formed. The body can make many of the amino acids it needs, but
eight of them, the essential amino acids, cannot be synthesized in the human body and must be
included in the diet.
The first step in the metabolic breakdown of amino acids is often the replacement of the – NH2 group with a C=O group by the action of α-ketoglutaric acid in a process called transamination.
Oxidative deamination then regenerates the α-ketoglutaric acid from the glutamic acid product
of transamination. These processes are illustrated in Figure 4.6. As a net result of transamination,
N(-III) is removed from amino acids and eliminated from the body. For this to occur, nitrogen is
first converted to urea:
O -
O
CH2OH C O
P
O
H
OH
C
H
C
C Glucose 1-phosphate
OH
H OH
41

86 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
Fats
NH +
4
Carbohydrates
Metabolic products,
O
H2N–C–NH2 ,
CO2 , H2O, energy
=
Digested proteins
Amino
acids
Amino acid pool
Figure 4.5 Main features of protein metabolism.
O
H2N C
C H
CH 3
Amino acid
(alanine)
OH
O
C OH
+ O C
H C H
H C H
HO C
O
α-ketoglutaric acid
+
NH 4
Amino acids
Nitrogenous compounds other
than protein, such as heme in
blood hemoglobin, nitrogenous
bases in nucleic acids,
and creatinine
To citric acid cycle
O
O
C OH C OH
O C + H2N C H
CH3 H C H
Pyruvic acid,
α-keto acid
H
HO
C
C
H
Glutamic acid
O
+ + {O}
Body protein
(muscle tissue,
enzymes)
Figure 4.6 Transamination of an amino acid and regeneration of α-ketoglutaric acid by oxidative deamination.
Urea is a solute that is contained in urine, and it is eliminated from the body via the kidneys and
bladder.
The α-keto acids formed by transamination of amino acids are further broken down in the citric
acid (Krebs) cycle. This process yields energy, and the body’s energy needs can be met with protein
if sufficient carbohydrates or fats are not available.
H +
H
O
H
N C N
H H
42
Urea

METABOLIC PROCESSES 87
4.4 ENERGY UTILIZATION BY METABOLIC PROCESSES
Energy in the form of free energy needed by organisms is provided by enzymatically mediated
oxidation–reduction reactions. Oxidation in a biological system, as in any chemical system, is the
loss of electrons, and reduction is the gain of electrons. A species that is oxidized by losing a
negatively charged electron may maintain electrical neutrality by losing H + ion; the loss of both e –
and H + is equivalent to the loss of a hydrogen atom, H.
A large number of steps within several major cycles are involved in energy conversion, transport,
and utilization in organisms. It is beyond the scope of this book to discuss all of these mechanisms
in detail. However, it is useful to be aware of the main mechanisms involving energy in relation
to biochemical processes in which chemical or photochemical energy is utilized by organisms.
They are the following:
• Glycolysis, in which, through a series of enzymatic reactions, a six-carbon glucose molecule is
converted to two three-carbon pyruvic acid (pyruvate) species with the release of a relatively small
amount of the energy in the glucose
• Cellular respiration, which occurs in the presence of molecular oxygen, O 2, and involves the
conversion of pyruvate to carbon dioxide, CO 2, with the release of relatively large amounts of
energy by way of intermediate chemical species
• Fermentation, which occurs in the absence of molecular O 2 and produces energy-rich molecules,
such as ethanol or lactic acid, with release of relatively little useable energy
4.4.1 High-Energy Chemical Species
Metabolic energy is provided by the breakdown and oxidation of energy-providing nutrients,
especially glucose. Usually, however, the energy is needed in a different location and at a different
time from the place and time where it is generated. This entails the synthesis of high-energy
chemical species that require energy for their synthesis and release it when they break down. Of
these, the most important is ATP:
- O
O O O
P O P O P
O -
O -
O -
which is generated by the addition of inorganic phosphate, commonly represented as P i, from
adenosine diphosphate (ADP):
- O
O O
P O P
O -
O -
N
NH 2
H O
N
O C
H C
H
H
C
H
C
C
H
HO OH
H
O C
H C
H
O
H
C
H
C
N
C
H
HO OH
43
N
NH 2
N
N
ADP
N
N
ATP
C
C
H
H

88 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
- O
- O
O
P
O
P
O
O
O
Figure 4.7 Structural formula of nicotinamide adenine dinucleotide in its reduced form of NADH + H + and its
oxidized form NAD + .
When ATP releases inorganic phosphate and reverts to ADP, a quantity of energy equivalent to 31
kJ of energy per mole of ATP is released that can be utilized metabolically. A pair of species that
are similar in function to ATP and ADP are guanine triphosphate (GTP) and guanine diphosphate
(GDP).
An important aspect of enzymatic oxidation–reduction reactions involves the transfer of hydrogen
atoms. This transfer is mediated by coenzymes (substances that act together with enzymes)
nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate
(NADP). These two species pick up H atoms to produce NADH and NADPH, respectively, both
of which can function as hydrogen atom donors. Another pair of species involved in oxidation–reduction
processes by hydrogen atom transfer consists of flavin adenine triphosphate (FAD)
and its hydrogenated form FADH 2. The structural formulas of NAD and its cationic form, NAD + ,
are shown in Figure 4.7.
4.4.2 Glycolysis
H
CH
HO
O
H H
H H
H
C H O
H
H
Reduced form NADH + H
H H
Oxidation
H
+ Reduced form NAD +
OH
H
N
HO OH
H
N
O
C
H +
N N
H
N
H
NH 2
Reduction
+ 2H
Nicotinamide adenine dinucleotide
Glycolysis is a multistepped, anaerobic (without oxygen) process in which a molecule of glucose
is broken down in the absence of O 2 to produce two molecules of pyruvic acid (pyruvate anion)
and energy. Glycolysis occurs in cell protoplasm and may be followed by either cellular respiration
utilizing O 2 or fermentation in the absence of O 2. The glycolysis of a molecule of glucose results
in the net formation of two molecules of energetic ATP and the reduction of two NAD + to two
molecules of NADH plus H + .
The first part of the glycolysis process consumes energy provided by the conversion of two
ATPs to ADP. It consists of five major steps in which a glucose molecule is converted to two
glylceraldehyde 3-phosphate molecules with intermediate formation of glucose 6-phosphate, fructose
6-phosphate, fructose 1,6-biphosphate, and dihydroxyacetone:
44
N
+
O
C
H
N
H

METABOLIC PROCESSES 89
CH2OH H
C
HO
C
H
OH
C
O
H
C
2ATP 2ADP + Pi H
C
Five steps, energy consumed
OH
H OH
Glucose
(4.4.1)
The second part of the glycolyis process is the five-step conversion of glyceraldehyde to pyruvate
accompanied by conversion of four ADPs to four ATPs:
H
O
H C
2
HO C H
C O
H
(4.4.2)
Since two molecules of ATP are converted to ADP in the first part of the glycolysis process,
there is a net gain of two molecules of ATP. The second part of the glycolysis process also yields
two molecules of NADH + H + per molecule of glucose. Subsequently, the energy-yielding conversion
of the two molecules of ATP back to ADP and the oxidation of NADH,
2NADH + 2H + + O 2 → NAD + + H 2O + energy (4.4.3)
can provide energy for metabolic needs. The three conversions accomplished in glycolysis are (1)
glucose to pyruvate, (2) ADP to ATP, and (3) NAD + to NADH. The net reaction for glycolysis may
be summarized as
Glucose + 2ADP + 2P i + 2NAD + → 2Pyruvate + 2ATP + 2NADH + 2H + + 2H 2O (4.4.4)
In addition to glucose, other monosaccharides and nutrients may be converted to intermediates in
the glycolysis cycle and enter the cycle as these intermediates.
4.4.3 Citric Acid Cycle
P O -
O
O
Glyceraldehyde
3-phosphate
4ADP + P i 4ATP
Five steps, energy released
2NAD + 2NADH + 2H +
P O -
H
O
H
2
HO
C
O O
C H
C O
H
Glyceraldehyde
3-phosphate
Glycolysis yields a relatively small amount of energy. Much larger amounts of energy may be
obtained by complete oxidation of bionutrients to CO 2 and 2H 2O, which occurs in heterotrophic
organisms that utilize oxygen for respiration. The pyruvic acid product of glycolysis can be oxidized
to the acetyl group, which becomes bound to coenzyme A in the highly energetic molecule acetyl-
CoA, as shown by the following reaction:
45
2
O
O
C
C
C
H
O -
H H
Pyruvate

90 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
O
C
C
OH
O
H C
H
H
S CoA
+ HS-CoA C O + CO2 + 2{H}
H C
H
H
(4.4.5)
Acetyl-CoA enters the citric acid cycle (also called the Krebs cycle), which occurs in cell mitochondria.
In the Krebs cycle, the acetyl group is oxidized to CO 2 and water, harvesting a substantial
amount of energy. This complex cycle starts with the reaction of oxaloacetate with acetyl-CoA,
O C O
Oxaloacetate Acetyl = CoA Citrate
-
O C
C
C O -
H
O
H
+
H
S CoA
C O
C H
H
C
C
C O -
HO
H
O
C O
H
-
O C O
H C H
O
-
(4.4.6)
to produce citrate. In a series of steps involving a number of intermediates, CO 2 is evolved and H
is removed by NAD + to yield NADH + H + and by FAD to yield FADH 2. Guanosine triphosphate
is also generated from guanosine diphosphate in the citric acid cycle and later generates ATP. The
anions of several four-, five-, and six-carbon organic acids are generated as intermediates in the
citric acid cycle, including citric, isocitric, ketoglutaric, succinic, fumaric, malic, and oxaloacetic
acids; the last of these reacts with additional acetyl-CoA from glycolysis to initiate the cycle again.
Structural formulas of the intermediate species generated in the citric acid cycle are shown in
Figure 4.8. The reduced carrier molecules generated in the citric acid cycle, NADH and FADH 2,
are later oxidized in the respiratory chain (see below) to produce ATP and are, therefore, the major
conduits of energy from the citric acid cycle. The reaction for one complete cycle of the citric acid
cycle can be summarized as follows:
Acetyl-CoA + 3NAD + + FAD + GDP + P i + 2H 2O →
3NADH + FADH 2 + 2CO 2 + 2H + + GTP + HS-CoA (4.4.7)
4.4.4 Electron Transfer in the Electron Transfer Chain
As indicated by Reaction 4.3.1, the driving force behind the high-energy yields of oxidative
respiration is the reaction with molecular oxygen to produce H 2O. Electrons removed from glucose
and its products during oxidative respiration are donated to O 2, which is the final electron receptor.
To this point in the discussion of oxidative respiration, molecular oxygen has not entered any of
the steps. It does so during transfer of electrons in the electron transfer chain, the step at which
most of the energy is harvested from oxidative respiration. Electrons picked up from glycolysis
and citric acid cycle intermediates are transferred to the electron transport chain via NAD + /(NADH
+ H + ) and FAD/FADH 2. The overall process, which occurs in several small increments, is represented
for NADH as
NADH + H + + ½O 2 → NAD + + H 2O (4.4.8)
46

METABOLIC PROCESSES 91
H
H C
H
O
O
C CoA HO C C O
Acetyl = CoA
-
O
H
C
C
O
H
-
H C H
C O -
O
C C O
O
-
O
H
C
C
O
H
-
C H
C O -
H
C
HO
C
C O
O
-
O
H H
O
O
-
From glycolysis
O
C
H C H
Citrate Isocitrate α-Ketoglutarate
O
H C H
O C
S
-
O
O C
H C H
H C H
CoA
-
O
C
H C H
C O
O
-
O
C
-
O
C
C
C O
O
-
O
H
C
H
-
O
C
C
C O
O
-
O
H OH
C H H
-
O
C
C
C O
O
-
O
H H
Oxaloacetate Malate Fumarate Succinate Succinyl CoA
Figure 4.8 Intermediates in the citric acid cycle shown in the ionized forms in which they exist at physiological
pH values. The final oxaloacetate product reacts with acetyl-CoA from glycolysis to start the cycle
over again.
The electron transfer chain converts ADP to highly energetic ATP, which provides energy in cells.
By occurring in several reactions, the oxidation of NADH + H + to NAD + releases energy in small
increments enabling its efficient utilization.
4.4.5 Electron Carriers
Electron carriers are chemical species that exist in both oxidized and reduced forms capable
of reversible exchange of electrons. Electron carriers consist of flavins, coenzyme Q, iron–sulfur
proteins, and cytochromes. As shown in Figure 4.9, cytochromes contain iron bound with four N
atoms attached to protein molecules, a group called the heme group. The iron ions in cytochromes
are capable of gaining and losing electrons to produce Fe 2+ and Fe 3+ , respectively. Interference with
the action of cytochromes is an important mode of the action of some toxicants. Cyanide ion, CN – ,
has a strong affinity for Fe 3+ in ferricytochrome, preventing it from reverting back to the Fe 2+ form,
thus stopping the transfer of electrons to O 2 and resulting in rapid death in the case of cyanide
poisoning.
4.4.6 Overall Reaction for Aerobic Respiration
From the discussion above, it is obvious that aerobic respiration is a complex process involving
a multitude of steps and a large number of intermediate species. These can be summarized by the
following overall net reaction for the catabolic metabolism of glucose:
C 6H 12O 6 + 10NAD + + 2FAD + + 36ADP + 36P i + 14H + + 6O 2 →
6CO 2 + 36ATP + 6H 2O + 10NADH + 6FADH 2
47
(4.4.9)

92 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
4.4.7 Fermentation
HC
HC
Figure 4.9 Heme group in a cytochrome involved in electron exchange.
N
N
Fe 3+
N
H
C
N
Fermentation occurs when O 2 is not utilized for aerobic respiration through the citric acid
cycle and the electron transport chain. Glycolysis still occurs as a prelude to fermentation with
some production of ATP, but the utilization of energy from glucose is much less than when aerobic
respiration occurs. Instead of complete oxidation of glucose to carbon dioxide and water, fermentation
stops with an organic molecule. Fermentation is carried out by a variety of bacteria and by
eukaryotic cells in the human body. Muscle cells carry out fermentation of pyruvate to lactate under
conditions of insufficient oxygen, and the accumulation of lactate in muscle cells is responsible
for the pain associated with extreme exertion. Nerve cells are incapable of carrying out fermentation,
which is why brain tissue is rapidly destroyed when the brain is deprived of oxygen.
Lactic acid fermentation occurs when lactate is the end product of fermentation. Coupled
with glycolysis, lactic acid fermentation can generate ATP from ADP and provide energy for cellular
processes. The fermentation step in lactic acid fermentation generates NAD + from NADH + H + ,
and the NAD + cycles back to the glycolysis process. The lactic acid fermentation cycle is illustrated
in Figure 4.10.
Alcoholic fermentation occurs when the end product is ethanol, as shown in Figure 4.11. In
this process the pyruvate is first converted enzymatically to acetaldehyde. The conversion of
acetaldehyde to ethanol produces NAD + from NADH + H + , and the NAD + is cycled through the
glycolysis process. As with lactic acid fermentation, the glycolysis process produces usable energy
contained in two molecules of ATP produced for each molecule of glucose metabolized.
4.5 USING ENERGY TO PUT MOLECULES TOGETHER: ANABOLIC REACTIONS
The preceding section has discussed in some detail the complicated processes by which complex
molecules are disassembled to extract energy for metabolic needs. Much of this energy goes into
anabolic metabolic processes to put small molecules together to produce large molecules needed
for function and structure in organisms. Typical of the small molecules so put together are glucose
monosaccharide molecules, assembled into starch macromolecules, and amino acids, assembled
into proteins. In all cases of macromolecule synthesis, an H atom is removed from one molecule
and an –OH group from the other to link the two together:
S
48
CH
CH
Fe 2+
H
C
Protein
S

METABOLIC PROCESSES 93
Fermentation Glycolysis
H
C
HO
CH2OH C O 2ADP 2ATP
H
H
C
OH H
2
OH
C C
Pyruvate
H OH 2NAD
Glucose
+ 2NADH + 2H +
O
O C
O C
H C H
H
2
-
O O
C
C
C
-
H OH
Lactate
H
H
H
Figure 4.10 Lactic acid fermentation in which the conversion of pyruvate to lactate is coupled with glycolysis
to produce energetic ATP.
Fermentation Glycolysis
CH2OH C O 2ADP 2ATP
H
H
H
C C
OH H
2
HO
OH
C C
Pyruvate
H OH 2NAD
Glucose
+ 2NADH + 2H +
O
O C
O C
H C H
H
-
2CO 2
H H
O H
2 HO C C H
2 C C H
H H
H
H
Ethanol Acetaldehyde
Figure 4.11 Alcoholic fermentation in which the conversion of pyruvate to ethanol through an acetaldehyde
intermediate is coupled with glycolysis to produce energetic ATP.
{Molecule A}–H + HO–{Molecule B} → {Molecule A}–{Molecule B} + H 2O (4.5.1)
Since a molecule of water is eliminated for each linkage formed, the anabolic reactions leading to
macromolecule formation are dehydration reactions. Recall from Section 4.2 that when macromolecular
nutrient molecules are digested prior to their entering the body’s system, a molecule of
water is added for each linkage broken — a hydrolysis reaction. The energy required for the
anabolic synthesis of macromolecules is provided by catabolic processes of glycolysis, the citric
acid cycle, and electron transport.
A variety of macromolecules are produced anabolically. The more important of these are listed
below:
• Polysaccharide glycogen (animals) and starch (plants) produced for energy storage from glucose
49

94 TOXICOLOGICAL CHEMISTRY AND BIOCHEMISTRY
• Polysaccharide chitin composing shells of crabs and similar creatures produced from modified
glucose
• Lipid triglyceride fats and oils used for energy storage produced from glycerol and three fatty acids
• Phospholipids present in cell membranes produced from glycerol, two fatty acids, and phosphate
• Globular proteins (in enzymes) and structural proteins (in muscle) produced from amino acids
• Nucleic acids that provide the genetic code and directions for protein synthesis composed of
phosphate, nitrogenous bases, deoxyribose (DNA), and oxyribose (RNA)
The anabolic processes by which macromolecules are produced are obviously important in life
processes. Remarkably, these processes generally occur properly, making the needed materials
when and where needed. However, in some cases things go wrong with potentially catastrophic
results. This can occur through the action of toxicants and is a major mode of the action of toxic
substances.
4.6 METABOLISM AND TOXICITY
Metabolism is of utmost importance in toxicity. Details of the metabolism of toxic substances
and their precursors are addressed in Chapter 7, “Toxicological Chemistry.” At this point it should
be noted that there are several major aspects of the relationship between toxic substances and
metabolism, as listed below:
• Some substances that are not themselves toxic are metabolized to toxic species. Most substances
regarded as causing cancer must be metabolically activated to produce species that are the ultimate
carcinogenic agents.
• Toxic species are detoxified by metabolic processes.
• Metabolic processes act to counter the effects of toxic substances.
• Metabolic processes of fungi, bacteria, and protozoa act to degrade toxic substances in the water
and soil environments.
• Adverse effects on metabolic processes constitute a major mode of action of toxic substances. For
example, cyanide ion bonds with ferricytochrome oxidase, a form of an enzyme containing iron(III)
that cycles with ferrouscytochrome oxidase, containing iron(II), in the respiration process by which
molecular oxygen is utilized, thus preventing the utilization of O 2 and leading to rapid death.
4.6.1 Stereochemistry and Xenobiotics Metabolism
Recall from Section 1.9 that some molecules can exist as chiral enantiomers that are mirror
images of each other. Although enantiomers may appear to be superficially identical, they may
differ markedly in their metabolism and toxic effects. Much of what is known about this aspect of
xenobiotics has been learned from studies of the metabolism and effects of pharmaceuticals. For
example, one of the two enantiomers that comprise antiepileptic Mesantoin is much more rapidly
hydroxylated in the body and eliminated than is the other enantiomer. The human cytochrome P-
450 enzyme denoted CYP2D6 is strongly inhibited by quinidine, but is little affected by quinine,
an optical isomer of quinidine. Cases are known in which a chiral secondary alcohol is oxidized
to an achiral ketone, and then reduced back to the secondary alcohol in the opposite configuration
of the initial alcohol.
50

METABOLIC PROCESSES 95
SUPPLEMENTARY REFERENCES
Brody, T., Nutritional Biochemistry, 2nd. ed., Academic Press, San Diego, 1999.
Finley, J.W. and Schwass, D.E., Eds., Xenobiotic Metabolism, American Chemical Society, Washington, D.C.,
1985.
Groff, J.L., Gropper, S.S., and Hunt, S.M., Advanced Nutrition and Human Metabolism, 2nd ed., West
Publishers, Minneapolis/St. Paul, 1995.
Hutson, D.H., Caldwell, J., and Paulson, G.D., Intermediary Xenobiotic Metabolism in Animals: Methodology,
Mechanisms, and Significance, Taylor & Francis, London, 1989.
Illing, H.P.A., Ed., Xenobiotic Metabolism and Disposition, CRC Press, Boca Raton, FL, 1989.
Salway, J.G., Metabolism at a Glance, 2nd ed., Blackwell Science, Malden, MA, 1999.
Stephanopoulos, G., Aristidou, A.A., and Nielsen, J., Metabolic Engineering Principles and Methodologies,
Academic Press, San Diego, 1998.
QUESTIONS AND PROBLEMS
1. Define metabolism and its relationship to toxic substances.
2. Distinguish between digestion and metabolism. Why is digestion relatively unimportant in regard
to toxic substances, most of which are relatively small molecules?
3. What is the fundamental difference between the digestion of fats and that of complex carbohydrates
(starches) and proteins? What role is played by bile salts in the digestion of fats?
4. What are the functions of ADP, ATP, NAD + , and NADH in metabolism?
5. What is the overall reaction mediated by the Krebs cycle? What does it produce that the body needs?
6. What is the amino acid pool? What purposes does it serve?
7. What is meant by an essential amino acid?
8. What is transamination? What product of amino acid synthesis is eliminated from the body by the
kidneys?
9. Give the definition and function of an energy carrier species in metabolism.
51

BYLAAG 2
Clark, JH and Macquarrie, D, 2002, Handbook of Green Chemistry And Technology, 2 nd ed., Blackwell
Science: Oxford, p. 1 – 28.
52

1 Introduction
1.1 Chemistry—past, present and future
Chapter 1: Introduction
Chemistry is having a difficult time. While society
continues to demand larger quantities of increasingly
sophisticated chemical products, it also regards the
industries that manufacture these products with
increasing degrees of suspicion and fear.
The range of chemical products in today’s society
is enormous and these products make an invaluable
contribution to the quality of our lives. In medicine,
the design and manufacture of pharmaceutical
products has enabled us to cure diseases that
have ravaged humankind throughout history. Crop
protection and growth enhancement chemicals have
enabled us to increase our food yields dramatically.
It is particularly revealing to note that, although the
twentieth century saw an increase in world population
from 1.6 to 6 billion, it also saw an increase in
life expectancy of almost 60% [1]!
Chemistry has played, and continues to play, a
fundamental role in almost every aspect of modern
society, and, as the enormous populations in China,
India and the emerging nations demand western
levels of healthcare, food, shelter, transport and consumer
goods, so the demands on the chemicals
industries will grow.
The successful development of the chemicals
industries has almost had an inverse relationship
with public perception. Since writing, over five years
ago, in the introduction to The Chemistry of Waste
Minimisation, that ‘The public image of the chemical
industry has badly deteriorated in the last ten
years . . .’ [2], the situation has worsened. Major surveys
of public opinion throughout Europe in 2000
revealed that in no country was the majority of
people favourably disposed towards the chemical
industry [3,4]. The most favourable interpretation of
the data is that in some of the major centres of chemicals
manufacturing (e.g. Germany) more people
gave positive than negative views on chemicals
JAMES H. CLARK
1
53
Handbook of Green Chemistry and Technology
Edited by James Clark, Duncan Macquarrie
Copyright © 2002 by Blackwell Science Ltd
manufacturing, but for many European countries
the ratio of unfavourable to favourable views was
alarmingly high (e.g. Sweden, 2.8; France, 2.2;
Spain, 1.5; Belgium, 1.3).
In the UK, a steady decline in public perception
over many years is clearly evident (Fig. 1.1). It is
especially disturbing to analyse the survey data more
closely and to note, for example, that the 16–24-year
age group has the lowest opinion of the chemicals
industries. This is the most critical group for chemistry.
We need to maintain a high level of interest
and enthusiasm for chemistry at secondary and tertiary
education levels so that we can maintain the
supply of a large number of highly intelligent,
motivated and qualified young people for our industries,
universities, schools and other walks of life. At
present, however, the poor image of chemistry is
adversely affecting demand. In the UK, for example,
the number of applicants to read chemistry at university
has been falling steadily for several years
(Fig. 1.2).
The number of applicants to read chemical engineering
is even more alarming (

2 Chapter 1
60
50favourable
40
30
20
10
unfavourable
1980 1990 2000
Fig. 1.1 Trends in the favourability to the chemical industry of
the general public (smoothed plots) (based on MORI Opinion
Poll figures in the period 1980–2000).
4000
3500
3000
1996
Fig. 1.2 Trend in the number of applications to study
chemistry in UK universities (source: UCAS).
2000
foods, drinks or consumer products. It is revealing to
note the recent change in name of the leading trade
association for the chemicals industry in the USA
from The American Chemical Manufacturers Association
to The American Chemistry Council. Indeed, a
cynical view might be that we can solve our image
problems overnight by reinventing ourselves as
‘molecular engineers’!
In 1995 I wrote that chemistry’s bad image was
‘. . . largely due to concerns over adverse environmental
impact’ [2]. The growth in the chemicals
54
industries in the twentieth century was at the cost
of producing millions of tonnes of waste, and if we
extend the discussion to include health and safety
issues then we must add the chemical disasters that
have led to much unfavourable publicity and have
hardened the views of many critics. The increasing
levels of environmental awareness among the
general public make it even more important that
the chemicals industries ‘clean up their act’. Public
acceptability of environmental pressure groups adds
to their influence and together they effectively force
governments to use legislation to force industry into
making improvements.
How much do we need to change? Although early
work to ‘green’ the manufacture of chemicals was
focused largely on reducing the environmental
impact of chemical processes, a much wider view
will be necessary in the new century. An exaggerated
but illustrative view of twentieth century chemical
manufacturing can be written as a recipe [5]:
(1) Start with a petroleum-based feedstock.
(2) Dissolve it in a solvent.
(3) Add a reagent.
(4) React to form an intermediate chemical.
(5) Repeat (2)–(4) several times until the final
product is obtained; discard all waste and spent
reagent; recycle solvent where economically
viable.
(6) Transport the product worldwide, often for longterm
storage.
(7) Release the product into the ecosystem without
proper evaluation of its long-term effects.
The recipe for the twenty-first century will be very
different:
(1) Design the molecule to have minimal impact
on the environment (short residence time,
biodegradable).
(2) Manufacture from a renewable feedstock (e.g.
carbohydrate).
(3) Use a long-life catalyst.
(4) Use no solvent or a totally recyclable benign
solvent.
(5) Use the smallest possible number of steps in the
synthesis.
(6) Manufacture the product as required and as
close as possible to where it is required.
The broader picture will apply not only to chemical
manufacturing but also to transportation, legislation

and, most critically, education. We must train the
new generation of chemists to think of the environmental,
social and economic factors in chemicals
manufacturing.
1.2 The costs of waste
In the time taken to read one page of this book,
several tonnes of hazardous waste will have been
released to the air, water and land by industry, and
the chemicals industry is by far the biggest source of
such waste. This is only a fraction of the true scale
of the problem. Substances classified as ‘hazardous’
only represent a very small number of the total
number of substances in commercial use. In the mid-
1990s in the USA, for example, only about 300 or
so of the 75000 commercial substances in use were
classified as hazardous. Clearly a much higher proportion
of commercial chemicals presents a threat to
humans and to the environment, and as mounting
pressure will lead to an ever-increasing number
of chemicals being tested then the scale of the
‘hazardous waste’ problem will take on ever more
frightening proportions. Yet this only represents one
‘cost’ of waste and the cost of waste can be truly
enormous.
Compliance with existing environmental laws will
cost new EU member states well over E10 billion; a
similar amount is spent each year in the USA to treat
and dispose of waste. Governments across the globe
are increasing the relative costs of waste disposal to
discourage the production of waste and to encourage
recycling and longer product lifetimes.
Although, in general terms, company accounting
practices are highly developed, when it comes to industrial
chemical processes, particularly for smaller
companies working with multi-purpose plants in the
speciality chemicals area, the true breakdown of
manufacturing costs is often unknown. Sophisticated
process monitoring and information technology
developments are beginning to allow the true
production costs to become evident. What this shows
is that the cost of waste can easily amount to 40%
of the overall production costs for a typical speciality
chemical product (Fig. 1.3).
However, the costs of effluent treatment and waste
disposal actually tell only part of the story. There are
other direct costs to production resulting from inefficient
manufacturing, by-product generation and
raw material and energy inefficiencies. Industry also
55
Labour
Capital
depreciation
Energy
utilities
Waste
is becoming increasingly aware of the indirect costs
of waste on deteriorating public relations (as
described in Section 1.1). These affect the attitudes
of the workforce and hence their morale and performance,
and also that of their neighbours who can
lobby local authorities to impose tighter standards
and legislation. As a society, we can add the largely
unknown but certain to be substantial (if not catastrophic)
costs to the environment (including human
health). All of these costs will grow into the future
through tougher legislation, greater fines, increased
waste disposal costs, greater public awareness and
diminishing raw materials, forcing the adoption of
more efficient manufacturing (Fig. 1.4).
1.3 The greening of chemistry
Introduction 3
Materials
Fig. 1.3 Production costs for speciality chemicals.
Sustainable development is now accepted by governments,
industry and the public as a necessary goal
for achieving the desired combination of environmental,
economic and societal objectives. The challenge
for chemists and others is to develop new
products, processes and services that achieve all the
benefits of sustainable development. This requires a
new approach whereby the materials and energy
input to a process are minimised and thus utilised
at maximum efficiency. The dispersion of harmful
chemicals in the environment must be minimised or,
preferably, completely eliminated. We must maxi-

