Off the Charts: Polychlorinated Biphenyl Levels in Coastal Dolphins and Insights into Human Exposure

Decades ago, chemical wastes containing a number of hazardous contaminants including toxic polychlorinated biphenyls (PCBs) were allowed to seep into estuaries near Brunswick, Georgia. While extensive remediation efforts have been conducted, a recent study of bottlenose dolphins from the area has identified some of the highest PCB concentrations (max = 2,895 mg/kg lipid) ever measured in marine wildlife.  Dolphins, which are apex predators in coastal ecosystems, are known to carry high contaminant loads due to biomagnification through the marine food web, but the levels found in dolphins inhabiting coastal waters near Brunswick were several times higher than levels previously reported for dolphins from other areas of the U.S. coast and approximately double the levels measured in killer whales (Orcinus orca), an even higher level predator. Of further concern is that high PCB levels were also found in dolphins near Sapelo Island National Estuarine Research Reserve, approximately 50 kilometers northeast of Brunswick and part of a network of protected estuaries managed through a partnership of federal and state government. PCB congener patterns from dolphins sampled from both areas resembled Aroclor 1268, a relatively unique PCB mixture implicated in one of the Brunswick contaminated sites. PCBs are known to produce adverse immunological, neurological and reproductive effects and are of particular concern for mammals because a significant portion of a mother’s PCB stores are transferred to vulnerable offspring during gestation and lactation. To investigate health impacts of the measured exposures, dolphins near Brunswick and Sapelo Island were temporarily captured and given complete health examinations. Multiple health endpoints, including immune status, were assessed and correlated with contaminant concentrations. The dolphins were also fitted with radio tags and 14 remote VHF receivers were deployed along a 90 kilometer stretch of the coast to monitor the dolphins’ movements. Determining where the dolphins feed helped to elucidate potential contaminant exposure sources and will assist in understanding health risks to coastal communities that rely on the local waters for seafood. Because of the persistence of these chemicals in the environment and the fact that the contaminants are passed from mother to offspring, the impacts on resident dolphins may continue for generations to come. The findings of this study suggest that the impacts may also reach farther than originally anticipated for both dolphins and coastal communities.