Farm Chemicals Accumulating in Wild Frogs in California

Jul 26, 2013 08:03 AM EDT

Commonly used chemicals in farms of California's Central Valley have accumulated in and affected a native frog species since many decades, researchers said.

Researchers found that pesticides are affecting the Pacific chorus frog Pseudacris Regilla- a species of frog that can be found in the Sierra Nevada mountain range. Chemicals, such as pesticides and insecticides, can disrupt the frogs' immune system, making it vulnerable to various diseases.

"Our results show that current-use pesticides, particularly fungicides, are accumulating in the bodies of Pacific chorus frogs in the Sierra Nevada," said Kelly Smalling a research hydrologist from the U.S. Geological Survey in a news release. "This is the first time we've detected many of these compounds, including fungicides, in these remote locations."

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Farms in California's Central Valley account for eight percent U.S. agricultural output, making them one of the major users of pesticides.

The frogs in the study were collected from regions that were further downward from the farms- such as the ponds in the Lassen Volcanic National Park and Giant Sequoia National Monument.

"The samples were tested for 98 types of pesticides, traces of which were found in frog tissues from all sites," said Smalling. "We found that even frogs living in the most remote mountain locations were contaminated by agricultural pesticides, transported long distances in dust and by rain."

Researchers found significant levels of DDE (Dichlorodiphenyldichloroethylene), which is a breakdown product of DDT.

The U.S. banned the chemical Dichlorodiphenyltrichloroethane (DDT) way back in 1972. It's presence in frog tissue shows just how a banned chemical can still affect the biodiversity.

Researchers also found traces of pyraclostrobin and tebuconazole, which are commonly used fungicides and a herbicide, simazine. This is the first time that these three chemicals have been found in tissues of wild frogs.

"Very few studies have considered the environmental occurrence of pesticides, particularly fungicides which can be transported beyond farmland. Our evidence raises new challenges for resource managers; demonstrating the need to keep track of continual changes in pesticides use and to determine potential routes of exposure in the wild," Smalling added.

The Pacific chorus frog, Pseudacris Regilla, can be found throughout North America and is classified as a species of least concern on the IUCN's Red List of Threatened Species.

The study findings are published in the journal Environmental Toxicology and Chemistry.

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