Inorganic mercury compounds volatility

New York Developing capacity to monitor for polyaromatic hydrocarbons (PAHs) in urine, polybrominated diphenyl ethers (PBDEs) in serum, organochlorine pesticides in serum, volatile organic compounds (VOCs) in blood, cotinine in saliva, trace elements in blood and urine, inorganic mercury in blood and to generate data on exposure to persistent organic pollutants (CDC 2005). 

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 ... 

Many bacteria are resistant to inorganic and organic mercury compounds. Mercuric reductase (MerA) is a key enzyme in the mercury detoxification pathway. MerA catalyzes the NADPH-dependent reduction of Hg to its volatile, uncharged, elemental state (Hg ). MerA is a cytosolic protein that is homologous to GR, but also has a short C-terminal extension and a long N-terminal extension not found in GR. MerA contains three pairs of cysteines one in the C-terminal extension, one in the N-terminal extension, and one in the GR-like region of the protein. The N-terminal domain binds one molecule of mercury and delivers it to the catalytic core of the protein, made up of the GR-like portion and the C-terminal extension, where it is reduced. The disulfide from... 

Mercuric acetate derivatives can be further reacted with inorganic halides yielding methoxyhalogeno-mercuri-derivatives, which are less polar and more volatile than the original mercury compounds and are more easily separated by chromatography [972,973] (see Chapter 6). The reaction is accomplished simply by adding a 10 % excess of sodium bromide in methanol to the mercuration mixture whenever the adduct formation is complete. After about 2 minutes, the new derivative is formed and the mixture is worked up as before. 

The unexpectedly high concentrations of mercury found in water and in fish tissues result from the formation of soluble monomethylmercury ion, CHjHg, and volatile dimethylmercury, (CH3)2Hg, by anaerobic bacteria in sediments. Mercury from these compounds becomes concentrated in fish lipid (fat) tissue and the concentration factor from water to fish may exceed 10. The methylating agent by which inorganic mercury is converted to methylmercury compounds is methylcobal-amin, a vitamin Bj2 analog ... 

The core techniques developed for mercury speciation take advantage of gaseous species separation after an initial derivatisation step. However GC may lead to some problems and there is increasing motivation to use LC separation methods, for which the derivatisation step and all implications connected with it, like species transformation, etc., is avoided. With LC, inorganic mercury and methylmercury compounds can be determined, but it is also possible to analyse less volatile or non-volatile species such as mersalic acid or aromatic mercury compounds, which are not accessible for GC separation. 

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