Accumulation features of total and methyl mercury and selenium in tissues of common minke, Bryde’s and sperm whales from the western North Pacific

To examine the inter-species difference of sensitivity to mercury toxicity in whales, total mercury (T-Hg), methyl mercury (MeHg) and selenium (Se) levels in the liver, kidneys and muscle of three whales (common minke whales Balaenoptera acutorostrata; Bryde’s whales B. edeni; sperm whales Physeter. macrocephalus) were measured. T-Hg and MeHg were higher in the order of sperm whale > common minke whale > Bryde’s whale, and their Se levels were higher in the order of sperm whale > Bryde’s whale > common minke whale. The order of the T-Hg and Se levels in the tissues of the common minke and Bryde’s whales was kidneys > liver > muscle, and that of MeHg was liver > muscle > kidneys. The order of the T-Hg and Se levels in the tissues of sperm whales was liver > kidneys > muscle. MeHg in the animal body is preferentially distributed in the liver and kidneys containing abundant metal binding proteins such as metallothioneins. The Se concentrations in the liver of marine mammals are correlated with the total mercury concentrations. MeHg/T-Hg (%) in the liver and kidneys of sperm whales were higher than those of the baleen whales in the same total Hg levels, while MeHg/T-Hg (%) vary inversely with T-Hg concentrations in the liver and kidneys of sperm, common minke and Bryde’s whales. Accumulation of high concentrations of inorganic Hg in the liver and kidneys were probably due to a difference of demethylation ability. These results indicate the potential usefulness of assessment of Hg toxicity in large whales.