Mercury-Selenium Correlations in Marine Mammals

Abstract

HIGH levels of mercury may occur in the tissues of seals, dolphins and porpoises^1–4. In the Netherlands from 225 to 765 p.p.m. (wet weight) in liver and from 9.9 to 31 p.p.m. in brain have been detected in adult specimens of the common seal (Phoca vitulina) which were found dead⁴. Brain concentrations were of the same order as those in the brain tissue of animals of various species poisoned experimentally by methyl-mercury compounds⁵. As most of the mercury in marine fish is present as methylmercury⁵, the high levels in seal brain suggest that these animals are affected by the toxic action of methylmercury compounds. Analyses of the methylmercury levels according to Westöö⁶ in the livers of six seals shot in the German part of the Wadden Sea and two adults found dead showed that only 2 to 14% of the total mercury was methylmercury. Similarly, of the 10 and 15 p.p.m. total mercury in the brain of the latter two seals, only 2.2 and 13% respectively could be recovered as methylmercury. Neutron activation analysis of the tissue precipitate remaining after benzene extraction of the acidified homogenates obtained in the methylmercury analysis has shown that on average more than 90 % of the mercury remains attached to the tissue components. In humans and in experimental animals poisoned by methylmercury compounds most or probably all mercury is in the form of methylmercury (refs 7 and 8 and S. Skerfving, report by the Department of Environmental Hygiene, Karolinska Institute, Stockholm). Thus the mechanism of binding of mercury to the tissues of seals may be different.