Pollution is a by-product of human civilization and arises from many sources including agriculture, industry and from chemicals used in our homes and offices. Persistent organic pollutants (POPs) are one class of contaminants that break down very slowly and remain in the environment decades after their release. POPs encompass a large number of chemicals, including “legacy” contaminants such as polychlorinated biphenyls (PCBs) and pesticides (i.e, DDT and chlordane), which were heavily used in the past but were banned in the U.S. beginning in the 1970s and 1980s. Some POPs are still in active use, such as a mixture of brominated compounds called “PBDEs” that is added to products to reduce flammability. Many legacy- and current-use POPs accumulate in wildlife that feed at the top of aquatic food webs, such as bottlenose dolphins, and have been linked to effects on the immune system, altered hormone regulation, learning deficiency, altered development, and cancer.
The occurrence of POPs in Sarasota Bay dolphins has been well described through a variety of studies. We know, for instance, that POPs in juvenile dolphins occur at concentrations believed to cause a variety of toxic effects and that exposure may impair reproduction. But, how do POP levels in Sarasota Bay dolphins compare to dolphin populations from other locations along the Gulf of Mexico and U.S. East coasts? We do know that the contamination of marine mammals by POPs is widespread, but is the contamination the same everywhere or are there populations of bottlenose dolphins at greater at risk from POP exposure?
To help address this question, many groups have been actively involved in the collection of blubber samples for the determination of POP concentrations. Blubber samples have been collected over the last decade from in-water health assessments and with the use of remote darts. The National Institute of Standards and Technology (NIST) has analyzed POPs in blubber biopsies from 480 bottlenose dolphins sampled at 14 Atlantic and Gulf of Mexico locations (see figure). The sites included rural and urban estuaries, a location (Brunswick, GA) with a known PCB dump site, and dolphins living near Bermuda. Blubber samples were analyzed for legacy POPs including PCBs, pesticides (DDTs, chlordanes, dieldrin and mirex), and the industrial chemical hexachlorobenzene. The current-use brominated flame retardants (PBDEs) were also measured. The data from each location were combined and statistically analyzed. We only compared male dolphins among sites because mature female dolphins transfer most of their POPs to their calves and can thereby alter their concentrations.
The levels of POPs in bottlenose dolphins vary from place to place. PCBs, for instance reached an astounding 430 parts per million (ppm) median concentration in dolphins sampled near Brunswick, GA. Fat in the blubber of one Brunswick area dolphin was nearly 0.3% PCBs! The pattern of PCB compounds in Brunswick dolphins was unique compared to other locations but was also readily detectable in dolphins sampled 40 km away near Sapelo Island, GA. By comparison, average concentrations of PCBs in Sarasota dolphins were near the median value (68 ppm) of the 14 sites. Dolphins sampled from Apalachicola Bay, FL, southern Biscayne Bay, FL, Beaufort, NC, and [pullquote]Sarasota Bay dolphins did show a significantly higher proportion of chlordane relative to other locations except northern Biscayne Bay and Tampa Bay.[/pullquote]Bermuda had the lowest PCB concentrations. Concentrations of DDT, a pesticide that was used extensively in the US at one time, were less influenced by location, although dolphins from Mississippi Sound had significantly higher concentrations. Because DDT was banned about 35 years ago, the residual DDT is likely more evenly distributed in the environment explaining why levels did not vary widely among dolphin sampling sites. In contrast, PBDE levels in Sarasota Bay dolphins were only about 60% of the median concentration of all sites. This may be due to the Sarasota Bay watershed generally having older homes and few sewage outfalls that enter directly into Sarasota Bay. Flame retardants are generally associated with newer homes, offices as well as sewage outfalls.
Sarasota Bay dolphins did show a significantly higher proportion of chlordane relative to other locations except northern Biscayne Bay and Tampa Bay. Homes built prior to the mid-1980s had their foundations treated with chlordane to prevent termite infestation. The Florida cities, Miami, Sarasota, and Tampa, have a large number of older homes that were treated with chlordane, thus explaining the high proportion of this pesticide in dolphin blubber.
Work continues on defining geographic trends of POPs in bottlenose dolphins. In August of 2009, a dolphin health assessment was conducted in Brunswick, GA mainly to assess the impact of PCB exposure on the health of the local dolphin population. In addition, dart biopsy samples from Choctawhatchee Bay on the Florida Panhandle and from dolphins offshore of the Florida Panhandle are currently being analyzed by NIST to expand our understanding of how dolphin POP concentrations vary with location.
We acknowledge the many contributors to this work in particular those involved in sampling and investigations of dolphin habitat use.