4 Chapter 1
Workforce Process waste
Public
relations
Neighbours
Raw
material
inefficiencies
Effluent
treatment
COSTS OF WASTE
Production losses
Energy
inefficiencies
Waste
disposal
mise the use of renewable resources and extend the
durability and recyclability of products, and all of this
must be achieved in a way that provides economic
benefit to the producer (to make the greener product
and process economically attractive) and enables
industry to meet the needs of society.
We can start by considering the options for waste
management within a chemical process (Fig. 1.5).
The hierarchy of waste management techniques
now has prevention, through the use of cleaner
processes, as by far the most desirable option. Recycling
is considered to be the next most favourable
option and, from an environmental standpoint,
is particularly important for products that do not dissipate
rapidly and safely into the environment.
Disposal is certainly the least desirable option. The
term ‘cleaner production’ encompasses goals and
principles that fall nicely within the remit of waste
minimisation. The United Nations Environmental
Programme describes cleaner production as:
‘The continuous application of an integrated preventative
environmental strategy to processes and
products to reduce risks to humans and the environment.
For production processes, cleaner production
includes conserving raw materials, and
Byproduct
formation
56
Damage to
environment
Fig. 1.4 The costs of waste.
reducing the quality and toxicity of all emissions
and wastes before they leave a process.’
Cleaner production and clean synthesis fall under
the heading of waste reduction at source and, along
with retrofitting, can be considered as the two
principal technological changes. Waste reduction
at source also covers good housekeeping, input
material changes and product changes.
There are many ways to define the efficiency of a
chemical reaction. Yield and selectivity traditionally
have been employed, although these do not necessarily
give much information about the waste produced
in a process. From an environmental (and
increasingly economic) point of view, it is more
important to know how many atoms of the starting
material are converted to useful products and how
many to waste. Atom economy is a quantitative
measure of this by, for example, calculating the percentage
of oxygen atoms that end up in the desired
product [6]. We can illustrate this by considering
a typical oxidation reaction whereby an alcohol,
for example, is converted to a carboxylic acid using
chromium(VI) as the stoichiometric oxidant. The
material inputs for this reaction are the organic substrate,
a source of chromium(VI), acid (normally sul-

Fig. 1.5 Options for waste
management within a chemical
manufacturing process.
Good
housekeeping
Table 1.1 ‘Atom accounts’ for a typical partial oxidation
reaction using chromate
Retro-fitting
Element Fate Atom utilisation
C Product(s) Up to 100%
H Product(s) + waste acid

6 Chapter 1
Table 1.3 Global ‘lost work’ in major chemical processes
Process Raw materials Final product a
The term ‘green chemistry’ is becoming the worldwide
term used to describe the development of
more eco-friendly, sustainable chemical products
and processes. The term was coined almost ten years
ago by the US Environmental Protection Agency and
has been defined as:
‘The utilisation of a set of principles that reduces
or eliminates the use or generation of hazardous
substances in the design, manufacture and application
of chemical products’ (Paul Anastas)
This is elaborated further in the form of the so-called
Principles of Green Chemistry:
• Waste prevention is better than treatment or
clean-up
• Chemical synthesis should maximise the incorporation
of all starting materials
• Chemical synthesis ideally should use and generate
non-hazardous substances
• Chemical products should be designed to be nontoxic
• Catalysts are superior to reagents
• The use of auxiliaries should be minimised
• Energy demands in chemical syntheses should be
minimised
• Raw materials increasingly should be renewable
• Derivations should be minimised
• Chemical products should break down into innocuous
products
• Chemical processes require better control
• Substances should have minimum potential for
accidents
The chemical technologies, both new and established,
that are described in this book address these
principles by considering atom efficiency, alternative
energy sources, the use of alternative feedstocks, in-
Theoretical work potential (kJmol -1 final product)
Natural gas + air Æ methanol 1136 717 63
Natural gas + air Æ hydrogen 409 236 58
Ammonia (from natural gas + air) Æ nitric acid 995 43 4
Copper ore Æ copper 1537 130 9
Bauxite Æ aluminium 4703 888 19
a Excludes any ‘steam credit’.
58
2.0 x 10 9 ha
for food
production
for 10 bn people
2.8 x 10 9 ha available
1 x 10 9 ta -1
for organics
Fig. 1.6 Biomass utilisation in 2040.
Thermodynamic efficiency (%)
0.8 x 10 9 ha
available for
non-foods
@ 40 t ha -1 a -1
32 x 10 9 ta -1
+ forests
+ waste streams
50 x 10 9 ta -1
of biomass
>40 x 10 9 ta -1
for energy
= 2 x 10 20 Ja -1
novative engineering, clean synthesis and process
improvements.
It is, perhaps, worth focusing briefly on one of
these principles as we enter the century where oil
reserves will be seriously diminished: ‘Raw materials
increasingly should be renewable’. Can we base
the future chemical industry on biomass? Remarkably,
at least some of the better calculations show
that this is a very likely scenario [10]. With a modest
increase in farming efficiency to improve crop yield
to about 40tha -1 year -1 we will need only less than
1% of the biomass available globally to provide all
the raw material necessary to feed the entire organic
chemicals industry by 2040 (Fig. 1.6).

Assuming a global population of 10 billion by
that year, we can still reasonably expect to produce
enough ‘spare’ biomass to supply some 19% of the
energy requirements of that future society (Table
1.4).
This would still make us very reliant on fossil fuels
but, significantly, much less dependent on oils, the
most vulnerable of the major energy sources based
on the current rate of utilisation. Feeding, maintaining
and providing material comforts for all is indeed
within our grasp if, to paraphrase Mahatma Gandhi,
we seek to satisfy our need and not our greed.
By incorporating raw materials considerations into
the ‘big picture’ we can move towards the ultimately
Table 1.4 From fossil to green
Energy source 1990 a
Percentage of
energy sources
2040 b
Oil 38 17
Coal 20 18
Gas 16 14
Biomass 16 19
Hydro 5 5
Nuclear 5 6
Solar — 14
Wind — 7
a Based on an energy consumption of 3.5 ¥ 10 20 J.
b Based on an energy consumption of 1 ¥ 10 21 J.
Fig. 1.7 Life-cycle assessment for
chemical products (E = energy input;
C = consumables input; W = waste).
E
Premanufacturing
essential concept of life-cycle assessment. The lifecycle
of a product can be considered as [11]:
Pre-manufacturing (materials acquistition)
Manufacturing (processing and formulation)
Product delivery (packaging and distribution)
Product use
End of (first) life
Introduction 7
This model can be elaborated for a life-cycle assessment
for chemical products (Fig. 1.7).
This quickly allows us to recognise the vital importance
of the other end of the product cycle: end of
life. The recycling of waste is not embraced strictly
by the principles of green chemistry, because they
are focused on avoiding waste at source, but its
importance cannot be ignored. If a product cannot
be dissipated quickly and safely into the environment,
then it is essential that it or its component
parts are efficiently recycled. We can no longer afford
single-use products.
Pollution prevention options can be considered at
every stage in the life-cycle of a chemical product
(Fig. 1.8) [11]. In general, we should be looking
C E C E E C
E
Manufacturing
W W W W W
59
remanufacture
recycle
Product
delivery
Product
use
refurbish
End of Life

8 Chapter 1
Premanufacturing
Alternative
feedstocks/
renewable
resources
Avoid
auxiliaries
Minimise
transportation
Utilise waste
Minimise
solvents
Manufacturing
Atom efficient
Catalysts
rather than
reagents
Solvent
substitution
Safer
chemistry
Simpler
chemistry
Minimum
energy
Avoid
additives
Fig. 1.8 Pollution prevention options in the life-cycle of a
chemical product.
increasingly at the industrial ecology goals for green
chemistry [11]:
• Adopt a life-cycle perspective regarding chemical
products and processes
• Realise that the activities of your suppliers and
customers determine, in part, the greenness of
your product
• For non-dissipative products, consider recyclability
• For dissipative products (e.g. pharmaceuticals,
crop-protection chemicals), consider the environmental
impact of product delivery
• Perform green process design as well as green
product design
Life-cycle assessment is given better and more
detailed consideration in later chapters in this book.
A number of green chemistry and sustainable
chemistry initiatives now are in place or becoming
Product
delivery
Minimal
transportation
Minimal
packaging/
eco-friendly
packaging
60
Product
use
Minimal
consumption/
maximum
efficiency
Minimal
auxiliary
needs
Minimal
energy usage
End of life
Biodegradable
Recyclable
Environmentally
compatible
established in various corners of the globe, including
the USA, UK, Australia and Japan. In the UK, the
Green Chemistry Network (GCN) [12] was established
in 1998 with funding from the Royal Society
of Chemistry. The GCN has its hub based at the University
of York in England and benefits from close
collaboration with the world-famous Science Education
Group and the Chemical Industries Education
Centre, as well as the staff of one of the UK’s most
successful Chemistry Departments. The GCN promotes
green chemistry through increased awareness,
education and training and facilitates the sharing of
good practice in green chemistry through conferences,
technology transfer activities and by acting as
a focal point for relevant information. It is doing this
by providing educational material for all levels, training
courses for industrialists and teachers, conferences
and seminars on green chemistry, technology
transfer brokerage, databases of green chemistry
articles and links to other relevant activities, notably
through a dynamic website.
The GCN works alongside the Royal Society of

Chemistry journal, Green Chemistry, which provides
news on grants, initiatives, educational and industrial
development and conferences, as well as a
who’s-who on green chemistry research and regular
peer-reviewed articles from chemistry and chemical
engineering university departments and chemical
and pharmaceutical companies across the world.
The US Green Chemistry Institute (GCI) has
been promoting the principles and practice of green
chemistry for several years. The GCI, which now has
core funding from, and links with, the American
Chemical Society (ACS), is dedicated to encouraging
environmentally benign chemical synthesis and promoting
research and education. The US Presidential
Green Chemistry Awards Programme recognises and
publicises achievements by industry and academe,
encouraging industry to talk openly about its innovative
clean chemistry and providing scientists and
education with some excellent case studies. There
are now green-chemistry-related award schemes
in several other countries, including the UK, Italy,
Australia and Japan. Major green chemistry or sustainable
chemistry networks and related initiatives
have been set up across the globe with significant
developments, including a series of Gordon Green
Chemistry conferences (in the USA and UK) and the
61
first International Union of Pure and Applied Chemistry
(IUPAC) International Symposium of Green
Chemistry (in India). The greening of chemistry is
truly underway!
References
Introduction 9
1. Breslau, R. Chemistry Today and Tomorrow. Awareness
Chemical Society, Washington, 1997.
2. Clark, J. H. The Chemistry of Waste Minimisation. Blackie
Academic, London, 1995.
3. MORI. The Public Image of the Chemical Industry. Research
study conducted for the Chemical Industries
Association. MORI, London, 1999.
4. CEFIC. CEFIC Pan European Survey 2000. Image of the
Chemical Industry Summary. CEFIC, Brussels, 2000.
5. Based on: Woodhouse, E. J. Social Reconstruction of a
Technoscience?: The Greening of Chemistry.
http://www.rpi.edu/~woodhe/docs/green.html
6. Trost, B. M. Angew Chem. Int. Food Engl., 1995, 34, 259.
7. Clark, J. H. Green Chem., 1999, 1, 1.
8. Sheldon, R. A. Chemtech, 1994, March, 38.
9. Hinderink, A. P., van der Kooi, H. J., & de Swaan
Arons, J. Green Chem., 1999, 1, G176.
10. Okkerse, C., & van Bekkum, H. Green Chem., 1999, 1,
107.
11. Anastas, P. T., & Lankey, R. L. Green Chem., 2000, 2,
289.
12. See http://www.rsc.org/greenchem/

1 Introduction
Chapter 2: Principles of Sustainable
and Green Chemistry
In the modern context, the terms ‘sustainable development’
and ‘green chemistry’ have been around for
less than 15 years. Discussion of sustainability began,
essentially, when the 1987 UN Commission on Environment
and Development (usually referred to as
the Bruntland Commission) noted that economic
development might lead to a deterioration, not an
improvement, in the quality of people’s lives [1].
This led to the now commonly accepted definition of
‘sustainable development’ as being:
‘Development which meets the needs of the
present without compromising the ability of future
generations to meet their own needs.’
This definition is intentionally broad, covering all
aspects of society. The debate on what it actually
means, in practical terms, for different disciplines
and sectors of society continues, and indeed there
are those who argue that it is a contradiction in
terms. However, working interpretations of the definition
are becoming established [2]. For example, in
planning it is the process of urban revitalisation that
seeks to integrate urbanisation with nature preservation;
in biology it is associated with the protection
of biodiversity; in economics it is the accounting for
‘natural capital’.
Sustainable development has particular relevance
for chemistry-based industries because it is concerned
with avoidance of pollution and the reckless
use of natural resources. In essence it is being recognised
increasingly as the pursuit of the principles and
goals of green chemistry.
The Green Chemistry Movement was started in
the early 1990s by the US Environmental Protection
Agency (EPA) as a means of encouraging industry
and academia to use chemistry for pollution prevention.
More specifically, the green chemistry mission
was:
‘To promote innovative chemical technologies that
reduce or eliminate the use or generation of haz-
MIKE LANCASTER
10
62
Handbook of Green Chemistry and Technology
Edited by James Clark, Duncan Macquarrie
Copyright © 2002 by Blackwell Science Ltd
ardous substances in the design, manufacture and
use of chemical products.’
In conjunction with the American Chemical Society,
the EPA developed green chemistry into a set of
twelve guiding principles [3]. These principles can be
summarised as being concerned with ensuring that:
• The maximum amounts of reagents are converted
to useful product (atom economy)
• Production of waste is minimised through reaction
design
• Non-hazardous raw materials and products are
used and produced wherever possible
• Processes are designed to be inherently safe
• Greater consideration is given to using renewable
feedstocks
• Processes are designed to be energy efficient
These principles and associated terminology are
becoming widely accepted as a universal code of
practice as the Green Chemistry Movement spreads
out of the USA into Europe, Australia and Asia. It is
evident from these principles that green chemistry
encompasses much more of the concepts of sustainability
than simply preventing pollution; two important
aspects are the design for energy efficiency and
the use of renewable feedstocks.
This chapter will explore some of the key features
of these principles, many of which will be dealt with
in greater depth in other parts of the book, and assess
the relevance and opportunities for the chemical
industry.
2 Green Chemistry and Industry
Chemical companies worldwide now are taking the
issue of sustainable and green chemistry seriously.
A combination of increasing amounts of legislation,
increased public awareness and concern and the
realisation that eco-efficiency is good for business are
rapidly increasing the rate of change. The first real
proof that the chemical industry was serious about
environmental concerns came with the ‘responsible

Table 2.1 Key principles and indicators
of the Responsible Care Programme
care’ concept, which was developed by the Canadian
Chemical Producers Association in 1989 and has
been adopted since by many industry association
members throughout the world. The key behind
responsible care is the continuous delivery of health,
safety and environmental improvements related to
both products and processes. Some of the guiding
principles and performance indicators of the Responsible
Care Programme are shown in Table 2.1; the
similarity of many of these to the principles of green
chemistry is self-evident.
Despite this overall commitment, environmental
protection also is often seen by industry as a necessary
cost to comply with increasingly stringent legislation.
There is a great deal of justification in this
view; a recent survey, commissioned by the UK
Department of Environment Transport and Regions
[4], showed that expenditure on environmental
protection, by the UK industry, had risen from £2482
million in 1994 to £4274 million in 1997. The chemical
industry bore the brunt of this expenditure,
which was some 24% of the total spend. Looking
at the capital expenditure element of these figures
(Fig. 2.1), it is evident that the chemical industry
is heavily focused on end-of-pipe solutions rather
than on the integrated process approach, which
would prevent many of the environmental issues
arising.
Clearly there is significant scope for wider adoption
and investment in cleaner and greener
processes, thus avoiding the need for much of the
end-of-pipe expenditure. One of the major goals of
green chemistry is to demonstrate that adoption of
the principles, by industry, can create a competitive
advantage [5]. In this context it is helpful to look at
green chemistry as a reduction process.
Principles of Sustainable and Green Chemistry 11
Principles Indicators
Resource Conservation—waste reduction Safety—lost time accidents
Experience Learning—sharing best practice Waste Emissions—continuous
reduction
Process Safety—risk management Energy Consumption—targeted
improvements
Product Stewardship—risk assessment
Policy—HSE policy to reflect commitment
Management Systems—address impact of activities
HSE, Health & Safety Executive.
63
300
250
200
150
100
50
0
End of Pipe
capex
Integrated
Process capex
Fig. 2.1 The 1997 capital expenditure by the UK chemical
industry (£million) on environmental protection.
Risk and
hazard
Cost Waste
REDUCING
Energy
Fig. 2.2 Green chemistry as a reduction process.
Materials
The simple model of Fig. 2.2 incorporates the key
elements of green chemistry in a way that finance
directors, environmentalists, production managers,
R&D technologists and chief executives can all
understand and, hopefully, buy into.
By looking at the principles of green chemistry as
a tool-kit for achieving this reduction process, it

12 Chapter 2
becomes more evident that as waste, energy, etc. are
reduced the cost of the process also normally will be
reduced. This economic advantage undoubtedly will
be the biggest driver for change. There will, however,
be other advantages for industry, not least of which
will be an improvement in the public image, which
is at an all time low in many countries [6] mainly
due to the perception that the industry is environmentally
unfriendly. We can see now how green
chemistry becomes connected to the increasingly
important business concept of the ‘triple bottom line’
in which business performance is measured not only
in terms of profitability but also in terms of the environmental
and social performance of the company.
Although it is easy to buy into the concepts of sustainable
development, it is often more difficult to
achieve the objectives in practice. Many of these difficulties
are to do with culture and the way chemistry
and related disciplines are taught and practised.
What is really required is a culture change both in
education and industry. In education the principles
of green chemistry need to be the underlying theme,
not taught in isolation. In industry the principles
of sustainability should form part of the company
ethos and be reflected in management systems and
procedures.
3 Waste Minimisation and Atom Economy
3.1 Atom economy
Generations of chemists, especially organic chemists,
have been educated to devise synthetic reactions
to maximise yield and purity. Although these are
worthy goals, reactions may proceed in 100% yield
to give a product of 100% purity and still produce
more waste than product. In simplistic terms, Equation
2.1:
SO 3 Na
+ 2NaOH
ONa
A + B Æ C + D + E (2.1)
in which A and B react to give product C in high
yield and high purity, also leads to the formation of
by-products (or waste) D and E in stoichiometric
quantities. For many years phenol was manufactured
via the reaction of sodium benzene sulfonate
(from benzene sulfonation) with sodium hydroxide;
the products of this reaction are sodium phenolate
(which is hydrolysed subsequently to phenol),
sodium sulfite and water. Even if the reaction proceeds
in quantitative yield, it is evident from looking
at the molecular weights of the product (sodium
phenolate) and unwanted by-products (sodium
sulfite and water) that, in terms of weight, the reaction
produces more waste than product. Historically,
however, the chemist would not consider the production
of this aqueous salt waste to be of any
importance when designing the process.
The atom economy concept proposed by Trost [7]
is one of the most useful tools available for design of
reactions with minimum waste. The concept is that
for economic and environmental reasons reactions
should be designed to be atom efficient, i.e. as many
of the reacting atoms as possible should end up in
useful products. In the example shown in Fig. 2.3 all
the carbon atoms present in the starting material are
incorporated into the product, giving a carbon atom
efficiency of 100%, but none of the sulfur ends up
as useful product and hence the atom efficiency for
sulfur is 0%. Overall, the atom efficiency of the reaction
is defined as the ratio of the molecular weights
of desired product to the sum of the molecular
weights of all materials produced in the process. In
the above example the atom efficiency would be
116/260 or 44.6%.
The concept of atom economy has been expanded
usefully by Sheldon [8,9], by the introduction of the
term ‘E factor’, which is the ratio of the kilograms of
+ Na 2 SO 3 + H 2 O
MWts 180 2 ¥ 40 116 126 18 Fig. 2.3 Benzene sulfonate route to
phenol.
64

y-product per kilogram of product. In this context,
by-product is taken to mean everything other than
useful product, including any solvent consumed.
This concept is particularly useful for comparing
industrial processes, where the yield also can be
taken into account. Assuming a 100% yield for the
example in Fig. 2.3, we would have an E factor of
144/116 or 1.24 (the water produced could be justifiably
ignored, improving the E factor to 1.08).
According to Sheldon, this is typical of a bulk chemicals
production process, however in the fine chemicals
industry the E factor can be as high as 50
whereas in the pharmaceuticals sector it may be
even higher, which is striking evidence of the waste
problem faced by chemistry-based industries.
The cost and associated environmental problems
of disposing the sodium sulfite produced in the
phenol process contributed to its replacement, on
economic grounds, by the cumene process. In this
process the final step involves the acid-catalysed
decomposition of cumene hydroperoxide to phenol
and acetone (Fig. 2.4). In this case both the phenol
and acetone are wanted products, hence apart from
a very small amount of acid (used to aid decomposition
of the hydroperoxide) this reaction has a
100% atom efficiency and a zero E factor, indicating
a completely waste-free process (assuming 100%
yield).
Of course the atom economy concept should not
replace consideration of yield, ease of product isolation,
purity requirements, etc. when devising a
chemical synthesis but it should be thought of as an
additional consideration. The economics of chemical
production are changing, particularly in the fine,
speciality and pharmaceuticals sectors, where waste
generation and other environmental considerations
are becoming an increasingly significant [10] proportion
of the overall manufacturing cost.
H3C CH3 OOH OH
Fig. 2.4 Cumene route to phenol.
+ CH 3COCH 3
Principles of Sustainable and Green Chemistry 13
65
3.2 Some inherently atom economic reactions
By their very nature some reaction types are likely
to produce less waste than others by virtue of being
inherently atom efficient. These reaction types are
worth considering when devising a synthetic strategy.
Obviously other factors also need to be taken
into account in determining the most efficient, competitive
and eco-friendly route. These factors
include:
• Cost and availability of raw materials
• Toxicity/hazardous nature of raw materials
• Yield
• Ease of product isolation and purification
• Solvent requirements
• Energy requirements
• Equipment requirements, cost and availability
• Process times
• Nature of waste materials
Pericyclic [11] reactions occur via a concerted
process through a cyclic transition state. These reactions
are typified by the Diels–Alder reaction, sigmatropic
rearrangements and cheletropic additions,
amongst others, and have theoretical atom efficiencies
of 100% and hence should be high on the
list of considerations when designing synthetic
pathways.
Organic fungicides have played a vital role in
ensuring the plentiful supply of food and, although
many are not perfect from an environmental point
of view, they are generally more eco-friendly and
less toxic than the mercury-based fungicides that
they replaced. One of the major classes of contact
fungicides used today are the sulfenamides, typified
by Captan and the related materials Folpet and
Difoltan [12]. The starting reaction to all these materials
is the Diels–Alder addition of maleic anhydride
to butadiene (Fig. 2.5).
Many Diels–Alder reactions are carried out in
organic solvents, and non-recoverable lewis acids
such as aluminium chloride frequently are used to
extend the range and speed up the reactions. Both
of these may detract from the ‘greenness’ but there
are examples where these reactions occur rapidly
without the use of catalysts or organic solvents.
2,2,5-Trisubstituted tetrahydrofurans are a novel
class of antifungal compounds; their synthesis
involves the key Diels–Alder reaction shown in Fig.
2.6. Saksena [13] found that the reaction proceeded

14 Chapter 2
in virtually quantitative yield when water was used
as solvent, whereas in organic solvents a highly complex
mixture of products was obtained.
Claisen rearrangements are another class of
‘waste-free’ pericyclic reactions of significant importance.
Claisen rearrangement of the propargyl ether,
which proceeds in 85% yield (Fig. 2.7), is at the
heart of a simple route to cordiachromene [14], a
natural product that shows significant antibacterial
and anti-inflammatory properties.
Addition reactions, in which two molecules
combine to form a single molecule of product, are
another class of inherently waste-free reactions of
66
Fig. 2.5 Captan synthesis.
Fig. 2.6 Water-based Diels–Alder
reaction—intermediate to antifungal
compounds.
Fig. 2.7 Claisen rearrangement en
route to cordiachromene.
Fig. 2.8 A green Michael addition.
widespread applicability. By their very nature, addition
reactions involve an unsaturated bond and are
typified by reactions such as electrophillic addition of
halogens to alkenes and nucleophilic additions to
carbonyls.
Michael additions normally are carried out with
base catalysts, however there have been several
recent examples of very green Michael additions
that occur in high yield in water. A striking example
of this is the addition of acrolein to 2-methyl-1,
3-cyclopentadione [15], which proceeds in quantitative
yield in water at ambient temperature (Fig.
2.8).

3.3 Some inherently atom
uneconomic reactions
Similarly there are reactions that will usually
produce some waste material; these are typified by
substitution and elimination reactions. These reactions
should be viewed with caution when designing
green syntheses and, if a viable alternative is not
possible, attempts made either to recycle or to find a
use for the eliminated or substituted product.
The Wittig reaction is highly useful for forming
carbon–carbon double bonds and is widely used
industrially in the manufacture of vitamins and
pharmaceuticals. Although normally proceeding in
high yield under mild conditions, it is an inherently
wasteful reaction producing a mole equivalent of
phosphine oxide per mole of product (Fig. 2.9).
The phosphine oxide normally is converted to
calcium phosphate for disposal. It is this 0% phosphorus
atom efficiency that makes the Wittig
reaction expensive, as well as environmentally problematic,
and limits its usefulness to the production of
high-value-added products. The greenness of the
reaction can be improved, however, by converting
the oxide back to triphenyl phosphine [16,17]. This
recycling process, developed by the multinational
chemical company BASF, involves chlorination of
the phosphine oxide with phosgene, reduction with
aluminium powder and hydrolysis. Although not a
particularly green process (because it involves the
use of hazardous reagents and produces aluminium
hydroxide waste), overall, comparing the whole
processes including triphenyl phosphine manufacture
(Equation 2.2), the BASF route is more environmentally
benign and cost effective.
PCl + 3CHCl + 6Na Æ P( C H ) + 6NaCl
3 6 5 6
(2.2)
Specific, more environmentally benign alternatives
to the Wittig reaction now are being sought. The key
(intermediate 1) to the anti-HIV drug Efavirenza has
been produced in a one-pot process (see Scheme 2.1)
with an overall yield of 92% [18]. The process
involves reaction of cyclopropylcarboxaldehyde (the
Fig. 2.9 Typical Wittig reaction.
5 3
Principles of Sustainable and Green Chemistry 15
67
same starting material as used in the Wittig reaction)
with trichloromethyl anion generated in situ, acetylation
and removal of acetate and chloride groups.
The process still produces significant amounts of
waste but it is much more environmentally benign
waste.
4 Reduction of Materials Use
Frequently, many chemical reactions involve the use
of reagents such as protecting groups and so-called
catalysts that do not end up in the useful product.
Organic solvents, often thought to be essential but
sometimes not actually required at all, fall into this
category. Some of these materials end up as waste
and some are recovered, but in all cases valuable
resources and energy are consumed that do not form
part of the required product.
Materials and money often are wasted in the
design of chemical reactors, and new thinking about
plant and ancillary equipment design (the process
intensification concept) is part of the chemical engineering
solution to greener chemical processes.
There is a significant amount of synergy between
the chemistry and engineering approaches to materials
reduction. Frequently, low reactor utilisation,
because of large solvent volumes for example, may
necessitate the building of additional plant. By using
the concepts of green chemistry to integrate the
Scheme 2.1

16 Chapter 2
chemistry and plant design, significant material
savings can be made.
4.1 Catalytic solutions
Organic chemists very rarely write balanced equations
and this can hide a multitude of sins. Taking
Friedel–Crafts reactions as an example, alkylation
and acylation reactions often are referred to as being
catalysed by lewis acids such as aluminium chloride;
although this is partially true, it is frequently ignored
that the acylation reaction requires more than stoichiometric
amounts of AlCl3 (Fig. 2.10) [19].
In the alkylation reaction AlCl3 is required only in
small amounts, but in the acylation reaction it complexes
with the ketone product and is taken out of
the catalytic cycle. In both cases, reactions usually
are quenched with water, leading to copious
amounts of aluminous waste and releasing three
equivalents of HCl. In the case of the acylation of
1,3-dimethylbenzene and assuming a quantitative
yield, more than 0.9kg of AlCl3 are wasted per kilogram
of dimethyl acetophenone produced.
A recent, but classic, example of overcoming the
wasted materials issue in aromatic acylations is the
Hoechst Celanese route to the analgesic ibuprofen
[20]. The reaction involves acylation of isobutylbenzene
with acetic anhydride, a process that had been
carried out traditionally with AlCl3 in an organic
solvent. The Hoechst Celanese process employs
liquid HF as both a true catalyst and solvent, the HF
68
being, for all practical purposes, completely recycled.
Although the purist could argue that this process
may not be particularly ‘intrinsically safe’ due to the
potential hazard associated with handling HF, it is
considerably greener in the context of reduced materials
consumption.
Much academic and industrial research effort has
gone into the greening of Friedel–Crafts processes,
with the aim of developing benign, easily recyclable,
inexpensive, active solid catalysts that are highly
selective and avoiding wasted raw materials and byproducts.
For the alkylation reaction zeolites generally
have provided the commercial solution to this
problem, with major areas of research work centred
on the avoidance of olefin oligomerisation and the
development of catalysts stable to the operating conditions.
Returning to the production of phenol from
cumene (see above), the first step involves the alkylation
of benzene with propene, which was carried
out originally with AlCl3; today, several commercial
zeolite-based processes have been developed. The
Mobil process, developed in 1993, employs a highsilica
catalyst ZMS-5 that gives almost stoichiometric
yields, whereas Dow Chemical have developed a
process based on de-aluminated mordøenite [21].
The development of solid acid catalysts to solve the
many problems associated with the acylation reaction
generally has proved more problematic, but for
activated substrates such as aryl ethers Rhone-
Poulenc have developed an H-beta-zeolite catalyst
[22].
Fig. 2.10 Typical Friedel–Crafts
reactions.

