Sediments inorganic mercury

In addition to the above factors, there is a general correlation between increasing temperature and methylation, while demethylation rates reduce with increased temperature.Dissolved organic carbon may also inhibit methylation in a similar manner to sulfide again by reducing the amount of available for methylation. For inland waters, there is an inverse correlation between pH and methylation. Finally there is a positive link between sediment " inorganic mercury concentration and methylation. 

Methylmercury in the marine environment may originate from industrial discharges or be synthesised by natural methylation processes. Fish do not themselves methylate inorganic mercury [62,64], but can accumulate methyl mercury from sea water [63]. Methylmercury has been detected in sea water only from Minamata Bay, Japan, an area with a history of gross mercury pollution from industrial discharge. It has been found in some sediments but at very low concentrations, mainly from areas of known mercury pollution. It represents usually less than 1% of the total mercury in the sediment, and frequently less than 0.1% [65-67]. Microorganisms within the sediments are considered to be responsible for the methylation [65,68], and it has been suggested that methylmercury may be released by the sediments to the sea water, either in... 

In their proposed method, contamination only from the ammoniacal glutathione solution is expected. However, any inorganic mercury in this solution will be adsorbed on the glass container walls with a half-life about 2d, i.e. the blank value becomes 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. Results are calculated as methylmercury. 

Cappon and Crispin-Smith [59] have described a method for the extraction, clean-up and gas chromatographic determination of alkyl and aryl mercury compounds in sediments. The organomercury compounds are converted to their chloroderivatives and solvent extracted. Inorganic mercury is then isolated as methylmercury upon reaction with tetramethyltin. The initial extract is subjected to a thiosulphate clean-up and the organomercury species are isolated as their bromoderivatives. Total mercury recovery was in the range 75-90% and down to lpg kg-1 of specific compounds can be determined. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

This excellent method was sufficiently sensitive to determine 0.02mg kg-1 methylmercury and 9mg kg inorganic mercury in river sediment samples. 

This method was applied to river sediment samples spiked with between zero and 0.06g gr1 methylmercury and 0.6pg g-1 mercuric chloride. Results indicated the presence in the original sediment of about 0.02pg g"1 methylmercury and 9pg g"1 inorganic mercury. 

Fig. 8.39 Distribution coefficients (K and defining the sorption of inorganic Hg(II) to estuarine particles versus salinity (S, in g/L) in the Beaulieu, Mersey, and Plym estuaries. Reprinted with permission from Turner A, Millward GE, LeRoux SM (2001) Sediment-water partitioning of inorganic mercuries in estuaries. Environ Sci Technol 35 4648-4654. Copyright 2001 American Chemical Society...

Mercrobes mercury reduction technology (Mercrobes) is a proprietary, ex situ technology for the treatment of soils, sludges, sediments, and waters contaminated with mercury and mercury compounds. The process uses proprietary microbes to reduce organic and inorganic mercury compounds to elemental mercury. The vendor claims that in addition to reducing charged... 

HgCl2 in the presence of estuarine sediments showed distinct seasonal variation, whose rhythm apparently relates to the seasonal ability of the microorganisms to carry out biomethylation (755, 156). The ability of different river sediments to perform biomethylation depended markedly on the nature of the sediments (157, 158) thus, organic sediments reacted appreciably faster than coarse sand. Activated sludge will methylate inorganic mercury compounds under both sterile and nonsterile conditions, suggesting the presence of both biotic and abiotic pathways (159). 

Uncontrolled species transformations during analysis form another source of error. For methylmercury determinations in sediments it was demonstrated that errors of up to 80% resulted from the formation of the compound from inorganic mercury during separation and analysis [28, 29], For the study of possible species transformations during analysis multiple isotope dilution could be used as a diagnostic tool for identifying the error and bias inherent in specific methods of storage, sample preparation and measurement [30, 31]. 

Inza, B., F. Ribeyre, R. Maury-Brachet, and A. Boudou. 1997. Tissue distribution of inorganic mercury, methylmercury and cadmium in the Asiatic clam (Corbicula fluminea) in relation to the contamination levels of the water column and sediment. Chemosphere 35 2817-2836. 

The most notorious mercury compounds in the environment are monomethyl mercury (CH3Hg+) salts and dimethylmercury ((CH3)2Hg). The latter compound is both soluble and volatile, and the salts of the monomethylmercury cation are soluble. These compounds are produced from inorganic mercury in sediments by anaerobic bacteria through the action of methylcobalamin, a vitamin B12 analog and intermediate in the synthesis of methane ... 

Bloom N.S., Preuss, E., Katon, J., and Hiltner, M. (2003) Selective extractions to assess the biogeochemically relevant fractionation of inorganic mercury in sediments and soils. Anal. Chim. Acta 479, 233-248. 

Metallic mercury is mostly a problem in confined spaces or where it is handled in industrial processes or in laboratories. It is not generally an environmental problem, more likely an industrial hazard. However, metallic mercury does occur naturally (it was mined in Spain and Slovenia, for example) and the use of mercury for metal reclamation is a potential environmental hazard in countries such as Brazil where miners use it to extract gold from river sediments. Inorganic and organic mercury may be produced from the metallic mercury during its use and subsequent release into the environment. 

How mercury from a Japanese factory contaminated fish in Minamata Bay. The effluent, containing inorganic mercury and discharged into the bay from the factory, was not dispersed in the water, but formed sediment at the bottom where micro-organisms converted the mercury into the more toxic methyl-mercury. The methylmercury accumulated in fish and was consumed by people eating the fish. 

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