Mercury species in the liver of ringed seals

Four types of mercury species, namely, methylmercury, organic mercury other than methylmercury, inorganic mercury, and insoluble mercury, deemed to be mercuric selenide (HgSe), were found in the liver of 45 ringed seals from the Canadian Arctic. On average, methylmercury, at 2%, made up the smallest fraction of the total mercury in the liver of these animals. Of the total mercury concentration in seal liver, 53% was insoluble mercury, estimated t o be largely mercuric selenide. Other workers have found this compound to b e present in mammalian liver and identified it to be HgSe. Organic mercury other than methylmercury made up 4%, and inorganic mercury 42% of the total mercury in the liver. The sum of the independently determined mercury spec ies agreed well with the total mercury concentration in the liver. Species other than mercuric selenide are known to be toxic. Mercuric selenide, cons idered to be a stable end product of the demethylation process of methylmer cury, although not readily eliminated from the liver, is inert and apparent ly non-toxic. Only approximately half of the total mercury in the liver was potentially toxic mercury. All four mercury species were positively correl ated with the age of animals, the regression slope on age being 20 times la rger for insoluble Hg (HgSe) than for methylmercury. A number of reported o bservations, such as the long half-life of Pig in liver (greater than or eq ual to 10 years), the dependence of Hg on age, and the often-observed one-t o-one relationship between Hg and Se (on a molar basis), are readily explai ned by the temporal accumulation of HgSe in the liver. In the future, a mor e accurate assessment of the health risk to animals and humans from the con sumption of contaminated animal tissues will be possible, by measuring all mercury species rather than just total mercury or methylmercury. Total merc ury alone in the liver is an inadequate indicator of toxicity to animals. M ethylmercury was analyzed by capillary gas-liquid chromatography with ECD d etection, and the other species were operationally/experimentally defined u sing physical/chemical methods. (C) 2000 Elsevier Science B.V. All rights r eserved.