Another very important industrial process that
essentially gives a free ride to a reactant is that of
aromatic nitration. Aromatic nitro compounds are
used widely as intermediates for dyes, plastics and
pharmaceuticals, and for monosubstituted aromatic
substrates it is often the para-isomer that is the
required product. Conventional nitration technology
uses a mixture of concentrated nitric and sulfuric
acids, the latter acid often being used in considerable
molar excess. The sulfuric acid is present in order
to generate nitronium ions, which are the active
nitration species and, in principle, are still present
unchanged in the product mix. In practice, the reaction
mix usually is quenched with water, leading
to copious amounts of acidic waste to be disposed
of. Smith et al. [23] have developed a more selective
para-alkylation procedure that does not involve the
use of sulfuric acid. Para-selectivity is enhanced
by the use of recoverable zeolites but more than
equimolar amounts of acetic anhydride are required
to generate the active nitrating species (CH3CO 2NO 2)
and to mop up the water formed; material usage
therefore is still high.
True catalytic nitration technology has been
developed using lanthanide(III) triflates [24]. Lanthanide(III)
triflates are unusual in that they function
as strong Lewis acids, are stable to water and
hence are recoverable from aqueous solutions. Using
ytterbium or scandium triflate at levels as low as 1
mol.% and equimolar amounts of nitric acid, nitration
of a range of aromatic compounds was achieved
at around 90% conversion.
Rearrangements inherently should be atom efficient
processes but sometimes the ‘catalyst’ required
to cause the rearrangement cannot be readily recovered
and reused. This is the case with some
production processes for ethylidene norbornene
(ENB) from vinylidene norbornene (VNB) (Fig.
2.11). The ENB is used as the ‘diene’ component in
ethene–propene diene monomer (EPDM) rubbers
and it is often manufactured by Diels–Alder reaction
of cyclopentadiene with butediene, followed by
rearrangement of the so-formed VNB using sodium/
potassium amalgam in liquid ammonia. Although
most of the liquid ammonia (which is also used as
a solvent) is recovered, there is significant loss of
metals. Sumitomo [25] have developed an alternative
solid base catalyst (Na/NaOH on g-alumina) that
avoids waste and improves the safety aspects of the
process.
Principles of Sustainable and Green Chemistry 17
69
Fig. 2.11 Rearrangement of vinylidene norbornene (VNB) to
ethylidene norbornene (ENB).
4.2 Question the need for protection
Another major source of raw material wastage comes
from the use of protecting groups, frequently used in
the synthesis of pharmaceuticals; these are necessarily
used in stoichiometric amounts. Not only are
the raw materials wasted but their use frequently
requires an additional two process steps, involving
increased uses of solvents, lower yields, etc. Wherever
possible, the use of ancillary reagents such
as protecting groups should be avoided. An excellent
example of process simplification in which a threestep
route has been reduced to a single step by
a biotransformation is the manufacture of 6aminopenicillanic
acid, an antibiotic intermediate
[26].
The original process involved protection of the carboxylate
group in penicillin G by silylation; this reaction
also requires dimethyl aniline to remove the HCl
produced during silylation (Fig. 2.12). In the biocatalytic
process, genetically engineered and immobilised
penicillin amidase is used to deacylate
penicillin G directly.
There are many additional green benefits to the
biocatalytic process, including:
• Avoidance of dichloromethane solvent—water is
used in the biocatalytic process
• Energy savings—reaction carried out at 30°C as
against -50°C for the protection step
• Fewer safety problems—PCl5 also was used in the
non-biocatalytic process
4.3 Reduction of non-renewable raw
material use
The debate on when the supply of crude oil and gas
will run out will not be settled for some considerable
time. There is, however a growing consensus of
opinion that, at least as far as oil is concerned, if we

18 Chapter 2
continue to use resources at the current rate we will
face a significant shortage (combined with a very
high price) some time in the second half of this
century [27]. The use of non-renewable resources
for chemicals manufacture must be put into perspective:
approximately 90% of crude oil currently
is used to provide energy via burning of oil, gasoline
and diesel, with only 8% of crude being converted
into chemicals. The two main arguments for reducing
our dependency on fossils and increasing our use
of renewable feedstocks are:
(1) To conserve valuable supplies of fossil fuels
for future generations (a core principle of
sustainability).
(2) To reduce global emissions of greenhouse gases,
especially carbon dioxide (renewable resources
being CO2-neutral overall).
Reduction in the use of fossil fuels for chemicals
manufacture will have some benefit on conserving
resources and reducing CO2 emissions, but these will
be small compared to what can be achieved by using
renewable resources for energy production. Chemicals
manufacture from renewable resources, therefore,
ideally should provide additional benefits such
as reduced hazard, more efficient process, reduced
cost, reduced pollution, meeting market needs, etc.
Additionally, it is important to look at the whole
process, including growing, transport, etc., to ensure
that the total energy consumed (or total CO2 emission)
is lower when employing the renewable
resource. Chemistry does have a vital role to play in
reducing the requirement for fossil fuels, e.g. more
efficient combustion processes, the development of
energy-efficient solar and fuel cells and the production
of biodiesel.
70
Fig. 2.12 Routes to 6-aminopenicillanic
acid.
Table 2.2 Some disadvantages of vegetable-oil-based diesel
High viscosity
Lower volatility
Reactivity of unsaturated chains, leading to gum formation
Increased coking
There is nothing particularly new about using
vegetable-based diesel oils [28] but during the last
60 years or so the advent of relatively inexpensive
and technically superior petroleum-based diesel has
prevented their widespread use. In recent years there
has been considerable renewed interest in the competitive
production of biodiesel to overcome many
of the environmental issues associated with the
petroleum-based material [29]. Some of the disadvantages
of vegetable-oil-based diesel are shown in
Table 2.2.
These disadvantages generally preclude the use of
unmodified vegetable oils, although there are many
examples of 20–50% blends with conventional diesel
being used for prolonged periods [30]. Transesterification
has been the major technique
employed to overcome these technical problems
(especially high viscosity), although at added cost.
Typically the anhydrous oil (triglycerides) is heated
with methanol and a basic catalyst to give a mixture
of methyl esters and glycerol, which is recovered as
a valuable co-product. Although sodium hydroxide
and sodium methoxide are widely used as catalysts,
a ‘green’ process involving a reusable immobilised
lipase catalyst and supercritical carbon dioxide has
been demonstrated [31].
The main obstacle to widespread use of biodiesel
is the cost, of which up to 75% can be the raw

Fig. 2.13 Polylactic acid synthesis.
vegetable oil cost; this has focused attention onto the
use of used cooking oil for example, but non-uniformity,
availability and collection issues have prevented
commercial use to date.
Use of renewable resources for making polymers
is an area receiving much attention due to the relative
ease of making biodegradable plastics with
useful chemical and physical properties. It is important
to caution against the perception, however, that
just because a plastic is made from a renewable
resource it is automatically greener than one made
from petroleum. Many petroleum-based polymers
such as polyethylene [32] and polyisoprene are fairly
readily biodegraded; it is the additives (antioxidants)
specifically added to prevent degradation, thus
ensuring a useful life, that are the causes of many
of the environmental problems. As in the case of
biodiesel, one of the main issues preventing growth
of the ‘renewable polymers’ sector is cost. In many
cases the cost is associated with the relatively small
amount of the required chemical being present in
the crop, entailing high extraction cost and the production
of large quantities of waste. In these cases a
holistic approach is required with, for example,
waste biomass being used as a fuel.
Recent advances in producing polylactic acid
(PLA) from corn starch have lead to the building of
the first large-scale commercial production unit by
Cargill-Dow [33]. The commercial viability of the
polymer relies on novel processing that can be used
to manipulate the molecular weight, crystallinity and
chain branching, enabling materials with a wide
range of end uses and markets to be made. Potential
applications for PLA include:
• Packaging—PLA can have the processability of
polystyrene and the strength properties of
poly(ethylene terephthalate), with good resistance
to fats and oils.
• Textiles—PLA has good drape, wrinkle and UVlight-resistance
properties.
Principles of Sustainable and Green Chemistry 19
71
The process involves fermentation of unrefined dextrose,
derived from corn, to give D- and L-lactic acids,
which are converted to D-, L- and meso-lactides
before polymerisation (Fig. 2.13). By controlling the
D, L and meso ratio, together with molecular weight,
polymer properties can be tailored to meet product
specifications [34].
Society in the not too distant future will need
to find viable alternatives to the use of fossil fuels
for energy and probably for the synthesis of many
chemicals. If the solution is to grow our energy, as
opposed to using solar cells for example, then we will
need to face the issues concerned with land usage
[35]. Although there is no real shortage of land on
the planet, there are serious debates as to the viability
of growing most of our energy needs. These
debates centre on land quality, accessibility, nearness
to population centres, etc.
4.4 Process intensification
When designing a chemical process the engineering
aspects are as important as the chemistry and it is
often the lack of interaction between chemists and
engineers at an early enough stage that results in
processes being developed that are not as green or
efficient as they otherwise could be. In many ways
process intensification can be regarded as the engineering
solution to green chemistry problems;
the concept originated in the 1970s as a means of
making large reductions in the cost of processing
systems [36]. Like many cost reduction concepts,
process intensification is concerned mainly with
reducing materials use and energy consumption by
reducing plant footprint and increasing throughput.
Some of the key aspects of process intensification are
shown in Fig. 2.14 [37].
A fuller account of process intensification is presented
elsewhere in the book but in the context
of materials reduction it is worth mentioning an

20 Chapter 2
Reaction Non-reaction
Spinning disc reactor
Supercritical fluids
Static mixer reactor
Reactor
Static mixing catalysts
Operation
Monolithic reactors
Microreactors
Heat exchange
reactors
Supersonic gas/liquid
reactor
Jet-impingement
reactor
Rotating packed-bed
reactor
Static mixers
Compact heat
exchangers
Microchannel heat
exchangers
Rotor/stator mixers
Rotating packed beds
Centrifugal adsorber
Process intensification
Equipment Methods
Multifunctional
reactors
Examples
Reverse-flow
reactors
Reactive distillation
Reactive extraction
Reactive crystallisation
Chromatographic
reactors
Periodic separating
reactors
Membrane reactors
Reactive extrusion
Reactive comminution
Fuel cells
Fig. 2.14 Adapted from Ref. 37. (Reproduced with permission
of American Institute of Chemical Engineers.)
example where process intensification has led to
significant improvements in throughput overcoming
the need for additional plant to be built. Formation
of a gel by-product necessitated frequent shut down
of a Dow Corning process involving a gas/liquid reaction
in a packed column [38]. Owing to increased
demand, the company were faced with building
another plant at a cost of some US$5 million or
making significant improvements in productivity.
The key problems were identified as poor gas–liquid
mixing and mass transfer, which were readily solved
at a cost of US$22000 by adding a static mixer.
The result was a 42% increase in productivity, avoid-
72
Hybrid
separations
Membrane absorption
Membrane distillation
Adsorptive distillation
Alternative
energy
sources
Centrifugal fields
Ultrasound
Solar energy
Microwaves
Electric fields
Plasma technology
Dynamic
ing the requirement for a new plant together with
all the materials and energy waste that this would
entail.
5 Reduction of Energy Requirement
Other
methods
More than 75% of the world’s energy comes from
fossil resouces [39], with approximately half of the
rest coming from biomass and the remainder coming
from non-carbon sources. This dependency on fossil
fuels has two major consequences:
(1) It is leading to rapidly diminishing reserves of
this valuable non-renewable resource.
(2) It is contributing to the increasing concentration
of CO2 in the atmosphere.

Although these consequences are not in dispute,
there is some dispute over the significance of both
rising CO2 levels and the level of contribution made
by the burning of fossil fuels [40]. Governments of
most countries now accept that reduction of both the
use of fossil fuels and CO2 emissions will be of environmental
benefit and agreements and legislation
are being put in place to meet these objectives
[41].
Energy requirements of chemical reactions frequently
are overlooked at the R&D stage and, for all
but the largest commodity processes, were not considered
seriously at the production stage either, at
least until the oil crisis in the 1970s. As energy has
become more expensive and legislative drivers have
encouraged greater energy efficiency and conservation,
we have seen significant changes in process
design. Many of these changes have focused on engineering
aspects, such as using hot process streams
from one part of a process to heat up incoming raw
materials, whereas a combination of process reengineering
and catalysis has led to energy savings
in many large-scale chemical processes. Even so,
energy conservation is one of the most ignored of the
12 Principles of Green Chemistry, especially by
chemists!
5.1 Some energy efficiency improvements
Ammonia has been synthesised chemically for
almost 100 years. The original electric ark process
operated at temperatures of over 3000°C and was
highly inefficient. The Haber process was a huge leap
for energy efficiency, brought about by the use of
a reduced magnetite catalyst [42]. Although the
underlying principles of the Haber process have
changed little, the energy consumption of the
process is now less than 40% of the original process
[43].
Initially the energy utilisation of the process was
less than 20%, however with the replacement of coal
by oil, and later gas, as the preferred feedstock the
energy efficiency rose to around 60%. Optimisation
of turbine equipment, the steam distribution networks
and the design of radical flow converters
with small-sized catalyst particles have made significant
contributions to energy efficiency improvements
without significant changes being made to the
chemistry.
Principles of Sustainable and Green Chemistry 21
73
The production of sulfuric acid has gone through
similar historical improvements [43]. The main
energy savings have been made in the production of
sulfur dioxide, which is the initial step in the process.
Originally this was produced by roasting the ore
(pyrites) in multiple hearth furnaces and later rotary
kilns, the energy produced being lost to the surroundings.
The development of fluidised bed technology
enabled more than 50% of the excess energy
to be recovered and used to raise steam. Many
modern plants use sulfur (recovered from oil and
gas) as the feedstock and this produces much cleaner
SO2, eliminating the requirement for a cleaning step
and saving further energy.
When considering the eco-efficiency and competitiveness
of competing processes it is vital that the
energy requirements of the process are considered.
Unfortunately this detailed information is not readily
available for most small- to medium-scale processes.
As a striking example of how the energy requirements
for producing a given chemical can vary from
process to process, let us consider titanium dioxide
production. The annual production of TiO2 is
approximately 4.5 million tonnes, made via two
competing processes—the sulfate process and the
chloride process.
The sulfate process essentially involves three
stages:
(1) Dissolution of the ore (ilmenite) in sulfuric acid
and removal of iron impurities
(2) Formation of hydrated TiO2 by treatment of the
sulfate with base
(3) Dehydration in a calciner
All three stages are energy intensive [44].
By contrast, the chloride process can, for simplicity,
be broken down into two steps:
(1) Chlorination of the ore with Cl2 and purification
of TiCl4 by distillation
(2) Oxidation by burning
Overall, the chloride process is much less energy
intensive (by a factor of around 5 [44]), one of the
main reasons being the avoidance of large amounts
of water that need to be removed by energyintensive
evaporation.
With such a huge energy differential it could be
assumed that the chloride process should have shutdown
economics, however around 40% of TiO2 is

22 Chapter 2
still produced via the sulfate route, although this is
diminishing. There are two main reasons for this:
the sulfate process can use lower grade and therefore
less-expensive ores; and it produces anatase pigments
as well as rutile, which is the sole product of
the chloride process.
5.2 Alternative energy sources
The energy required to bring about chemical reactions
is supplied largely by external thermal sources
of heat, such as steam, hot oil and electrical heating
elements. When designing a process for energy efficiency
these conventional energy sources, which do
not target the energy, may not be the most efficient
and alternatives should be considered. There is
currently growing interest in alternative sources of
energy that can target specific molecules or bonds,
giving both energy savings and improved selectivity.
Such alternative energy sources include microwaves
and photochemical, ultrasonic and electrochemical
sources, some of which are discussed in detail in
other chapters of this book. Industrial manufacturing
processes using electrochemistry [45] (the
obvious example being chlorine/sodium hydroxide
manufacture) and, to a somewhat lesser extent, photochemistry
[46] (e.g. the synthesis of vitamin D3, as
discussed in most photochemistry textbooks) have
been used for many years, with a great deal of
success for niche products. Others, such as the use
of microwave reactors, are still confined largely
to the R&D laboratory. One fairly rare example of
microwave energy being used for chemical production
is in the vulcanisation of rubber [47], where
heat-up rates can be up to 100 times faster than
when conventional heating methods are used. As
well as saving energy, process productivity is greatly
improved and the rubber obtained is less contaminated
than that produced using a liquid curing
medium.
Although strictly speaking outside the scope of
green chemistry, the importance of photochemical
and electrochemical techniques to remediation and
74
end-of-pipe technologies should not be overlooked.
For example, photocatalysis plays an important role
in the purification and treatment of wastewater [48],
whereas the use of electrochemical techniques for
the recovery of heavy metals from electroplating
processes is becoming widespread [49].
6 Reduction of Risk and Hazard
6.1 Inherently safe design
December 1984 saw the worlds’ worst chemical disaster,
with over 3000 people killed and 50000 people
injured. The name Bhopal became synonymous with
all that was bad about the chemical industry [50]
and the repercussions from the tragedy transformed
industries’ views on risk and hazard forever. The
product made at Bhopal was the insecticide carbaryl
(Fig. 2.15); although the chemistry involved was
fairly simple, it involved the use of two highly
hazardous chemicals, phosgene and methylisocyanate
(MIC).
The immediate cause of the accident was the
ingress (during routine maintenance) of a large
quantity of water into a storage tank containing up
to 60 tonnes of intermediate MIC. This caused a large
increase in temperature and pressure, eventually
causing the storage tank to explode and a toxic gas
cloud containing MIC and its hydrolysis products,
including hydrogen cyanide, to be released over the
nearby town.
It is very easy to blame people, procedures and
equipment failure in cases such as this but statistically
these will always occur because people are
subject to human error, procedures can always be
improved with hindsight and even the most wellengineered
equipment will fail eventually. It is much
more beneficial to identify the real root cause of the
problem and to eliminate it. In this case the root
cause was the large-scale storage of toxic MIC, so the
question is: could carbaryl have been manufactured
efficiently without MIC being stored? The answer
is yes, but that is irrelevant; what is relevant is that
Fig. 2.15 The Bhopal route to carbaryl.

such questions are addressed seriously at the process
design stage—the concept of ‘inherently safer design’
[51].
In simple terms, the risk to the environment,
human life, etc. is a function of the hazard and the
exposure to that hazard. Conventionally, for a given
known hazard (e.g. the toxic effects of MIC) the risk
has been controlled by reducing exposure through
protective equipment, safety devices and other
control methods. The basic concept of inherently
safer design is that instead of controlling exposure it
is the hazards that are, as far as possible, designed
out of the process—the ‘what you don’t have can’t
harm you approach’. In the Bhopal case such a
design would have avoided the storage of both MIC
and phosgene. Phosgene would have been made on
site (the ‘just in time’ concept) and the use of MIC
could have been avoided altogether by initially reacting
naphthol with phosgene and subsequently reacting
the so-formed chloroformate with methylamine.
Adipic acid manufacture provides a suitable case
study that not only involves inherently safe design
but also embraces many of the principles of green
chemistry discussed above.
World production of adipic acid is approximately
2 milliontyear -1 , the majority of which goes into the
manufacture of Nylon 6:6 [52]. More than 90%
of adipic acid is manufactured by the oxidation
of cyclohexane via a two-stage process (Fig. 2.16)
involving initial oxidation with air using a cobalt
naphthenate or boric acid catalyst followed by oxidation
of the ketone/alcohol mix with an excess of
nitric acid [53].
Although this process has been operated successfully
for many years by many large chemical
companies, there are many associated green and sustainable
issues connected with it:
(1) The Flixborough disaster in 1974 occurred in a
cyclohexane oxidation plant operating at 150°C
and 10bar pressure. In order to get high selec-
Fig. 2.16 Conventional route to adipic
acid.
Principles of Sustainable and Green Chemistry 23
75
tivity, the plant needed to operate at low
conversions (

24 Chapter 2
encouraging our young chemists and engineers to
adopt.
• Is the product (adipic acid) required or is there an
alternative?
• Are there any alternative routes that can be
evaluated and compared?
• Can the ketone/alcohol mix be produced avoiding
the inherent hazards involved with oxidation?
• Can the ketone/alcohol mix be produced with
lower risk?
• Can the large hydrocarbon inventory be reduced?
• Is there an alternative to the nitric acid oxidation
step?
• Can nitrous oxide be recycled in the process to a
useful material?
• Can nitrous oxide emissions be avoided?
These types of questions need to be addressed from
both the technical and economic viewpoint, with the
aim of identifying a more environmentally friendly
product or route that is also commercially viable.
Of course many of these questions have been
addressed, sometimes in an attempt to improve
process and eco-efficiency, and at other times industry
has been forced to consider alternatives based on
public and legislative pressure following Flixborough
and increased concern over the greenhouse effect for
example.
Following pressure to reduce nitrous oxide emissions,
all major adipic acid manufacturers agreed
to adopt some form of nitrous oxide abatement
measure by 1998. Most of these procedures involve
end-of-pipe technology that overcomes the immediate
problem, at some significant cost, but does not
address the real issue of avoiding nitrous oxide production.
Some of the abatement technologies involved
are: catalytic reduction in the presence of
methane to nitrogen and carbon dioxide; catalytic
dissociation into nitrogen and oxygen; and oxidation
to nitric oxide, which can be used to make nitric acid.
76
In the cyclohexane oxidation stage, small
improvements to rate and conversion have been
made by improved design of air/liquid mixers and
heat exchangers (process intensification) [51], but
the inherent hazards associated with stage 1 of the
process largely remain.
Perhaps the preferred answer to achieving a
greener, more inherently safe process is to find an
alternative route. Production of cyclohexanol by catalytic
hydrogenation of phenol proceeds in high
yield and high selectivity, and at first sight overcomes
the cyclohexane oxidation issues. However, the
starting material for both routes is benzene, and
phenol production involves a similar oxidation step
(see cumene route discussed above). Thus, it may
be argued that cyclohexanol production has been
‘greened’ but the issues have been put back a stage.
On the other hand, it could be argued that because
phenol is produced anyway the number of oxidation
plants required has been reduced and therefore the
overall risk has been reduced. Although the phenol
route is practised, unfavourable economics have prevented
widespread adoption of this process.
What could be—at least if the economics were
more favourable—the perfect green and sustainable
solution has been identified by Frost [56]. The
process involves synthesis of adipic acid from glucose
via catechol (Fig. 2.17) using a genetically modified
Escherichia coli biocatalyst.
Several other processes, with varying degrees of
greenness, have been developed over the years,
including carboalkoxylation of butadiene [57] and
dicarbonylation of 1,4-dimethoxybut-2-ene [58],
but for various reasons these have not been commercially
successful.
The most successful move towards sustainability
has been made by Asahi Kasei Corp. [59], who have
developed a commercial route to cyclohexanol based
on the hydration of cyclohexene (Fig. 2.18). The
process relies on the use of a novel high-silica H-
Fig. 2.17 Green route to adipic acid.

Fig. 2.18 Asahi route to cyclohexanol.
ZMS-5 catalyst and the hydrophobic properties of
this catalyst enable selective adsorption of cyclohexene
to take place.
6.2 Alternative solvents
The use of benign solvents is of vital importance to
the development of green chemistry. The concept is
introduced here for convenience but could have
been discussed equally under waste minimisation
and materials reduction. The use of organic solvents
in industry is widespread and, although they play a
valuable ‘enabling’ role, they are responsible for significant
amounts of pollution to air and water. To
control the pollution, industry is spending increasing
amounts on volatile organic compounds and other
effluent control measures. Many organic solvents are
also toxic, necessitating the use of personal protective
equipment; although these are being phased
out by industry, many are still commonly used in
research.
The greenest solution is to use no solvent at all, a
concept not considered by most practising chemists,
at least where solid reactants are concerned. Raston
[60] has reported a striking example of what can
be achieved. The widely used aldol condensation
usually is carried out in solvents such as ethanol,
however Raston’s group have demonstrated that
selective, high-yielding conversions could be
achieved by grinding together a solid carbonyl compound
with sodium hydroxide using a pestle and
mortar.
Water is also a much under-utilised solvent for
organic reactions and offers the potential for cheaper
and safer processes. Water is especially worth considering
as a solvent for high-temperature reactions
where the ionic product of water is high, making it
a stronger acid and base, and where the polarity is
lower, making it a better solvent for organic com-
Principles of Sustainable and Green Chemistry 25
77
pounds. Largely because of legislation on volatile
organic compounds the use of water as a solvent
is being more widely studied by industry, where
the cost and environmental benefits are becoming
realised [61].
Supercritical carbon dioxide, ionic liquids and fluorous
biphase systems all are being studied actively
as eco-friendly alternatives to the use of organic solvents.
These solvents are discussed elsewhere; all
have potential benefits and some disadvantages that
should be considered.
Having moved away from highly toxic solvents
such as benzene and carbon tetrachloride some years
ago, we are now entering a new era where there
are real alternatives being developed to common
solvents such as toluene, dichloromethane and
dimethylformamide. When developing a process, all
these alternatives should be considered.
Approaches such as life-cycle assessment are vital
in enabling sound decisions to be made. For
example, when considering the use of supercritical
carbon dioxide against toluene, one should take
account of the energy involved in generating
and recirculating the supercritical CO2 as well as
assessing the potential pollution risk involved with
using toluene and the comparative hazards of
flammability versus the use of high-pressure equipment,
etc.
7 Conclusions
Chemicals, subtly disguised as medicines, pesticides,
cosmetics, clothing, fuel, protective packaging,
household items, etc., have contributed enormously
to the improved quality of life and increased
longevity the human race has experienced during
the twentieth century. Unfortunately, without intent
but sometimes without adequate knowledge or
thought, chemists and engineers, through the products
and processes devised, have caused significant
harm to the environment.
The challenge to chemists and engineers in the
twenty-first century is to continue to reap all the
social and economic benefits that chemistry has to
offer but without causing damage to the environment
(in the widest sense) or preventing our children
and grandchildren from doing the same in the
next century. This is what green and sustainable
chemistry is all about, but how can we achieve this
worthy goal? The answer is complex, involves all of

26 Chapter 2
society and will involve aspects of all of the following,
coming together as a coherent package:
(1) Technology. A significant amount of valuable
green technology exists, as is evident from publications
such as this and the references therein.
Further green technology needs to be developed
and, more importantly, this technology needs
to be commercially viable. In the short- to
medium-term future we are likely to see significant
reductions in the use of hazardous volatile
organic solvents through increased use of benign
alternatives. More widespread use of catalysts
to reduce waste and improve selectivity, particularly
in the speciality and pharmaceutical
industry, undoubtedly will be forthcoming.
Engineeringwise, we will see something of a
design revolution, reducing materials and
energy use and improving safety. However, in
terms of sustainability we require significant
advances in the development of renewable
sources of energy.
(2) Education. Increased environmental awareness
and the role that science can play need to be
taught at an early age. In tertiary education the
principles of green chemistry need to underpin
the whole undergraduate and graduate course
structure and not be taught as a separate course.
It is the culture and mind-set that we teach students
of today that will determine the greenness
of tomorrow’s processes and products.
(3) Society in general has a huge role to play. Consumer
power is a major force in determining the
products that industry produces. Sometimes sustainability
comes at a price, either economic- or
performancewise; it is the informed consumer
who needs to make this choice, e.g. water-based
versus solvent-based paint. As stakeholders in
industry, individuals and organisations also can
have an influential role in ensuring that sustainable
practices are adopted.
(4) Governments have a role to play in formulating
policies to encourage sustainable development
and in ensuring that there is an even competitive
playing field throughout the world.
Governments also should be encouraging the
development of green technologies through R &
E funding mechanisms.
(5) Industry has the prime purpose of adding value
to shareholder investment. However, there is the
78
growing realisation that the key to future success
lies with not one but three bottom lines: economic,
environmental and social. The costs
of causing environmental harm are becoming
unacceptably high in every sense. This, coupled
with increasing knowledge of the long-term
effects that chemicals have on the environment
and the technical advances are helping to ensure
that new products and processes are much
greener than those being replaced.
The goal of a green and sustainable society cannot
be achieved overnight; the path is long and uncertain.
Undoubtedly we will take a few wrong turns
along the way, but there is growing agreement on
the general way forward. Although science can
help move towards the ideal of completely avoiding
risk, hazard, pollution, etc., society at large will
ultimately determine what is acceptable in terms
of the cost–benefit issues posed by sustainable
development.
Although, as discussed at the beginning of the
chapter, the modern ideas of sustainable and green
chemistry are only around ten years old, we should
not lose sight of the fact that some of the objectives
have been pursued for many years. A quote from
R. W. Hofmann, the first President of The Royal
College of Chemistry, London, made in 1848 is just
as relevant today as it was then:
‘In an ideal chemical factory there is, strictly
speaking, no waste but only product. The better a
real factory makes use of its waste, the closer it
gets to its ideal, the bigger is the profit.’
References
1. World Commission on Environment and Development.
Our Common Future. Oxford University Press,
Oxford, 1987.
2. Basiago, A. D. Sustain. Dev., 1995, 3, 109.
3. Anastas, P. T., & Warner, J. C., Green Chemistry, Theory
and Practice. Oxford University Press, Oxford, 1998.
4. Environmental Protection Expenditure by UK Industry.
Survey of 1997 Expenditure, final report to the DETR.
ECOTEC Research and Consulting, Birmingham, UK,
1999.
5. Lancaster, M. Environ. Bus. Mag., 1999, May, 34.
6. MORI. The Public Image of the Chemical Industry, report
for the CIA. MORI, London, 1999.
7. Trost, B. M. Science, 1991, 254, 1471.
8. Sheldon, R. A. Chemtech, 1994, March, 38.
9. Sheldon, R. A. J. Chem. Tech. Biotechnol., 1997, 68, 381.

