Study offers clues to loss of state's rare amphibians

LISA M. KRIEGER AND PAUL ROGERS / San Jose Mercury News 8dec00

The same pesticides that protect California crops are apparently killing the state's rare native frogs, federal scientists announced Thursday after completion of a major study.

Common farm pesticides are blown east by winds from Central Valley fields to Sierra Nevada lakes, where they are absorbed by the moist bodies of frogs, a team of scientists from the U.S. Geological Survey and Department of Agriculture reported.

``Pesticides are getting into pristine areas, and they are having biological effects,'' said Gary Fellers, a USGS biologist based at Point Reyes National Seashore in Marin County.

``We are losing amphibians in the places they are best protected -- large parks and wilderness areas,'' he said.

The scientists' findings offered clues to one of the state's major environmental mysteries. They spurred calls by environmentalists to ban the chemicals and are expected to become a political headache for California's farmers.

The most comprehensive survey of the vanishing California frogs, the study found two leading pesticides -- diazinon and chlorpyrifos -- in tissues of more than half of the frogs caught at Yosemite National Park. Frogs living out of reach of Central Valley winds, however, were largely uncontaminated. Only 9 percent of frogs in the Coast Range carried pesticides in their tissues. In the Lake Tahoe area, as many as 86 percent of frogs were found contaminated.

The two pesticides disrupt insects' nervous systems; they do the same to frogs and tadpoles, whose moist skin readily absorbs chemicals, said Fellers and co-investigator Donald Sparling of the USGS Patuxent Wildlife Research Center in Maryland.

These findings explain only part of the mysterious global decline of frogs and other amphibians, added Fellers and his colleagues at a conference of the Amphibian Research and Monitoring Initiative Workshop in Reston, Va., where the data was announced.

The conference was sponsored by the $5.6 million federal Task Force on Amphibian Declines and Deformities, made up of experts from eight federal agencies. The study is to be published in July in the journal Environmental Toxicology and Chemistry.

Numerous causes -- including habitat destruction, parasites, ultraviolet radiation and viral infections -- are thought to contribute to frog disappearances, first noted in the late 1980s but now believed to have started decades earlier. Among the world's vanishing species are the tangerine-colored Costa Rican golden toad and the Australian gastric brooding frog, which nurtures its young in its stomach.

Dramatic population declines of the foothills yellow-legged frog, mountain yellow-legged frog, Yosemite toad and the endangered California red-legged frog have occurred in the past 10 to 15 years, but no single cause has been identified. In some high mountain lakes, stocked trout have emptied the waters of frogs.

But of all the possible causes, San Joaquin Valley pesticides from Fresno, Kern and nearby counties ``would certainly be No. 1 on my list,'' Fellers said.

With thin, permeable skin, frogs are essentially environmental sponges, soaking up chemicals from water. Other creatures -- such as garter snakes, dragonflies and caddis flies, also dwindling in the Sierra Nevada -- may also be affected, he said.

Most of the pesticides found in the frogs and their adjacent waters are short-acting and break down within a week. The pesticides do not necessarily kill the frogs directly. But they can cause behavioral changes that can prove fatal.

If frogs survive the initial exposure, they may recover, said Fellers. The chemicals are transported in air and arrive in ponds and meadows with dust, rain or snow.

The scientists collected 170 tadpoles and 117 adult Pacific tree frogs from a total of 23 sites in the coast range, Sierra foothills, Lake Tahoe Basin, and Yosemite and Sequoia national parks. They studied Pacific tree frogs because they are more abundant than the more rare species. The team started documenting frog declines in 1991 and conducted pesticide sampling in 1999.

The scientists were reluctant to suggest major changes in pesticide laws Thursday, saying that is the role of lawmakers. But they urged farmers to seek alternatives.

``These kinds of results, if confirmed, call for the need to evaluate how pesticides are used in modern agricultural practice,'' said James Hanken, curator of herpetology at Harvard University.

Environmentalists, however, called for the federal government to ban diazinon and chlorpyrifos.

``We as humans seem to be wiping out the other species with alarming rapidity,'' said Susan Kegley, a chemist with Pesticide Action Network in San Francisco. ``It's depressing. We can only hope this is one more nail in the coffin for these pesticides.''

Kegley noted that some farmers, assisted by state agencies and the University of California extension system, already have reduced their use of diazinon in recent years. Statewide, the chemical's use has fallen by about one-third since 1993. Alternatives include natural predators such as parasitic wasps, or bacteria or changing planting patterns, she said.

``We need a change in farming systems to things that are more compatible with nature,'' she said. ``But these chemicals are huge moneymakers for the companies that manufacture them. It's very political.''

Farmers said the chemicals are key to food production, especially of nuts and produce.

``Can we find new ways to use them, different methods?'' said Bob Krauter, of the California Farm Bureau Federation in Sacramento. ``We have a need for an affordable, high-quality food supply. The bugs aren't going away. They are getting to be a bigger problem. Where does that leave the farmer?''

The pesticides named as culprits -- diazinon and chlorpyrifos -- are among the most widely used agricultural chemicals in California.

Farmers commonly spray them on orange and walnut orchards, as well as on lettuce and other row crops, to kill aphids, mites, caterpillars, moths and other pests.

Both also are used heavily by exterminators to kill roaches and ants in suburban homes. Last year, farmers and commercial pest companies used 2.2 million pounds of chlorpyrifos and 958,000 pounds of diazinon statewide, according to state records.

Both chemicals belong to a controversial class of pesticides known as organophosphates. Developed during the early 19th century, organophosphates disrupt the nervous system. They were used in World War II as nerve agents. However, they usually are not persistent in the environment, and are not listed by the U.S. Environmental Protection Agency as carcinogens. Most health problems for humans come from very high levels of exposure that could occur in chemical accidents.

Their effect on children has been a source of increasing concern. This year, EPA Administrator Carol Browner banned both for home and garden use, starting Dec. 31, 2001, for chlorpyrifos, known commercially as Dursban; the target date for diazinon is August 2003.

Government agencies said they plan to pore over the report when it is published this summer.

``I'm not aware that EPA has seen this data,'' said Dave Deegan, a spokesman for the EPA in Washington, D.C. ``We'll definitely want to look at it and follow up.''

Similarly, Sacramento officials took notice.

``We are certainly interested in this latest research,'' said Glenn Brank, a spokesman for the California Department of Pesticide Regulation. ``We look forward to reviewing the data to determine how it may help us better regulate pesticides in California to protect people and the environment.''

Biologists said the study lays the groundwork for further research.

``Amphibians may be the universal sentinel for disturbance in an area,'' said Carol Meteyer of the USGS-supported National Wildlife Health Center in Madison, Wis., who studies frog deformities. ``While their threat does not suggest harm to humans, you keep your eyes open.''

Contact Lisa M. Krieger at lkrieger@sjmercury.com or (408) 920-5565. Contact Paul Rogers at progers@sjmercury.com or (408) 920-5045