Hexavalent Chromium in Drinking Water

Hexavalent Chromium in 

Drinking Water 

myths and mysteries resolved 

USEPA Method 218.7 

Presented by 

Jay Gandhi, PhD – Metrohm USA 

Johnson Mathew – USEPA Region 6 (Houston) 

E. Prince – U of H – Clearlake (Houston) 

WEAT 2012 - Austin TX (Dr. Jay Gandhi) 1


Disclaimer – working with USEPA 

*Reference herein to any specific commercial products or nonprofit 

organization, process, or service by trade name, trademark, 

manufacturer, or other-wise, does not necessarily constitute or 

imply its endorsement, recommendation, or favoring by the 

United States Government. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the 

United States Government and shall not be used for advertising 

or product endorsement purposes. 


What we’ll we ll cover today 

• USEPA method for Chromium-6 Analysis 

– A Collaborative approach with USEPA 

• Principle of the method 

• Hexavalent Chromium Analysis 

• USEPA Method 218.7….. Updated from 218.6 

• Sample Preservation Study 

• Various Buffer Chemistries 

• Data for Sample Preservation study 

• Data from common Drinking water matrix 

• Summary 


Background 

• Environmental Working Group Study 

• www.ewg.org – December 2010 report (pdf) 

• 31 cities in US – affected by Cr +6 in drinking water 

• Watch group studies indicate that 89% of US water 

utilities (water supply) have Cr +6 in their DW 

• News media picked up this report 

http://thechart.blogs.cnn.com/2010/12/20/carcinogenfound-in-31-of-35-cities-water-supply/ 

• EPA’s response to investigation 


Background 

• Cr +6 & human health? 

• “This study clearly identifies a linear trend of increasing risk of 

lung cancer mortality with increasing cumulative exposure to 

water soluble hexavalent chromium.” 

Park, et al , Risk Analysis, Vol 24, 2004 

• Debate over Level (concentration exposure) vs Risk 

• Is all Chromium bad for our health? 

• Chromium in oxidation state +3 is an essential 

micronutrient to metabolize fat into energy 

• Chromium in oxidation state +6 is a carcinogen 

• No EPA defined limit for Cr +6 …MCL -100 ppb for Total Cr 


Current USEPA Methods 

For Drinking Water: 

USEPA Method 218.6 

Updated in December 2011 to USEPA method 218.7 


Principle of the Method 

Cr (VI) - 

Chromate 

CrO -2 

4 

Cr -2 

2O7 pH = 9.5 

or higher 

In post column reactor 

1N H 2 SO 4 + Diphenyl 

Carbazide (DPC) 

Cr (VI) 

forms 

complex in 

presence of 

excess H + 

to form 

Magenta color 


Typical instrument setup (Dosino for PCR) 


Alternate instrument setup (HP pump for PCR) 

Auto sampler IC System PCR/VIS (DPC) 


Chromium System at work (USEPA, Cincinnati OH) 


USEPA Method 218.7 – Option 1 

• Current app notes (AW US6-0134, US6-0152 and CH6-1049) 

• Metrohm: 

• Column: ASUPP5 – 150 (4mm ID Column) 

• Eluent: 12.8 mM Na2CO3 + 4.0mM NaHCO3 + 2.5mM 

Amm.Sulfate 

• Flow rate: 0.7 mL/min 

• PCR: Diphenyl Carbazide 

• PCR flow: 0.24 mL/min 

• Sample loop: 2 mL 

• Reaction coil – 375uL Volume 

(optimized for correct reaction ratio) 

• Vis Detector: 530nm 


USEPA Method 218.7 – Option 2 

• Metrohm: 

• Column: ASUPP10 – 100 (2mm ID column) 

• Eluent: 15g/L Amm.Sulfate + 6.5mL/L 

Amm.Hydroxide 

• Flow rate: 0.45 mL/min 

• PCR: Diphenyl Carbazide 

• PCR flow: 0.22 mL/min 

• Sample loop: 1 mL 

• Reaction coil – 375uL Volume 

(optimized for correct reaction ratio) 

• Vis Detector: 530nm 


Chromatogram 

mAU 

6.0 

4.0 

2.0 

0.0 

Chrom-6 

0.0 1.0 2.0 3.0 4.0 5.0 6.0 min 

Column: ASUPP 10-250 

Loop size 2000 microliters 

Eluent: 15g/L (NH4)2SO4 + 6.5ml/L NH4OH 

Flow rate: 0.8mls per minute 

PCR: DPC reagent 

PCR flow: 0.4mls per minute 

UV detection at 530nM 

(mAU) x min 

6.0 

5.0 

4.0 

3.0 

2.0 

1.0 

0.0 

0.0 1.0 2.0 3.0 4.0 5.0 ppb 

0.025 ppb in DW Calibration Range 

0.025 – 5.00 ppb 


MDL Study Data 

MDL study (0.025ppb and 0.050ppb) 

