Inorganic Mercurials

Toxicity. Inorganic mercury compounds, aryl mercury compounds, and alkoxy mercurials are generahy considered to be quite similar in their toxicity. Alkyl mercury compounds are considered to be substantiahy more toxic and hazardous. Mercury and its compounds can be absorbed by ingestion, absorption through the skin, or by inhalation of the vapor. The metal itself, however, rarely produces any harmful effects when ingested (16). 

Alkyl mercury compounds in the blood stream are found mainly in the blood cehs, and only to a smah extent in the plasma. This is probably the result of the greater stabhity of the alkyl mercuric compounds, as well as their pecuflar solubiUty characteristics. Alkyl mercury compounds affect the central nervous system and accumulate in the brain (17,18). Elimination of alkyl mercury compounds from the body is somewhat slower than that of inorganic mercury compounds and the aryl and alkoxy mercurials. Methylmercury is eliminated from humans at a rate indicating a half-life of 50—60 d (19) inorganic mercurials leave the body according to a half-life pattern of 30—60 d (20). Elimination rates are dependent not only on the nature of the compound but also on the dosage, method of intake, and the rate of intake (21,22). 

Most inorganic mercury compounds have very low vapor pressures, and generally do not contribute to high mercury vapor readings. MetaUic mercury is the most potent and troublesome in this respect. Organic mercurials also contribute to mercury vapor readings, possibly by virtue of the presence of extremely small amounts of metallic mercury present as an impurity. 

When an aqueous effluent stream containing organomercurials cannot be recycled, it may be treated with chlorine to convert the organomercury to inorganic mercury. The inorganic compounds thus formed are reduced to metallic mercury with sodium borohydride. The mercury metal is drained from the reactor, and the aqueous solution discarded. The process utilising sodium borohydride is known as the Ventron process (27). 

MERCURY Total inorganic mercury in Preshift 35 )i.g/g creatinine B... 

Organic S A Methyl mercury Bacterial activity on inorganic mercury Pesticides... 

The site of accumulation may define tlie point of toxic action. Inorganic mercury accumulation in the kidneys causes sever functional impairment Kidney damage has been shown to occur when the accumulated total of cadmium in the kidney cortex reaches 100-200 ppm... 

Elemental mercury and inorganic mercury compounds human health aspects (No. 50, 2003) Ethylenediamine (No. 15, 1999)... 

Apart from the release of human-made organomercurial compounds, methyl mercury can also be generated from inorganic mercury in the environment as indicated in the following equation ... 

FIGURE 8.2 Methylation of inorganic mercury by methylcobalamine (from Crosby 1998). 

Another type of detoxication involves the production of cysteine conjugates, which are readily excreted. (Again, organomercury compounds show their affinity for -SH groups). Methyl mercuric cysteine is an important biliary metabolite in the rat and is degraded within the gut (presumably by microorganisms) to release inorganic mercury (see IAEA Report 137, 1972). 

As noted earlier, diverse forms of organomercury are released into the environment as a consequence of human activity. Methyl mercury presents a particular case. As a product of the chemical industry, it may be released directly into the environment, or it may be synthesized in the environment from inorganic mercury which, in turn, is released into the environment as a consequence of both natural processes (e.g., weathering of minerals) and human activity (mining, factory effluents, etc.). 

Apart from CH3 Hg+, other forms of R-Hg+ have been found in the natural environment, which originate from anthropogenic sources but are not known to be generated from inorganic mercury. These forms have been found in terrestrial and aquatic food chains. A major source has been fungicides, in which the R group is phenyl, alkoxy-alkyl, or higher alkyl (ethyl, propyl, etc.). These forms behave in a similar manner... 

While methylmercury occurs naturally in tlie environment, it is reasonable to expect that methylmercury levels have increased in modem times as a result of increased inorganic mercury concentrations. Whether methylmercmy concentrations have increased to a similar extent as inoiganic mercuiy is not known. It is clear, however, that elevated fish mercuiy concentrations can currently be found in remote lakes, rivers, reservoirs, estuaries, and marine conditions, typically in predators such as sportfish at the top of food webs. As of 2003, 45 states had fish consumption advisories related to mercuiy, and 76% of all fish consumption advisories in the United States were at least partly related to mercury (USEPA 2004a). The number of advisories is increasing with time, although this is due at least partly to more sites being sampled (Wiener et al. 2003). 

Francesconi KA, Lenanton RCJ. 1992. Mercury contamination in a semi-enclosed marine embayment organic and inorganic mercury content of biota, and factors influencing mercury levels in fish. Mar Envhon Res 33 189-212. 

Tsui MTK, Wang WX. 2004. Uptake and elimination routes of inorganic mercury and methyknercury in Daphnia magna. Environ Sci Technol 38 808-816. 

Newman J, ZUhoux E, Rich E, Liang L, Newman C. 2004. Historical and other patterns of monomethyl and inorganic mercury in the Florida panther Puma concolor cotyi). Arch Environ Contam Toxicol 48 75-80. 

Rossi AD, Viviani B, Zhivotovsky B, Manzo L, Orrenius S, Vahter M, Nicotera P. 1997. Inorganic mercury modifies Ca + signal, triggers apoptosis and potentiates NMDA toxicity in cerebellar granule neurons. Cell Death Differentiation 4 317-324. 

Silhnan AJ, Weidner WJ. 1993. Low levels of inorganic mercury damage the comeal endothelium. Exper Eye Res 57 549-555. 

Misra, T.K., Bacterial resistances to inorganic mercury salts and organomercurials, Plasmid, 27 (1), 4-16, 1992. 

---