Abstract

To better elucidate the immune-related health effects of contaminant exposure on the health of polar bears (Ursus maritimus) and ringed seals (Pusa hispida), we conducted high-quality tissue collection from native harvested East Greenland polar bears and ringed seal, thus providing a unique opportunity to collect fresh biological samples. Long-range transported anthropogenic contaminants, including perfluoroalylated substances (PFAS; e.g. perfluorooctanoic acid-PFOA, perfluorooctanesulfonic acid-PFOS) and polychlorinated biphenyls (PCB), are ubiquitous chemicals in the environment and shown to bioaccumulate and/or persist in the tissues of numerous arctic marine mammals. Domoic acid (DA) is a biotoxin produced during harmful algal bloom events and has also been measured in numerous arctic marine mammals. This project tested the hypothesis that "PFAS, PCBs, and DA are immunotoxic in polar bears and ringed seals upon either in vitro or in vivo exposure," using the following specific objectives: (1) measure the effects of in vitro exposure to different classes of PFAS and PCBs, as well as DA, on mitogen-induced lymphocyte proliferation, (2) measure changes in mitogen-induced lymphocyte proliferation and cytokine concentrations in naturally exposed animals and correlate with serum PFAS concentrations, and (3) determine the risk associated with exposure to PFAS, PCBs, and DA on polar bear and ringed seal health upon natural exposure. Live lymphocytes isolated from either the spleen or mesenteric lymph nodes were collected within 10 to 60 minutes after death, processed, and cryopreserved in liquid nitrogen in East Greenland, and shipped to our laboratory. For objective 1, PFOS, only at 10 ng/g upon in vitro exposure, increased ringed seal spontaneous lymphocyte proliferation, while PFOA had no effect on lymphocyte proliferation at the concentrations tested in vitro. The non-coplanar PCBs 138, 153, and 180, but not the coplanar PCB 169, reduced ringed seal lymphocyte proliferation between 10 and 20 ppm upon in vitro exposure. DA significantly increased ringed seal lymphocyte proliferation at 0.001 and 10 µM upon in vitro exposure. For objective 2, a significant negative correlation was found between polar bear serum PFOA and B lymphocyte proliferation. A negative correlation existed between the pro-inflammatory cytokine TNFα and ringed seal serum PFOS. For objective 3, concentrations of toxicants that modulated immune functions upon in vitro exposure were within the range measured in free-ranging polar bears and ringed seals, suggesting these species are at risk for immunotoxic effects upon natural exposure. Taken together, these data provide 'weight of evidence' that PFAS, PCBs, and DA are immunotoxic in ringed seals and polar bears, as previously demonstrated in laboratory animals, humans, and other marine mammals (e.g. California sea lions, beluga whales). Modulation of lymphocyte proliferation, whether stimulatory or suppressive, is of concern, as a decrease in function can prevent a proper immune response to pathogens, while an increase in function (without proper regulation) could lead to cancer. These data will contribute to our understanding of the impacts of global pollution of our oceans on top arctic predators depending on the complex marine food chain, as well as local Inuit populations who depend on marine mammals as a food source.

Acknowledgements

We thank local subsistence Scoreby Sound hunters for helping with the sample collection, as well as colleagues from four countries (Denmark, Norway, Canada, United States) as part of the AURORAE project. Major funding for this project was provided by the DANCEA (Danish Cooperation for Environment in the Arctic) and ARC (Arctic Research Centre). Additional travel support (for Levin) was provided by the University of Connecticut Research Foundation and the University of Connecticut's Interdisciplinary Research and Training Initiative on Coastal Ecosystems and Human Heath (I-RICH). We also thank Atli G. Atlason from IceTransport for assisting in the international transport of samples.

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