Spatial variations in the concentrations of mercury and persistent organic pollutants in free-ranging bottlenose dolphins from South Florida

The bottlenose dolphin (Tursiops truncatus) is an abundant top predator found in nearshore waters of South Florida including heavily developed and remote coastal waters. The objective of this study was to quantify total mercury (T-Hg) and persistent organic pollutant (POPs: NDL-PCBs, PBDEs, DDT, HCH, HCB, PCDD/Fs and DL-PCBs) levels in bottlenose dolphins found off the highly populated island of Key West (n = 27) and from the undeveloped Florida Coastal Everglades (FCE; n = 20). T-Hg and POPs were analyzed in skin and blubber tissues, respectively, using a Direct Mercury analyzer (for T-Hg), GC-ECD (POPs) and GC-HRMS (DLCs). The 7 ICES PCBs were the main compounds found in bottlenose dolphins from Key West (8229 ng.g-1 lipids) and the FCE (2289 ng.g-1 lipids), while the concentrations of PCDD/Fs remained low (Key West: 104 pg.g-1 lipids, FCE: 102 pg.g-1 lipids). POP concentrations were higher in individuals from Key West compared to those from the FCE. However, POP concentrations in Key West dolphins were lower than those from other locations in Florida and around the world. Unlike organic pollutants, T-Hg concentrations were significantly higher in FCE dolphins (Key West: 2941 ng.g-1 dw versus, FCE: 9314 ng.g-1 dw), with the highest concentrations reported from the southeastern US. PCB concentrations remained under previously suggested threshold for adverse health effects (including immunosuppression) in marine mammals of 17 000 ng/kg lipid. To conclude, sources of T-Hg and POPs differed between Key West and the FCE as reflected by their concentrations in skin and blubber of free-ranging bottlenose dolphins highlighting their role as sentinels of their environment.