Mercury biological methylation

Landner L (1971) Biochemical model for biological methylation of mercury suggested from methylation studies in-vivo with Neurospora crassa. Nature 230 452-454. 

It is now well established that organometallic compounds are formed in the environment from mercury, arsenic, selenium, tellurium and tin and hence were also deduced on the basis of analytical evidence for lead, germanium, antimony and thallium. Biological methylation of tin has been demonstrated by the use of experimental organisms. Methylgermanium and methyllead were widely found in the environment but it is debatable whether germanium and lead are directly methylated by biological activity in natural environment. 

Berman, M. and R. Bartha. 1986. Levels of chemical versus biological methylation of mercury in sediments. Bull. Environ. Contam. Toxicol. 36 401-404. 

Mercury dimethyl is a toxic environmental pollutant. It is found in polluted bottom sediments and in the bodies of fishes and birds. In the bodies of fishes and birds it occurs along with monomethyl mercury. The latter, as CH3Hg+ ion, is formed by microorganism-induced biological methylation of elemental mercury or agricultural fungicide mercury compounds that are discharged into the environment. 

In addition to manufactured organolead compounds, the possibility exists of biological meth-ylation of lead, such as occurs with mercury (see Section 12.7). However, there is a great deal of uncertainty regarding biological methylation of lead in the environment. 

Discovery that methylmercury compounds can be generated by microorganisms from inorganic mercury by biological methylation. 

Jensen, S. and Jernelov, A., 1969. Biological methylation of mercury in aquatic organisms. Nature, 223 753—754. 

The major complicating factor in environmental biogeochemistry of mercury and its speciation is the biological methylation of Hg " " to CHjHg" and (CH3)2Hg. This process converts inorganic mercury to organo-mercury, which is both more lipophilic and toxic (see below). 

The biological methylation of mercury (e.g., from weathering, volcanism, fossil fuels, chloralkali electrolysis) is effected by microorganisms that utilize methylco-balamin (2c) see Section 5.1.2. 

Finally, we note that mercury released to the environment, as metal, e.g., by losses from electrolytic cells used for NaOH and Cl2 production, or as compounds such as alkylmercury seed dressings or fungicides, constitutes a serious hazard.50 This is a result of biological methylation to give (CH3)2Hg or CH3Hg+. It is known that models for vitamin B12 such as methylcobaloximes or methylpentacyanocobaltate (Section 25-F) which have Co—CH3 bonds will transfer the CH3 to Hg2 +. There are a number of microorganisms that can perform the same function, possibly by similar routes. 

Arsenic has a considerable ability to accumulate in river sediments and aquatic organism. Similarly to mercury, organic methyl derivatives can be formed by the biological activity. 

Ebbestad, U., Gundersen, N. and Torgrimsen, T. (1975) A simple method for the determination of inorganic mercury and methyl mercury in biological samples by flameless atomic absorption. Atom. Abs. Newsl., 14,142-144. 

Jensen, S., A. Jernelov, 1969, Biological Methylation of Mercury in Aquatic Organisms, Nature 223, pp. 753-754. 

Jernelov, A., Wennergren, G., Studies of Concentrations of Methyl Mercury in Sediments from the St. Clair System and Rate of Biological Methylation in Incubated Samples of Sediments, Inst. Vatten Luftv rdsforsk. Publ. B IVL 531 [1980]. 

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