- published: 21 Oct 2009
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Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula [CH3Hg]+. It is a bioaccumulative environmental toxicant.
"Methylmercury" is a shorthand for "monomethylmercury", and is more correctly "monomethylmercury(II) cation". It is composed of a methyl group (CH3-) bonded to a mercury atom; its chemical formula is CH3Hg+ (sometimes written as MeHg+). As a positively charged ion it readily combines with anions such as chloride (Cl−), hydroxide (OH-) and nitrate (NO3−). It also has very high affinity for sulfur-containing anions, particularly the thiol (-SH) groups on the amino acid cysteine and hence in proteins containing cysteine, forming a covalent bond. More than one cysteine moiety may coordinate with methylmercury, and methylmercury may migrate to other metal-binding sites in proteins.
In the past, methylmercury was produced directly and indirectly as part of several industrial processes such as the manufacture of acetaldehyde. Currently there are few anthropogenic sources of methylmercury pollution other than as an indirect consequence of the burning of wastes containing inorganic mercury and from the burning of fossil fuels, particularly coal. Although inorganic mercury is only a trace constituent of such fuels, their large scale combustion in utility and commercial/industrial boilers in the United States alone results in release of some 80.2 tons (73 tonnes) of elemental mercury to the atmosphere each year, out of total anthropogenic mercury emissions in the United States of 158 tons (144 tonnes)/year. Natural sources of mercury to the atmosphere include volcanoes, forest fires and weathering of mercury-bearing rocks.