By Brian Balmer, MS, PhD Student, Chicago Zoological Society and University of North Carolina Wilmington
Bottlenose dolphins are apex predators in coastal southeastern U.S. waters, and as such can be sensitive indicators of persistent organic pollutants (POPs) in coastal ecosystems. The concentrations of POPs and patterns of specific compounds measured in a dolphin’s blubber are influenced by a number of factors, including the animal’s sex and ranging pattern in relation to POP point sources. Extremely high concentrations of POPs, specifically polychlorinated biphenyls (PCBs), have been measured in the soils, groundwater, and estuarine biota within the Turtle/Brunswick River Estuary (TBRE), located along the southern coast of Georgia. The primary PCB congeners found in the TBRE are those that comprise Aroclor 1268, a highly chlorinated mixture of PCBs. This mixture was used by LCP Chemicals, a chlor-alkali plant in operation within the TBRE from 1955 to 1994.
This study examined concentrations of POPs measured in blubber of bottlenose dolphins sampled from the southern Georgia coast in relation to their individual ranging patterns and specifically, distance of sightings in relation to a POP point source (LCP Chemicals) near Brunswick, Georgia. Dolphin ranging patterns were determined based upon 5 years of photo-identification data from two field sites approximately 40 kilometers apart; (1) the Brunswick field site, which included the TBRE, and (2) the Sapelo field site, which included the Sapelo Island National Estuarine Research Reserve (SINERR). The SINERR is part of a federal network of protected areas and was chosen with the intent that dolphins in this area could potentially act as a reference group for comparison with dolphins inhabiting the more contaminated TBRE. Dolphins were categorized into three distinct ranging patterns from photo-identification data. Individuals with sighting histories exclusively within one of the defined field sites were considered to have Brunswick or Sapelo ranging patterns. Individuals sighted in both the Brunswick and Sapelo field sites were classified as having a Mixed ranging pattern.
Brunswick male dolphins had the highest levels of PCBs ever reported for any marine mammal. PCB levels in Sapelo males were lower than Brunswick males, but comparable to the highest levels previously measured in other dolphin populations along the southeastern U.S. Female dolphins had higher proportions of Aroclor 1268 than male dolphins from their respective ranging patterns suggesting that the highly chlorinated congeners associated with the Aroclor 1268 mixture may not be offloaded to their calves as observed in other regions of the southeastern U.S. In addition, individual dolphins that were sighted farther from the Superfund point source were identified to have lower proportions of Aroclor 1268 congeners.
Results of this study suggest that POP, and specifically Aroclor 1268, contamination extends further outside of the TBRE than previously documented. Numerous studies have linked high tissue levels of PCBs to negative effects on reproduction and immune function. The high levels of PCBs and limited ranging patterns of bottlenose dolphins along the southern coast of Georgia provide a unique opportunity to identify any deleterious effects associated with chronic PCB exposure.
Funding for this research was provided by NOAA’s Ocean and Human Health Initiative, NOAA’s Marine Mammal Health and Stranding Response Program, and the Chicago Zoological Society. This research would not have been possible without additional support from the University of North Carolina Wilmington, and the Georgia Department of Natural Resources.