10. Lancaster, M. Green Chem., 2000, 2, G65.
11. For a full introduction to pericyclic reactions, see:
Fleming, I. Frontier Orbitals and Organic Chemical Reactions.
J. W. Arrowsmith, Bristol, 1992.
12. Heaton, A. The Chemical Industry, Chapt. 7. Blackie
Academic & Professional, Glasgow, 1996.
13. Saksena, A. K., Girijavallabhan, V. M., Chen, Y. T., Jao,
E., et al. Heterocycles, 1993, 35, 129.
14. Kahn, P. H., & Cossy, J. Tetrahedron Lett., 1999, 40,
8113.
15. Lavallee, J. F., & Deslongchamps, P. Tetrahedron Lett.,
1988, 29, 6033.
16. German patent DE 4 326 952 to BASF, 1993.
17. German patent DE 4 326 953 to BASF, 1993.
18. Wang, Z., Campagna, S., Xu, G., Pierce, M. E., Fortunak,
J. M., & Confalone, P. N. Tetrahedron Lett., 2000,
41, 4007.
19. Doyle, M. P., & Mungwall, W. S. Experimental Organic
Chemistry. John Wiley, Chichester, 1980.
20. European Patent Application 0284310 to Hoechst
Celanese, 1988.
21. Tanabe, K., & Holderich, W. F. Appl. Catal. A: General,
1999, 181, 399.
22. WO Patent 96/35655 to Rhodia, 1996.
23. Smith, K., Musson, A., & DeBoos, G. A. Chem.
Commun., 1996, 469.
24. Barrett, A. G. M., Waller, F. J., Braddock, D. C., &
Ramprasad, D. Chem. Commun., 1997, 613.
25. Nojiri, N., & Misono, M. Appl. Catal. A, 1993, 93, 103.
26. Verweij, J., & de Vroom, E. Rec. Trav. Chim. Pays-Bas,
1993, 112, 66.
27. Campbell, C. J., & Laherrere, J. H. Sci. Am., 1998,
March, 60.
28. Shay, E. G. Biomass Bioen., 1993, 4, 227.
29. Ma, F., & Hanna, M. A. Bioresource Technol., 1999,
70, 1.
30. Adams, C., Peters, J. F., Rand, M. C., Schroer, B. J., &
Pzremke, M. C. J. Am. Oil Chem. Soc., 1983, 60, 1574.
31. Jackson, M. A., & King, J. W. J. Am. Oil Chem. Soc.,
1996, 62, 815.
32. Wasserbauer, R., Beranova, M., Vancurova, D., &
Dolezel, B. Biomaterials, 1990, 11, 36.
33. Environmental Data Services. ENDS Report 2000, Vol.
300. ENDS, London, pp. 19–21.
34. Dartee, M. Green-Tech 2000, Utrecht, April 2000.
35. Okkerse, C., & van Bekkum, H. Green Chem., 1999, 1,
107.
36. Ramshaw, C. Green Chem., 1999, 1, G15.
Principles of Sustainable and Green Chemistry 27
79
37. Stankiewick, A. I., & Moulijn, J. A. Chem. Eng. Prog.,
2000, Jan., 23.
38. Green, A., Johnson, B., & John, A. Chem. Eng., 1999,
Dec., 66.
39. Victor, D. Nature, 1998, 395, 837.
40. Armor, J. N. J. Appl. Catal. A: General, 2000, 194/195,
3.
41. For a summary of the Kyoto agreement, see:
www.unfccc.de
42. Adams, C. Chem. Ind., 1999, 19, 740.
43. Muller, H. In Ullmans Encyclopedia of Industrial Chemistry,
5th edn, Vol. 25. VCH, Wurzburg, 1994, pp.
635–703.
44. Brown, H. L., Hamel, B. B., & Hedman, B. A. Energy
Analysis of 108 Industrial Processes. Fairmont Press,
Lilburn, 9A, 1996.
45. Scott, K. Electrochemical Processes for Clean Technology.
Royal Society of Chemistry, London, 1995.
46. Bouchy, A., Andre, J. C., George, E., & Viriot, M. L. J.
Photochem. Photobiol., 1989, 48, 447.
47. Meredith, R. J. J. Elast. Plast., 1996, 8, 191.
48. Ollis, D. F., & Al-Ekabi, H. Photocatalytic Purification and
Treatment of Water and Air, Trace Metals in the Environment,
Vol. 3. Elsevier, Amsterdam, 1993.
49. Robinson, D., & Walsh, F. C. Hydrometallurgy, 1991,
26(93), 115.
50. Everest, L. Behind the Poison Cloud: Union Carbide’s
Bhopal Massacre. Banner Press, Birmingham, AL,
1986.
51. Kletz, T. Process Plants. A Handbook for Inherently Safer
Design. Taylor & Francis, London, 1998.
52. Eur. Chem. News, 1999, 71, 18.
53. Davis, D. D. In Ullmans Encyclopedia of Industrial Chemistry,
5th edn, Vol. A1. VCH, New York, 1985, pp.
269–278.
54. Scott, R. Process Optimisation, Symposium Series 100.
Institution of Chemical Engineers, Rugby, UK, 1987.
55. Thiemens, M. H., & Trogler, W. C. Science, 1991, 251,
932.
56. Draths, K. M., & Frost, J. W. In Green Chemistry, Frontiers
in Benign Chemical Synthesis and Processes (Anastas,
P. T., & Williamson, T. C. eds). Oxford University Press,
Oxford, 1998.
57. US Patent 4 259 520 to BASF, 1981.
58. Chem. Eng. News, 1984, 62(18), 28.
59. DE Patent 3441072 to Asahi Kasei Corp., 1985.
60. Raston, C. L., & Scott J. L., Green Chem., 2000, 2, 49.
61. Cook, S. J. Green Chem., 1999, 1, 138.

BYLAAG 3
Baird, C and Cann, M, 2008, Environmental chemistry, 4 th ed., W. H. Freeman and Company: New York,
NY, p. 601 – 660.
80

C H A P T E R 14
THE POLLUTION AND
PURIFICATION OF WATER
In this chapter, the following introductory chemistry
topics are used:
Acid–base and equilibrium concepts and calculations; pH
Basic structural organic chemistry (as in the Appendix)
Oxidation numbers; redox half-reactions
Catalysis
Distillation
Background from previous chapters used in this chapter:
Maximum contaminant levels (Chapter 10)
BOD (Chapter 13)
VOCs (Chapter 3)
Adsorption (Chapter 4)
Photochemical reactions; UV light (Chapters 1–5)
Free radicals (Chapter 1)
BTX hydrocarbons (Chapter 7)
ppm concentration scale in water (Chapter 10)
No effects level, NOEL (Chapter 11)
Introduction
The pollution of natural waters by both biological and chemical contaminants
is a worldwide problem. There are few populated areas, whether in developed
or undeveloped countries, that do not suffer from one form of water pollution
or another. In this chapter, we shall survey the various methods—both traditional
and innovative—by which water can be purified. We begin by discussing
techniques that are used to purify drinking water from relatively
uncontaminated sources, and then consider the pollution and remediation of
81
601

602 Chapter 14 The Pollution and Purification of Water
groundwater and of sewage and wastewater. Lastly, we investigate modern
advanced techniques whereby polluted air and water can be cleansed.
Water Disinfection
The quality of “raw” (untreated) water, whether drawn from surface water or
groundwater, that is intended eventually for drinking varies widely, from
almost pristine to highly polluted. Because both the type and quantity of pollutants
in raw water vary, the processes used in purification also vary from
place to place. The most commonly used procedures are shown in schematic
form in Figure 14-1. Before discussing the major topic of disinfection, we shall
discuss the various nondisinfection steps that are often taken in the overall
purification process.
Aeration of Water
Aeration is commonly used in the improvement of water quality. Municipalities
aerate drinking water that is drawn from underground aquifers in order
to remove dissolved gases such as the foul-smelling hydrogen sulfide, H2S, and organosulfur compounds, as well as volatile organic compounds, some of
which may have a detectable odor. Aeration of drinking water also results in
reactions that produce CO2 from the most easily oxidized organic material. If
necessary for reasons of odor, taste, or health, most of the remaining organics
can be removed by subsequently passing the water over activated carbon,
although this process is relatively expensive, so rather few communities use it
(see Box 14-1). Another advantage to aeration is that the increased oxygen
content of water oxidizes water-soluble Fe 2 to Fe 3 , which then forms insoluble
hydroxides (and related species) that can be removed as solids.
Fe 3 3 OH 9: Fe(OH) 3(s)
(Recall that ions listed in equations without a state specified are assumed to
be in aqueous solution.)
After aeration, colloidal particles in the water are removed. If the water
is excessively hard, calcium and magnesium are removed from it before the
final stages of disinfection and the addition of fluoride. All these procedures
are described below (see Figure 14-1).
Removal of Calcium and Magnesium
If the water comes from wells in areas having limestone bedrock, it will contain
significant levels of Ca 2 and Mg 2 ions, which are usually removed during
processing since these ions can interfere with soaps and detergents used
by consumers for washing. Calcium can be removed from water by addition of
phosphate ion in a process analogous to that discussed later for phosphate
removal; here, however, phosphate is added in order to precipitate the
82

BOX 14-1 Activated Carbon
Activated carbon (activated charcoal) is a
very useful solid for purifying water of
small organic molecules present in low concentrations.
The ability of this material to
remove contaminants from water and to
improve its taste, color, and odor has been
known for a long time; indeed, the ancient
Egyptians used charcoal-lined vessels to store
water for drinking purposes.
Activated carbon is produced by anaerobically
charring a high-carbon-content material
such as peat, wood, or lignite (a soft brown
coal) at temperatures below 600°C, followed by
a partial oxidation process using carbon dioxide
or steam at a slightly higher temperature.
The removal of contaminants by activated
carbon is a physical adsorption process and
therefore is reversible if sufficient energy is
applied. The characteristic that makes activated
carbon such an excellent adsorber is its
huge surface area, about 1400 m 2 /g. This surface
is internal to the individual carbon particles,
so that crushing the material neither
Aeration Settling and
precipitation
Air
Al or Fe salt to
precipitate colloids
Hardness
removal
Phosphate
FIGURE 14-1 The common stages of purification of drinking water.
Water Disinfection 603
Disinfection
Ammonia
and fluoride
Ca 2+ pptd. as phosphate Cl 2 or ozone or ClO 2
83
increases nor decreases the area. The internal
structure of the solid involves series of channels
(pores) of progressively decreasing size
that are produced by the charring and partial
oxidation processes. The internal sites where
adsorption occurs are large enough only for
small molecules, including chlorinated solvents.
At the typical ppm concentrations
found for organic contaminants in water, each
gram of activated carbon can adsorb a few
percent of its mass in contaminants such as
chloroform and the dichloroethenes as well as
much higher masses of TCE, PCE, and pesticides
such as dieldrin, heptachlor, and DDT.
Once a sample of activated carbon has
reached near-saturation in terms of adsorbed
organics, three alternatives are available. It
can be simply disposed of in a landfill, it can be
incinerated to destroy it and the adsorbed contaminants,
or it can be heated to rejuvenate the
surface by driving off the organic pollutants,
which can then be incinerated or catalytically
oxidized.
Consumer
Water
Suspended
particles

604 Chapter 14 The Pollution and Purification of Water
calcium ion. More commonly, calcium ion is removed by precipitation and
filtering of the insoluble salt calcium carbonate, CaCO 3 . The carbonate
ion is either added as sodium carbonate, Na 2 CO 3 , or if sufficient HCO 3 is
naturally present in the water, hydroxide ion, OH , is added in order to
convert dissolved bicarbonate ion to carbonate:
OH HCO 3 9: CO3 2 H2 O
Ca 2 CO 3 2 Δ CaCO3 (s)
Magnesium ion precipitates as magnesium hydroxide, Mg(OH) 2, when the
water is made sufficiently alkaline, i.e., when the OH ion content is increased.
After removal by filtration of the solid CaCO 3 and Mg(OH) 2 , the pH of the
water is readjusted to near-neutrality by bubbling carbon dioxide into it.
PROBLEM 14-1
Ironically, calcium ion is often removed from water by adding hydroxide ion
in the form of Ca(OH) 2 . Deduce a balanced chemical equation for the reaction
of calcium hydroxide with dissolved calcium bicarbonate, Ca(HCO 3 ) 2 ,
to produce insoluble calcium carbonate. What molar ratio of Ca(OH) 2 to
dissolved calcium should be added to ensure that almost all the calcium is
precipitated?
Disinfection to Prevent Illness
In terms of causing immediate sickness and even death, biological contaminants
of water are almost always much more important than chemical ones.
For that reason, we begin our discussion of the purification of water by extensively
discussing its disinfection, i.e., the elimination of microorganisms that
can cause illness.
Many of the microorganisms in raw water are present as a result of contamination
by human and animal feces. The microorganisms are principally
• bacteria, including those of the Salmonella genus, one species of which
causes typhoid. In this category is also Escherichia coli O157:H7, whose transmission
in water has caused a number of deaths in recent years, including
those from an outbreak in Walkerton, Ontario, in 2000;
• viruses, including polio viruses, the hepatitus-A virus, and the Norwalk
virus; and
• protozoans (single-celled animals), including Cryptosporidium and Giardia
lamblia.
Because many microorganisms of these three types are pathogenic, causing
mild to serious and sometimes fatal illnesses, they must be largely removed
from water before it is suitable for drinking.
84

Notwithstanding well-known techniques for water disinfection, many of
which have been used extensively for more than a century in developed
countries, there are still about 1 billion people in the world who do not yet
have access to safe drinking water. According to the World Health Organization,
about 4500 children die daily from the consequences of polluted water
and inadequate sanitation.
Filtering of Water
In addition to dissolved chemicals, the raw water that is obtained from
rivers, lakes, or streams contains a multitude of tiny particles, some of which
consist of or contain microorganisms. Many of the small, suspended particles
consist of clay, resulting from the erosion of soil and rock, whether by natural
forces or due to plowing of land for agriculture, mining, or commercial or
housing development. The suspended particles increase water’s turbidity and
thereby reduce the ability of light to penetrate deeply enough to support
photosynthesis.
The larger of the particles suspended in water are often removed by simply
filtering it. Indeed, the filtration of water by passing it through a bed of
sand is the oldest form of water purification known, dating back to ancient
times. The sand retains suspended solids of all types, including microorganisms,
down to about 10 mm in size.
Recently it was realized that forcing raw water through filters having
especially small openings can be used instead of chemicals or light to disinfect
water of some viruses and bacteria, and even some dissolved chemicals, by
just removing them.
Removal of Colloidal Particles by Precipitation
Most municipalities allow raw water to settle, since this permits large particles
to settle out or to be readily separated. However, much of the insoluble matter
originating from rocks and soil, and from the disintegration and decomposition
of water-based plants and animals, will not precipitate spontaneously
since it is suspended in water in the form of colloidal particles. These are particles
that have diameters ranging from 0.001 to 1 mm and consist of groups of
molecules or ions that are weakly bound together. These groups dissolve as a
unit, rather than breaking up and dissolving as individual ions or molecules. In
many cases, the individual units within a colloidal particle are spatially organized
such that the surface of the particles contains ionic groups. The ionic
charges on the surface of one particle repel those of like charge on neighboring
particles, preventing their aggregation and subsequent precipitation.
Colloidal particles must be removed from drinking water for both aesthetic
and health and safety reasons. To capture the colloidal particles, a
small amount of either iron(III) sulfate, Fe2(SO4) 3, or aluminum sulfate,
85
Water Disinfection 605

606 Chapter 14 The Pollution and Purification of Water
Al 2 (SO 4 ) 3 (“alum”), is deliberately dissolved in the water. By then making
the water neutral or alkaline in pH (7 and up), both the Fe 3 and Al 3 ions
produced from the salts form gelatinous hydroxides that physically incorporate
the colloidal particles and form a removable precipitate. The water is
greatly clarified once this precipitate has been removed. Commonly, after the
removal of the colloidal particles, the water is filtered through sand and/or
some other granular material.
Although the idealized formulas of the precipitates are Fe(OH) 3 and
Al(OH) 3 , the actual situation is much more complex. For example, aluminum
actually forms a polymeric cation, Al 13 O 4 (OH) 24 7 , which produces
a loose network structure that is held together by hydrogen bonds. This network
entraps the colloidal particles and forms the precipitate. Only if the pH
rises to quite a high value does the aluminum in solution form the expected
hydroxide Al(OH) 3 . Since the concentration of aluminum sulfate added to
the water is only about 10 mm/L, very little residual aluminum ion is left in
the treated water.
PROBLEM 14-2
Calculate the approximate number of atoms contained in colloidal particles
of (a) 1-mm and (b) 0.01-mm diameters, assuming that their densities are similar
to that of water and that the atomic mass of the atoms averages 10 g/mol.
Disinfection of Water by Membrane Technology
Water can be purified of most contaminant ions, molecules, and small particles,
including viruses and bacteria, by passing it through a membrane in
which the individual holes, called pores, are of uniform and microscopic size.
The range of sizes of the various contaminants in raw water are summarized in
Figure 14-2. Clearly, for a technique to be effective in providing a barrier, the
pore size of the membrane must be smaller than the contaminant size.
In the processes of microfiltration and ultrafiltration, a membrane or
some other analogous barrier containing pores of 0.002- to 10-mm diameter
(2–10,000 nm) is employed to remove larger constituents from water. The
water can be forced through the barrier by pressure or can be drawn through it
by suction, leaving behind the larger impurities. In one modern version of this
technology, the barrier is composed of thousands of strands of plastic tubing
having walls that are pierced with thousands of tiny pores of similar size.
Some bacteria and colloid particles are as small as 0.1 mm and so can pass
through conventional filters and even some microfilters (Figure 14-2).
Viruses can be as small as 0.01 mm and therefore require at least the ultrafiltration
level to eliminate them. However, filtration using membranes can be
86

Pressure
Microfiltration
Ultrafiltration
Bacteria
and
colloids
Viruses
Nanofiltration
Ca 2+
Mg 2+
M 2+
Reverse osmosis
10 1 0.1 0.01 0.001 0.0001
Size of contaminant ( μm)
used to disinfect water if a sufficiently small pore size is used and if the water
is later irradiated with ultraviolet light to eliminate any microbes that have
passed through the filtration stage.
Neither microfiltering nor ultrafiltering removes dissolved ions or small
organic molecules. Generally speaking, before water is treated using membranes
with even smaller pores (see below), it must be pretreated to remove
the larger particles—especially colloids—which would otherwise foul the
finer membrane by leaving deposits.
Membrane systems have been developed recently that purify water of virtually
all contaminants by nanofiltration. Water is pumped under pressure
through fine membranes that have pores only about 1 nm wide, which therefore
remove not only most bacteria and viruses, but also any larger organic
molecules that would nourish the regrowth of bacteria. These nanofilters still
allow water molecules to pass through the filter, since the molecules are only
a few tenths of a nanometer in size. Unlike ultrafiltration, nanofiltration can
be used to soften water, since hydrated divalent ions such as Ca 2 and Mg 2
are larger than the pores and so do not pass through. Hydrated monovalent
ions such as sodium and chloride also pass through some nanofilters, but not
through ones with subnanometer pore sizes. As a consequence, some nanofilter
membrane systems can be used to desalinate seawater and to help purify
wastewater, as discussed later in this chapter.
Na +
K +
87
Water Disinfection 607
H 2O
FIGURE 14-2 Filtration of
contaminants by various
methods.

608 Chapter 14 The Pollution and Purification of Water
Reverse Osmosis
The ultimate in membrane filtration occurs in the widely used technique
called reverse osmosis, sometimes called hyperfiltration. Here, water is forced
under high pressure to pass through the pores in a semipermeable membrane,
composed of an organic polymeric material such as cellulose acetate or triacetate
or a polyamide. Since only water (and other molecules of its small size)
can pass efficiently through the pores, the liquid on the other side of the
membrane is purified water. The solution on the impact side of the membrane
becomes more and more concentrated in contaminants as time goes on and is
discarded. The procedure is called reverse osmosis because, by use of pressure,
the natural phenomenon of osmosis—by which pure water would spontaneously
migrate through the membrane into solution, thereby diluting it—is
reversed.
Particles, molecules (including small organic molecules), and ions down
to less than 1 nm (0.001 mm) in size, or about 150 g/mol in mass, are removed
by reverse osmosis. It is particularly useful for removing alkali and alkaline
earth metal ions, as well as salts of heavy metals. Thus it is employed in hospitals
and renal units to produce water that is particularly free of ions. Reverse
osmosis is used on large scale for the desalination, i.e., the removal of salts,
from seawater and brackish water, a topic considered in Box 14-2.
BOX 14-2 The Desalination of Salty Water
Desalination is the production of fresh
water from salty water, often seawater, by
the removal of its ions. There are more than
15,000 large-scale desalination plants in operation,
located in more than 125 countries.
Reverse osmosis is widely used in some areas of
the world, such as the Middle East, to generate
drinking water from salt water.
The other main commercial desalination
process is the thermal distillation—evaporation—
of seawater or brackish water. Desalination of
seawater by evaporation is a technique that
goes back to ancient times; it is especially
suited even today for seawater that contains
particularly high levels of dissolved salts and
suspended solids in areas such as the Persian
Gulf. The evaporation method is even more
energy-intensive than is reverse osmosis.
Modern, large-scale thermal distillation plants
use energy to raise salty water to the boiling
point, then reduce the air pressure above the
liquid to create a partial vacuum into which
the liquid readily “flash” evaporates, leaving
the salt behind in the remaining liquid. The
vapor is removed and condensed as desalted
water. Thermal distillation plants are often
incorporated within electricity-generating
plants to use the low-grade waste steam from
the latter as their energy source.
Desalination of water is also sometimes
accomplished using the technique of electrodialysis,
which is described later in this chapter.
88

Water destined for drinking purposes is commonly pretreated, e.g., by
filtering it through sand and gravel, and passing it over activated carbon to
remove the larger particles such as bacteria, etc., and treating it with chlorine,
before subjecting it to reverse osmosis in order to minimize fouling and
degradation of the membrane.
Because of the high pressures needed to force water through the small
pores in the membrane, reverse osmosis is an energy-intensive process. A
pressure of about 2 atm is sufficient for portable and domestic units, but a
greater force must be applied to brackish or salty water. However, advances in
the engineering of large-scale desalination plants have markedly reduced
energy consumption by redirecting pressure from waste brine to low-pressure
incoming water.
Reverse osmosis tends to be wasteful of water, since so much of it—a
third to a half—is discarded. Also, the accumulated discharges of brine—
sometimes called concentrate—from desalination processes of any kind can
cause cumulative environmental problems, such as harming fish populations,
in the immediate area of the seacoast into which it is deposited if it is not first
treated. In some locations, the brine is injected into an underground saltwater
aquifer. In others, the brine is left to evaporate in large outdoor pools, and
the salts disposed of later.
Some domestic consumers of drinking water have installed small underthe-sink
reverse osmosis units to further purify their water by removing
unwanted contaminants such as heavy metal cations (e.g., lead), hard water
cations (calcium and magnesium), anions (e.g., nitrate and fluoride), and
organic molecules from water obtained from domestic supplies. Small reverse
osmosis units are also used in medical facilities for producing water that is
particularly ion-free.
Some bottled water has been purified and deionized by reverse osmosis,
but small amounts of salts are reintroduced into it before it is sold to consumers.
Drinking large amounts of deionized water is not healthy, since the
ion balance in the body can be upset as a consequence.
Disinfection by Ultraviolet Irradiation
Ultraviolet light can also be used to disinfect and purify water. Powerful
lamps containing mercury vapor whose excited atoms emit UV-C light (see
Chapter 1) centered at a wavelength of 254 nm are immersed in the water
flow. About 10 seconds of irradiation are usually sufficient to eliminate the
toxic microorganisms, including Cryptosporidium, which is resistant to treatment
by some other methods. The germicidal action of the light disrupts the
DNA in microorganisms, preventing their subsequent replication and
thereby inactivating the cells. At the molecular level, absorption of UV-C
light results in the formation of new covalent bonds between nearby thymine
units on the same strand of DNA. If sufficient such thymine dimers are
89
Water Disinfection 609

