Negative correlation between plasma thyroid hormone levels and chlorinatedhydrocarbon levels accumulated in seals from the coast of Hokkaido, Japan

Chlorinated hydrocarbon (CHC) levels in the blubber of larga seals (Phoca l argha) and ribbon seals (Phoca fasciata) collected from the coastal waters of Hokkaido, Japan, were determined in order to assess the hormonal effects of CHC exposure in free-ranging pinnipeds. Plasma thyroid hormone levels, including total thyroxine (T4), free thyroxine (free T4), total triiodothyr onine (T3), and free triiodothyronine (free T3), were also measured. Higher concentrations of polychlorinated biphenyl congeners (PCBs), dichlorodiphe nyltrichloroethane and its metabolites, and chlordane compounds were found in the range of 380 to 2,600 ng/g, 350 to 2,600 ng/g, and 120 to 760 ng/g o n a wet-weight basis, respectively. Spearman rank correlation analyses show ed that in larga seals, plasma total T3 and free T3 levels negatively corre lated with levels of all the CHCs analyzed, although there was no such corr elation between total or free T4 levels and CHC concentrations. In ribbon s eals, total T3 levels significantly decreased with an increase of di-ortho PCB (PCB 170 and 180) residues. These findings indicated that the plasma T3 deficiency could be associated with some CHC exposure in larga and ribbon seals and that the responses of plasma thyroid hormones may be useful bioma rkers for CHC exposure in ribbon seals.