Spatial variation in the concentrations of mercury and persistent organic pollutants in free-ranging bottlenose dolphins (Tursiops truncatus) from South Florida

The bottlenose dolphin (Tursiops truncatus) is an abundant apex predator found in
nearshore waters of South Florida, especially in the Lower Florida Keys (Key West)
and the coastal waters of Everglades National Park (ENP). The objective of this
study was to assess variation in contamination levels of total mercury (T-Hg) and
persistent organic pollutants (NDL-PCBs, PBDEs, DDT, HCH, HCB, PCDD/Fs and
DL-PCBs) in bottlenose dolphins found offshore of the densely populated Key
West (n = 27) and from undeveloped ENP (n = 20). T-Hg and POPs were analysed
in skin and blubber, respectively, by the mean of Direct Mercury analyser (for THg),
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 ENP (2289 ng.g-1 lipids), while the concentrations of PCDD/Fs remained low
(Key West: 104 pg.g-1 lipids, ENP: 102 ng.g-1 lipids). POP concentrations were
higher in individuals from Key West compared to those from the ENP. However,
POPs 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 ENP dolphins (Key West: 2941 ng.g-1
dw versus ENP: 9314 ng.g-1 dw) highlighting the specific cycle of Hg in mangrove
ecosystems. To conclude, sources of T-Hg and POPs differed between Key West
and ENP as reflected by their concentrations in skin and blubber of free-ranging
bottlenose dolphins highlighting their role as sentinels of their environment.