Abstract

Though PCBs are nearly ubiquitous in all aquatic environments, the health affects on animals contaminated with these compounds have yet to be fully elucidated. In particular, the immunotoxic effects of PCBs on marine mammals warrant further investigation, since the immune system plays a central role in the overall health and disease management of the animal. The effects of exposure to individual PCB congeners have been previously studied in laboratory animals, but little work has been done on the effects of mixtures of organochlorine compounds, which may act synergistically, additively, or antagonistically on immune functions. The present study is aimed at characterizing immunotoxic potential for mixtures of organochlorines compared to that of individual compounds, and compares the relative sensitivity of different species of marine mammals. Immune assays evaluated included: (1) lymphocyte proliferation, the ability of lymphocytes to divide upon stimulation with a mitogen; and (2) phagocytosis, the ability of phagocytic cells to engulf fluorescent microspheres. Blood samples were collected from beluga whales and fur seals from Mystic Aquarium, CT. Four PCB congeners, PCB 138, PCB 153, PCB 169, and PCB 180, as well and 2,3,7,8-TCDD were tested. Preliminary results from the lymphocyte proliferation assays suggest that belugas and fur seals are sensitive to similar PCB mixtures, while mice are sensitive to different PCB mixtures (the only exception was PCB 153+169, for which the beluga had a higher relative sensitivity). Beluga whales also appear to be sensitive to a larger number of PCB mixtures, compared to the mice and fur seals. The phagocytic ability of beluga monocytes was reduced significantly for some mixtures of two three, four, and five PCBs (each mixture contained TCDD). No significant changes were detected for neutrophils. Only one PCB mixture, 180+TCDD, significantly affected both phagocytosis of beluga monocytes and proliferation of beluga T cells. Future assays will include NK cell activity, the respiratory burst (ability to produce peroxides), and immunophenotyping of T and B cell subsets. Our results suggest that the widely used mouse model may not accurately represent the risks associated with exposure to mixtures of organochlorines in all species. Therefore, testing the relative sensitivity to immunomodulatory effects of contaminants and contaminant mixtures between different species of marine mammals will have important implications for risk assessment as well as conservation and management strategies.

Acknowledgements

We would to thank the staff at Mystic Aquarium for providing samples. This study was partially funded by a grant from the Research Foundation, University of Connecticut.