Amphibians are struggling to survive around the world due to loss of habitat, a virulent fungus and now, a third reason - pesticides, says Don Sparling, associate professor of zoology at Southern Illinois University Carbondale.

Mr. Sparling, a researcher and associate director of the Cooperative Wildlife Research Laboratory at SIUC, has been involved with the issue for years. The second edition of his textbook and reference, "Ecotoxicology of Amphibians and Reptiles," is due out early next year. His most recent study was published in the August edition of "Environmental Toxicology and Chemistry."

Along with other researchers, he recently discovered that the same chemicals that make California's Central Valley so successful as a farming area also make the nearby Sierra Mountains deadly for frogs. Specifically, the study looked at Pacific tree frogs and foothill yellow-legged frogs, both of which are native to the mountain meadows and are declining in population.

Mr. Sparling and the team found neurotoxin pesticides are finding their way up out of the valley and into the snow and eventually the streams where the frogs live and breed.

And the results are devastating.

Using laboratories at SIUC, Mr. Sparling and his graduate students found that as little as 0.3 parts per billion of endosulfan -- the active ingredient in many pesticides -- in water is enough to kill half of the frogs living in it.

"At 0.8 parts per billion, we lose all of them," Mr. Sparling says. "We always thought there was an association between pesticides and declining amphibian populations, and we're building up a body of evidence to show this is the case."

His research studies the effects of "environmentally realistic" amounts of pesticides on amphibians, such as frogs. California's Central Valley, with its great diversity of farming and heavy use of chemicals, along with its nearby mountains and declining amphibian populations, provided the perfect opportunity.

"The Central Valley is an extremely intense agriculture area, with everything from grapes to peaches, to nuts and tomatoes grown there," Mr. Sparling says. "Along with that, you have literally hundreds of thousands of pounds of active-ingredient pesticides, this is before it's diluted, applied each year in this area."

Mr. Sparling and his colleagues looked at whether the pesticides were involved in the amphibian population declines. A main question they faced involved finding out how the chemicals worked their way up out of the valley and up into the Sierra.

Using sampling techniques, the team found the chemicals were indeed making their way into the frogs' environment, most likely by wind.

"These pesticides are applied by airplanes and we found that the wind would blow some of it up into the mountains, for instance," says Mr. Sparling. "In other cases, these chemicals would volatize after being applied, turning into a gaseous state, which could also be picked up and spread into the mountains by wind."

Timing was also a major factor in the damage caused by the chemicals. Chemicals applied in late winter and early spring would find their way into snows packed in the cooler mountain region. As the snow melted each year, the chemical released into the streams just as frogs begin to breed.

"As soon as ice is out of those streams, frogs start breeding," Mr. Sparling says. "The newly hatched frog larvae are at their most vulnerable right at this time, when the chemicals are getting into the water."

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