Organochlorine dynamics in free-ranging polar bears and their cubs

Polar bears(Ursus maritimus) are top predators of the Arctic marine ecosystem, and as a consequence, accumulate relatively high burdens of organochlorine (OC) contaminants in their fat tissue. Depending on their nutritional and reproductive status, polar bears undergo extreme annual fluctuations in their adipose tissue depots. I determined the dynamics of OCs in adipose tissue, milk, and plasma of polar bears during seasonal fasting and feeding, pregnancy, and the first two months of lactation. I collected tissue samples from free-ranging polar bears both before and after a period of fasting and feeding, and analyzed them for concentrations and total body burdens of chlorobenzenes (S-ClBzs), hexachlorocyclohexanes (S-HCHs), chlordanes (S-CHLORs), dichlorodiphenyl-trichloroethane compounds (S-DDTs) and polychlorinated biphenyls (S-PCBs). During seasonal fasts, mean body burdens of S-DDTs declined by 50% while burdens of S-ClBzs, S-CHLORs, and S-PCBs remained the same for most bears. Females with high OC concentrations in their adipose tissue also had high concentrations in their milk. The OC body burdens of females with COYs correlated positively to those of their cubs. Adipose tissue concentrations of some specific OC compounds decreased during fasting whereas other compounds became concentrated. By contrast, specific OC compounds in adipose time of feeding bears remained relatively constant with little variation between captures. The relationship of OC compounds between mother and cub generally remained the same during fasting; some compounds were always higher in the cubs than mother and others the opposite. The fate of stored lipophilic OCs during pregnancy and lactation in an animal that is fasting and the consequent OC dynamics in their young cubs is unknown. I determined total body burden (total body fat * OC concentration) and concentration change of OCs in female polar bears during pregnancy and the first 2-3 months of lactation. In March soon after den emergence, I also determined OC concentrations in adipose tissue and plasma from cubs. Organochlorine body burdens in seven female polar bears declined during gestation and the initial lactation period. Lactation was estimated to account for 59%-66% of the decrease in S-PCBs and S-CHLORs burdens, 37%-49% for S-HCHs and S-ClBzs burdens, and 5% of the decrease for S-DDTs burdens. Total body burdens of OCs for cubs in spring were calculated to be 1-4% of pregnant females and 3-7% of nursing mothers. Whole body concentrations for mothers and cubs were similar for all OCs except for S-PCBs, where cubs had lower whole body concentrations than their mothers. Cubs and mothers had similar concentrations of S-DDTs in their adipose tissue and plasma. There was a positive relatonship between the concentration of allOCs in adipose tissue and milk from females with young cubs. Females who lost their cubs had significantly higher mean OC concentrations in their milk in spring than did females who kept their cubs. This correlation between OC concentration in mother's milk and the subsequent survival of their cubs warrants further investigation. This first year for the cub is a period of rapid growth and development that may be impaired with the presence of high OC loads. (Abstract shortened by UMI.