Persistent organic pollutants magnify every step up a food web to top predators such as dolphins, seals and sea lions. Killer whales are the most contaminated wild creatures on the planet. Sea turtles vary in their pecking order, and chemicals build up in them accordingly. Because some can live to 100 years old, they can accumulate high levels of contaminants.
In leatherbacks, research has shown that some contamination is passed on to their eggs. PCBs and flame retardants correlate with smaller turtle eggs, according to a recent study by Keller. Research in birds has shown similar effects.
"If this is a cause and effect relationship, smaller eggs could lead to smaller hatchlings and reduced fitness," Keller said.
Young marine animals are most at risk. "It's in the young that we tend to see the most poignant evidence of effects, and those effects can be permanent," Ross said.
PFCs, used as water and grease repellants, have been found in humans and wildlife around the world. PFOS, or perﬂuorooctane sulfonate, produced by 3M and used in Scotchgard, was phased out in 2001, but remains the predominant PFC in the environment.
Keller found that PFOS was the main PFC in sea turtles, which is similar to what's found in other wildlife, said Craig Butt, an environmental chemist at Duke University.
"This is true whether you look at sea turtles off the coast of Georgia or polar bears in the Arctic," Butt said.
Concentrations of the five most abundant PFCs in these turtles are related to their different levels on the food web, with decreasing concentrations beginning with Kemp’s ridley, then loggerhead, leatherback and green turtles.
Hawksbill turtles, which are spongivores, have "surprisingly high concentrations of PFOS and PFCs," the researchers wrote in the study. Crab-eating Kemp's ridleys had even higher levels. The data support previous PFC measurements in Kemp's ridley and loggerhead turtles.
In dolphins and some other marine mammals, PFCs have been linked to damage to the immune system, blood cells, kidneys and liver.
"We know they're exposed, and we know at least for PFOS, sea turtles approach concentrations that cause thyroid and neurological disruptions and immune suppression [in mammals],” Keller said.
To see if the damage to reptiles mirrors the damage seen in mammals, Celine Godard-Codding, an environmental toxicologist at Texas Tech University in Lubbock, has been examining how turtle cells respond to PFCs. Preliminary data from her lab found that PFOA doses that are toxic to mammalian cells will also kill 80 percent of reptilian cells tested. More recent experiments with PFOS found similar results.
"So far turtle cells react identically to mammal cells," said Sarah Webb, the research project manager at Texas Tech.
The doses used are higher than those found in sea turtle blood. That's because PFCs build up in tissues, so an animal's cells will have more PFCs than its blood. No one has measured them in turtle tissues yet.
All five species of sea turtles in Keller's study were at risk for potential immune suppression, according to the researchers' estimated margins of safety. This calculation is based on effects seen in lab mice and rats. Regulatory agencies use these margins of safety to determine potential risk of toxic effects.
For the highly exposed hawksbills and Kemp's ridleys, the safety margins also put them at risk of liver, thyroid and neurobehavioral damage.