Abstract
The rate and extent of the methylation of inorganic mercury has been shown to depend markedly on the chemical speciation of the mercury and the methylating agent. The presence of mercury (II)—chlorine covalent bonding has an inhibitory effect on methylation by methyl cobalamin (CH 3CoB 12) and in natural sediments. The rôle of radical and carbonium ion methylation mechanisms has also been investigated. In a typical estuarine sediment the extent of mercury methylation is as follows: Hg(OAc) 2 ⪢ Hg(cyst) 2 > Hg(cyst) (Hcyst)Cl > Hg(meth) 2 2+ > Hg(eth) 2 2+ > Hg(Hcyst)Cl 2 > HgCl 2 > (HgCl 2) 2 pen, where OAc = acetateHcyst = cysteine, meth = methionine, eth = ethionine and pen = penicillamine. This is consistent with mercury methylation arising by attack of a methyl carbanion (CH 3 −) on inorganic mercury (II) ions derived by microbial breakdown of the original and mercury compounds added.
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