Bottlenose dolphins are long-lived, fish-eating marine mammals that are at or near the top of the food web in coastal ecosystems. As a result, they are vulnerable to accumulating heavy burdens of persistent organohalogen contaminants (POCs). POCs are man-made compounds that are used in industry, agricultural and domestic settings as electrical insulating fluids, flame retardants and insecticides. They were released into the environment before their toxicities and environmental consequences were fully understood; however, we now know that POCs can persist in the environment for decades and can have effects ranging from cancer to effects on the immune system, and perhaps increase the rate of first-born mortality. POCs found in dolphins now include compounds such as the polychlorinated biphenyls (PCBs) and chlorinated pesticides (for example, DDT and its metabolites) which were banned from production in the 1970s, as well as compounds in active use such as the polybrominated diphenyl ethers (PBDEs). Mixtures of all of these compounds have been readily detected in the blubber, milk, and blood of the resident bottlenose dolphins of Sarasota Bay.
It is well known that contaminant mixtures may have toxicities differing significantly from those found for single compounds. Therefore, knowledge regarding mixture composition is important for understanding the link between contaminant burden, adverse health, and reproductive effects in marine mammals. Many factors influence how dolphins are exposed to contaminant mixtures, including maternal exposure, birth order, diet, age, sex, reproductive maturity, and nutritional state. The Sarasota Dolphin Research Program provides an unparalleled opportunity for assessing contaminant exposure at the population level as many of these parameters are known for the resident bottlenose dolphins.
Levels of POC’s in prey fish are lower than those in dolphin blubber, suggesting that contaminants are magnified through the food web.
To assess the degree of POC exposure and potential health and reproductive effects in the Sarasota Bay bottlenose dolphin population, approximately 195 blubber, blood and milk samples were collected for contaminant analysis during capture and release health assessments since June 2000. In addition, major dolphin prey fish, including pinfish, pigfish, and mullet were analyzed for 81 POC compounds to assess the role of diet on contaminant exposure.
In dolphin blubber, legacy compounds such as PCBs and 4,4’-DDE (a toxic metabolite of DDT) were found at high levels (0.5- 52 parts per million or ppm). Previous work suggests that 17 ppm is a threshold level above which health and reproductive impacts might be expected for bottlenose dolphins. Emerging POCs such as PBDEs were still detected at significant concentrations (0.01-9.7 ppm). POC levels in dolphin milk (0.13- 2.3 ppm) and prey fish (0.002-0.08 ppm) were dramatically lower than those found in dolphin blubber suggesting that dolphins efficiently take up contaminants from their diet and that POCs are biomagnifying in dolphins within Sarasota Bay.
Jennifer Yordy carefully places samples in liquid nitrogen for transport to the lab.
Statistical analyses of POCs in dolphin blubber and milk indicated that adult females and milk had POC mixtures that are different from those found in juvenile and adult male dolphins. These results suggest that females selectively offload POCs through the milk to their calves. Since POC mixtures differ in toxicity, there may be health implications for the different life history groups within the Sarasota population. Future plans include assessing the toxicity of these mixtures using in-vitro bioassays. This data may also be used in the future to assess potential health effects in other wild cetacean populations.
Funding for this project is provided by NOAA’s Fisheries Service and the National Institute of Standards and Technology. Dolphin Quest provided opportunities for sample collection through the health assessment research.