Contaminant Exposure And Associated Biological Responses In Southern Beaufort Sea Polar Bears

Abstract

Concentrations of mercury (Hg) and polychlorinated biphenyls (PCBs) were examined in polar bear (Ursus marititnus) to assess variations among sex and age cohorts, and evaluate possible adverse impacts of combined toxicant exposures. Biomarkers of selenium (Se) status (whole blood and serum Se concentrations, glutathione peroxidase activity), and thyroid status (total and free concentrations of thyroxine and tri-iodothyronine) were examined in Southern Beaufort Sea (SBS) polar bears. Both Hg and PCBs tended to be greater in female than in male polar bears and likely related to the type and proportion of marine-based prey in their overall diet. Significant positive relationships between circulating concentrations of PCBs, specific blood lipids (e.g., triglycerides and free fatty acids) and reduced body condition scores suggest combined contaminant-environmental stressors for SBS polar bears. Polar bear milk contained detectable concentrations of both Hg and PCBs. Estimated tolerable daily intake levels for PCBs through milk consumption by cubs of the year (< 6 months of age) exceeded available toxicity thresholds and could indicate possible adverse consequences of contaminant exposure during critical stages of neonatal development. Significantly positive and negative associations between contaminants and biomarkers indicated a possible oxidative stress response and thyroid disruption in SBS polar bears. Definitive relationships between contaminants and these physiologically-based biomarkers, however, could not exclude natural variations and equally possible impacts of nutritional stress and changes in physiological status. Female and young polar bears are the cohorts of concern for chronic low-level exposure to chemical mixtures. These data provide a better understanding of the physiological interactions underlying toxicity, and the multiple environment-toxicant stressors projected for arctic species with changes in climate.