METHYLMERCURY AND TOTAL MERCURY IN TISSUES OF ARCTIC MARINE MAMMALS

Concentrations of methylmercury, total mercury and selenium in marine mammal tissues were determined in liver, muscle, skin (muktuk) and blu bber of belugas, ringed seals and narwhal, using atomic absorption and capillary gas chromatography with ECD detection. Mean MeHg levels in the types of tissues analysed, except blubber, generally exceeded the Canadian Federal Consumption Guideline for mercury in fish (0.5 mu g/g wet wt.). A spatial trend of higher MeHg levels in western compared t o eastern Arctic belugas and ringed seals was found which followed a s imilar trend observed for total mercury. Factors which could explain t his trend are discussed. Robust linear regression of MeHg on total Hg and MeHg on age of animals was performed and a strong correlation betw een the two variables was found in each case. The ratio of MeHg to tot al mercury as indicated by the regression coefficients was close to on e for muscle and skin (muktuk) while for liver it was < 1. The mean pe rcentage of MeHg in the liver of marine mammals was 3-12% of the total Hg in this tissue depending on species and location. It is postulated that the formation and deposition of mercuric selenide in the liver i s part of the demethylation process in this tissue. This is based on t he relatively low fraction of MeHg in the liver not withstanding the f act that the predominant form of mercury taken up via food is MeHg. Th e long half-life for total mercury and the relatively short half-life for MeHg in this organ are in accord with this postulate as is the 1:1 stoichiometric relationship between mercury and selenium in the liver . (C) 1998 Published by Elsevier Science B.V. All rights reserved.