For nearly four decades, some have suspected that persistent organic pollutants - a large group of man-made chemicals that, as their name indicates, persist in the environment - contributed to a green turtle's susceptibility to the virus that causes fibropapilomatosis, a disease that forms large benign tumors that can inhibit the animal's sight, mobility and feeding ability.
A new paper by researchers from the Hollings Marine Laboratory (HML) and university and federal collaborators in Hawaii demonstrated these man-made chemicals are not a co-factor linked to the increasing number of green sea turtles afflicted with fibropapilomatosis.
Persistent organic pollutants were blamed because they can spread great distances through air and water, accumulate in human and animal tissues, increase in concentration up food chains, and might have carcinogenic and neurodevelopmental effects. They are easy to implicate because they include banned substances such as DDT, toxaphenes and polychlorinated biphenyls (PCBs).
Two previous studies attempting to link POPs and FP were didn't find a causal connection but didn't rule out the impact of the pollutants on the disease.
"We wanted to do a thorough study looking at a large, statistically valid population of turtles and using methods that could detect even tiny levels of POPs in their tissues," says National Institute of Standards and Technology (NIST) research biologist Jennifer Keller, lead author on the paper appearing in the journal Environmental Science and Technology.
Keller and her colleagues collected turtle blood samples at four locations across Hawaii, each one having a different prevalence of FP—none, low, moderate and high—in the marine turtle population residing there. "We analyzed the plasma for 164 different organic compounds to see if POP concentrations increased with increasing prevalence of FP," Keller says. "We also looked at the levels of halogenated phenols, chemicals which can come from either man-made [POP] sources or naturally from the green turtle's main food source, marine algae."
The researchers discovered that increasing POP concentrations did not correspond with a like rise in the numbers of FP tumors observed. "Our findings show that POPs are not the trigger for FP, so we can eliminate these pollutants from future studies trying to explain why the disease is more common in certain areas or why its prevalence is changing with time," Keller says.
As for halogenated phenols, the team found that the sampled turtles did have detectable concentrations of the compounds. "While it's a novel discovery for sea turtles, we believe that these phenols are likely from the turtle's diet of algae rather than man-made POPs," Keller explains.