Relationships between plasma levels of organochlorines, retinol and thyroid hormones from polar bears (Ursus maritimus) at Svalbard

Associations were determined between retinol and the thyroid hormones thyro xine (T4) and triiodothyronine (T3), respectively, and the organochlorine c ontaminants (OCs) polychlorinated biphenyls (PCBs), 1,1-dichloro-2,2-bis-(4 -chlorophenyl)ethylene (DDE), hexachlorobenzene (HCB), and hexachlorocycloh exanes (HCHs) in blood plasma from polar bears (Ursus maritimus) caught at Svalbard. The blood samples were collected from free-ranging polar bears of different age and sex in 1991-1994. The retinol concentration and the rati o of total T4 (TT4) to free T4(FT4) (TT4/FT4 ratio) decreased linearly with increasing concentrations of PCBs and HCB. Retinol was also negatively ass ociated with HCHs, while the TT4/FT4 ratio was positively associated with D DE. The concentrations of retinol and thyroid hormones were significantly h igher in females than in males. However, the TT4/FT4 and TT3/FT3 ratios wer e significantly higher in males than in females. The concentrations of thyr oid hormones were negatively correlated with age in male bears, while in fe males, thyroid hormones did not change with age. The OCs were found to expl ain 12, 30, and 7% of the variation of retinol concentrations and the TT4/F T4 and TT3/FT3 ratios, respectively, after correcting for age and sex. The potential consequence of these associations for the individual and the popu lation is unknown.