Pesticides From California's Central Valley Drift And Contaminate Remote Regions Of National Parks

The pesticides that are used in large quantities in California’s Central Valley — one of the most productive agricultural regions in the world — have now been found miles and miles away from their place of use, in the bodies of frogs living in the remote mountains of several national parks. This research is the first to demonstrate just how far the pesticides used in the region can drift — contaminating regions that are located great distances from the place of use.

Image Credit: Pacific Tree Frog via Flickr CC
Image Credit: Pacific Tree Frog via Flickr CC

Roughly 8% of total US agricultural production occurs in the Central Valley — making it one of the most intensely farmed regions in the whole of North America, and the world. Pesticides are widely used in the region, and in enormous quantities — completely eclipsing pesticide use in other US states.

“Our results show that current-use pesticides, particularly fungicides, are accumulating in the bodies of Pacific chorus frogs in the Sierra Nevada,” stated Kelly Smalling a research hydrologist from the US 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 — is a relatively common species throughout much of the California’s Sierra Nevada mountain range. Just as with most other amphibians — pesticides, fungicides, and other agrochemicals, cause significant problems for chorus frogs, in particular greatly weakening their immune system.

For the new work — the researchers collected frogs, water samples, and sediment samples, from a number of different 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,” stated 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.”

The USGS has more:

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. Another commonly detected pesticide was DDE (Dichlorodiphenyldichloroethylene) a breakdown product of DDT which was banned in the United States in 1972. The continued presence of a DDT byproduct reveals how long this banned chemical can impact biodiversity.

A comparison of the frog tissue with water and sediment collected from the same sites shows that the frogs were the more reliable indicator of chemical exposure. This is partly due to the physical-chemical properties of the l compounds and biological influences such as such as organism specific metabolism and life history. 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,” stated Smalling. “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.”

The new research was just published in the journal Environmental Toxicology and Chemistry.

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