610 Chapter 14 The Pollution and Purification of Water
formed, the DNA molecule becomes so distorted that subsequent replication
of the organism is prevented.
The use of ultraviolet light to purify water is complicated by the presence
of dissolved iron and humic substances, both of which absorb the UV light
and thus reduce the amount available for disinfection. Small solid particles
suspended in the water also inhibit the action of the UV light since they can
shade or absorb bacteria and also scatter or absorb the light. An advantage of
UV disinfection technology is that small units can be employed to serve small
population bases, whether in the developed or developing world, so the continuous
monitoring activity of chemical systems is avoided. As discussed
later, UV light can also be used to purify water of dissolved organic compounds,
but by a different mechanism.
Disinfection by Chemical Methods:
Ozone and Chlorine Dioxide
To rid drinking water of harmful bacteria and viruses, especially those arising
from human and animal fecal matter, by use of a chemical agent requires an
oxidizing agent more powerful than O2 . In some localities, particularly in
France and other parts of western Europe but also in some North American
cities—Montreal and Los Angeles are examples—ozone is used for this purpose.
Since O3 cannot be stored or shipped because of its very short lifetime,
it must be generated on-site by a relatively expensive process involving electrical
discharge (20,000 V) in dry air. The resulting ozone-laden air is bubbled
through the raw water; about 10 minutes of contact is usually sufficient for
disinfection. Since the lifetime of ozone molecules is short, there is no residual
protection in the purified water to ensure that it will not be subject to
future contamination. Some pollutants in water react with the ozone itself
and others with free radicals such as hydroxyl and hydroperoxy (Chapters
1–5) that are produced when ozone reacts with water.
Unfortunately, the reaction of ozone with bromine in water leads to the
formation of oxygen-containing organic compounds, particularly those con-
taining the carbonyl group, C"O , such as formaldehyde and other low-
molecular-weight aldehydes and various other compounds, some of which are
toxic. In addition, ozone reacts with bromide ion, Br , present in the water
to produce the bromate ion, BrO 3 , a carcinogen in test animals and probably
also in humans. The reaction of ozone with bromide, a natural constituent
of water that is often present at ppm concentrations, occurs in several
steps; the overall reaction is
Br 3 O 3 9: BrO 3 3 O2
The bromate ion produced by ozonation may subsequently react with
organic matter in the water to produce toxic organobromine compounds,
though experiments have shown that the only brominated product under
90

water treatment conditions is dibromoacetonitrile, CHBr 2 CN, produced by
the reaction of bromate ion with acetonitrile. The MCL (maximum contaminant
level) of bromate ion in drinking water is set at 10 ppb (0.010 ppm) by
the U.S. EPA. Substances such as bromate ion that are produced during water
purification are called disinfection by-products, or DBPs. All known chemical
methods of disinfecting water produce DBPs of one type or another.
Similarly, chlorine dioxide gas, ClO 2 , is used in more than 300 North
American and several thousand European communities to disinfect water.
The ClO 2 molecules, themselves free radicals, operate to oxidize organic
molecules by extracting electrons from them:
ClO 2 4 H 5 e 9: Cl 2 H 2 O
The organic cations created in the accompanying oxidation half-reaction
subsequently react with oxygen and eventually become more fully oxidized.
Since chlorine dioxide is not a chlorinating agent—it does not generally
introduce chlorine atoms into the substances with which it reacts—and since
it oxidizes the dissolved organic matter, much smaller amounts of toxic
organic chemical by-products are formed than if molecular chlorine were
used (see below).
As is the case with ozone, ClO 2 cannot be stored since it is explosive in
the high concentrations that its practical use calls for, so it must be generated
on-site. This is accomplished by oxidizing its reduced form, the chlorite ion,
ClO2 , from the salt sodium chlorite, NaClO2 :
ClO2 9: ClO2 e
Some of the chlorine dioxide in these processes is converted to chlorate ions,
ClO 3
. The presence of chlorite and chlorate ions as residuals in the final
water has raised health concerns due to their potential toxicity. The U.S.
EPA has set an MCL of 1.0 ppm for chlorite ion, and a MRDL (maximum
residual disinfectant level) of 0.8 ppm for chlorine dioxide, in drinking water.
Disinfection by Chlorination: History
The most common water purification agent used in North America is
hypochlorous acid, HOCl. About half the U.S. population uses surface
water, and one-quarter of the population uses groundwater, that is disinfected
by HOCl. This neutral, covalent compound kills microorganisms, as it readily
passes through their cell membranes. In addition to being effective, disinfection
by chlorination is relatively inexpensive. Incorporating a small excess
of the chemical in the treated water provides it with residual disinfection
power during its subsequent storage and transmission to the consumer. Chlorination
is more common than ozonation in North America because generally
the raw water is less polluted. Chlorination of public water supplies in the
United States, Canada, and Great Britain began in the early years of the
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612 Chapter 14 The Pollution and Purification of Water
twentieth century. For the previous 50 years, chlorination had been practiced
on an emergency basis during epidemics caused by water-borne pathogens.
Disinfection by Chlorination: Production
of Hypochlorous Acid
Like ozone, HOCl is not stable in concentrated form and so cannot be stored.
For large-scale installations, e.g., municipal water treatment plants, it is generated
by dissolving molecular chlorine gas, Cl2 , in water. At moderate pH
values, the equilibrium in the reaction of chlorine with water lies far to the
right and is achieved in a few seconds:
Cl2(g) H2O(aq) Δ HOCl(aq) H Cl
Thus a dilute aqueous solution of chlorine in water contains very little aqueous
Cl 2 itself. If the pH of the reaction water were allowed to become too
high, the result would be the ionization of the weak acid HOCl to the
hypochlorite ion, OCl , which is less able to penetrate bacteria on account
of its electrical charge. Once chlorination is complete, the pH of the water is
adjusted upward, if necessary, by the addition of lime, CaO.
In small-scale applications of chlorination, as in swimming pools, the
handling of cylinders of Cl 2 is inconvenient and dangerous. The chlorine gas
can be produced as needed on the spot by the electrolysis of salty water. More
commonly, hypochlorous acid instead is generated from the salt calcium
hypochlorite, Ca(OCl) 2 , or is supplied as an aqueous solution of sodium
hypochlorite, NaOCl. In water, an acid–base reaction occurs to convert most
of the OCl in these substances to HOCl:
OCl H 2O Δ HOCl OH
Close control of the pH in an environment like a swimming pool is necessary
to avoid the shift to the left side in the position of equilibrium for this reaction
that occurs if a very alkaline condition is permitted to prevail. On the
other hand, corrosion of pool construction materials can occur in acidic
water, so the pH is usually maintained above 7 to prevent such deterioration.
Maintenance of an alkaline pH also prevents the conversion of dissolved
ammonia, NH 3, to the chloramines NH 2Cl, NHCl 2, and especially NCl 3,
which is a powerful eye irritant:
NH 3 3 HOCl 9: NCl 3 3 H 2 O
Significant respiratory and eye irritation problems from exposure to chloramines
in the air around indoor swimming pools has been reported when
appropriate ventilation is unavailable.
It is desirable to adjust the equilibrium point in the OCl 9: HOCl
reaction to favor the predominance of the disinfectant molecular species,
HOCl. Since the equilibrium between HOCl and OCl shifts rapidly in
favor of the ion between pH values of 7 and 9, however, the acidity level must
92

e meticulously controlled. Swimming pool acidity can be adjusted by the
addition of acid (in the form of sodium bisulfate, NaHSO 4 , which contains the
acid HSO 4 ) or a base (sodium carbonate, Na2 CO 3 ) or a buffer (sodium
bicarbonate, NaHCO 3, which contains the amphoteric anion HCO 3 ).
Chlorine must be constantly replenished in outdoor pools since UV-B and
the short-wavelength components of UV-A light in sunshine are absorbed
by and decompose the hypochlorite ion, thereby affecting the equilibrium in
the OCl 9: HOCl process toward the ion:
UV
2 ClO 9: 2 Cl O 2
Hypochlorous acid can also be generated by the reaction with water of
the chlorine-containing compound isocyanuric acid, C 3 N 3 O 3 H 3 :
H
O
N N
Either the trichloro derivative, in which each hydrogen is replaced by Cl to
give C 3 N 3 O 3 Cl 3 , or the sodium dichloro derivative, C 3 N 3 O 3 Cl 2 Na, is used.
In either case, the OH group from water combines with the chlorine to
produce HOCl and the hydrogen of H 2 O becomes bonded to the nitrogen,
giving isocyanuric acid, C 3 N 3 O 3 H 3 :
C 3 N 3 O 3 Cl 3 3 H 2 O Δ C 3 N 3 O 3 H 3 3 HOCl
Since this process is an equilibrium, not all the compound is immediately
converted to hypochlorous acid. As HOCl is used up, both by its use as a disinfectant
and through dissociation in sunlight of its ionic form, the equilibrium
shifts to the right and more HOCl is produced. None of the various
forms of isocyanuric acid absorb UV light, so its chlorine is “protected”
against decomposition by sunlight. Since the bulk chlorinated forms of isocyanuric
acid are expensive, it is common to supply hypochlorite from a
cheaper source and to add isocyanuric acid as a stabilizer, temporarily reversing
the above reaction to “store” the chlorine until it is needed.
Disinfection by Chlorine: By-Products and
Their Health Effects
An important drawback to the use of chlorination in disinfecting water is the
concomitant production of chlorinated organic substances, some of which
are toxic, since HOCl is not only an oxidizing agent but also a chlorinating
agent. Examples of these important by-products are the group of halogenated
H
O N O
H
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614 Chapter 14 The Pollution and Purification of Water
acetic acids (haloacetic acids), such as CH 2 Cl9COOH, which the U.S. EPA
restricts to 60 ppb as an MCL annual average for drinking water, and haloacetonitriles,
such as CH 2 Cl9CN. Dichloroacetic acid, CHCl 2 9COOH, is
a more potent carcinogen than is chloroform.
If the water to be disinfected contains phenol, C 6 H 5 OH, or a derivative
thereof, chlorine readily substitutes for the hydrogen atoms on the ring to
give rise to chlorinated phenols: These compounds have an offensive odor
and taste and are toxic. Some communities switch from chlorine to chlorine
dioxide when their supply of raw water is temporarily contaminated with
phenols to avoid the formation of chlorinated phenols.
A more general problem with chlorination of water lies in the production
of trihalomethanes, THMs. Their general formula is CHX 3, where the
three X atoms can be chlorine or bromine or a combination of the two. The
THM of principal concern is chloroform, CHCl 3 , which is produced when
hypochlorous acid reacts with organic matter dissolved in the water (see
Box 14-3). Chloroform is a suspected liver carcinogen in humans, and it
may also give rise to negative reproductive and developmental effects. Its
BOX 14-3 The Mechanism of Chloroform Production in Drinking Water
Humic acids, with which HOCl reacts
to form chloroform, are water-soluble,
nonbiodegradable components of decayed
plant matter. Of particular importance are
humic acids that contain 1,3-dihydroxybenzene
rings. The carbon atom (#2) located between
those carrying the 9OH groups is readily
chlorinated by HOCl, as in this elementary
case:
OH O
OH
HOCl
Subsequently the ring cleaves between C-2
and C-3 to yield a chain:
R9C9CHCl 2
O
1
2
3
Cl
Cl
OH
In the presence of the HOCl, the terminal carbon
becomes trichlorinated, and the 9CCl 3
group is readily displaced by the OH in water
to yield chloroform:
R9C9CHCl 2
O
HOCl
R9C9CCl 3
Analogous sequences of reactions produce
bromoform, CHBr 3, and mixed chlorine–
bromine trihalomethanes from the action on
humic materials of hypobromous acid, HOBr,
which is formed when bromide ion in water
displaces chlorine from HOCl:
94
OH
H
O
R9C9OH CHCl 3
O
HOCl Br EF HOBr Cl

presence, even at very low levels of approximately 30 ppb, raises the specter
that chlorinated drinking water may pose a health hazard, though one that
pales by comparison with the benefits that it confers in the elimination of
fatal waterborne diseases. The annual average limit of total THMs in drinking
water in the United States and the European Union (EU) has been
reduced to 80 ppb. The previous limit of 100 ppb is still used in Canada. In
fact, these 80–100-ppb limits are set not only to regulate the THM chemicals
themselves but also as an indicator that the production of other chlorinated
organic DBPs (see below) is not excessive.
The U.S. EPA has set a maximum contaminant level goal, MCLG, of
70 ppb for THMs in drinking water. An MCLG is the maximum level at which
the contaminant is believed to be safe, allowing for adequate margins of safety, but
unlike the MCL (Chapter 10), it is not an enforceable standard. A nonzero
goal is considered by some scientists and policymakers to be appropriate to
substances, like chloroform, that are believed to operate indirectly as carcinogens.
They do not damage DNA directly but cause tissue damage that leads to
rapid cell proliferation, which in turn increases the likelihood that cancer will
form in the damaged tissue. A threshold below which no effects are likely to
be observed is expected for carcinogens that operate in this manner.
The level of trihalomethanes formed in water depends sharply on the
organic content of the raw water since the THMs are formed from the reaction
of organics with HOCl (see Box 14-3). THM levels can reach 250 ppb
in areas of Scotland and Northern Ireland that have peat moorlands. Water
exposed to bogs in Newfoundland, Canada, has generated THM levels in
excess of 400 ppb. As of the early 1990s, about 1% of the larger U.S. drinking
water utilities that used surface waters, but none that used groundwater, had
average THM levels exceeding 100 ppb. The THM content of chlorinated
water could be decreased by using activated carbon either to remove dissolved
organic compounds before the water is chlorinated or to remove
THMs and other chlorinated organics after the process, although THMs are
not very efficiently adsorbed by the carbon and it is an expensive process.
An analysis of epidemiological studies relating the chlorination of water
to cancer rates in various communities in the United States led to the conclusion
that the risk of bladder cancer in humans increased by 21%, and that
of rectal cancer by 38%, for Americans who drank chlorinated surface water
in the past. A similar study in Ontario found even higher bladder cancer risk
factors for people who drank water for 35 years or more that had THM levels
greater than 50 ppb, and for colon cancer when the concentration exceeded
75 ppb, but found no correlations of THMs with rectal cancer rates. A recent
study found no increased risk for pancreatic cancer from lifetime exposure to
the by-products of chlorinated water.
Given that slightly more than half the population of the United States
drinks surface water, one effect of chlorination is to have increased bladder
cancer incidence by about 4200 cases per year and rectal cancer incidence by
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616 Chapter 14 The Pollution and Purification of Water
about 6500 cases annually. Because of these risks, some communities are considering
a switch, or have already switched, to water disinfection by ozone or
chlorine dioxide, since these agents produce little or no chloroform. The
extent of chlorination has already been reduced in most American communities
relative to the levels that led to these statistics.
Several other mutagenic chlorinated organic DBPs formed during chlorination
have been detected in water, in addition to chloroform. It is not clear
whether the main carcinogens in the chlorinated drinking water are the
THMs themselves or some nonvolatile, higher-molecular-weight mutagenic
by-product present at still lower concentrations but whose concentration
would presumably be proportional to THM. The same risks do not usually
apply to chlorinated well water, since its organochlorine content is much less
(only 0.8 ppb on average, versus 51 ppb for surface water) because it contains
much smaller amounts of organic matter that could become chlorinated.
Exposure to chloroform by dermal contact and inhalation of the gases deabsorbed
from the hot water during showers, baths, and hand-washing of dishes
contribute more to one’s intake of THMs, as measured by the blood levels of
these compounds, than does drinking the water itself. Swimming in pools in
which the water is chlorinated for disinfection also contributes significantly
to dermal exposure. Recently it has been found that use of the disinfectant
triclosan, a phenol-based compound present in some hand soaps, in chlorinated
water can produce additional chloroform and chlorinated phenols, to
which the user is then exposed.
Recently, public health officials have expressed concern about the possible
link between THMs and adverse human reproductive outcomes, including
first-term miscarriages, stillbirths, impaired fetal growth, and certain birth
defects. Even though the existing research in this area is not yet definitive,
some officials suggest that women drink bottled water rather than chlorinated
tap water during their first three months of pregnancy.
Disinfection by Chlorine: Advantages over Other Methods
Notwithstanding the preceding discussion of chlorination by-products, it is
important to point out that the disinfection of water by chlorine is extremely
important in protecting public health and saves many more lives—by a very
wide margin—than are affected negatively. For example, both typhoid and
cholera were widespread in both Europe and North America a century ago
but have been almost completely eradicated in the developed world, thanks
to chlorination and the other disinfection methods for drinking water and to
improved sanitation in general. The same is not true in many developing
countries; e.g., there were more than half a million cases of cholera in Peru in
the early 1990s. Overall, about 20 million people, most of them infants, die
from waterborne diseases annually worldwide in underdeveloped countries,
where water purification is often erratic or even nonexistent. Under no
96

circumstances should effective disinfection of water be abandoned because of
concern for the by-products of chlorination!
An advantage chlorination has over disinfection by chlorine dioxide or
ozone or by UV is that some chlorine remains dissolved in water once it has
left the purification plant, so that the water is protected from subsequent bacterial
contamination before it is consumed. Indeed, some chlorine is usually
added to water purified by the other methods to provide this protection.
There is very little danger of significant chloroform production in the purified
water since its organic content has been virtually eliminated before the chlorine
is introduced. If the chlorine level in water purified by chlorination is too
high, it can be lowered by the addition of sulfur dioxide.
The residual chlorine in water often exists in the form of the chloramines
NH 2 Cl, NHCl 2 , and NCl 3 , which are produced from reaction with dissolved
ammonia gas, NH 3 . Although not as fast as HOCl in disinfecting water, the
mono- and dichloroamines especially are good disinfectants. The mixture of
chloramines, called combined chlorine, is longer-lived in water than is
hypochlorous acid and thus provides longer residual protection. Indeed,
ammonia is often added to purified drinking water in order to convert the
residual chlorine to the combined form (Figure 14-1). Chloramines are sometimes
used, rather than chlorine or ozone or chlorine dioxide, as the main disinfectant
in the purification of drinking water. They have the advantage over
chlorine of producing little (though not zero) amounts of THMs and
haloacetic acids. The U.S. EPA has set MRDLs of 4.0 ppm for both chlorine
and chloramine in drinking water.
Bromine rather than chlorine is sometimes used as the disinfectant in
swimming pools. The main disinfecting agent in bromination is hypobromous
acid, HOBr, in analogy with the role of hypochlorous acid in chlorination.
HOBr reacts more rapidly with dissolved ammonia than does HOCl,
producing mainly NH 2 Br, which is also a good disinfectant.
To disinfect water for drinking purposes, hikers either boil raw water or
treat it chemically with either chlorine, in the form of bleach, which provides
HOCl, or iodine, as elemental I 2 or hypoiodous acid, HIO. Concerns have
been expressed about chronic health problems such as thyroid dysfunction
associated with long-term usage of iodine, however. Treating the water with
elemental iodine tends to make it unpalatable as well.
PROBLEM 14-3
Assuming that the nitrogen atom in monochloramine, NH 2 Cl, has an oxidation
number of 3, calculate that of the chlorine atom. Using the principle
that unlike charges attract, predict whether it will be the hydrogen ion or the
hydroxide ion from dissociated water molecules that will extract the Cl from
NH 2 Cl; from your result, predict the products of the decomposition reaction
of chloramine in water.
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618 Chapter 14 The Pollution and Purification of Water
Surface
Water table
FIGURE 14-3 Groundwater
location in relation
to regions in the soil.
Precipitation
Soil moisture
Aeration zone
(unsaturated)
Groundwater in
saturated zone
(aquifer)
Clay or impervious rock
A drinking-water quality issue of current concern involves the pathogenic
protozoa called Cryptosporidium, which was responsible for the death of
100 people and for about 400,000 cases of watery diarrhea in Milwaukee in
1993. Less serious Cryptosporidium outbreaks occurred in Oxford, England, in
1989, and in Saskatchewan, Canada, in 2001. This deadly parasite is resistant
to standard methods of disinfection, such as chlorination at normal levels,
and is so small (about 5-mm diameter) that it easily passes through the standard
filters used to separate sediments. Several possible solutions have been
advanced, including ozonation or the use of ultrafiltration or UV irradiation
or the application of monochloramine following chlorination. A longerthan-usual
exposure of water containing Cryptosporidium is necessary with
ozonation, since the activation energy for inactivation of protozoa by ozone
is about twice as large as that for bacteria (80 vs. about 40 kJ/mol).
Another protozoa, Giardia lamblia, also causes many instances of waterborne
disease. Like Cryptosporidium, it is also somewhat resistant to chlorination,
but since it is larger (about 10-mm diameter), it is more easily removed
by filtration through sand.
Groundwater: Its Supply, Chemical
Contamination, and Remediation
The Nature and Supply of Groundwater
The great majority of the available fresh water on Earth lies underground,
half of it at depths exceeding a kilometer. As one digs into the ground below
the initial belt of soil moisture, the aeration or unsaturated zone, where the
particles of soil are covered with a film of water but in
which air is present between the particles, is next
encountered. At lower depths is the saturated zone, in
which water has displaced all the air from these pore
spaces. Groundwater is the name given to the fresh
water in the saturated zone (see Figure 14-3); it makes
up 0.6% of the world’s total water supply. The ultimate
source of groundwater is precipitation that falls onto
the surface; a small fraction of it eventually filters
down to the saturated zone. Underground water ranges
in “age” from a few years to millions of years. For
example, in zones that are now arid, much of the
groundwater currently being accessed has been present
since the wetter conditions of the last ice age and will
not be quickly replaced.
The top of the groundwater (saturated) region is
called the water table. In some places it occurs right at
the surface of the soil, a phenomenon that gives rise to swamps. Where the
water table lies above the soil, we encounter lakes and streams.
98

Groundwater: Its Supply, Chemical Contamination, and Remediation 619
If groundwater is contained in soil that is composed of porous rocks such
as sandstone, or in highly fractured rock such as gravel or sand, and if the
water is bounded at its lower depths by a layer of clay or impervious rocks,
then it constitutes a permanent reservoir—a sort of underground lake—
called an aquifer. Some aquifers lie below several layers of impermeable rock
or soil; these are called confined or artesian aquifers.
Groundwater in aquifers can be extracted by wells, and it is the main supply
of drinking water for almost half the population of North America and
over 1.5 billion people worldwide. In the United States in 1990, groundwater
supplied 39% of the water used for public supplies and 96% of that withdrawn
for individual domestic systems, the latter being very common in rural homes.
In Europe the proportion of public drinking water extracted from aquifers
ranges from nearly 100% for Denmark, Austria, and Italy, to about two-thirds
in Germany, Switzerland, and the Netherlands, to less than one-third in
Great Britain and Spain.
In the United States, the majority of groundwater usage is for irrigation
purposes, almost all of it in the western states. The massive extraction of
water from American aquifers has given rise to fears about future supplies of
fresh water (and about the sinking of land above the aquifers), since such
aquifers are replenished only very slowly. In the High Plains of the central
United States, more than half the groundwater in storage has been depleted
in some areas. In northern China, the depletion of shallow aquifers is forcing
the sinking of wells more than 1 km deep in order to reach a new supply
of groundwater. Indeed, groundwater depletion—along with the buildup
of salts in the soil—is now the dominant threat to irrigated agriculture. In
addition, the contamination of groundwater by chemicals is becoming a
serious concern in many areas. A side effect of the rise in sea levels that will
accompany global warming is the intrusion of salt water into aquifers near
coasts.
The Contamination of Groundwater
Groundwater has been traditionally considered to be a pure form of water.
Because of its filtration through soil and its long residence time underground,
it contains much less natural organic matter and many fewer disease-causing
microorganisms than water from lakes or rivers, although the latter point may
be a misconception, according to recent evidence. Some groundwater is naturally
too salty or too acidic for either drinking or irrigation purposes and
may contain too much sodium, sulfide, or iron for many uses.
Humans have been concerned about the pollution of surface water in
rivers and lakes for a long time. Indeed, a recent survey indicated that stream
water in both agricultural and urban areas of the United States contains pesticide
concentrations that exceed human-health benchmark standards. In
contrast, the contamination by chemicals of groundwater was not recognized
as a serious environmental problem until the 1980s, notwithstanding the fact
99

620 Chapter 14 The Pollution and Purification of Water
that it had been occurring for half a century. To a large extent, groundwater
contamination was neglected because it was not immediately visible—it was
“out of sight, out of mind”—even though groundwater is a major source of
drinking water. We were ignorant of the long-range consequences of our
waste disposal practices. Ironically, surface water can be cleaned up relatively
easily and quickly, whereas groundwater pollution is a much harder, much
more expensive, long-range problem to solve.
Because we are now aware of the consequences—including high remediation
costs—of the uncontrolled disposal of organic chemical wastes, most
large corporations in developed countries have become much more responsible
in their disposal of chemicals. Unfortunately, the collective discharges
from smaller sources, including many municipalities, small industries, and
farms, have not yet been controlled in like manner. Similarly, the huge number
of septic tanks that exist are collectively a major source of nitrate, bacteria,
viruses, detergents, and household cleaners to groundwater.
Nitrate Contamination of Groundwater
The inorganic contaminant of greatest concern in groundwater is the nitrate
ion, NO3 , which commonly occurs in both rural and suburban aquifers.
Although uncontaminated groundwater generally has nitrate nitrogen levels
of 4–9 ppm, about 9% of shallow aquifers—from which water is often
extracted via privately owned wells—in the United States now have nitrate
levels that exceed the 10-ppm nitrogen MCL value. Indeed, elevated levels
of about 100 ppm can result from agricultural activity. The location of areas
in the United States that have a high risk of nitrate contamination of
groundwater is shown in Figure 14-4. Exceeding the 10-ppm MCL limit is
much rarer (1%) for public U.S. groundwater supplies, partially because they
are drawn from deeper aquifers; these are generally less contaminated because
of their depth, because their location is remote from large sources of contamination,
and because natural remediation via denitrification of nitrate in the
low-oxygen conditions can occur.
The expenditure of public money on nitrate-level reductions in drinking
water has become a controversial subject. In Great Britain, in particular, hundreds
of millions of dollars have been spent on achieving the 50-ppm maximum
level of nitrate ion set by the European Union. Because nitrate removal
from well water is very expensive, water contaminated with high levels of the
ion are not normally used for human consumption, at least in public supplies.
PROBLEM 14-4
Convert the EU nitrate standard of 50 ppm to its nitrogen content alone.
Is the EU standard more or less stringent than the U.S. regulatory limit of
10 ppm nitrogen as nitrate per liter?
100

Increasing risk of
groundwater
contamination
Groundwater: Its Supply, Chemical Contamination, and Remediation 621
Nitrogen
input
High
High
Low
Low
Aquifer
vulnerability
High
Low
High
Low
Nitrate in groundwater originates mainly from four sources:
• application of nitrogen fertilizers, both inorganic and animal manure, to
cropland,
• cultivation of the soil,
• human sewage deposited in septic systems, and
• atmospheric deposition.
Concern has been expressed about the increasing levels of nitrate ion in
drinking water, particularly in well water in rural locations; the main source
of this NO 3 is runoff from agricultural lands into rivers and streams. Almost
12 million tons of nitrogen is applied annually as fertilizer for agriculture in
the United States, and manure production contributes almost 7 million tons
more. Initially, oxidized animal wastes (manure), unabsorbed ammonium
nitrate, NH 4 NO 3 , and other nitrogen fertilizers were thought to be the culprits
in nitrate contamination of groundwater, since reduced nitrogen unused
by plants is converted naturally to nitrate, which is highly soluble in water
101
FIGURE 14-4 The risk of
nitrate contamination of the
groundwaters in the United
States. [Source: B. T. Nolan
et al., “Risk of Nitrate in
Groundwaters of the
United States—A National
Perspective,” Environmental
Science and Technology 31
(1997): 2229.]

