Organometallic compounds in saline sediments 211
out in which identical samples were collected and homogenised. Some of the samples
were sterilised by treatment with an approximate 4% w/w solution of formaldehyde.
Several samples of both sterilised and unsterlised sediments were analysed at intervals
and all of the samples were stored at ambient room temperature (18
◦ C) in the laboratory. It can be seen from Figure 7.2 that there is a difference in behaviour between
the sterilised and unsterlised samples. Some of the samples were separately inoculated
into various growth media to test for microbiological activity.
This work suggests that the application of laboratory-derived results directly to
natural conditions could, in these cases, be misleading: analytical results for day ten
of the extrapolated directly might lead to the conclusion that natural methylmercury
levels and rates of methylation are much greater than in fact they really are. Work
in this area with model or laboratory systems needs to be interpreted with particular
caution.
Bartlett et al [22] determined methylmercury compounds by a method in which
samples of 2–5 g were extracted with toluene after treatment with copper sulphate
and an acidic solution of potassium bromide. Methylmercury was then back extracted
into aqueous sodium thiosulphate. This was then treated with acidic potassium bromide and copper sulphate following which methylmercury was extracted into pesticide
grade benzene containing approximately 100 µg dl
−1 of ethyl mercuric chloride as
an internal standard. The extract was analysed by electron capture gas chromatography with a Ni
65 detector. The glass column (1 m × 0.4 cm) was packed with 5%
neopentyl glycol adipate on Chromosorb G (AW-DMCS). Methylmercury was measured by comparing the peak heights with standards of methyl mercuric chloride made
up in the methylmercury-benzene solution. The results were calculated as nanograms
of methyl-mercury per gram of dry sediment. The detection limit was 1–2 ng g
−1 .
Craig and Morton et al [26] found 2.2 µg L
−1 mean total mercury level in 136
samples of bottom deposits from the Mersey Estuary.
Detection limits
Organo mercury compounds have been encountered in river and marine waters,
respectively in the concentration ranges 0.00001–0.004 mg kg
−1 and 0.00001–
0.0004 mg kg
−1 . Available methods involving atomic absorption [23–28], with limit of
0.0002 mg kg
−1 are insufficiently sensitive to analyse at the 0.000 01 mg kg
−1 level and
it would seem that a preconcentration technique would be needed to effect analysis of
these very low levels.
REFERENCES
[1] Jacobs, L.W., Syers, J.K. & Keeney, D.R. (1970) Proceedings of the Soil Science of
America, 34, 750.
[2] Andreae, M.W. (1977) Analytical Chemistry, 49, 820.
[3] Johnson, D.L. & Braman, R.S. (1975) Deep Sea Research, 22, 503.
[4] Inverson, D.G., Anderson, A.A., Holm, T.R. & Stanforth, R.R. (1979) Environmental
Science and Technology, 13, 1491.
[5] Maher, W.A. (1981) Analytica Chimica Acta, 126, 157.
[6] Persson, J. & Irgun, K. (1982) Analytica Chimica Acta, 138, 111.
out in which identical samples were collected and homogenised. Some of the samples
were sterilised by treatment with an approximate 4% w/w solution of formaldehyde.
Several samples of both sterilised and unsterlised sediments were analysed at intervals
and all of the samples were stored at ambient room temperature (18
◦ C) in the laboratory. It can be seen from Figure 7.2 that there is a difference in behaviour between
the sterilised and unsterlised samples. Some of the samples were separately inoculated
into various growth media to test for microbiological activity.
This work suggests that the application of laboratory-derived results directly to
natural conditions could, in these cases, be misleading: analytical results for day ten
of the extrapolated directly might lead to the conclusion that natural methylmercury
levels and rates of methylation are much greater than in fact they really are. Work
in this area with model or laboratory systems needs to be interpreted with particular
caution.
Bartlett et al [22] determined methylmercury compounds by a method in which
samples of 2–5 g were extracted with toluene after treatment with copper sulphate
and an acidic solution of potassium bromide. Methylmercury was then back extracted
into aqueous sodium thiosulphate. This was then treated with acidic potassium bromide and copper sulphate following which methylmercury was extracted into pesticide
grade benzene containing approximately 100 µg dl
−1 of ethyl mercuric chloride as
an internal standard. The extract was analysed by electron capture gas chromatography with a Ni
65 detector. The glass column (1 m × 0.4 cm) was packed with 5%
neopentyl glycol adipate on Chromosorb G (AW-DMCS). Methylmercury was measured by comparing the peak heights with standards of methyl mercuric chloride made
up in the methylmercury-benzene solution. The results were calculated as nanograms
of methyl-mercury per gram of dry sediment. The detection limit was 1–2 ng g
−1 .
Craig and Morton et al [26] found 2.2 µg L
−1 mean total mercury level in 136
samples of bottom deposits from the Mersey Estuary.
Detection limits
Organo mercury compounds have been encountered in river and marine waters,
respectively in the concentration ranges 0.00001–0.004 mg kg
−1 and 0.00001–
0.0004 mg kg
−1 . Available methods involving atomic absorption [23–28], with limit of
0.0002 mg kg
−1 are insufficiently sensitive to analyse at the 0.000 01 mg kg
−1 level and
it would seem that a preconcentration technique would be needed to effect analysis of
these very low levels.
REFERENCES
[1] Jacobs, L.W., Syers, J.K. & Keeney, D.R. (1970) Proceedings of the Soil Science of
America, 34, 750.
[2] Andreae, M.W. (1977) Analytical Chemistry, 49, 820.
[3] Johnson, D.L. & Braman, R.S. (1975) Deep Sea Research, 22, 503.
[4] Inverson, D.G., Anderson, A.A., Holm, T.R. & Stanforth, R.R. (1979) Environmental
Science and Technology, 13, 1491.
[5] Maher, W.A. (1981) Analytica Chimica Acta, 126, 157.
[6] Persson, J. & Irgun, K. (1982) Analytica Chimica Acta, 138, 111.