Abstract

Organochlorines (OCs), notably polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are ubiquitous environmental contaminants and have been measured in the tissues of marine mammals. OC-induced immunosuppression has been implicated as a co-factor in the deaths of thousands of marine mammals in infectious disease epizootics over the last two decades, and accumulating in vivo and in vitro studies support the hypothesis that PCBs are immunomodulatory [1-4]. The aim of this study was to assess potential differences in susceptibility to OCs between captive and free-ranging Southern sea otters (Enhydra lutris) originating from the same genetic population. The following hypothesis was tested, "Immunomodulatory effects upon in vitro exposure to OC mixtures are similar between captive and free-ranging Southern sea otters." In vitro assays were utilized to evaluate neutrophil and monocyte phagocytosis and respiratory burst, as well as LPS and Con A-induced B and T lymphocyte proliferation. Individual PCB congeners (138, 153, 169, and 180) as well as TCDD and all 26 possible combinations were tested. Mixtures were tested as they represent 'real life' exposure. A repeated measures one-way ANOVA with Dunnett's test was used to compare the different experimental groups to the unexposed control group. Our results suggest that 1) different immune functions were sensitive to different OC mixtures in both magnitude and direction (enhancement/suppression), and 2) immunomodulatory effects upon in vitro exposure to OCs were not similar between free-ranging and captive sea otters. Differences in susceptibility could be explained by the acute stress of capture, the chronic stress of captivity, or nutritional differences. In terms of risk assessment and management, it will be necessary to understand the effects of OCs, as well as other environmental contaminants, in all population of sea otters to better direct local conservation and management efforts.

References

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