The Pacific Chorus Tree frog is a tiny thing (if you’re from the east coast, think Spring Peeper). It puffs up its throat three times bigger than its head to sing. The chameleon of the frog world, this small amphibian can be brown, tan, grey or green. The Pacific Chorus frog eats bugs and helps control mosquitoes.
In a recent study conducted by US Geological Survey researchers, Central Valley pesticides were detected in the Pacific Chorus frog.
The Pacific Chorus frog is found throughout Northern California including the Sierras, Yosemite and elsewhere, but the source of the pesticide contamination appears to be agricultural areas in the Central Valley. According to USGS, a study on frogs in remote Sierra Nevada mountain habitats, including Yosemite National Park and Giant Sequoia National Monument, detected the concentrations of pesticides in frog tissue. The USGS study author said the contamination “potentially came from California’s Central Valley sources.”
USGS Research hydrologist and lead author of the study, Kelly Smalling, said in a press release. “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.”
USGS Pacific Region Director Mark Sogge added, “Having experts such as hydrologists, chemists, and biologists working together on our staff is part of what USGS can uniquely bring to address complex environmental problems.”
Researchers sampled seven sites across Lake Tahoe, Yosemite National Park, Lassen Volcanic 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, Smalling said.
Two fungicides commonly used in agriculture, pyraclostrobin and tebuconazole, and one herbicide, simazine, were the most frequently detected compounds, said Smalling, warning, “This is the first time these compounds have ever been reported in wild frog tissue.” Smalling said DDE, a byproduct of the pesticide DDT, was another compound frequently found in frogs collected — “though this is not surprising since DDE is one of the most widely detected compounds globally, even decades after DDT was banned in the United States.” All four were found in Lake Tahoe’s Pacific tree frogs.
Airborne contamination is suspected because among sites where pesticides were detected in frog tissue, none of those compounds was detected in water samples and only a few were detected in sampled sediment (such as mud at the bottom of a lake or creek), Smalling said. “This suggests that frogs might be a more reliable indicator of environmental accumulation for these types of pesticides, than either water or soil.”
Pesticides continue to be a suspected factor in the decline of amphibian species across the U.S. and the world, she said, “but much remains to be learned about how pesticides impact amphibians, and whether pesticide exposure could influence other amphibian decline factors like the deadly chytrid fungus.”
A USGS amphibian ecologist who collected the frog samples, Patrick Kleeman, said, “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.” Establishing linear cause and effect is difficult, he said, because, “unfortunately, these animals are often exposed to a cocktail of multiple contaminants.”
The research was done by the USGS California Water Science Center and USGS Western Ecological Research Center and was published July 26 in the journal “Environmental Toxicology and Chemistry.” A PDF version of this report along with additional information on this and similar research is available online.
E-mail outdoors and nature-related news and events to Sacramento Nature Examiner Carol Bogart at firstname.lastname@example.org.