By Brett
Israel and Environmental Health News | Thursday, March 14,
2013 | 2
From the
moment they are born, sea turtles fight to survive. Buried alive, they dig
themselves out and evade hungry crabs and birds as they crawl to the ocean,
where they begin a long and treacherous migration. One out of 1,000
will survive into adulthood. And those that do will bear a toxic burden.
Scientists are
discovering that sea turtles, long ignored by toxicologists who study wildlife,
are highly contaminated with industrial chemicals and pesticides.
Loggerhead
turtles have altered immune systems and smaller eggs that
some studies have linked to contaminants. These chemicals kill turtle
cells in lab experiments, and based on research in other marine life,
scientists suspect that sea turtles may be vulnerable to thyroid, liver and
neurological damage.
No one,
however, knows the extent to which sea turtles in the wild may be harmed.
While other
ocean creatures, including whales, seals and some fish, are well-studied, the
chemical threats to sea turtles remain mostly hidden under a shell.
Decimated by
climate change, poaching, accidental snaring and ocean trash, all U.S. species of
sea turtles are protected by the Endangered Species Act, which makes studying
them difficult.
"We
really have just barely touched the tip of the iceberg," said Jennifer
Keller, a marine biologist at the Hollings Marine Laboratory in Charleston, S.C.
She is the top expert on pollution in sea turtles.
Sea turtles
have some industrial compounds in their blood nearing levels that damage marine
mammals. Keller's lab last year measured perfluorochemicals (PFCs) in
the blood of five sea turtle species off the southeastern U.S. coast, and
her calculations suggest that the turtles' potential risk for toxic effects is
high.
Other
long-lived chemicals also contaminate sea turtles, including
polychlorinated biphenyls (PCBs), which are widely used industrial compounds
banned in the late 1970s, and brominated flame retardants.
"These
chemicals may not acutely poison the animals, but they can make exposed
individuals a little more vulnerable to opportunistic infections or new and
emerging infectious diseases," said Peter Ross, a research scientist in Canada who is
one of the world’s leading experts on marine mammals and contaminants.
Some
chemicals, particularly PCBs, have been shown to suppress the immune
systems of wildlife, contributing to mass die-offs of seals and other marine
mammals in the late 1980s and early 1990s.
This
catastrophic damage hasn't been seen in turtles. Pollutants in their blood are
orders of magnitude lower than levels in marine mammal blood, Keller said.
Nevertheless,
Keller’s research with loggerheads caught off South Carolina has linked immune system
changes to a variety of contaminants. As levels of chlordane and mirex – two pesticides
banned in the United States
decades ago but still in the environment – went up in the turtles,
their production of some disease-fighting immune cells decreased. And as PCBs
and the pesticide DDT went up, some of their immune cells increased.
"Any
alteration of immune function, even enhancement, can be considered an
adverse effect," the authors wrote. Enhanced immune responses can lead to
autoimmune diseases and hypersensitivity.
"Exposure
to even relatively low concentrations of persistent pollutants can reduce the
effectiveness of immune defense against any number of pathogens," Ross
said.
The chemical
soup inside turtles comes from the food they eat, which varies from the
crab-eating Kemp's ridleys, jellyfish-eating leatherbacks, omnivorous loggerheads,
spongivorous hawksbills and herbivorous green sea turtles.
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.
To learn more,
Keller's lab is looking to the U.S. Pacific, where sea turtles haven't been
tested for contaminants.
One hypothesis
is that chemicals might be responsible for a virus, called fibropapillomatosis,
that promotes the growth of tumors in the Pacific’s sea turtles. If chemicals
suppress their immune system, the virus could grow into tumors.
But so far
Keller has not found any evidence of that. "Our pilot study is showing
that it does not look like organic contaminants are the trigger or cause,"
she said.
Since the 2001
phaseout of PFOS, levels have decreased in many marine animals. From 2000 to
2008, PFOS declined by 20 percent annually in loggerhead turtles
tested near Charleston, S.C. Yet PFOS and its precursors remain in
older consumer products, and sea turtles remain contaminated.
"PFOS is
still out there in consumer products. It's still on couches and carpets,"
Keller said. "Eventually those things are going to go to the landfill. We
need better ways to dispose of them."
This article
originally ran at Environmental Health News, a news source published by
Environmental Health Sciences, a nonprofit media company.
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