New Study Documents Agricultural Chemicals in Sierra Frogs

SACRAMENTO, Calif. (AP) Scientists have known for years that pesticides drift from California's agricultural heartland and accumulate in frogs at remote locations in the Sierra Nevada.

Now they have a better understanding of exactly which pesticides collect in the frogs' tissue.

A study by the U.S. Geological Survey released on Friday tested for nearly 100 of California's most commonly used pesticides. It found concentrations of two fungicides – pyraclostrobin and tebuconazole – and one herbicide – simazine – in Pacific chorus frogs.

"Our results show that current-use pesticides, particularly fungicides, are accumulating in the bodies of Pacific chorus frogs in the Sierra Nevada," says Kelly Smalling, a research hydrologist with the U.S. Geological Survey and lead author of the study. "This is the first time we’ve detected many of these compounds, including fungicides, in the Sierra Nevada. The data generated by this study support past research on the potential of pesticides to be transported by wind or rain from the Central Valley to the Sierras."

Researchers sampled seven sites across Lassen Volcanic National Park, Lake Tahoe, Yosemite National Park, Stanislaus National Forest and Giant Sequoia National Monument. They collected and analyzed water and sediment samples and frogs for more than 90 different types of pesticides. The Pacific chorus frog (Pseudacris regilla) was chosen because it is commonly found in water bodies across the Sierra Nevada, allowing researchers to compare results across locations.

"One notable finding was that among sites where pesticides were detected in frog tissue, none of those compounds were detected in the water samples and only a few were detected in the sediment samples," adds Smalling. "This suggests that frogs might be a more reliable indicator of environmental accumulation for these types of pesticides, than either water or soil."

Scientists say the study is a first step in determining why amphibian populations are declining. Climate change and habitat degradation from livestock grazing also are thought to contribute to the decline.

"Documenting the presence of environmental contaminants in amphibians found in our protected federal lands is an important first step in finding out whether the frogs are experiencing health consequences from such exposure," says Patrick Kleeman, a USGS amphibian ecologist who collected the frog samples. "Unfortunately, these animals are often exposed to a cocktail of multiple contaminants, making it difficult to parse out the effects of individual contaminants."

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