622 Chapter 14 The Pollution and Purification of Water
and can easily leach down into groundwater. It now appears that intensive
cultivation of land, even without the application of fertilizer or manure, also
facilitates the oxidation of reduced nitrogen to nitrate in decomposed organic
matter in the soil by providing aeration and moisture. The original, reduced
forms of nitrogen become oxidized in the soil to nitrate, which, being mobile,
then migrates down to the groundwater, where it dissolves in water and is
diluted. Denitrification of nitrate to nitrogen gas (see Chapter 6) and uptake
of nitrate by plants can occur in forested areas that separate agricultural farms
from streams, thereby lowering the risk of contamination in areas with significant
woodland. However, rural areas with high nitrogen input, well-drained
soil, and little woodland are at particular risk for nitrate contamination of
groundwater.
The atmospheric deposition of nitrate results from its production in the
atmosphere when NO X emissions from vehicles and power plants, and its
natural sources in thunderstorms, are oxidized in air to nitric acid and then
neutralized to ammonium nitrate (see Chapters 3 and 5).
In urban areas, the use of nitrogen fertilizers on domestic lawns and golf
courses, parks, etc. contributes nitrate to groundwater. Septic tanks and
cesspools also are significant contributors where they exist.
Excess nitrate ion in wastewater flowing into seawater, e.g., the Baltic
Sea, has resulted in algal blooms that pollute the water after they die. Nitrate
ion normally does not cause this effect in bodies of fresh water, where phosphorus
rather than nitrogen is usually the limiting nutrient; increasing the
nitrate concentration there without an increase in phosphate levels does not
lead to an increased amount of plant growth. There are, however, instances
where nitrogen rather than phosphorus temporarily becomes the limiting
nutrient even in fresh waters.
PROBLEM 14-5
The nitrate concentration in an aquifer is 20 ppm, and its volume is 10 million
liters. What mass of ammonia upon oxidation would have produced this
mass of nitrate?
Health Hazards of Nitrates in Drinking Water
Excess nitrate ion in drinking water is a potential health hazard since it can
result in methemoglobinemia in newborn infants as well as in adults with a
specific enzyme deficiency. The pathological process, in brief, runs as follows.
Bacteria, e.g., in unsterilized milk-feeding bottles or in the baby’s stomach,
reduce some of the nitrate to nitrite ion, NO 2 :
NO 3 2 H 2 e 9: NO2 H2O
The nitrite combines with and oxidizes the iron ions in the hemoglobin in
blood from Fe 2 to Fe 3 and thereby prevents the proper absorption and
102

Groundwater: Its Supply, Chemical Contamination, and Remediation 623
transfer of oxygen to cells. The baby turns blue and suffers respiratory failure.
(In almost all adults, the oxidized hemoglobin is readily reduced back to its
oxygen-carrying form, and the nitrite is readily oxidized back to nitrate; also,
nitrate is mainly absorbed in the digestive tract of adults before reduction to
nitrite can occur.) Methemoglobinemia, or blue-baby syndrome, is now relatively
rare in industrialized countries. It was a serious problem in Hungary up
until the late 1980s and in Romania.
The U.S. EPA MCL of 10 ppm of nitrate nitrogen was set in order to
avoid blue-baby syndrome. Since the syndrome is now almost nonexistent in
the United States (only two cases since the mid-1960s), some policy analysts
think this value is too stringent.
Recently, an increase in the risk of acquiring non-Hodgkin’s lymphoma
has been found for persons in some communities in Nebraska who consume
drinking water having the highest levels (long-term average of 4 ppm or more
of nitrogen as nitrate) of nitrate. As discussed in the next section, excess
nitrate ion in drinking water is also of concern because of its potential link
with stomach cancer. Recent epidemiological investigations have, however,
failed to establish any positive, statistically significant relationship between
nitrate levels in drinking water and the incidence of stomach cancer. A study
reported in 2001 found that older women in Iowa who drank water from
municipal supplies having elevated nitrate levels ( 2.46 ppm) were almost
three times as likely to be diagnosed with bladder cancer than those least
exposed ( 0.36 ppm in their drinking water). However, a recent large-scale
study from the Netherlands failed to find an association between nitrate
exposure and the risk of bladder cancer. A review of the current literature
concluded that there is also no association between nitrate exposure from
drinking water and adverse reproductive effects.
Nitrosamines in Food and Water
Some scientists have warned that excess nitrate ion in drinking water and
foods could lead to an increase in the incidence of stomach cancer in
humans, since some of it is converted in the stomach to nitrite ion. The
nitrites could subsequently react with amines to produce N-nitrosamines,
compounds that are known to be carcinogenic in animals. N-nitrosamines
are amines in which two organic groups and an 9N"O unit are bonded to
the central nitrogen:
R
R
N9N"O
H 3 C
H 3 C
N9N"O
N-nitrosamines NDMA
103

624 Chapter 14 The Pollution and Purification of Water
Of concern not only with respect to its production in the stomach and its
occurrence in foods and beverages (e.g., cheeses, fried bacon, smoked and/or
cured meat and fish, and beer), but also as an environmental pollutant in
drinking water, is the compound in which R in the above structure is the
methyl group CH 3 ; it is called N-nitrosodimethylamine, or NDMA for short.
This organic liquid is somewhat soluble in water (about 4 g/L) and somewhat
soluble in organic liquids. It is a probable human carcinogen, and a potent
one if extrapolation from animal studies is a reliable guide. It can transfer a
methyl group to a nitrogen or oxygen of a DNA base, thereby altering the
instructional code for protein synthesis in the cell.
In the early 1980s, it was found that NDMA was present in beer to the
extent of about 3000 ppt. Since that time, commercial brewers have modified
the drying of malt so that the current levels of NDMA in American and
Canadian beers are now only about 70 ppt.
Large quantities of nitrate are used to “cure” pork products such as bacon
and hot dogs. In these foods, some of the nitrate ion is biochemically reduced
to nitrite ion, which prevents the growth of the organism responsible for
botulism. Nitrite ion also gives these meats their characteristic taste and color
by combining with hemoproteins in blood. Nitrosamines are produced from
excess nitrite during frying (e.g., of bacon) and in the stomach, as discussed.
Government agencies have instituted programs to decrease the residual nitrite
levels in cured meats. Some manufacturers of these foods now add vitamin C
or E to the meat in order to block the formation of nitrosamines. Based upon
average levels of NDMA in various foods and the average daily intake for each
of them, most of us now ingest more NDMA from consumption of cheese
(which is often treated with nitrates) than from any other source.
Even though the commercial production of NDMA has been phased out,
it can be formed as a by-product due to the use of amines in industrial
processes such as rubber tire manufacturing, leather tanning, and pesticide
production.
The levels of NDMA in drinking water drawn from groundwater is of
concern in some localities that have industrial sources of the compound. For
example, following the discovery that the water supply of one town had been
contaminated by up to 100 ppt NDMA from a tire factory, Ontario, Canada,
adopted a guideline maximum of 9 ppt of NDMA in drinking water, which
corresponds to a lifetime cancer risk of 1 in 100,000. By contrast, the guideline
for water in the United States is set at 0.68 ppt, which corresponds to a
cancer risk of 1 in a million, but which actually lies considerably below the
detection limit (about 5 ppt) for the compound.
PROBLEM 14-6
Write balanced redox half-reactions (assuming acidic conditions) for the
conversion of NH4 to NO3 , and of NO2 to N2.
104

Perchlorates
Groundwater: Its Supply, Chemical Contamination, and Remediation 625
Perchlorate ion, ClO 4 , is analogous to nitrate ion in that both oxyanions
involve nonmetals in their highest common oxidation numbers (7 inthe
case of perchlorate; see Additional Problem 13 to generate a summary of
chlorine with its many oxidation numbers). For that reason, both ions are
oxidizing agents, and both have been used in explosives and propellants. Both
have both natural and anthropogenic sources. Perchlorate is a newly discovered
(late 1990s) pollutant in the drinking-water supply of about 15 million
Americans. Large quantities of ammonium perchlorate, NH 4ClO 4, are manufactured
for use as oxidizing agents in solid rocket propellants, fireworks,
batteries, and automobile air bags. Because rocket fuel has a limited shelf life,
it must be replaced regularly. Large amounts of perchlorates were washed out
of missiles and rocket boosters onto the ground or into holding lagoons in the
second half of the twentieth century.
Perchlorate contamination has been established in 23 U.S. states,
including much of the Colorado River and aquifers in the deserts of the
Southwest. Concentrations of perchlorate in drinking water in the U.S.
Southwest range from 5 to 20 ppb. The map (Figure 14-5) of perchlorate
releases in the United States indicates that most occur in the south-central
and western states, especially California. Perchlorate has also been found in
garden fertilizers at concentrations approaching 1%. It occurs naturally in
some Chilean deposits of nitrate which are exported to the United States and
elsewhere as fertilizers. Perchlorate also exists naturally in some minerals
Confirmed sites
Unconfirmed sites
Urbanized areas
Major rivers
Affected states
105
FIGURE 14-5 Regions
of perchlorate use and
contamination in the
United States. [Source: B. E.
Logan, “Assessing the Outlook
for Perchlorate Remediation,”
Environmental Science and
Technology (1 December
2001): 484A.]

626 Chapter 14 The Pollution and Purification of Water
found in the U.S. Southwest. A recent analysis indicates that both its use as an
oxidizer, in fireworks, rockets, etc., and its presence in fertilizer make important
contributions to its contamination of foodstuffs in the United States.
At high doses, perchlorate affects human health by reducing hormone
production in the thyroid, where it competes with iodide ion. Its hazard
at low concentrations, if any, is not known, making the development of a
drinking-water standard for the ion a difficult problem. No federal MCL for
the ion has yet been set, but several states have set their own limits, ranging
from 1 to 18 ppb; e.g., California’s limit is 6 ppb. In 2002, a draft report by the
U.S. EPA proposed a drinking-water standard of 1 ppb as safe for human
health, but this value has been criticized as too low by the Department of
Defense and companies that make or use perchlorates. Research reported in
2002 on volunteers indicated that the no-effect level (NOEL; Chapter 10) for
the inhibition of iodine uptake corresponds to a drinking-water concentration
of at least 180 ppb. The EPA based its 1-ppb recommendation on studies
indicating that mothers who drink perchlorate-contaminated water could
give birth to children whose IQs would be affected negatively because correct
maternal thyroid hormone levels are vital to fetal brain development.
Like nitrate, perchlorate is a difficult ion to remove from water supplies
since it is a highly water-soluble anion that is very inert and does not adsorb
readily either to mineral surfaces or to activated carbon. Barrier methods,
using elemental iron, etc. are not successful because the anion is so unreactive.
The primary technologies currently in use to remediate perchlorate in
water are ion exchange and biological treatment. Some ion exchange resins
successfully remove perchlorate, though it tends to remain in solution until
all other anions have been absorbed. Ion exchange is used especially when
perchlorate concentrations are low to begin with.
Certain bacteria found naturally in many soils, sediments, and natural
waters biodegrade perchlorate by reduction to chloride ion:
ClO4 9: 9: Cl 2 O2
Perchlorate can be biodegraded in bioreactors, large vats that are engineered
to maintain a high concentration of the appropriate bacteria in contact with
the water.
Groundwater Contamination by Organic Chemicals
The contamination of groundwater by organic chemicals is a major concern.
Many organic substances decay rapidly or are immobilized in the soil, so the
number of compounds that are sufficiently persistent and mobile to travel to
the water table and to contaminate groundwater there is relatively small.
The compounds that are most often detected in groundwater-based U.S.
community public water supplies, including those near hazardous waste sites,
are summarized in Table 14-1. Municipal landfills as well as industrial waste
106

TABLE 14-1
Groundwater: Its Supply, Chemical Contamination, and Remediation 627
Organic Compounds Commonly Found in U.S. Groundwater-Based
Community Water Supplies and Their Properties
Chemical Density (g/mL) Water Solubility (g/L)
Present at 25–50% of sites:
Chloroform (trichloromethane) 1.48 8.2
Bromodichloromethane 1.98 4.4
Dibromochloromethane 2.45 2.7
Bromoform (tribromomethane)
Present at a smaller fraction of sites:
2.89 3.0
Trichloroethene 1.46 1.1
Tetrachloroethene (perchloroethene) 1.62 0.15
1,1,1-Trichloroethane 1.34 1.5
1,2-Dichloroethenes 1.26, 1.28 3.5, 6.3
1,1-Dichloroethane 1.18 5.5
Carbon tetrachloride 1.46 0.76
Dichloroiodomethane 1.58
Xylenes 0.86–0.88 0.18 (o)
1,2-Dichloropropane 1.16 2.8
Benzene 0.88 1.8
Toluene
Also commonly present at wells close to
hazardous waste sites:
0.87 0.54
Methylene chloride 1.33 20
Ethylbenzene 0.87 0.15
Acetone 0.79 sol
1,1-Dichloroethene 1.22 2.3
1,2-Dichloroethane 1.24 8.5
Vinyl chloride (chloroethene) gas 8.8
Methyl ethyl ketone 0.80 268
Chlorobenzene 1.11 0.47
1,1,2-Trichloroethane 1.44 4.5
Chloroethane 0.90 5.7
Fluorotrichloromethane gas 1.1
1,1,2,2-Tetrachloroethane 1.60 2.7
Methyl isobutyl ketone 0.80 19
Source: Based on U.S. EPA surveys of about 2% of U.S. water supplies.
disposal sites are often the source of the contaminants. Liquid that contains
dissolved matter that drains from a terrestrial source, such as a landfill, is called
a leachate. In rural areas, the contamination of shallow aquifers by organic
pesticides, such as atrazine (Chapter 10) leached from the surface, has become
107

628 Chapter 14 The Pollution and Purification of Water
a concern. The insecticide dieldrin (Chapter 10), which has been banned since
1992, is the pesticide found most often to exceed human-health guideline
levels in U.S. groundwater. Ironically, shallow groundwater aquifers used to
supply drinking water are often more polluted by pesticides at greater than
acceptable levels than are those in agricultural areas in the United States.
The typical organic contaminants in most major groundwater supplies are:
• Chlorinated solvents, especially trichloroethene (TCE, “tric,” also called
trichloroethylene), C2HCl3, and perchloroethene (PCE, “perc,” also called
perchloroethylene or tetrachloroethene), C2Cl4 . These molecules contain a
C"C bond, with three or four of the four hydrogen atoms of ethene (ethylene)
replaced by chlorine:
H
Cl
C"C
Cl
Cl
C"C
By a large margin, chlorinated solvents are the most prevalent organic pollutants
in groundwater.
• Hydrocarbons from the BTX component of gasoline and other petroleum
products: benzene, C6H6 , and its methylated derivatives toluene,
C6H5(CH3), and the three isomers of xylene, C6H4(CH3) 2. (See Chapter 7
for structures.)
• MTBE (methyl tertiary-butyl ether) from gasoline (see Chapter 8)
The chemicals in the groups mentioned above occur commonly in
groundwater at sites where manufacturing and/or waste disposal occurred,
especially from 1940 to 1980. In that period, little attention was paid to the
ultimate fate and residence following the in-ground injection of these chemicals.
The sources of these organic substances also include leaking chemical
waste dumps, leaking underground gasoline storage tanks, leaking municipal
landfills, and accidental spills of chemicals on land.
Trichloroethene is an industrial solvent, used to dissolve grease on metal, as
is perchloroethene. The U.S. MCL for TCE in drinking water is 5 ppb, and the
same limit is now used in Canada as well. A 2006 report by the U.S. National
Academy of Sciences concluded that TCE is a possible cause of kidney cancer,
can impair neurological function, and can cause reproductive and developmental
damage. A link between TCE exposure and an abnormally low sperm count
in males has been established. The International Agency for Research on
Cancer has classified TCE as “probably carcinogenic to humans.”
PCE is used not only in metal degreasing but also finds wide application
as the solvent in dry-cleaning operations, so it is released from a large number
of small sources. A group of women in Cape Cod, Massachusetts, who were
inadvertently exposed over several decades to high levels of PCE in their
Cl
Cl
TCE PCE
108
Cl
Cl

Groundwater: Its Supply, Chemical Contamination, and Remediation 629
drinking water were found to have small to moderate increases in their risk of
contracting breast cancer.
Gasoline enters the soil via surface spills, leakage from underground storage
tanks, and pipeline ruptures. Before 1980, underground gasoline storage tanks
were made from steel; almost half of them were sufficiently corroded to leak
by the time they were 15 years old. Once they descend to groundwater, the
water-soluble components of the gasoline are preferentially leached into the
water and can migrate rapidly in the dissolved state. The BTX component,
which is the most soluble of the hydrocarbons, often occurs at concentrations
of 1–50 ppb in groundwater. However, the alkylated benzenes are rapidly
degraded by aerobic bacteria and consequently are not long-lasting.
The MTBE component of gasoline (Chapter 7) is more water-soluble
than the hydrocarbons, but unlike them, it is not readily biodegraded. It is
not highly toxic. The main problem is the odor and taste that it gives to
water; as little as 15 ppb in water can be tasted or smelled. MTBE contamination
of well water, albeit at low levels, has become of concern in the United
States since it has occurred at about a quarter of a million sites.
The Ultimate Sink for Organic Contaminants
in Groundwater
The subsequent behavior of the organic compounds that do migrate to the
water table depends significantly upon their density relative to that of 1.0 g/mL
of water. Liquids that are less dense (“lighter”) than water and have low solubility
in it form a mass that floats on the top of the water table. All hydrocarbons
having a small or medium molecular mass belong to this group,
including the BTX fraction of gasolines and other petroleum products (see
Table 14-1). In contrast, polychlorinated solvents are more dense (“heavier”)
than water and insoluble in it, so they tend to sink deeply into aquifers;
important examples are methylene chloride, chloroform, carbon tetrachloride,
1,1,1-trichloroethane, TCE, and PCE (see Table 14-1). Nonchlorinated but
insoluble high-molecular-weight organic materials, such as creosote and coal
tar, also belong to the heavier-than-water group. These substances are sometimes
referred to as dense nonaqueous-phase liquids, DNAPLs.
Although the oily liquid blobs that these organic compounds form generally
are found in an aquifer at a position either directly below their original
point of entry into the soil or close to it, the implication that they are horizontally
immobile is misleading. Very slowly—in a process that often takes
decades or centuries to complete—these low-solubility compounds gradually
dissolve in the water that passes over the blob and so provide a continuous
supply of contaminants to the groundwater. The complete removal of such
deposits usually is not feasible since they may exist as several blobs whose
exact location is difficult to pinpoint. In addition, disturbance of the deposit
during removal or treatment may increase its net exposure to the water phase.
Even removing 90% of the substance does not necessarily result in reduction
109

630 Chapter 14 The Pollution and Purification of Water
FIGURE 14-6 The contamination
of groundwater
by organic chemicals.
Aquifer
Direction of
groundwater flow
Surface source
BTX
Chlorinated
solvents
Water table
Plume of
BTX-polluted
water
Plume
of solventpolluted
water
of its groundwater concentration. Thus, plumes of polluted water grow, in the
direction of the water’s flow, and thereby contaminate the bulk of the aquifer
(see Figure 14-6). Because of such contamination, many wells used for drinking
water have had to be closed.
Decontamination of Groundwater:
Physical and Chemical Processes
In the last two decades, considerable energy and money have been spent in
the United States on attempts to control aquifer pollution by the oily liquids
discussed above. Dense organic leachates, especially PCE and TCE, have
contaminated the groundwater that lies below the waste sites associated with
the U.S. Superfund remediation initiative (see Chapter 16). Unfortunately,
no easy cure to the problem of contamination has been found. Control usually
consists of pump-and-treat systems that pump contaminated water from the
aquifer, treat it to remove its organic contaminants (using methods of the type
described later in this chapter), and return the cleaned water to the aquifer or
to some other water body. Alternatively, a fine mist of the contaminated
groundwater is sprayed into the air above agricultural land using a long, moveable
sprinkler system; the contaminant volatile organic compounds (VOCs)
evaporate into the air and the cleansed water is used for irrigation.
110

Groundwater: Its Supply, Chemical Contamination, and Remediation 631
The volume of water that must be pumped and treated in a given
aquifer is huge. For organic contaminants with low water solubility, recontamination
of water returned to the aquifer by additional dissolution from
the blob will occur. Consequently, the treatment systems must operate in
perpetuity, and there are already thousands of them spread across the
United States.
Both in situ heating, to vaporize the organic liquids so their vapors rise
to the soil surface, and the addition of oxidants to convert the substances to
products such as carbon dioxide have been tried in some locations. Typically,
temperatures close to 100°C are used in heating, though it is not known if
this is optimal in most cases. Heating and/or the production of gases or precipitates
by oxidation may inadvertently change the geologic and biological
conditions in the immediate vicinity of the treatment, with unforeseen
effects on the distribution and mobility of the remaining pollutant.
Decontamination of Groundwater:
Bioremediation and Natural Attenuation
Bioremediation is the term applied to the decontamination of water or soil
using biochemical rather than chemical or physical processes. Recently there
has been interesting progress reported in using bioremediation to cleanse
water of chlorinated ethene solvent contamination.
The biodegradation of chloroethenes by aerobic bacteria becomes less
and less efficient as the extent of chlorination increases, so it is ineffective
for perchloroethene. However, under anaerobic conditions, the reductive
biodegradation of PCE and TCE proceeds more quickly, particularly if an easily
oxidized substance such as methanol is added to supply electrons for the
reduction processes. Unfortunately, the stepwise dechlorination of these
compounds proceeds through vinyl chloride, CH2" CHCl, a known carcinogen.
Recently, a bacterium has been discovered that removes all the
chlorine from organic solvents such as TCE and PCE.
Owing to the high cost and limited effectiveness of many groundwater
cleanup technologies, the inexpensive process of natural attenuation—
allowing natural biological, chemical, and physical processes to treat groundwater
contaminants—has become popular. Indeed, it is now used at more
than 25% of Superfund program sites in the United States and is the leading
method to remedy the contamination of groundwater from leaking underground
storage sites.
However, there is great controversy about whether or not natural
attenuation is an appropriate strategy for managing groundwater contamination:
Many environmentalists feel that it is a cheap way for industry to
avoid expensive cleanup costs. The U.S. National Research Council in
1997 appointed a committee to determine which pollutants could be
treated successfully by this technique. Table 14-2 summarizes their results.
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632 Chapter 14 The Pollution and Purification of Water
TABLE 14-2
Likelihood of Success of Groundwater Remediation
by Natural Attenuation for Various Substances
Dominant Attenuation Likelihood of Success Given
Chemical Class Processes Current Level of Understanding
Organic Compounds
Hydrocarbons
BTEX Biotransformation High
Gasoline, fuel oil Biotransformation Moderate
Nonvolatile aliphatic Biotransformation,
compounds immobilization Low
PAHs Biotransformation,
immobilization Low
Creosote Biotransformation,
Oxygenated hydrocarbons
immobilization Low
Low-molecular-weight
alcohols, ketones, esters
Biotransformation High
MTBE
Halogenated aliphatics
Biotransformation Low
PCE, TCE, carbon tetrachloride Biotransformation Low
TCA Biotransformation,
abiotic transformation Low
Methylene chloride Biotransformation High
Vinyl chloride Biotransformation Low
Dichloroethylene
Halogenated aromatics
Highly chlorinated
Biotransformation Low
PCBs, tetrachlorodibenzofuran, Biotransformation,
pentachlorophenol,
multichlorinated benzenes
Less chlorinated
immobilization Low
PCBs, dioxins Biotransformation Low
Monochlorobenzene Biotransformation Moderate
Inorganic Substances
Metals
Ni Immobilization Moderate
Cu, Zn Immobilization Moderate
Cd Immobilization Low
Pb Immobilization Moderate
112

TABLE 14-2
Groundwater: Its Supply, Chemical Contamination, and Remediation 633
Likelihood of Success of Groundwater Remediation
by Natural Attenuation for Various Substances
Dominant Attenuation Likelihood of Success Given
Chemical Class Processes Current Level of Understanding
Cr Biotransformation,
immobilization Low to moderate
Hg Biotransformation,
immobilization Low
Nonmetals
As Biotransformation,
immobilization Low
Se Biotransformation,
immobilization Low
Oxyanions
Nitrate Biotransformation Moderate
Perchlorate Biotransformation Low
Source: Adapted from J. A. Macdonald, “Evaluating Natural Attenuation for Groundwater Cleanup,” Environmental Science and
Technology (1 August 2000): 346A.
Only three pollutants are highly likely to be successfully treated by natural
attenuation:
• BTEX hydrocarbons (i.e., BTX hydrocarbons plus ethylbenzene),
• low-molecular-weight oxygen-containing organics, and
• methylene chloride.
In all three cases, biotransformation is the dominant process by which attenuation
occurs. Notice that neither MTBE nor highly chlorinated organics,
including TCE and PCE, are usually successfully treated in this way, nor is
mercury or perchlorate ion.
Decontamination of Groundwater: In Situ Remediation
Scientists have developed a promising in situ technique for treating groundwater
contaminated by volatile (mainly C1 and C2 ) chlorinated organics.
They construct an underground permeable “wall” of material (mostly coarse
sand) along the path of the water. The water is cleansed as a result of its
passage through the wall and never has to be pumped out of the ground (see
Figure 14-7).
The ingredient that is placed within the sand bed and that chemically
cleans the water is metallic iron, Fe 0 , in the form of small granules, a common
113

634 Chapter 14 The Pollution and Purification of Water
FIGURE 14-7 In situ
purification of groundwater
using an “iron wall.”
Permeable subsurface
treatment wall composed
of iron filings and sand
Clean
groundwater
Gravel
Stream of
chemicals
waste product of manufacturing processes. When placed in contact with certain
chlorinated organics dissolved in water, the iron acts as a reducing agent,
giving up electrons to form the ferrous, or Fe(II), ion Fe 2 , which dissolves
in the water:
Fe(s) 9: Fe 2 (aq) 2 e
Usually, these electrons are donated to chloroorganic molecules that are temporarily
adsorbed onto the metal’s surface; the chlorine atoms contained in
these molecules are consequently reduced to chloride ions, Cl , which are
released into aqueous solution. This technique is an example of reductive
degradation. For example, the reduction of trichloroethene to its completely
dechlorinated form, ethene, can be written in unbalanced form as
C 2 HCl 3 9: C 2 H 4 3 Cl
Chemical source
Direction of
groundwater
flow
Upon application of a standard redox balancing technique for alkaline solution,
we obtain the balanced half-reaction
C 2 HCl 3 3 H 2 O 6 e 9: C 2 H 4 3 Cl 3 OH
Combination of the half-reactions (after tripling the oxidation step to ensure
the number of electrons lost and gained is the same) yields the overall reaction
3 Fe(s) C 2HCl 3 3 H 2O 9: 3 Fe 2 (aq) C 2H 4 3 Cl 3 OH
One of the by-products of the reaction is hydroxide ion, OH . Recall
from Chapter 13 that in limestone-rich areas, the groundwater contains
114

significant concentrations of dissolved calcium bicarbonate, Ca(HCO 3 ) 2 .
The hydroxide ions produced in the groundwater remediation reaction react
with bicarbonate to produce carbonate ion, CO 3 2 , which combines with dissolved
calcium ions to produce insoluble calcium carbonate, CaCO 3, which
then precipitates in the sand–iron mixture.
Field trials indicate that this new technology can work successfully for
several years at least, and it may replace the pump-and-treat methods for
many applications involving chlorinated methanes and ethanes dissolved in
underground water.
Recently, it has been found that coating the iron filings with nickel
speeds up the rate of degradation of the organic compounds by a factor of 10;
with this modification, the technique may be even more useful than first
imagined. In addition, it has been discovered that the elemental iron in the
barriers will reduce soluble Cr 6 ions to insoluble Cr 3 oxides and can therefore
remediate groundwater contaminated by Cr 6 . (The environmental chemistry
of chromium is discussed in more detail in Chapter 15). A technique for
the in situ creation of elemental iron from its ions (Fe 2 and Fe 3 ) by the
injection of aqueous reducing agents has also been tested.
An in situ technique of treating TCE and PCE by hydrogenation has
been developed. The process uses dissolved H 2 gas to rapidly dechlorinate
these two organics, eventually forming ethane and HCl. The reaction, which
uses a palladium catalyst, can be done within a well bore so that the water
need not be brought up to the surface.
PROBLEM 14-7
The dissolution of iron in the process described above produces some molecular
hydrogen gas, H 2 . Show by balanced equation(s) how the hydrogen could
arise from the reduction of water rather than of TCE.
PROBLEM 14-8
Suppose that this “iron wall” technology reduced an appreciable fraction
of TCE to vinyl chloride rather than completely to ethene. Why would this
be an unacceptable result environmentally? (Note that in practice a sufficiently
thick wall of iron is used to convert any vinyl chloride by-product to
ethene.)
PROBLEM 14-9
Groundwater: Its Supply, Chemical Contamination, and Remediation 635
Deduce the overall reaction by which perchloroethene is converted to
ethene by metallic iron.
115

636 Chapter 14 The Pollution and Purification of Water
PROBLEM 14-10
At one test site for this remediation process, the water contained 270 ppm
TCE and 53 ppm perchloroethene. Calculate the mass of iron required to
remediate 1 L of this groundwater.
The Chemical Contamination and
Treatment of Wastewater and Sewage
Most municipalities treat the raw sewage collected from homes, buildings,
and industries (including food processing plants) through a sanitary sewer
system before the liquid residue is deposited into a nearby source of natural
waters, whether a river, lake, or ocean. In contrast, since the rainwater and
melted snow that drain from streets and other paved surfaces are usually not
highly contaminated, they are often collected separately by storm sewers and
deposited directly into a body of natural water. Unfortunately, in some
municipalities, storm-driven overflow occurs in the sanitary sewer system
and the overflow is combined with storm water and deposited, untreated,
into waterways.
The main component of sewage—other than water—is organic matter of
biological origin. It occurs mainly as particles—ranging from those of macroscopic
size large enough to be trapped (together with such objets d’art as facial
tissues, stones, socks, tree branches, condoms, and tampon applicators) by
mesh screens to those which are microscopic in size and are suspended in the
water as large colloids.
Sewage Treatment
In the primary (or mechanical) treatment stage of wastewater (see the
schematic diagram in Figure 14-8), the larger particles—including sand and
silt—are removed by allowing the water to flow across screens and slowly
along a lagoon or settling basin. A sludge of insoluble particles forms at the
bottom of the lagoon, while “liquid grease” (a term which here includes not
only fat, oils, and waxes but also the products formed by the reaction of soap
with calcium and magnesium ions) forms a lighter-than-water layer at the top
and is skimmed off. About 30% of the biochemical oxygen demand (BOD,
Chapter 13) of the wastewater is removed by the primary treatment process,
even though this stage of the process is entirely mechanical in nature. The
treatment and disposal of the sludge is discussed later.
After passing through conventional primary treatment, the sewage water
has been much clarified but still has a very high BOD—typically several
hundred milligrams per liter (ppm)—and is detrimental to fish life if released
at this stage (as occurs in some jurisdictions that discharge into the ocean).
The high BOD is due mainly to organic colloidal particles. In the secondary
(biological) treatment stage, most of this suspended organic matter as well as
116

Wastewater
Water
Grease
Solid matter
The Chemical Contamination and Treatment of Wastewater and Sewage 637
Primary treatment Secondary treatment Tertiary
Microorganism-
treatment
Grease
catalyzed oxidation
Sludge
Disposal
that actually dissolved in the water is biologically oxidized by microorganisms
to carbon dioxide and water or converted to additional sludge, which can
readily be removed from the water. Either the water is sprinkled onto a bed of
sand and gravel or of plastic covered with the aerobic bacteria (trickling filters),
or it is agitated in an aeration reactor (activated sludge process) in order to
effect the microorganism-driven reaction. The system is kept well-aerated to
speed the oxidation. In essence, by deliberately maintaining in the system a
high concentration of aerobic microorganisms, especially bacteria, the same
biological degradation processes that would require weeks to occur in open
waters are accomplished in several hours.
The biological oxidation processes of secondary treatment reduce the
BOD of the polluted water to less than 100 ppm, which is about 10% of the
original concentration in the untreated sewage. For comparison, Canadian
wastewater quality standards require that the BOD in treated water be 20 ppm
or less. The process of nitrification also occurs to some extent, converting
organic nitrogen compounds to nitrate ion and carbon dioxide (see below). In
summary, the secondary treatment of wastewater involves biochemical reactions
that oxidize much of the oxidizable organic material that was not removed in
the first stage. Treated water diluted with a greater amount of natural water
can support aquatic life. Normally, municipalities take the water produced by
secondary treatment and disinfect it by chlorination or irradiation with UV
light before pumping it into a local waterway. Recent research in Japan has
shown that chlorination of the effluent before its release produces mutagenic
compounds, presumably by interaction of chlorine-containing substances with
the organic matter that remains in the water.
A few municipalities employ tertiary (or advanced or chemical) wastewater
treatment as well as primary and secondary ones. In the tertiary phase,
specific substances are removed from the partially purified water before its
final disinfection. In some cases, the water produced by tertiary treatment is
117
Sludge
Removal
of various
chemicals
River
or lake
FIGURE 14-8 The
common stages in the
treatment of wastewater.

