What's Killing the Frogs?

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What's Killing the Frogs?

Scientists are finding that even low levels of pollutants can harm

amphibians-and possibly people

By Fred Guterl

NEWSWEEK

May 13 issue - As a boy, Fellers spent summers chasing after frogs in

the lakes and ponds of Yosemite National Park. He even kept a field

notebook, just like naturalists in the early 20th century who described

mountain yellow-legged frogs covering the lakeshores. When Fellers returned

years later to the park as an ecologist for the U.S. Geological Survey, he

was dismayed. " I've gone back to many of the same sites, and frogs don't

occur there anymore, " he says. " It's not just that they're not abundant.

They're absent. "

LATELY FELLERS HAS been trying to figure out why half the frogs in Yosemite

seem to have disappeared. When he collects tadpoles in the park and releases

them in Lassen Volcanic National Park to the north, they thrive. But when he

tries to raise Lassen tadpoles in Yosemite, they fare as poorly as the

natives: they are often born with 1 leg, or 3 legs, or in some cases as many

as 10. The likely cause: pesticides wafting over the Sierra Nevada mountains

from fruit and nut farms in California's Central Valley.

Ecologists first sounded the alarm about frogs and other amphibians

in the early 1990s. Since then, they've stomped around enough swamps and

ponds to know for certain that the decline is both real and steep: 32

species have gone extinct around the world in the last few decades, and 200

more are in decline. The reasons are varied: climate change, infectious

diseases and new malls and housing developments play a role. But what

scientists have learned recently about pesticides is especially worrisome,

not only for the frogs but for what it implies about human health.

Since frogs live in the water, lay eggs in the water and absorb

oxygen through their skin, they are hypersensitive to water pollutants.

Fellers has found pesticides at the bottom of lakes and ponds in Yosemite.

When absorbed, the chemicals damage the frogs' nervous systems. If frogs are

having so much trouble in protected parks like Yosemite, they are likely to

be faring even worse where pollution is more extreme.

Even low doses of pesticides are proving harmful. Last month Tyrone

, a biologist at the University of California, Berkeley, reported in

Proceedings of the National Academy of Sciences that trace amounts of

atrazine, a common herbicide, acts as an " endocrine disruptor " -it

interferes with the secretion of natural hormones. Tadpoles exposed to

atrazine developed deformed genitals. This may shed some light on why so

many frogs in recent years have been found with deformities, but it also

underscores a knowledge gap. Scientists have learned a lot about how various

pollutants kill laboratory mice and people, but they know little about such

nonlethal effects as deformed legs and hermaphroditic genitals. " We really

don't have a good understanding of what low-level hormones and endocrine

disruptors may have on wildlife or on people, " says Don Sparling, a wildlife

toxicologist at USGS in Laurel, Md.

Coal miners used to use canaries to warn of lethal gases. Scientists

are beginning to learn what the world's disappearing frogs are trying to

tell us.

© 2002 Newsweek, Inc.