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Environment: Frogs up and down the Sierra Nevada are tainted with pesticides from the Central Valley

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USGS sampling found that Pacific chorus frogs in many remote Sierra Nevada locations are contaminated by pesticides and fungicides used in agricultural production in California’s Central Valley. Photo courtesy USGS.

Study even finds trace remnants of DDT, banned 40 years ago

By Summit Voice

FRISCO — Frogs in remote Sierra Nevada backcountry ponds are contaminated with traces of pesticides, including a byproduct of DDT, which was banned more than 40 years ago, showing how long some pollutants can persist in the environment.

The chemicals are heavily used in California’s Central Valley, one of the most productive agricultural regions in the world, and transported via wind, dust and precipitation to the High Sierra.

Pesticides such as triazines, endosulfan and organophosphates are commonly used across the U.S., but California uses more pesticides than any other state.

“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. “This is the first time we’ve detected many of these compounds, including fungicides, in these remote locations.”

The Pacific chorus frog (Pseudacris Regilla) can be found in abundance across the state’s Sierra Nevada mountain range. As with other amphibians, agrochemicals potentially pose a threat to chorus frogs, as exposure to pesticides can decrease their immune system, thereby increasing the risk of disease.

“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,” said 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.”

Pesticides continue to be a suspected factor in the decline of amphibian species across the U.S. and the world. In one recent study, scientists hypothesized that the sudden spread of the amphibian-killing chytrid fungus has been especially deadly because pesticides have compromised the immune systems of amphibians. The same study also looked at the role of pesticides in bird, bat and bee die-offs.

The team collected frogs, as well as water and sediment samples, from seven ponds ranging from Lassen Volcanic National Park at the northern most point of Central Valley, to the Giant Sequoia National Monument in the valley’s southern extent. All sites were downwind of agricultural areas.

“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.”

Two fungicides, commonly used in agriculture, pyraclostrobin and tebuconazole, and one herbicide, simazine, were the most frequently detected compounds, and this is the first time these compounds have ever been reported in wild frog tissue.

“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,” 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.”

Documenting the occurrence of these compounds is an important first step in figuring out the health consequence associated with the exposures.

“Very few studies have considered the environmental occurrence of pesticides, particularly fungicides which can be transported beyond farmland,” Smalling concluded. “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.”

Select Pesticide Types Detected in Study
Compound Pesticide Type Lassen Volcanic NP – Reading Peak Lake Tahoe Page Meadow Stanislaus NF – Spicer Sno-Park Stanislaus NF – Ebbetts Pass Yosemite NP – Summit Meadow* Yosemite NP – Tioga Pass* Giant Sequoia NM – Rabbit Meadow
Tebucanoazole Fungicide Detected Detected Detected Detected Not Detected Detected Detected
Simazine Herbicide Not Detected Detected Not Detected Detected Not Detected Not Detected Detected
Pyraclostrobin Fungicide Detected Detected Detected Detected Not Detected Detected Detected
DDE Insecticide degradate Detected Detected Detected Detected Detected Not Detected Detected
Data collected during 2009 and 2010 sampling. Asterisk denotes sampling only took place in 2010.
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