638 Chapter 14 The Pollution and Purification of Water
of sufficiently high quality to use as drinking water. Alternatively, river
water into which the effluent from sewage treatment plants has been
deposited is used by municipalities downstream as drinking water. The reuse
of water after it has been cleansed is particularly prevalent in Europe, where
less fresh water is available than in North America and the population
density is high.
Depending upon locale, tertiary treatment can include some or all of the
following chemical processes:
• further reduction of BOD by removal of most remaining colloidal material,
using an aluminum salt in a process that operates in the same manner as
described previously for the purification of drinking water;
• removal of dissolved organic compounds (including chloroform) and
some heavy metals by their adsorption onto activated carbon, over which the
water is allowed to flow (see Box 14-1);
• phosphate removal (as discussed in the next section; some phosphorus is
removed in the secondary treatment stage since microbes incorporate it as a
nutrient for their growth);
• heavy metal removal by the addition of hydroxide or sulfide ions, S 2 , to
form insoluble metal hydroxides or sulfides, respectively (see Chapter 15);
• iron removal by aeration at a high pH to oxidize it to its insoluble Fe 3
state, possibly in combination with use of a strong oxidizing agent to destroy
organic ligands bound strongly to the Fe 2 ion, which would otherwise prevent
its oxidation; and
• removal of excess inorganic ions, as discussed below.
In some wastewaters, the further removal of nitrogen compounds—usually
either ammonia or organic nitrogen compounds—is deemed necessary. Ammonia
removal can be achieved by raising the pH to about 11 (with lime) to convert
most ammonium ion to its molecular form, ammonia, NH3 , followed by
bubbling air through the water to air-strip it of its dissolved ammonia gas. This
process is relatively expensive, however, because it is energy-intensive. Ammonium
ion can also be removed by ion exchange, using certain resins that have
their exchange sites initially populated by sodium or calcium ions.
Alternatively, both organic nitrogen and ammonia can be removed by
first using nitrifying bacteria to oxidize all the nitrogen to nitrate ion. Then
the nitrate is subjected to denitrification by bacteria to produced molecular
nitrogen, N2, which bubbles out of the water. Since this reduction step
requires a substance to be oxidized, methanol, CH3OH, is added if necessary
to the water and is converted to carbon dioxide in the process:
bacteria
5 CH 3 OH 6 NO 3 6 H 9: 5 CO2 3 N 2 13 H 2 O
118

Of course, water contaminated by nitrate ion can also be treated by this latter
step. A mathematical analysis of the kinetics of the transformations is
given in Box 14-4.
PROBLEM 14-11
The Chemical Contamination and Treatment of Wastewater and Sewage 639
BOX 14-4 Time Dependence of Concentrations
in the Two-Step Oxidation of Ammonia
The bacteria-catalyzed oxidation of ammonia
(or of other reduced organic nitrogen
compounds) to nitrate is a reaction with two
main steps, with nitrite ion, NO2 , an intermediate:
Step 1
3
NH3 2 O2 9:
NO2 H H2O
Step 2
1
NO2 O2 9: NO3 2
If sufficient oxygen is available, the rate of
each reaction is first-order only in the concentration
of the nitrogen reactant, so the
sequence can be represented as
k 1
k 2
A 9: B 9: C
where A stands for ammonia, B for nitrite ion,
and C for nitrate ion, and k 1 and k 2 are the
pseudo-first-order rate constants. Since the rate
of step 1 depends on the first power of the ammonia
concentration, then the rate of disappearance
of this species is
d[A]
dt k 1[A]
Since B (nitrite) is produced at this rate by
step 1, but is consumed in step 2 by a process
whose rate is proportional to the first power of
its concentration, we can write
These differential equations can be coupled
and integrated to yield the following
expressions for the evolution of [A] and [B]
with time, relative to [A] 0, the original concentration
of A:
[A]/[A] 0 e k 1t
[B]/[A] 0 k 1(e k 1t e k 2t )/(k2 k 1)
As can be seen from the solution to Problem 1,
the concentration of B (nitrite) rises exponentially
at first, reaches a peak value, then
declines slowly. Thus significant concentrations
of nitrite ion occur in water undergoing
the two-step conversion of ammonia to
nitrate.
PROBLEM 1
d[B]
dt k 1[A] k 2[B]
(a) Derive a general expression relating the
time at which [B] reaches a peak to k 1 and k 2 .
(b) Draw a graph showing the evolution of
[A] and of [B] with time for the values k 1 1
and k 2 2.
Given that the K b value for ammonia is 1.8 10 5 , deduce a formula giving
the ratio of ammonia to ammonium ion as a function of the pH of water.
What is the value of this ratio at pH values of 5, 7, 9, and 11?
119

640 Chapter 14 The Pollution and Purification of Water
The Origin and Removal of Excess Phosphate
One of the world’s most famous cases of water pollution involves Lake Erie,
which in the 1960s was said to be dying. Indeed, one of the authors of this
book can recall visiting a once-popular beach on Lake Erie’s north shore in the
early 1970s and being repulsed by the sight and smell of dead, rotting fish on
the shoreline. Lake Erie’s problems stemmed primarily from an excess input of
phosphate ion, PO 4 3 , in the waters of its tributaries. The phosphate sources
were the polyphosphates in detergents (as explained in detail later), raw
sewage, and the runoff from farms that used phosphate products. Since there is
commonly an excess of other dissolved nutrients in lakes, phosphate ion usually
functions as the limiting (or controlling) nutrient for algal growth: The
larger the supply of the ion, the more abundant the growth of algae—and its
growth can be quite abundant indeed. When the vast mass of excess algae
eventually dies and starts to decompose by oxidation, the water becomes
depleted of dissolved oxygen, with the result that fish life is adversely affected.
The lake water also becomes foul-tasting, green, and slimy, and masses of dead
fish and aquatic weeds rot on the beaches. The series of changes, including
rapid degradation and aging, that occur when lakes receive excess plant nutrients
from their surroundings is called eutrophication. When the enrichment
arises from human activities, it is called cultural eutrophication.
To correct the regional problem, the United States and Canada in 1972
signed the Great Lakes Water Quality Agreement. Since that time, over $8 billion
has been spent in building sewage treatment plants to remove phosphates
from wastewater before it reaches the tributaries and the lake itself. In addition,
the levels of polyphosphates in laundry detergents were restricted in Ontario
and in many of the states that border the Great Lakes. The total amount of
phosphorus entering Lake Erie has now decreased by more than two-thirds. As
a result, Lake Erie has sprung back to life: Its once-fouled beaches are regaining
popularity with tourists, and its commercial fisheries have been revived.
As we have pointed out, the presence of excess phosphate ion in natural
waters can have a devastating effect on an aquatic ecology because it overfertilizes
plant life. Formerly, one of the largest sources of phosphate as a pollutant
was detergents, and in the material that follows, the role of such
phosphates is discussed.
The reaction of synthetic detergents with calcium and magnesium ions,
forming complex ions, diminishes the cleansing potential of the detergent.
Polyphosphate ions, which are anions containing several phosphate units
linked by shared oxygens, are added to detergents as builders that preferentially
form soluble complexes with these metal ions and thereby allow the
molecules of the detergent to operate as cleansing agents rather than being
complexed with the Ca 2 and Mg 2 naturally present in the water. Another
role of the builder is to make the wash water somewhat alkaline, which helps
remove the dirt from certain fabrics. With soap itself, the ions form insoluble
complexes that foul the cleaning water.
120

(a)
The Chemical Contamination and Treatment of Wastewater and Sewage 641
O
O9P9O9P9O9P9O
O
O
O
O
O
Great quantities of sodium tripolyphosphate (STP), Na5P3O10, were
formerly added as the builder in most synthetic detergent formulations. As
shown in Figure 14-9a, STP contains a chain of alternating phosphorus and
oxygen atoms, with one or two additional oxygens attached to each phosphorus.
In solution, one tripolyphosphate ion can form a complex with one calcium
ion by forming interactions between three of its oxygen atoms and the
metal ion (Figure 14-9b).
Substances like STP, which have more than one site of attachment to the
metal ion and thereby produce ring structures that each incorporate the
metal, are called chelating agents (from the Greek word for “claw”). Because
several bonds are formed, the resulting chelates are very stable and do not
normally release their metal ions back into the free form. The use of chelating
agents to remove metals from the human body is discussed in Chapter 15.
5
Tripolyphosphate ion, P3O10 , like phosphate ion itself, is a weak base
in aqueous solution and thus provides the alkaline environment that is
required for effective cleaning:
5
P3O10 H2O 9: P3O10H 4 OH
Unfortunately, when wash water containing STP is discarded, the excess
tripolyphosphate enters waterways, where it slowly reacts with water and is
transformed into phosphate ion (sometimes called orthophosphate):
5 3
P3O10 2 H2O 9: 3 PO4 4 H
Note that when tripolyphosphate decomposes, STP behaves as an acid rather
than a base (since H is formed in the reaction).
Because of environmental concerns, polyphosphates are now used only
sparingly as builders in detergents in many areas of the world. In Canada and
parts of Europe, STP was replaced largely by sodium nitrilotriacetate (NTA)
(see Figure 14-10a). The anion of NTA acts in a similar fashion to that of
STP, chelating calcium and magnesium ions using three of its oxygen atoms
and the nitrogen atom (Figure 14-10b). NTA is not used as a builder in the
United States because of concerns that its slow rate of degradation might lead
to health hazards in drinking water. However, the early experiments with test
animals that led to this concern are open to question, as are fears about its
persistence and its tendency to solubilize heavy metals into water supplies.
Other builders now used include sodium citrate, sodium carbonate (washing
soda), and sodium silicate. Currently, substances called zeolites are also
employed as detergent builders. Zeolites are abundant aluminosilicate minerals
(b)
121
O
O O O
P
Ca2 O P
O9P
O
O
O
O
FIGURE 14-9 Structure
of the polyphosphate ion:
(a) uncomplexed and
(b) complexed with
calcium ion.

642 Chapter 14 The Pollution and Purification of Water
FIGURE 14-10 Structure
of the nitrilotriacetate ion:
(a) uncomplexed and
(b) complexed with
calcium ion.
O
CH 2 9C
(a)
N
(b)
O
C
CH2 O O
CH29C (see Chapter 16) consisting of sodium, aluminum, silicon, and oxygen. The
latter three elements are bonded together to form cages, which the sodium ions
can enter. In the presence of calcium ion, zeolites exchange their sodium ions
for Ca 2 (though not for Mg 2 ), thereby sequestering it in a manner similar to
polyphosphates. Like polyphosphates, they also control pH. One disadvantage
to the use of zeolites is that they are insoluble, so their use increases the amount
of sludge that must be removed at wastewater treatment plants.
Phosphate ion can be removed from municipal and industrial wastewater
by the addition of sufficient calcium as the hydroxide Ca(OH) 2 , so
that insoluble calcium phosphates such as Ca 3 (PO 4 ) 2 and Ca 5 (PO 4 ) 3 OH
are formed as precipitates that can then be readily removed. Phosphate
removal could be a standard practice in the treatment of wastewater, but it
is not yet practiced in all cities. Some policymakers believe that the optimum
environmental solution is to use polyphosphates, rather than some
other builder, in detergents and then to efficiently remove phosphates at
wastewater treatment plants.
Geographically, phosphate ion enters waterways from both point and nonpoint
sources. Point sources are specific locations such as factories, landfills,
and sewage treatment plants that discharge pollutants. Nonpoint sources are
numerous large land areas such as farms, logged forests, septic tanks, golf courses
and individual domestic lawns, stormwater runoff, and atmospheric deposition.
Although each nonpoint source may provide a small amount of pollution, on
account of the large number of them involved they can generate larger total
quantities than do point sources. For example, now that sewage treatment
plants and detergent controls have been instituted, much of the remaining
phosphate arises from nonpoint agricultural sources in many areas.
Green Chemistry: Sodium Iminodisuccinate—
A Biodegradable Chelating Agent
Because most chelating agents are not biodegradable or are only slowly
biodegradable, not only do they place a load on the environment (e.g., phosphates
acts as nutrients), but it may be necessary to remove them during
122
O
O
H 2 C
H 2 C
CH 2
O
C
C
C
O
O
O
N Ca 2
O O

The Chemical Contamination and Treatment of Wastewater and Sewage 643
treatment of wastewater in a wastewater
treatment plant. Unlike many chelating
agents, sodium iminodisuccinate (IDS, see
Figure 14-11) [also known as D,L-aspartic-N-
(1,2-dicarboxylethyl) tetrasodium salt] readily
degrades in the environment. Not only is IDS
biodegradable, it is also nontoxic.
IDS can be used as an effective chelating
agent for absorption of agricultural nutrients,
metal ion scavenging in photographic processing, groundwater remediation,
and as a builder in detergents and household and industrial cleaners. The
Bayer Corporation won a Presidential Green Chemistry Challenge Award in
2001 for the development of IDS as a chelating agent and for its synthesis
from maleic anhydride (Figure 14-11). This synthesis is accomplished under
mild conditions, in water as the only solvent. The excess ammonia is recycled
back into the production of more IDS. This synthesis stands in stark contrast
to typical syntheses of aminocarboxylate chelating agents, which employ
hydrogen cyanide as a reagent. Bayer markets IDS as a chelating agent under
the name Baypure.
Reducing the Salt Concentration in Water
The decomposition of organic and biological substances during the secondary
phase of wastewater treatment usually results in the production of inorganic
salts, many of which remain in the water even after the techniques listed
above have been applied. Water can also become salty due to its use in irrigation
or because water softener units have been recharged and their discharge
disposed of as sewage. Inorganic ions can be removed from water by desalination
by using one of the techniques listed below or using the precipitation methods
mentioned above.
• Reverse osmosis As previously mentioned, this technique is also used to
produce drinking water from salty water, such as seawater.
• Electrodialysis Here a series of membranes permeable either only to
small inorganic cations or only to small inorganic anions are set up vertically
in an alternating fashion (see Figure 14-12) within an electrochemical cell.
Direct current is applied across the water, so cations migrate toward the cathode
and anions toward the anode. The liquid in alternating zones becomes
more concentrated (enriched) or less concentrated (purified) in ions; eventually
the ion-concentrated water can be disposed of as brine and the purified
water released into the environment. This technology is also used to desalinate
seawater for drinking purposes.
• Ion exchange Some polymeric solids contain sites that hold ions relatively
weakly, so one type of ion can be exchanged for another of the same charge that
123
O
O
O
maleic anhydride
NH 3
NaOH
NaO
NaO
O
NH
O
O O
sodium iminodisuccinate
ONa
ONa
FIGURE 14-11 Synthesis
and structure of sodium
iminodisuccinate, a
biodegradable chelating
agent.

644 Chapter 14 The Pollution and Purification of Water
Outgoing
brine
–
–
–
–
–
–
–
+
+
+
–
+
+
+
–
–
–
+
–
–
–
+
+
+
+
+
+
+
Cathode Anode
Incoming
salty water
+ Cations
– Anions
FIGURE 14-12 Electrodialysis
unit (schematic) for
the desalination of water.
[Adapted from S. E. Manahan.
1994. Environmental Chemistry,
6th ed. Boca Raton, FL:
Lewis Publishers.]
Outgoing
purified
water
Cationpermeable
membrane
Anionpermeable
membrane
Outgoing
brine
PROBLEM 14-12
happens to pass by it. Ion exchange resins
can be formulated to possess either cationic
or anionic sites that function in this manner.
The exchange sites of a cationic resin of this
type are initially occupied by H ions, and
the exchange sites of an anionic exchange
resin are occupied by OH ions. When water
polluted by M and X ions is passed sequentially
through the two resins, the H ions on
the first are replaced by M , and then the
OH ions on the second resin are replaced by
X . Thus the water that has passed through
contains H and OH ions, rather than
those of the salt, which remain behind in
the resins. Of course, these two ions immediately
combine to form more water molecules.
Thus ion exchange can be used to
remove salts, including those of heavy
metals, from wastewater.
Water polluted by inorganic ions could be purified by distilling it or by freezing
it. Why do you think such techniques are not generally used on a mass
scale to purify water?
Transition metal cations can be removed from water using either precipitation
or reduction techniques, in either case to form insoluble solids. Precipitation
of sulfides or hydroxides has already been mentioned; a disadvantage
of the latter is the production of a voluminous sludge that must be disposed of
in an acceptable manner. Electrolytic reduction of metals leads to their deposition
on the cathode. If, instead of the elemental metal, a concentrated
aqueous solution of it is desired, the deposited metal can be reoxidized chemically
by adding hydrogen peroxide or electrolytically by reversing the polarity
of the cell.
The Biological Treatment of Wastewater and Sewage
An alternative to the processing of wastewater through a conventional treatment
plant in small communities is biological treatment in an artificial marsh
(also called a constructed wetland) that contains plants such as bullrushes and
reeds. The decontamination of the water is accomplished by the bacteria and
other microbes that live among the plants’ roots and rhizomes. The plants
124

The Chemical Contamination and Treatment of Wastewater and Sewage 645
themselves take up metals through their root systems and concentrate
contaminants within their cells. In facilities that have been constructed to
deal with sewage, primary treatment to filter out solids, etc. in a lagoon is
usually implemented before the wastewater is pumped to the marsh, where
the equivalent of secondary and tertiary treatment occurs. The plant growth
uses up the pollutants and increases the pH—which serves to destroy some
harmful microorganisms.
One advantage of biological treatment is that great amounts of sludge are
not generated, in contrast to conventional treatments. Furthermore, it requires
neither the addition of synthetic chemicals nor the input of commercial
energy. Among the problems in such facilities are decaying vegetation, which
must be limited so that the BOD of the processed water does not rise too
much, and the fact that the marshes usually require a great deal of land unless
they are constructed so that part of the routing is vertical.
In many rural and small communities, septic tanks are used to decontaminate
sewage since central sewage facilities are not available. These underground
concrete tanks receive the wastewater, often from only one home.
Although solids settle in the tank, grease and oil rise to the top, from which
they are periodically removed. The bacteria in the wastewater feed on the
bottom sludge, thereby liquefying the waste. Partially purified water flows out
of the tank into an underground drain, where further decontamination takes
place. The system is relatively passive, compared to central facilities, and as
in the case of artificial marshes, time is required for the processes to occur. In
addition, nitrogen compounds are converted to nitrate, but the latter is not
reduced to molecular nitrogen, so groundwater under the septic system can
become contaminated by nitrate, as discussed earlier in this chapter.
Drugs in Wastewater from Sewage Treatment Plants
In recent years, trace concentrations of various drugs—prescription, overthe-counter,
illegal, and veterinary—have been detected in the waters leading
from sewage treatment plants, and in rivers and streams into which this
water then flows, at concentrations up to the ppb level. About 100 substances
have been detected in various rivers, lakes, and coastal waters. The
substances—commonly including estradiol, ibuprofen, the antidepressant drug
Prozac (fluoxetine), the anti-epileptic drug carbamazepine, and degradation
products associated with cholesterol-reducing pharmaceuticals—are present
in raw sewage after their excretion in urine or feces from humans and animals
since most drugs are poorly absorbed and metabolized by the body. They also
result from the disposal of unused or expired medication in toilets.
Most commonly, concentrations of drugs in drinking water are at the
parts-per-trillion level, so their risk to human health is probably small.
Research is under way to determine whether there could be effects on human
health from sustained exposure to a combination of these substances. The
125

646 Chapter 14 The Pollution and Purification of Water
synthetic hormones are thought to pose the greatest risk to aquatic species.
Certain fish have been found to undergo some skewed sexual development
due to exposure to sewage effluent containing the synthetic estrogen in birth
control pills (see Chapter 12).
The Treatment of Cyanides in Wastewater
The cyanide ion, CN , binds strongly to many metals, especially those of
the transition series, and is often used to extract them from mixtures. Consequently,
cyanide is widely used in mining, refining, and electroplating metals
such as gold, cadmium, and nickel. Unfortunately, cyanide ion is very poisonous
to animal life since it binds strongly to metal ions in living matter,
e.g., to the iron in proteins that are necessary for molecular oxygen to be utilized
by cells.
Cyanide is a very stable species and does not quickly decompose on its
own or in the environment. Thus it is an important water pollutant and
should be destroyed chemically rather than simply disposed of in a waterway.
We can deduce the type of treatment that will be effective for cyanide by
considering its acid–base and redox characteristics. Cyanide ion is the conjugate
base of the weak acid hydrocyanic acid, HCN, which has limited solubility
in water. Thus, acidification of cyanide solutions will result in the release of
poisonous HCN gas from it and therefore is not a good solution to the problem
of cyanide contamination.
The redox chemistry of cyanide ion can be predicted by considering the
oxidation numbers of the two atoms involved. If nitrogen, the more electronegative
atom, is considered to be in its fully reduced 3 oxidation form,
then the carbon must be 2. Thus one way to destroy cyanide ion is to oxi-
dize the carbon more fully, to 4 as it is in CO2 and HCO3 . This oxidation
can be accomplished by dissolved molecular oxygen if high temperatures and
elevated air pressures are used:
2 0
4 2
2 CN O 2 4 H 2 O 2 HCO 3 2 NH3
3
The use of stronger oxidizing agents, such as Cl 2 or ClO , not only oxidizes
the carbon from 2 to 4, but can also oxidize the nitrogen from the 3
state to the zero oxidation number of molecular nitrogen:
2 3 0 4
0
1
2 CN 5 Cl 2 8 OH 2 CO 2 N 2 10 Cl 4 H 2 O
(Four of the ten electrons gained collectively by the chlorines are used by the
carbons and six by the nitrogens in this overall process.) Other oxidizing
agents that are used in cyanide treatment include hydrogen peroxide, H 2 O 2 ,
and/or molecular oxygen, in both cases with a copper salt added as a catalyst.
126

The process can also be carried out electrochemically for high cyanide concentrations;
the remaining low concentration can be subsequently oxidized
by ClO .
Sodium cyanide is now used in some shallow tropical waters such as those
in Indonesia to stun reef fish so that they can be captured and sold live as
seafood or pets. Unfortunately, the cyanide kills smaller fish and destroys the
coral.
PROBLEM 14-13
If an oxidizing agent even more powerful than chlorine or hypochlorite were
to be used in the treatment of cyanide, what other possibilities for the nitrogencontaining
product would there be?
PROBLEM 14-14
The Chemical Contamination and Treatment of Wastewater and Sewage 647
For HCN in water, K a 6.0 10 10 . Calculate the fraction of cyanide that
exists as the anion rather than in the molecular form at pH values of 4, 7,
and 10.
The Disposal of Sewage Sludge
The sludge from both the primary and secondary treatment stages of sewage
is principally water and organic matter. It can be digested anaerobically, in
a process that takes several weeks to complete. Bacteria levels in the sludge
are not thereby completely eliminated, but the levels are reduced about a
thousandfold. The sludge that remains after this further organic decomposition
has occurred and after the supernatant water is removed is sometimes
then incinerated or simply dumped into a landfill or into a water body such
as the ocean. However, sludge is high in plant nutrients, so about half the
sewage sludge in North America and Europe is spread on farm fields, golf
courses, and even residential lawns as low-grade fertilizer sometimes called
biosolid.
Unfortunately, sewage sludge may contain toxic substances, which potentially
could be incorporated into food grown on the land or could contaminate
groundwater under the fields. In particular, heavy metal concentrations often
are higher in sewage sludge than in soil, principally because industrial wastes
are sometimes released directly into sewage lines shared by households. For
example, the lead level in municipal sludge can range from several hundred
to several thousand parts per million, compared to an average of about 10 ppm
in the Earth’s crust. In a few communities, an attempt is made to eliminate
these toxic materials before final disposal occurs. Some scientists have worried
that food crops grown in soil fertilized by sewage sludge may incorporate
127

648 Chapter 14 The Pollution and Purification of Water
some of the increased amounts of heavy metals. Control experiments indicate
that vegetables vary greatly in the extent to which they will absorb increased
amounts of the metals; e.g., the uptake of lead by lettuce is particularly large,
but that by cucumbers is negligible. The concentration of arsenic in agricultural
soils is greatly increased if arsenic pesticides are applied to them; crops
planted on these soils subsequently absorb some of the adsorbed arsenic.
Other substances of concern in using sewage sludge as fertilizer for food are
alkylphenols from detergents, brominated fire retardants, and pharmaceuticals—
especially antibiotics given to farm animals.
Modern Wastewater and
Air Purification Techniques
The most important chemical (as opposed to biological) pollutants dissolved
in wastewater are usually chloroorganics, phenols, cyanides, and heavy metals.
Below we describe some of the high-tech methods that have recently been
developed and put into practice to purify wastewater, particularly for removal
of chloroorganics. Some of these same techniques are also used to cleanse the
compounds from contaminated air.
The Destruction of Volatile Organic Compounds
The major stationary sources in North America of VOCs (Chapter 3) are the
evaporation of organic solvents, the manufacture of chemicals, and the petroleum
industry and its storage activities. Wastewater effluent that is contaminated
with VOCs, e.g., the water emanating from chemical or petrochemical
plants, is commonly treated by a two-step process:
1. The VOCs are removed from the wastewater by air stripping. In this
process, air is passed upward into a downward stream of the water, and
the volatile materials are transferred from the liquid to the gas phase. This
technique does not work well for compounds that are highly water soluble.
2. The resulting VOCs, now present in low concentration in a contained
mass of humid air, are destroyed by a process of catalytic oxidation. For
example, air heated to 300–500°C is passed for a short time over platinum
or, depending upon the VOC, some other precious metal that is supported
on alumina. The energy costs of this step are very high since it involves
heating a large volume of humid air. Note that the outlet air from such
processes contains hydrogen chloride, HCl, if the VOCs originally contained
chlorine; this compound must be removed by scrubbing with a basic substance
before the air is released into the atmosphere.
The removal of VOCs from gaseous emissions from industries usually
operates by the same catalytic oxidation process; typically the concentration
128

Modern Wastewater and Air Purification Techniques 649
of VOCs in the air stream is thereby reduced by 95%. A primary heat
exchanger recovers and reuses the VOCs’ heat of combustion to warm
incoming gases to the operating temperature.
The adsorption of compounds onto activated carbon (see Box 14-1) or
onto synthetic carbonaceous adsorbents is a cost-effective technology used
for the removal of low-level VOC concentrations from both liquid and vapor
streams; it is also useful for nonvolatile organic compounds. These adsorbents
can be easily regenerated by treatment with steam or by other thermal techniques
as well as by solvents; the concentrated pollutants can be subsequently
destroyed by catalytic oxidation.
Advanced Oxidation Methods for Water Purification
Conventional water purification methods often do not successfully deal with
synthetic organic compounds such as chloroorganics that are dissolved at low
concentrations; examples include the common groundwater pollutants
trichloroethene and perchloroethene. The conventional method for the
treatment of water containing such pollutants is adsorption of the chloroorganics
onto activated carbon; this removes the compounds but doesn’t
destroy them. The wastewater from pulp-and-paper mills also contains
organochlorines that are resistant to conventional treatments.
In order to cleanse water of these extra-stable organics, so-called
advanced oxidation methods (AOMs) have been developed and deployed.
The aim of these methods is to mineralize the pollutants, i.e., to convert
them entirely to CO2 , H2O, and mineral acids such as HCl. Most AOMs are
ambient-temperature processes that use energy to produce highly reactive
intermediates of high oxidizing or reducing potential, which then attack and
destroy the target compounds. The majority of the AOMs involve the
generation of significant amounts of the hydroxyl free radical, OH, which
in aqueous solution is a very effective oxidizing agent, as it is in air (see
Chapters 1–5). The hydroxyl radical can initiate the oxidation of a molecule
by extraction of a hydrogen atom or addition to one atom of a multiple bond,
as it does in air (Chapter 5); in water, as an additional alternative, it can also
extract an electron from an anion.
Since the generation of OH in solution is a relatively expensive process,
it is economical to use AOMs to treat only the components of the wastes that
are resistant to the cheaper, conventional treatment processes. Thus, integrating
an AOM with pretreatment of the wastewater by biological or other
processes to first dispose of the easily oxidized materials is often appropriate.
Ultraviolet (UV) light is often used to initiate the production of hydroxyl
radicals and thus to begin the oxidations. Commonly, hydrogen peroxide,
H2O2, is added to the polluted water and UV light from a strong source in the
200–300-nm range is shone on the solution. The hydrogen peroxide absorbs
the ultraviolet light (especially that closer to 200 nm than to 300 nm) and
129

