Mercury in pilot whales: possible limits to the detoxification process.

The ability of pilot whales (Globicephala melas) to concentrate cadmium and mercury is well established. The levels of these metals were generally higher than those encountered in other species of marine mammals. The biological data have not revealed a major toxic problem in the population, and this suggests a remarkable tolerance of this species to heavy metals. Cellular distribution of mercury was carried out in liver samples. The presence of metallothionein-like proteins in the soluble fraction has been demonstrated, but 95% of mercury was mainly bound to the insoluble fraction, showing that these proteins had no role in this metal detoxification. The molar ratio between mercury and selenium suggests that the major mechanism of detoxification is through the formation of a complex Hg-Se which leads to the demethylation of mercury. The site of this process is the liver in which mercury mainly appeared as inorganic, whereas in the muscle the percentage of organic to total mercury was much higher. Nevertheless, this detoxification is limited in lactating females and in all the individuals of one school. This could be the result of changes in the diet and could constitute a toxicological risk for the species.