Scientists find farm pesticides in Sierra frogs

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Dozens of pesticides widely used on Central Valley farm crops have been detected in the bodies of frogs throughout the remote High Sierra, government scientists report in a study demonstrating how pervasive the chemicals are in the mountain environment.

The study published Friday was conducted by specialists with the U.S. Geological Survey who reported finding residues of 98 potent agricultural chemicals in the tissues of the common amphibians, Pacific Chorus Frogs, and in the sediments of the Sierra ponds where they live.

The compounds had apparently been blown by the wind as dust, or carried in rains sweeping eastward for scores of miles from the great valley to the mountains, the scientists concluded.

Biologist Vance T. Vredenberg of San Francisco State University, who was not involved in the new report, said the research "provides solid evidence that pesticides are making their way into natural ecosystems."

"I would guess that pesticides could have major effects, but now we need to test it," he said.

The next step

Kelly L. Smalling, a USGS research hydrologist, organic chemist and lead author of the report, said that should be the next step. Scientists should determine in detail whether even trace amounts of the compounds found in the frogs and ponds can affect the amphibians' lives and the ecology of mountain wildlife, she said.

"We need really good studies," she said.

Curiously, in the first phase of their research, one of the chemicals the scientists detected in the frogs was the breakdown product of DDT, the highly toxic compound that has been banned in America since 1972, but is still widely used in many developing countries on crops and to protect humans from mosquito-borne diseases.

That compound, called DDE, was detected in the frogs in trace amounts, indicating how persistently some chemicals can remain in the environment for long periods, Smalling said.

The average concentrations of all 98 pesticides detected in the bodies of the frogs ranged from 13 to 235 parts per billion, which Smalling described as "significant because it has never been documented before."

The report was published Friday in the journal Environmental Toxicology and Chemistry.

Among the pesticides the group detected in the frogs were a weed-killer called simazine, and pyraclostrobin and tebuconazole, two of the most commonly used fungicides. All three are sold under several different brand names to Central Valley farmers and home gardeners.

Spanning the Sierra

The Pacific Chorus Frog, Pseudacris regilla, is widespread throughout the Sierra. To carry out the study, chemists and biologists from the USGS staked out ponds at seven separate research sites, from Lassen Volcanic National Park in the north to the Giant Sequoia National Monument in the south. The sites included Lake Tahoe and Yosemite National Park.

During two years of field work, in 2009 and 2010, the researchers reported finding traces of the chemicals in the frogs tested at all the sites.

A frog expert

Vredenberg, the San Francisco State University biologist, is noted for his research into the fungus plague called chytrid disease, which is responsible for the mysterious decline and in many cases the extinction of entire frog populations in the Sierra and throughout the world.

"What we still don't know is how important those pesticides are in driving the collapse of many frogs in the region," he said of the new study.

Scientists involved in the pesticide research are wildlife biologists Gary M. Fellers and Patrick M. Kleeman, of the Geological Survey's Western Ecological Research Center at the Point Reyes National Seashore, and organic chemist Kathryn Kuivilla, at the survey's Oregon Water Science Center in Portland.