650 Chapter 14 The Pollution and Purification of Water
uses the energy obtained to split the O9O bond, resulting in the formation
of two OH radicals:
UV
H 2O 2 9: 2 OH
Alternatively, and less commonly, ozone is produced and then photochemically
decomposed by UV light. The resulting oxygen atom reacts with water
to efficiently produce OH via the intermediate production of hydrogen peroxide,
which is photolyzed:
UV
O 3 9: O 2 * O *
UV
O * H 2 O 9: H 2 O 2 9: 2 OH
A fraction of the oxygen atoms produced by ozone photolysis are electronically
excited, and these react with water to directly produce hydroxyl radicals,
as discussed in Chapter 1.
PROBLEM 14-15
Given that the enthalpies of formation for H 2 O 2 and OH are, respectively,
136.3 and 39.0 kJ mol 1 , calculate the heat energy required to dissociate
one mole of hydrogen peroxide into hydroxyl free radicals. What is the maximum
wavelength of light that could bring about this transformation? [Hint:
See Chapter 1]. Given that light of 254-nm wavelength is usually used, and
that all the energy of each photon that is in excess of that required to dissociate
one molecule is lost as waste heat, calculate the maximum percentage of
the input light energy that can be used for dissociation itself.
Hydroxyl radicals for wastewater treatment can also be efficiently produced
without the use of UV light by combining hydrogen peroxide with
ozone. The chemistry of the intermediate processes is complex, but the overall
reaction between these two species is
H2O2 2 O3 9: 2 OH 3 O2 This ozone/H2O2 method is more cost-effective and easier to adapt to existing
water treatment systems than is any other AOM system.
It is also possible to generate the hydroxyl radical electrolytically. In most
such applications, a metal ion (such as Ag or Ce 3 ) is first oxidized to a
more positively charged ion (Ag 2 or Ce 4 in our examples) that will subsequently
oxidize water to H and OH.
The biggest liability associated with advanced oxidation processes is that
their action produces toxic chemical by-products. For example, in the ozone/
peroxide and peroxide/UV treatments of groundwater contaminated with
130

trichloroethene and perchloroethene, the toxic intermediates trichloroacetic
acid, CCl 3 COOH, and dichloroacetic acid, CHCl 2 COOH, are formed in about
1% yield.
Photocatalytic Processes
Modern Wastewater and Air Purification Techniques 651
Another innovative technology for wastewater treatment involves the irradiation
by UV light of solid semiconductor photocatalysts such as titanium
dioxide, TiO 2, small particles of which are suspended in solution. Titanium
dioxide is chosen as the semiconductor for such applications since it is nontoxic,
is very resistant to photocorrosion, is cheap and plentiful, absorbs light
efficiently in the UV-A region, and can be used at room temperature. Irradiation
at wavelengths less than 385 nm produces electrons, e , in the conduction
band and holes, h , in the valence band of the metal oxide. The holes in the
semiconductor can react with surface-bound hydroxide ions or with water
molecules, thereby producing hydroxyl radicals in both cases:
h OH 9: OH
h H 2O 9: OH H
The holes can also react directly with adsorbed pollutants, producing radical
cations that readily engage in subsequent degradation reactions.
Normally, O 2 molecules dissolved in the water react with the electron
produced at the semiconductor surface, a process that eventually produces
more reactive free radicals but is relatively slow. If hydrogen peroxide is added
to the water instead, it will react with the electron to form the anion radical
and generate reactive radicals more quickly.
The cost of the electrical energy required to generate the needed UV
light is usually the major expense in operation of AOM systems. On this
basis, the titanium dioxide methods are even less cost-effective than those
described previously, since considerably more electricity is required per pollutant
molecule destroyed. Sunlight could be used to supply the UV light, but
only about 3% of its light lies in the appropriate UV-A range and is absorbed
by the solid. Another problem with the TiO 2 processes is the difficulty in separating
the various reactants and products from the TiO 2 particle if the metal
oxide has been used in the form of a fine powder. However, there are now
closed systems in which the titanium dioxide slurry is efficiently separated
from the purified water and recycled back to the inlet stream.
Some scientists have experimented with immobilizing TiO 2 as a thin film
(1 mm thick) on a solid surface such as glass, tile, or alumina. Indeed,
TiO 2 -coated tiles are now used on walls and floors in some buildings. The
low-level UV light from fluorescent lighting in such rooms is sufficient to
allow the destruction of gaseous and liquid-phase pollutants that touch the
oxide on the tiles! For example, odors that upset people are usually present in
131

652 Chapter 14 The Pollution and Purification of Water
Review Questions
air at concentrations of only about 10 ppm; at such levels, the UV from
normal fluorescent lighting should be sufficient to destroy them with TiO 2
photocatalysts. Bacterial infections such as those that cause many secondary
infections in hospitals can also be eliminated by spraying walls and floors (in
rooms lit by fluorescent bulbs) to give them a titanium dioxide film. Photocatalysts
are quiet, unobtrusive cleansing materials.
Other Advanced Oxidation Methods
A process called direct chemical oxidation has been proposed for the destruction
of solid and liquid organic wastes in the aqueous phase, particularly in
environments such as those under buildings, where the light required for
UV processes cannot conveniently be supplied. It uses one or another of
the strongest known chemical oxidants—e.g., acidified peroxydisulfate
2
anion, S2O8 , under ambient pressure and moderate temperatures to oxidize
the wastes. Such a process needs no catalysts and produces no secondary
wastes of concern. The sulfate that results from the peroxydisulfate can be
recycled back to the oxidant. Other very strong oxidizing agents that have
been tested are the peroxymonosulfate anion, HSO5 , and the ferrate ion,
2
FeO4 ; in the latter, iron has an oxidation number of 6, so it is not surprising
that it is a strong oxidizing agent. Unfortunately, ferrate ion suffers from
the problem of instability.
PROBLEM 14-16
1. Describe the function of (a) aeration and
(b) addition of aluminum or iron sulfate in the
purification of drinking water.
2. Describe the chemistry underlying the removal
of excess calcium and magnesium ions from drinking
water.
3. Describe how water can be disinfected by
(a) membrane filtration and (b) ultraviolet
irradiation.
Deduce the balanced half-reaction (acidic media) in which the peroxydisulfate
ion is converted into sulfate ion. Repeat the exercise for the conversion of
oxalic acid, C 2 H 2 O 4 , into carbon dioxide. Combine these half-reactions into
a balanced equation, and calculate the volume of 0.010 M peroxydisufate that
is required to oxidize one kilogram of oxalic acid.
4. What two other chemical methods, other than
chlorination, are used to disinfect water? What are
some advantages and disadvantages to these
alternatives?
5. Explain the chemistry underlying the disinfection
of water by chlorination. What is the
active agent in the destruction of the pathogens?
What are the practical sources of the active
ingredient?
132

6. Explain why pH control of water in swimming
pools is important. What compounds are formed
when the chlorinated water reacts with ammonia?
7. Discuss the advantages and disadvantages of
using chlorination to disinfect water, including the
nature of the THM compounds.
8. What is meant by the terms groundwater and
aquifer? How does the saturated zone of soil differ
from the unsaturated?
9. Why did concern about groundwater pollution
lag far behind that about surface water?
10. Name three important sources of nitrate ion
to groundwater.
11. Construct a table that shows the common
oxidation numbers for nitrogen. Deduce in which
column the following environmentally important
compounds belong: HNO2 , NO, NH3 , N2O, N2 ,
HNO3, NO3 . Which of the species become
prevalent in aerobic conditions in a lake? Under
anaerobic conditions? What is the oxidation
number of nitrogen in NH2OH? 12. Explain why excess nitrate in drinking water
or food products can be a health hazard; include
the relevant balanced chemical reaction showing
how nitrate becomes reduced.
13. What is an N-nitrosamine? Write the structure
and the full name for NDMA.
14. What is the formula for the perchlorate ion?
What is the origin of perchlorate ion in U.S.
drinking water?
15. Define leachate.
16. Name two types of organic contaminants
found in groundwater, and give two examples of
each type.
17. Explain the difference in vertical location in
an aquifer between compounds such as chloroform
and those such as toluene.
133
Review Questions 653
18. Define the term plume and describe how it
forms in an aquifer.
19. Why are the BTX and MTBE components
of gasoline the ones that are most often found
in groundwater? Are both components easily
biodegraded?
20. What is meant by reductive degradation?
Describe the in situ technique by which chloroorganics
in aquifers can be destroyed by reductive
dechlorination.
21. What procedures are involved in primary
wastewater treatment? In secondary treatment?
22. List five possible water purification processes
that are associated with the tertiary treatment
of wastewater, including one that removes
phosphate ion.
23. What polyphosphate was commonly used in
detergents, and why did its use lead to environmental
problems? What are the other main sources
of phosphate to natural waters? What other
builders are used in detergents?
24. Describe two important methods that are used
to desalinate wastewater.
25. Describe the chemical processes by which
cyanide ion can be removed from wastewater.
26. Describe how VOCs dissolved in wastewater
are usually removed and destroyed.
27. Describe what AOMs stands for, and state the
most common reactive agent in such processes.
Describe three methods by which this reactive
species can be generated.
28. Describe two photocatalytic methods that can
destroy organic wastes.
29. What is direct chemical oxidation? What are
two of the strong oxidizing agents that can be used
for such procedures?

654 Chapter 14 The Pollution and Purification of Water
Green Chemistry Questions
See the discussion of focus areas and the principles
of green chemistry in the Introduction before
attempting these questions.
1. What are the environmental advantages of using
iminodisuccinate compared to most chelating agents?
2. The development of iminodisuccinate by
Bayer won a Presidential Green Chemistry
Challenge Award.
Additional Problems
1. Given that for HOCl, K a 2.7 10 8 , deduce
the fraction of a sample of the acid in water that
exists in the molecular form at pH values (predetermined
by the presence of other species) of 7.0, 7.5,
8.0, and 8.5. [Hint: Derive an expression that relates
the fraction of HOCl that is ionized to the concentration
of hydrogen ions.] Would it be a good idea to allow
the pool water’s pH to rise to 8.5?
2. The equilibrium constant for the reaction of
dissolved molecular chlorine with water to give
hydrogen ions, chloride ions, and HOCl is 4.5
10 4 , where as usual the concentration of water is
included in the K value. If the pH of the solution is
determined by other processes so that the amount
of hydrogen ion contributed by the chlorine reaction
is negligible, calculate the fraction of the original
50 ppm chlorine which remains as Cl 2 at pH
values of 0, 1, and 2. [Notes: (1) The dissociation of
HOCl into ions is negligible at these low pH values.
(2) Approximate solutions to the quadratic
equation involved in these calculations will not be
accurate due to the high percentage of reaction.]
3. Calculate the volume of Ca 5(PO 4) 3OH, the
density of which is 3.1 g/mL, which is produced for
each gram of sodium tripolyphosphate present in a
detergent when it is removed in tertiary wastewater
treatment. Estimate the annual mass of detergent
used for laundry purposes for a typical household of
four persons. Assuming that the phosphate levels in
(a) Into which of the three focus areas for these
awards does this award best fit?
(b) List at least three of the twelve principles of
green chemistry that are addressed by the green
chemistry developed by Bayer.
laundry detergents used were about 50%, calculate
the volume that was required annually to dispose
of its waste laundry phosphate.
4. Calculate the oxidation number of the
chlorine in molecular chlorine, HOCl, chlorine
dioxide, monochloramine (NH 2Cl), and
sodium chloride. Given that the last item is
the most stable form of chlorine, predict whether
the other substances mentioned are likely to be
oxidizing agents or reducing agents, and rank
them in likely order of this redox behavior. Using
this analysis and the section on chlorine compounds
in your introductory chemistry textbook,
suggest other compounds that might be useful to
disinfect water.
5. Given their names, can you deduce the nature
of the similarity in molecular structure between
hydrogen peroxide and the sulfur compounds that
are used in direct chemical oxidation methods?
By calculating the oxidation number of the atoms
in hydrogen peroxide, deduce why it can act as an
oxidizing agent.
6. What could be done to dispose of the solvents
that are used to extract VOCs from adsorbents?
7. Write the initial reaction step that occurs if
methyl chloroform, CH 3CCl 3, were to be
destroyed by (a) reductive degradation and (b)
hydroxyl radical attack.
134

8. Water samples from three wastewater streams
were analyzed, and the important pollutants
determined to be those listed below. In each case,
devise economical, practical processes (other than
activated carbon treatment) for purifying the water
of the three pollutants:
(a) Phosphate ion, ammonium ion, and salt
(in water containing bicarbonate ion)
(b) Nitrite ion, PCE, and Fe(II)
(c) Cadmium ion, carbon tetrachloride, and glucose
9. Write the reaction that occurs between hydroxyl
radical and carbonate ion dissolved in water. What
are two alternative substances that you could add to
the water to decrease the carbonate ion concentration,
one that operates by elimination of carbon dioxide
and the other by precipitation of the ion, so as to
decrease the amount of hydroxyl radical destroyed by
this reaction? Given the solubility product constants
in this chapter, estimate the lowest practical carbonate
concentration you could reach by this process,
and comment on the desirability of the ions that you
have introduced into the water.
10. Treated drinking water should contain
0.5 mg/L of Cl 2 after most of the chlorine has
been converted to HOCl. What pressure of Cl 2(g)
is required to maintain this concentration?
K H 8.0 10 3 M for Cl 2.
Additional Problems 655
11. At a particular temperature, K a for HOCl is
3.5 10 8 . What would be the pH values for
1.00 M and 0.100 M concentrations of HOCl at
this temperature? What percentages of the HOCl is
undissociated at these two concentrations?
12. To desalinate seawater by reverse osmosis,
pressure in excess of a solution’s osmotic pressure,
p, must be applied across the membrane. The total
osmotic pressure exerted in a solution is determined
by the total molar concentration, M, of its solutes,
and is given by the equation p MRT. Using the
composition of seawater listed in Chapter 13, determine
the minimum pressure that must be exerted
on seawater to desalinate it using reverse osmosis at
20°C. Recall that R 0.082 L atm mol 1 K 1 .
13. Chlorine-containing substances covering a wide
variety of oxidation numbers have been encountered,
some within this chapter and others previously
in the book. For each substance in the list
below, write out its formula, deduce the oxidation
number of its chlorine, and fill in the appropriate
row of the table below, as in the example shown:
chlorite ion perchlorate ion
molecular chlorine hypochlorous acid
chlorine dioxide chlorine monoxide
chloride ion chlorate ion
Oxidation Number Formula of Example Name of Example
1
0
1
2
3
4
5
6
7
ClO3 Chlorine trioxide
135

656 Chapter 14 The Pollution and Purification of Water
Further Readings
1. A. Kolch, “Disinfecting Drinking Water with UV
Light,” Pollution Engineering (October 1999): 34.
2. F. Bove et al., “Drinking Water Contaminants
and Adverse Pregnancy Outcomes: A Review,”
Environmental Health Perspectives 110 (supplement 1)
(2002): 61.
3. J. R. Nuckols et al., “Influence of Tap Water
Quality and Household Use Activities on Indoor
Air and Internal Dose Levels of Trihalomethanes,”
Environmental Health Perspectives 113 (2005): 863.
See also ibid, 114 (2006): 514.
4. U. van Gunten, “Ozonation of Drinking Water,”
Parts I and II, Water Research 37 (2003): 1443, 1469.
5. S. D. Richardson et al., “Identification of New
Ozone Disinfection Byproducts in Drinking
Water,” Environmental Science and Technology 33
(1999): 3368.
6. R. F. Service, “Desalination Freshens Up,”
Science 313 (2006): 1088.
7. “Chlorinated Solvent Source Zones,” Environmental
Science and Technology (June 1, 2003): 225A.
8. P. B. Hatzinger, “Perchlorate Biodegradation for
Water Treatment,” Environmental Science and Technology
(June 1, 2005): 239A.
9. L. Fewtrell, “Drinking-Water Nitrate, Methemoglobinemia,
and Global Burden of Disease: A
Discussion,” Environmental Health Perspectives 112
(2004): 1371.
10. M. P. Zeegers et al., “Nitrate Intake Does Not
Influence Bladder Cancer Risk: The Netherlands
Cohort Study,” Environmental Health Perspectives
114 (2006): 1527.
11. M. A. Montgomery and M. Elimelech,
“Water and Sanitation in Developing
Websites of Interest
Log on to www.whfreeman.com/envchem4/ and click on Chapter 14.
Countries,” Environmental Science and Technology
41 (2007): 17.
12. B. T. Nolan et al., “Risk of Nitrate in Groundwaters
of the United States—A National Perspective,
Environmental Science and Technology 31
(1997): 2229.
13. J. A. MacDonald, “Evaluating Natural Attenuation
for Groundwater Cleanup,” Environmental
Science and Technology (August 1, 2000): 346A.
14. L. W. Canter, R. C. Knox, and D. M.
Fairchild, Groundwater Quality Protection (Boca
Raton, FL: Lewis Publishers, 1987).
15. E. K. Nyer, Groundwater Treatment Technology,
2nd ed. (New York: Van Nostrand Reinhold, 1992).
16. D. M. Mackay and J. A. Cherry, “Groundwater
Contamination: Pump-and-Treat Remediation,”
Environmental Science and Technology 23
(1989): 630.
17. R. J. Gilliom, “Pesticides in U.S. Streams
and Groundwater,” Environmental Science and
Technology 41 (2007): 3409.
18. “Environmental Processes ’96: A Special
Report,” Hydrocarbon Processing Magazine (International
Edition) 75 (1996): 85 [reviews many emerging
technologies that can handle water and air
pollution problems].
19. D. Simonsson, “Electrochemistry for a cleaner
environment,” Chemical Society Reviews 26 (1997):
181.
20. N. C. Baird, “Free Radical Reactions in Aqueous
Solutions: Examples from Advanced Oxidation
Processes for Wastewater and from the
Chemistry in Airborne Water Droplets,” Journal of
Chemical Education 74 (1997): 817.
136

Environmental
Instrumental
Analysis V
Ion Chromatography of Environmentally Significant Anions 657
The quantitative determination of levels of environmentally
important ions, such as those discussed in
the preceding chapters, can be accomplished using
chromatographic methods described in this box.
The need to determine the prevalence of
3
common anions like phosphate (PO4 ),
nitrate (NO3 ), or fluoride (F ) isn’t immediately
clear. The biospheric significance of
these ubiquitous ions is not as obvious as is, for
example, the presence of PCBs, pesticides, or
toxic metals like lead, mercury, or cadmium.
These ionic components are important
because they give an indication of the relative
reduction–oxidation potential in an aqueous
sample taken from an environment such as a
3
stagnant lake (PO4 ), or of the contamination
of groundwater from fertilizer runoff
(NO 3
), or of whether municipal water sup-
plies need to be supplemented with fluoride
(F ) for the health of children’s teeth.
Although these charged ions can be detected
by widely available ultraviolet detectors
common in most high-performance liquid
chromatographic systems (Janos and Aczel,
1996), a more sensitive means of detection
involves ionic conductivity. This chromatographic
method is called ion chromatography
with ionic conductivity detection. Although
cations can also be separated by ion chromatography
(IC), only anionic separations
will be discussed here.
The heart of the separation process in
an ion chromatograph is a short column
(10–15 cm) packed with small-diameter particles
called ion exchange resins. These are often
made of a styrene/divinylbenzene polymer or
Ion Chromatography of Environmentally
Significant Anions
137
microparticles of silica coated with compounds
containing an anionic functional group such
as a quaternary amine, ¬N(CH3) 3 OH ,ora
primary amine, ¬NH3 OH , when they are
to be used for anion separation.
The actual process of chromatographic
separation occurs after a sample containing
analyte anions (and their associated cations)
is injected onto the chromatographic column.
With gas chromatography (see Environmental
Instrumental Analysis Box II), the mobile
phase is an inert gas that does not chemically
interact with the chromatographic surface.
The mobile phase in ion chromatography, on
the other hand, is a solution of cations and
anions with a carefully controlled pH; often
buffers are used. This complex mixture of
mobile-phase ions—carefully chosen for each
group of analyte ions to be separated—interacts
with the analyte ions and the functional
groups of the column’s chromatographic
surface. That interaction involves competition
of the mobile-phase anions and the analyte
anions for chromatographic sites on the
packing material (the charged functional
groups such as ¬N(CH3) 3 or ¬SO3 ). This
competition yields different overall travel
times for each of the analytes as they pass down
the column; some are retained longer than
others. (The overall down-column movement
is provided by a pumping of the mobile
phase by an external pump.) Different analyte
travel times—as in gas chromatography—
translate into different exit (or retention)
times for each anion in the original mixture.
The result is chromatographic separation of
anions.
(continued on p. 658)

658 Environmental Instrumental Analysis V
Environmental
Instrumental
Analysis V
The process for anionic ion chromatographic
retention by ion exchange resins can
be represented by the equation
RN(CH3) 3 HCO3 (s) anion (aq) 9:
RN(CH3) 3 anion (s) HCO3
Ion Chromatography of Environmentally
Significant Anions (continued)
(aq)
In this equation, the term anion represents
any of the analyte anions mentioned above.
When a sample is injected onto the column,
this anion is quickly retained by complexation
with the stationary phase near the head of the
column. The next step in the chromatographic
process takes place as a mobile phase, with a
carefully controlled amount of anionic ion
such as bicarbonate, HCO3 , is pumped
through the column. The presence of the bicarbonate
anion in the mobile phase forces the
equilibrium in the above equation to the left;
the retained analyte anion is freed and moves
down the column in the flowing mobile phase.
As the analyte moves along, it repeatedly
undergoes this same process of retention and
movement (or exchange between the stationary
and mobile phases). Most importantly, different
analyte anions (e.g., fluoride or phosphate
or chloride) undergo this exchange process to
differing degrees and therefore travel at different
overall rates during their time in the IC
column. The result is that different analytes
exit the chromatographic column at different
times, i.e., separation has taken place.
The task of detecting analyte anions in
the presence of the anions always present in
the mobile phase is by no means a trivial one.
Since both kinds of anions—the analytes’ and
the mobile phase’s—conduct electricity, using
an ordinary conductivity cell as a detector at
the end of the IC column is normally not
practical. The problem is especially difficult
because, in order to obtain adequate separation
of some important anions, the mobile
phase often has to have high ionic content to
displace the analyte anions from the chromatographic
surface—something that is
obviously required for separation. Therefore,
most of the ionic conductivity passing through
the detector is attributable to the mobilephase
ions and not the analyte—an unworkable
situation when trying to detect the
analyte anions by their conductivity.
An ingenious solution to this problem is
called conductivity suppression or eluent (mobilephase)
suppression. This technology converts
the mobile-phase anions from an easily dissociated
ionic form to a (soluble) molecular form
that does not strongly influence the signal
produced by the conductivity detector. The
suppression module is placed after the chromatographic
column but before the conductivity
detector. In an anion exchange system,
the suppression module might carry out the
following reaction:
Na
(aq) HCO3 (aq) resin H (s) 9:
resin – Na (s) H2CO3 (aq)
Here resin H represents a cation exchange
resin that will exchange cations—instead of
anions as in the chromatographic column
described. This process basically prevents (or
suppresses) the mobile phase’s anions from
contributing to the conductivity by converting
current-conducting bicarbonate anion into
relatively undissociated H 2CO 3. Therefore, the
conductivity detector’s signal is based almost
138

Mobilephase
pump
Ion Chromatography of Environmentally Significant Anions 659
Injector
Sample is
introduced.
Ion exchange
column
Analytes’
retention times
based on
interaction
of analyte,
ion exchange
column, and
mobile-phase
ions.
completely on the passage of analyte anions
through the detector cell. (Those anions are
not affected by the cation ion exchange resin.)
This results in lower (i.e., better) detection
limits for the analytes of interest and a more
stable baseline (less noise and drift) than a
similar system without eluent suppression.
The figure above is a schematic of an ion
chromatographic system. Detailed are an injector,
chromatographic column, eluent suppression
module, and conductivity detector, as well
as the processes that occur at each step.
The figure at right is an example of the
kind of chromatogram that a system of this
type would generate. The anions detected are
fluoride, chloride, phosphate, and nitrate. As
with all chromatograms, detector signal intensity
is plotted versus time.
Researchers have used this method
recently to determine nitrate and nitrite anions
in dew, rain, and snow collected in Massachusetts
(Zuo et al., 2006). Instead of conductivity
detection, these authors used a UV absorption
139
Eluent
suppression
module
Mobile-phase
ions are
converted
to molecular
forms that do
not produce
significant
signals
in detector.
Conductivity
detector
Analyte ions
are detected
against a quiet,
stable background
by
their electrical
conductivity.
detector and chose an analytical wavelength at
which neither the mobile phase nor other
anions would absorb (205 nm). Surprisingly,
dew had the highest concentrations of these
Detector signal
Fluoride
Chloride
Phosphate
Nitrate
0 4 8 12 16 20
Time (minutes)
(continued on p. 660)

660 Environmental Instrumental Analysis V
Environmental
Instrumental
Analysis V
* Detection limit for nitrite 10 ppb.
anions compared to rain and snow collected at
the same site (see table above). The authors proposed
that these dew nitrate concentrations,
ranging from 4.79 to 5.99 g/mL, suggest that
dew is acting as a nighttime sink for these
anionic species; they also note that this may be
important for vegetation because these anions
are held in contact with the leaf surface for long
time periods as dew forms, and the concentration
may spike as dew evaporates in the morning.
Since photolysis of both these anions in
shallow aqueous solution can lead to the formation
of hydroxyl radical and hydrogen peroxide,
this may be a source of oxidative stress
for plants on which the dew forms (Kobayashi
et al., 2002):
NO2 H2O light 9: OH NO OH
NO 3 H2O light 9: OH NO 2 OH
Studies of this process on red pine needles on
trees on Mount Gokurakuji in western Japan
Ion Chromatography of Environmentally
Significant Anions (continued)
Sample Date Nitrite (ppb) Nitrate (ppm)
Dew 1 27.09.2005 640 4.87
2 27.09.2005 620 4.79
3 26.09.2005 830 5.99
Rain 1 02.10.2005 < DL* 2.63
2 02.09.2005 < DL* 2.62
3 28.05.2005 140 1.20
Snow 1 29.01.2005 21 0.320
2 18.01.2005 32 0.376
3 12.01.2005 32 0.60
4 12.01.2005 26 0.56
have concluded that 40% of hydroxyl radial
production in dew on those trees originates
from nitrite and nitrate (Nakatani et al.,
2001).
References: P. Janos and P. Aczel, “Ion Chromatographic
Separation of Selenate and Selenite Using a
Polyanionic Eluent,” Journal of Chromatography A 749
(1996): 115–122.
T. Kobayashi, N. Natanani, T. Hirakawa, M. Suzuki,
T. Miyake, M. Chiwa, T. Yuhara, N. Hashimoto,
K. Inoue, K. Yamamura, N. Agus, J. R. Sinogaya,
K. Nakane, A. Kume, T. Arakaki, and H. Sakugawa,
Environmental Pollution 118 (2002): 383–391.
N. Nakatani, T. Miyake, M. Chiwa, M. Hashimoto,
T. Arakaki, and H. Sakugawa, “Photochemical Formation
of OH Radicals in Dew Formed on the Pine
Needles at Mt. Gokurakuji,” Water, Air and Soil
Pollution 130 (2001) 397–402.
Y. Zuo, C. Wang, and T. Van, “Simultaneous Determination
of Nitrite and Nitrate in Dew, Rain, Snow and
Lake Water Sample by Ion-Pair High-Performance
Liquid Chromatography,” Talanta (2006): 281–285.
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Matthews, P, 1992, Advanced chemistry, Cambridge: Chennaice: Oxford, p. 291 – 303, 518 – 524.
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Hill, JW, Petrucci, RH, McCreary, TW and Perry, SS, 2005, General chemistry, 4 th ed., Pearson: Upper
Saddle River, NY, p. 996 – 1003.
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