2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P12 ThE DETERMINATION OF
METhyLMERCuRy IN wATER ECOSySTEMS
LEnKA TUHOVČáKOVá, HELEnA DOLEŽALOVá
WEISSMAnnOVá, JOSEF ČáSLAVSKý and MILADA
VáVROVá
Brno University of Technology, Faculty of Chemistry, Purkyňova
118, Brno, Czech Republic,
dolezalova@fch.vutbr.cz
Introduction
Alkyl mercury compounds belong to a group of organometallic
compounds with a high bioaccumulation potential.
They are formed from inorganic forms in a methylation
process and exhibit 100 times higher toxicity than inorganic
forms 1 . Methyl mercury is a neurotoxin which attacks the
central nervous system (CnS). The most frequent pathway
by which methyl mercury enters the body is through the gastrointestinal
tract which may absorb up to 95 % of methyl
mercury received by a man via fish meat. It may also penetrate
through the skin. It is well soluble in fat which explains
its transport through blood-brain barrier and diffusion into
cell membranes. It also passes the foetal placenta; the risk
of damage to the foetus occurs at a mercury concentration in
hair as low as 15–20 mg kg –1 . The tolerated dose of mercury
in man is 33 μg per 70 kg of body weight 2,3,4 . Methyl mercury
was responsible for a large number of intoxications in the past.
For example, fish living in water polluted with waste from a
chemical company producing chlorine caused intoxication by
methyl mercury in Japan while mercury intoxications in Iraq
were caused by the grain treated with methyl-mercury-containing
fungicides that was originally intended as seed 5 . Methyl
mercury is the most common organic form occurring in biological
systems. It is soluble in water and is relatively stable.
It passes biological membranes easily and has a long halftime
of decomposition up to 70 days 4 . Methyl mercury has
the highest partition coefficient K ow , which explains its high
affinity towards fat. Methylation is one of the mercury’s most
important environmental reactions. Methylation takes place
in the sediment as well as in sea water and fresh water. The
fastest rate of methylation was observed on the sediment’s
surface that was in contact with water 6,7 .
Experimental
The optimization of the method was carried out using
the Certified Reference Material CRM 464; tuna fish containing
a total amount of THg = 5.24 μg g –1 and methyl mercury
MeHg = 5.5 μg g –1 . The sample weighed 0.1 g. A total
of 5 samples were extracted and each sample was subjected
to three parallel measurements. Extraction was performed
according to the published method 8 . Gas chromatography
was used as the final analytical method. The results of parallel
measurements were evaluated as mean values and their standard
deviation was calculated.
s357
Table I
The conditions of the GC/μECD analysis
Parametrers of GC/μECD
Column DB-608, 30 m × 0.530 mm × 0.5 μm
Injection splitless
Injector temperature 250 °C
Carrier gas He,3 ml min –1 , constant flow
Detector temperature 250 °C
Make-up gas n2, 20 ml min –1
Results
The Certified Reference Material was used particularly
for the determination of metrological parameters of the
method. The mean recovery of extraction was found to be
64.9 ± 2.0 %. The lower recovery rate as compared to the
literature(ref. 8 ) could be caused by the certified reference
material used which just passed the expiry date. As a result,
the content of methyl mercury might differ from that provided
in the certificate. Fig. 1. shows the chromatogram of
the analysis of MeHg isolated from the certified reference
material.
Fig. 1. Chromatogram for the certified reference material
Table II contains the results of recovery from individual
parallel measurements of methyl mercury levels in the CRM
(Marked as 1–5).
To determine the accuracy of methyl mercury determination
using GC/μECD, 5 parallel measurements of the
certified reference material were carried out. The results are
provided in Table III.
Table II
Recoveries for 5 parallel samples of certified reference materials.
Declared value of MeHg – 5,500 [ng g –1 ]
CRM Mean c MeHg Recovery
peak area [ng ml –1 ] [ng g –1 ] exper. [%]
1 6,163.81 40.05 3,559.60 64.72 ± 0.51
2 7,030.21 45.67 3,653.96 66.44 ± 3.80
3 6,938.18 45.08 3,606.12 65.57 ± 1.71
4 6,884.60 44.73 3,578.27 65.06 ± 0.61
5 6,625.99 43.05 3,443.86 62.62 ± 3.59