Volume 16, Issue 30 - July 24 - July 30, 2008

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Voyages of Discovery by Lynn Teo Simarskiand Guy G. Guthridge

Stewing in the Toxic Soup

Live long and mutate

Beware of Attack Turtle warns a bumper sticker on the door of biologist Chris Rowe’s laboratory in Solomons. But the turtles inside are actually helping Rowe figure out how human pollution is attacking them and other creatures — such as ourselves.

“Turtles are the bristlecone pines of the animal world,” Rowe says. They live for a long time. But during their long lives, turtles pick up a cocktail of contaminants from the environment and concentrate them in their bodies. These pollutants weave a tangled web inside a turtle that is hard to trace.

We humans share much with turtles, including life patterns. Snapping turtles like those Rowe studies at the Chesapeake Biological Laboratory mature sexually at about age 10 or 12 and may survive 50 to 75 years in the wild. Turtles and humans also employ the same thyroid and steroid hormones, which can be thrown awry by pollutants.

Inside the lab, hundreds of small white buckets line the shelves. All contain turtles whose mothers came from the Hudson River. Rowe reaches for bucket No. 206. At the bottom, in about a quarter-inch of water, is a dark, quarter-sized, baby snapping turtle. The turtles stay calmer when isolated like this.

Some of the babies carry PCBs, a chemical once used in the electrical industry. In the middle of the last century, General Electric released large quantities of PCBs into the river. That ecological bad actor was banned in the 1970s, but it lingers in the environment.

The jury is still out on whether the contaminants passed on by a mother turtle affect her young. Such a bequest probably wouldn’t kill her offspring outright, but it could still damage it, perhaps changing the baby’s behavior so it’s less likely to survive.

To test this theory, the baby snapping turtles are placed, one by one, in a tank of water lit by an overhead light. A lab technician then simulates the threat of a predator by passing a hawk silhouette overhead.

Glimpsing a real hawk, a healthy young snapper would freeze and wait. But the baby turtles with PCBs in their tissues don’t react to the threat in the normal way. Early results show that the PCB babies have faster metabolisms and get hyperactive. Movement can give real predators a fix on their position.

“Essentially, it’s like putting a sign on their back that says eat me,” Rowe says.

Pollution also makes staying alive cost more in energy terms. A turtle battling pollution could expend energy that might otherwise have gone into stocking up reserves for the winter or for producing more eggs.

Brewing the Toxic Soup

Earlier in his career, Rowe studied tadpoles of bullfrogs near a South Carolina coal plant. These babies faced an assault of toxic metals like arsenic, selenium, chromium and more. The tiny fringes around their mouths — which they use to scrape their algae food — were misoriented or missing. In captivity, the malformed tadpoles lost weight over two weeks compared to their normal siblings.

Headline-grabbers like oil spills and fish kills are far more dramatic than a tiny tadpole’s malformed mouth or a turtle’s subtle change in behavior. But the slow, steady harm from low levels of contaminants in the environment may pose more damage to creatures in the long run.

Even so, most wildlife managers focus on monitoring populations, not the fine-scale, subtle damage contaminants may be wreaking on individuals.

“There are probably 75,000 chemical contaminants in the Chesapeake Bay,” says Carys Mitchelmore, another biologist at the Solomons lab who studies creatures and contaminants. One source in the Bay is sewage treatment plants, which contribute an estimated tens of thousands of pollutants, she says.

There aren’t near enough researchers or dollars to study even a fraction of what these substances might do.

The first human-created compounds like DDT went into use only about 70 years ago. Ones like PCBs, which still hang around in the environment long after being banned, are called legacy contaminants. Some newer substances like the flame-retardants more recently applied to upholstery, mattresses and carpets persist just as long in the environment as the older ones now banned.

The Damage Done

Long-lived animals that accumulate fat can carry loads of some contaminants at much higher levels than the environment.

“Unlike a human, a fat turtle is a healthy turtle,” says Rowe. Turtles need to store energy as fat for when food is scarce or for making eggs. A mother snapper supplies her babies with a dollop of fat in each egg, up to 30 percent by weight. We humans load up our own young with fat through breast milk, which studies have shown contain compounds like flame retardants and PCBs.

Rowe and others worry that a complex chemical brew would make it hard for a species to adapt over time.

“Maybe we shouldn’t be surprised 30 years from now when we look around and start asking, Where are the turtles, the alligators, the long-lived birds?” he says. We may not notice until the damage is done.

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