This is an important thread that directly pertains to my area of research.

Prior risk assessments have been based on the assumption that mercury’s mechanisms of toxicity were through direct initiation of oxidative damage or through mercury interactions with sulfur moieties of various biomolecules. Because of the significant differences between the mercury and sulfur concentrations in tissues of animals showing toxic effects, it was assumed that mercury caused harm through first order or pseudo-first order reactions.

However, a number of researchers have now shown that the mode of action of mercury involves inhibition of selenium-dependent enzymes. All forms of life that possess recognizable brains possess selenium-dependent enzyme to prevent and reverse oxidative damage. The selenium contents of brain and neuroendocrine tissues such as pituitary, thyroid, adrenals, testes/ovaries are remarkably well protected against loss of selenium. The only environmental insult that has been shown to substantially diminish selenoenzyme activities in these tissues is high methylmercury exposures. It is important to note that mercury toxicity is not necessarily associated with mercury exposure. The same amount of mercury that causes death in animals with poor selenium intakes is without any observable effects in animals fed diets containing slightly less than average selenium concentrations in ocean fish. Although exposure was an unreliable indicator of risk, mercury exposures assessed in relation to dietary selenium intakes provide Hg:Se molar ratios that are reliably and accurately related to mercury toxicity in animal and human studies.

Mercury’s binding affinity for sulfur is famously high, but its affinity for selenium is a million times higher. As a result, mercury binds the selenium present at the active sites of a variety of genetically unique and functionally elite enzymes, permanently abolishing availability of that selenium for performing the catalytic functions of these enzymes. Any agent that binds to the active site of an enzyme, is (by biochemical definition) an irreversible inhibitor. Since the most prominent functions of selenium dependent enzymes involve preventing and reversing oxidative damage, it is not surprising that oxidative damage occurs in tissues when mercury exposures are high enough to inhibit selenoenzyme activities. Increasing numbers of articles on this subject are coming out, including work showing that dietary selenium not only prevents, but also is effective in reversing mercury toxicity. =A0=A0

In regard to elemental mercury, since exposure to mercury vapors at high concentrations results in accumulation of large amounts of mercury in tissues, the selenium status of these tissues can rapidly become endangered and the potential risks may be greater than have previously been assumed.

Best regards,

Nick =A0