Body burdens and tissue concentrations of organochlorines in polar bears ( Ursus maritimus) vary during seasonal fasts

Abstract

Lipophilic organochlorines (OCs) are ingested by mammals through their foods and are generally stored in adipose tissue depots. For some species, such as polar bears, the size of these depots can fluctuate seasonally by several-fold. However, the effect of these fluctuations on the fate of stored OCs in an animal with such labile lipid depots is unknown. We determined the whole body burden and tissue concentrations of OCs in free-ranging polar bears categorized by age (cubs-of-the-year, yearlings and adults) and sex before and after a fast averaging 56 days. Adipose tissue, plasma, and milk samples were analysed for sum of chlorobenzenes (Σ-ClBzs), hexachlorocyclohexanes (Σ-HCHs), chlordanes (Σ-CHLORs), dichlorodiphenyltrichloroethane compounds (Σ-DDTs) and polychlorinated biphenyls (Σ-PCBs). Decline in body mass during fasting ranged from 0.2 kg/day for cubs-of-the-year to 0.9 kg/day for sub-adult and adult males. Although all bears showed a decline in both lipid and lean mass during fasting, patterns of OC whole body burden changes were not consistent among compounds and bear classes. The burdens of Σ-DDTs declined by 11–50% for most bears during fasting, those of Σ-CHLORs declined by 67% during fasting in sub-adult and adult males but remained constant for all females, indicating male-specific metabolism of Σ-CHLORs. As fat depots became depleted, OC concentrations in the remaining adipose tissue varied; Σ-DDTs and Σ-HCHs declined while those of Σ-CHLORs and Σ-PCBs generally increased. Thus, within a 3–4 month fast, most polar bears were able to significantly rid their adipose tissue of Σ-DDTs and Σ-HCHs. Burdens of Σ-CHLORs (except males), Σ-ClBzs and Σ-PCBs remained constant for all classes of bears, therefore there was no significant excretion or metabolism during the fast of the specific congeners in these compound classes typically found in polar bears. The ratio of plasma/adipose tissue and milk/adipose tissue OC concentrations was the same for before and after the fast indicating that OC concentrations in polar bears are probably at a steady state among various body compartments. Concentrations of Σ-CHLORs and Σ-PCBs in milk almost doubled during the fast. As a consequence of this rise in milk OC concentrations, the whole body concentrations of these compounds increased in nursing cubs. Since developing young may be susceptible to the effects of environmental contaminants, the increased exposure of nursing cubs to OCs during a fast by their mothers is noteworthy.