Persistent organic pollutant (POP) mixtures in wild bottlenose dolphins: The influences of life history, dietary exposure, physiology and their potential for endocrine disruption

As apex predators within marine ecosystems, cetaceans are predisposed to the accumulation of high levels and complex mixtures of persistent organic pollutants (POPs); however, inherent challenges to the study of cetaceans have precluded direct assessments of contaminant-related health impacts in wild populations. Bottlenose dolphins (BNDs) have unique characteristics that allow risk-assessments to move beyond the limitations encountered with larger, pelagic cetaceans. The main objectives of this research were to identify factors that influence the exposure and bioavailability of POP mixtures in cetaceans, and assess their potential to increase the risk of endocrine disruption, using bottlenose dolphins as a model species. The measurement of a large suite of POPs in dolphin blubber, blood, milk, and prey items collected from Sarasota Bay, Florida, has confirmed that bioaccumulated mixtures vary significantly amongst individuals of a resident community. Age-related variations among male dolphins were associated with the accumulation of recalcitrant compounds and a depletion of congeners mediated by CYP450 metabolism. Mixture differences between immature and mature females were attributed to the selective offloading of smaller, less lipophillic compounds during lactation. Contaminant patterns in the youngest juvenile BNDs mirrored patterns found in milk, the primary food source for their first year. Despite the gradual transition to a prey-based diet, age-related changes in juvenile mixtures were more closely related to metabolism than to a switch in diet. Investigations of the tissue distribution of POPs in wild dolphins confirmed that blubber is the major repository for POPs, but suggested that physiological conditions that reduce blubber lipid (i.e. disease, starvation, seasonal temperature changes) may result in a redistribution of contaminants from blubber to blood and internal tissues; thus increasing the potential risk for exposure-related health effects. Finally, the (anti) estrogenic activity of contaminant mixtures extracted from dolphin blubber was assessed with the ESCREEN bioassay. The significant estrogenic activity detected in blubber suggests that POPs may act additively, at biologically relevant concentrations, to exert estrogenic effects in select BND populations. Overall, these studies emphasize toxicological potential of POP mixtures and the importance of accounting for exposure to complex mixtures when assessing risks in cetaceans.