Trace element bioaccumulation in grey seals Halichoerus grypus from the Faroe Islands

Grey seals Halichoerus grypus were sampled in the Faroe Islands archipelago during the summers of 1993 to 1995. Concentrations of Cd, Cu, Hg, Se and Zn were measured in the liver, kidney and muscle of 68 seals. All elements except Zn exhibited lowest concentrations in the muscle. The liver contained the highest concentrations of Cu, Hg, Se and Zn, while the kidney contained the highest Cd concentrations. However, trace element concentrations within the tissues were influenced by sex and age. Thus, females had clearly higher Cd concentrations than males. Age was the most important factor influencing the concentration of Cd, Hg and Se in the liver, and of Cd and Hg in the kidney. A strong positive correlation between Cd, Hg and Zn in the kidney suggests the presence of a detoxification process involving metallothionein proteins. Similarly, a strong positive correlation between Hg and Se and a molecular Hg:Se ratio close to 1 in the liver suggests a demethylation process leading to the formation of mercuric selenide granules. High Hg concentrations could be related to fish consumption by the grey seal, but a piscivorous diet could not be responsible for the very high Cd concentrations. This suggests that the seals’ diet changes during the year, and may include a significant proportion of cephalopods in seasons other than summer. Finally very high Cd concentrations in grey seal tissues compared to other grey seal populations also suggest that the Faroe Islands are subject to sub-arctic influences.