It is widely accepted that persistent environmental contaminants are present at levels to cause concern in top predators (see, for example, R. J. Letcher et al. Sci. Tot. Environ. 408: 2995–3043; 2010). The long banned industrial chemical polychlorinated biphenyls (PCBs) remains a major threat to marine top predators such as killer whales because of its persistence and empirically demonstrated adverse effects on almost all physiological systems in the mammalian body, including importantly reproduction and immunity (J.-P. Desforges et al. Environ. Internat. 86:126–139; 2016).

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