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Green sea turtles had the lowest concentration of toxins in the study.
The results of research carried out by scientists at the Hollings Marine Laboratory (HML) in Charleston, South Carolina and four partner organizations have found worrying concentrations of 13 perfluoroalkyl compounds (PFCs) in five different endangered species of sea turtles.
PFCs have been used in a number of products ranging from fire-fighting foams to stain-resistant coatings, and have become recognized as widespread pollutants over recent years. They will pass up the food chain, and have been found in samples taken from wildlife and people.
This new study involved the green (Chelonia mydas), hawksbill (Eretmochelys imbricata), leatherback (Dermochelys coriacea), loggerhead (Caretta caretta), and Kemp's ridley (Lepidochelys kempii) turtles, with researchers keen to see how dietary influences may have impacted the level of PFC residues in their tissues. The preferred diets of these turtles range up the food chain from sea grasses and algae in the case of the green turtle through to the crabs favored by the Kemp's ridley.
The scientists anticipated that any toxins would be more concentrated in the latter species, because of its feeding preferences. The crabs on which these particular turtles fed would already have higher PFC residues than plant matter.
The results were broadly in line with this hypothesis, as the vegetarian green turtles displaying the lowest plasma concentrations. The leatherbacks, loggerheads and Kemp’s ridleys had a progressively higher plasma figure, but it was the hawksbill turtles in the study that threw up a surprise.
They were second only to the Kemp’s ridleys, in spite of feeding at a low level in the food chain, eating mainly sponges. The hawksbill was also the only species that had a measurable level of a type of PFC known as perfluorooctanoic acid, or PFOA in its tissues. It is still unclear as to why this was the case. It may have been as a result of where the turtles were feeding, or perhaps sponges themselves concentrate these chemicals in their tissues for some reason.
"In our experiment, we wanted to accomplish two goals," explains NIST research biologist and study lead Jennifer Keller, based in Charleston, SC. "We wanted to get the first accurate measurements of the plasma blood concentrations of PFCs in five sea turtle species across different trophic [food chain] levels, and then compare those concentrations to ones known to cause toxic effects in laboratory animals. That way, we could estimate the potential health risks from PFC exposure for these five species of turtle."
It emerged that all of them had PFC levels capable of adversely affecting their immune system, based on other studies, with hawksbills, loggerheads and Kemp's ridleys also having perfluorooctane sulfonate (PFOS) concentrations approaching those linked to liver and neurobehavioral toxicity. In the latter two cases, the levels were so high that they also threatened interference with functioning of the thyroid glands.
"Better understanding the threat of PFCs to sea turtles can help wildlife managers and others develop strategies to deal with potential health problems," Keller says. "Our study provides the first baseline data in this area but more research is needed—especially for hawksbills, after seeing their unexpectedly high PFC exposure."
REFERENCE: Jennifer M. Keller, Lily Ngai, Joanne Braun McNeill, Lawrence D. Wood, Kelly R. Stewart, Steven G. O'Connell, John R. Kucklick. Perfluoroalkyl contaminants in plasma of five sea turtle species: Comparisons in concentration and potential health risks. Environmental Toxicology and Chemistry, 2012; 31 (6): 1223 DOI: 10.1002/etc.1818