180 Organic compounds in soils, sediments & sludges
Aromatic organic compounds such as benzene, which are not oxidised in the digestion, absorb at the same wavelength as mercury. This represents a positive interference
in all cold vapour methods for the determination of mercury. For samples containing
aromatics (i.e. those contaminated by some industrial wastes), blank analysis must
be performed and the blank results must be subtracted from the sample results. The
blank analysis is accomplished by replacing the potassium persulfate reagent and the
stannous chloride reagent with distilled water and reanalysing the sample.
Umezaki and Iwamoto et al [59] have reported that organic mercury can be reduced
directly with stannous chloride in the presence of sodium hydroxide and copper (II).
The determination of organic mercury can be simplified, particularly if the reagent
used for back extraction does not interfere with the reduction of organic mercury.
Matsumaya and Takahasi et al [53] found that back extraction with an ammoniacal glutathione solution was satisfactory. In this method, contamination only from
the ammoniacal glutathione solution is expected. However, any inorganic mercury in
this solution will be absorbed on the glass container walls with a half-life about 2 d
(i.e. the blank value becomes effectively zero if the solution is left to stand for more
than a week). This method for mercury in sediments does not distinguish between
the different forms of organomercury. Down to 0.2 µg kg
−1 mercury in sediments
can be determined by this method with a standard deviation of 0.03 µg kg
−1 . In this
method, a large weight sample (10–20 g) is extracted with hydrochloric acid for two
days and organic mercury then extracted from the filtrate with benzene. Mercury is
back extracted from the benzene with aqueous ammoniacal glutathione. This extract
is then added to aqueous solution containing sodium hydroxide, cupric sulphate and
stannous chloride and the elemental mercury released is swept off with nitrogen and,
in a further concentration step is collected on gold granules. Finally, the granules are
heated at 500
◦ C re release mercury which is determined by flameless atomic absorption
spectrophotometry at 253.7 nm.
Workers at the Department of the Environment, UK [60] have described a procedure for the determination of methylmercury compounds in soils and sediments which
involves extraction with a carbon tetrachloride solution of dithizone, reduction to
elemental mercury then analysis by atomic absorption spectrometry.
Various other workers have discussed the application of atomic absorption spectrometry to the determination of organomercury residues in non-saline sediments
[52, 54, 60–69].
Gas chromatography
Bartlett et al [70] and Longbottom et al [71] observed unexpected behaviour of
methylmercury-containing river Mersey sediments during storage. They experienced
difficulty in obtaining consistent methylmercury values; supposedly identical samples
analysed at intervals of a few days gave markedly different results. They followed
the levels of methylmercury in selected sediments over a period, to determine if any
change was occurring on storage. They found that the amounts of methylmercury
observed in the stored sediments did not remain constant; Initially there was a rise in
the amount of methylmercury observed, and then, after about 10 days, the amount
present began to decline to levels which in general only approximated those originally present. They observed this phenomenon in nearly all of the Mersey sediment
Aromatic organic compounds such as benzene, which are not oxidised in the digestion, absorb at the same wavelength as mercury. This represents a positive interference
in all cold vapour methods for the determination of mercury. For samples containing
aromatics (i.e. those contaminated by some industrial wastes), blank analysis must
be performed and the blank results must be subtracted from the sample results. The
blank analysis is accomplished by replacing the potassium persulfate reagent and the
stannous chloride reagent with distilled water and reanalysing the sample.
Umezaki and Iwamoto et al [59] have reported that organic mercury can be reduced
directly with stannous chloride in the presence of sodium hydroxide and copper (II).
The determination of organic mercury can be simplified, particularly if the reagent
used for back extraction does not interfere with the reduction of organic mercury.
Matsumaya and Takahasi et al [53] found that back extraction with an ammoniacal glutathione solution was satisfactory. In this method, contamination only from
the ammoniacal glutathione solution is expected. However, any inorganic mercury in
this solution will be absorbed on the glass container walls with a half-life about 2 d
(i.e. the blank value becomes effectively zero if the solution is left to stand for more
than a week). This method for mercury in sediments does not distinguish between
the different forms of organomercury. Down to 0.2 µg kg
−1 mercury in sediments
can be determined by this method with a standard deviation of 0.03 µg kg
−1 . In this
method, a large weight sample (10–20 g) is extracted with hydrochloric acid for two
days and organic mercury then extracted from the filtrate with benzene. Mercury is
back extracted from the benzene with aqueous ammoniacal glutathione. This extract
is then added to aqueous solution containing sodium hydroxide, cupric sulphate and
stannous chloride and the elemental mercury released is swept off with nitrogen and,
in a further concentration step is collected on gold granules. Finally, the granules are
heated at 500
◦ C re release mercury which is determined by flameless atomic absorption
spectrophotometry at 253.7 nm.
Workers at the Department of the Environment, UK [60] have described a procedure for the determination of methylmercury compounds in soils and sediments which
involves extraction with a carbon tetrachloride solution of dithizone, reduction to
elemental mercury then analysis by atomic absorption spectrometry.
Various other workers have discussed the application of atomic absorption spectrometry to the determination of organomercury residues in non-saline sediments
[52, 54, 60–69].
Gas chromatography
Bartlett et al [70] and Longbottom et al [71] observed unexpected behaviour of
methylmercury-containing river Mersey sediments during storage. They experienced
difficulty in obtaining consistent methylmercury values; supposedly identical samples
analysed at intervals of a few days gave markedly different results. They followed
the levels of methylmercury in selected sediments over a period, to determine if any
change was occurring on storage. They found that the amounts of methylmercury
observed in the stored sediments did not remain constant; Initially there was a rise in
the amount of methylmercury observed, and then, after about 10 days, the amount
present began to decline to levels which in general only approximated those originally present. They observed this phenomenon in nearly all of the Mersey sediment