Chrom‐6 

Chrom‐6 

parts per billion 

parts per billion 

MDL‐1 day 1 0.026 MDL‐2‐Day 1 0.051 

MDL‐1 day 1 0.028 MDL‐2‐Day 1 0.044 

MDL‐1 day 2 0.029 MDL‐2‐Day 2 0.040 

MDL‐1 day 2 0.028 MDL‐2‐Day 2 0.046 

MDL‐1 day 2 0.031 MDL‐2‐Day 2 0.055 

MDL‐1 day 3 0.030 MDL‐2‐Day 3 0.051 

MDL‐1 day 3 0.024 MDL‐2‐Day 3 0.047 

average 0.028 average 0.048 

std dev 0.0024 std dev 0.005 

calculated MDL 0.007 calculated MDL 0.016 

*MDL = 3.14 x SD *MDL = 3.14 x SD 


MRL Study Data 

MRL Data 

analysis‐1 

Chrom‐6, ppb 

0.026 

analysis‐2 0.028 






Mean 0.0279 

std.Dev 0.0018 

HPPIR True Concentration 

0.0070 

0.025 

Upper HP PIR 

Lower HP PIR 

139.5311638 

83.32597905 

Must be less than 150 

Must be greater than 50 


Sample 

Preservation 

Study 


Work at US EPA to validate new method 

• Cincinnati & Region 6 laboratories 

• Sample preservation study data 

• Various preservatives were studied 

•NaHCO3/Na2CO3 •(NH4) 2SO4/NH4OH •NaHCO3/Na2CO3 + amm. sulfate 

• Borate buffer 

•NaOH + Na2CO3 WEAT 2012 - Austin TX (Dr. Jay Gandhi) 18

Sample Preservation Buffer Studied 

Buffer Chemical Composition 

Initial 

measured pH 

A 2 mM Na 2 CO 3 + 10 mM NaOH in 1000 mL 12.0 

B 1.25 mM Na 2 CO 3 + 1.25 mM NaHCO 3 in 1000 mL 10.2 

C 0.4 g (NH 4 ) 2 SO 4 + 0.65 mL NH 4 OH in 1000mL 10.0 

D 

E 

In each matrix 

1ppb Cr +6 

1.25 mM Na 2 CO 3 + 1.25 mM NaHCO 3 + 0.15 g/L 

(NH 4 ) 2 SO 4 in 1000 mL 

5 mM NaHCO 3 + 10 mM Na Tetra Borate in 1000 

+6 & 

mL 

& 1ppb Cr +6 + 1ppb Cr +3 

9.25 

9.10 


Buffer Study Data 

Buffer B - pH ~ 10.2 

1.25 mM Na 2 CO 3 + 1.25 mM NaHCO 3 

Buffer A - pH ~ 12.0 

2 mM Na 2 CO 3 + 10 mM NaOH 



Buffer D - pH ~ 9.7 

1.25 mM Na 2 CO 3 + 1.25 mM NaHCO 3 

+ 0.15 g/L (NH 4 ) 2 SO 4 

Buffer C - pH ~ 9.0 

0.4 g (NH 4 ) 2 SO 4 + 0.65 mL NH 4 OH 



Buffer E - pH ~ 9.5 

5 mM NaHCO 3 + 10 mM Na Tetra Borate 


Other Ions of Drinking water 

• Chloride (100ppm), Sulfate (150ppm) and 

Total Hardness as CaCO3 (450ppm) 


Reducing Agents 

• Fe +2 and Fe +3 (10ppm), Mn +2 (5ppm) and Humic 

Acid (Total carbon 25ppm) 


Reducing Agent – Only Humic Acid 

• Humic Acid (Total carbon 25ppm) 


Summary 

• Sample preservation study concluded that 

• pH greater than 9.5 is preferred for sample preservation 

• For DW, due to Chlorine as disinfectant, ammonium salt 

added to sample preservation helps Chromium species 

inter-conversion issue 

• Two buffers that worked best in this study are 

• Ammonium Sulfate + Ammonium Hydroxide 

• Sodium Carbonate + Sodium Bicarbonate + Ammonium Sulfate 

• In Collaboration with USEPA – Metrohm developed simple yet 

robust method for Hexavalent Chromium in drinking water 

• With modern Metrohm IC instrumentation trace level 

detection of Chromium-6 is possible 

• Metrohm Also has online analyzers for continuous 

monitoring of Hexavalent chromium 

WEAT 2012 - Austin TX (Dr. Jay Gandhi) 

26

Acknowledgements 

• Mr. Johnson Mathew – USEPA Region – 6 

• Mr. David Neliegh – USEPA Region –6 

• Dr. Melvin Ritter – USEPA Region –6 

• Ms. Marvyln Humphrey – USEPA Region –6 

• Dr. David Munch – Retired USEPA –ODW/OGW 

• Dr. Steve Wendelken – USEPA –ODW/OGW 

• Mr. Alan Zaffiro - Shaw Group/USEPA – Cincinnati OH 

• Metrohm AG applications team 

especially, Dr. Katinka Ruth and Dr. Andrea Willie 

• Dr. Hari Narayanan – Metrohm USA Applications Lab 

• Dr. Chunlong Zhang– University of Houston - Clearlake 

WEAT 2012 - Austin TX (Dr. Jay Gandhi) 

27

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Hexavalent Chromium in Drinking Water

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