November 29, 2010

Pesticide Harmful to Amphibians is Banned in U.S.

Last week the U.S. Environmental Protection Agency announced that it would ban the use of endosulfan. Endosulfan is an organochlorine pesticide that was developed in the 1950s. Although it is an effective compound against many crop pests it comes with serious health risks to humans and wildlife, including acute neurotoxicity and endocrine disruption. As a consequence endosulfan is banned in more than 63 countries, including the European Union.

Several studies indicate that because endosulfan persists in the environment for years it can be transported long distances from application sites. For example, endosulfan is commonly detected in the Sierra Nevada despite the fact that it is not applied anywhere nearby. The idea that endosulfan detected in the Sierra Nevada originates from applications in upwind agricultural areas is supported by the fact that endosulfan concentrations in the Sierra Nevada correspond very closely with application rates in the Central Valley, with a lag time of 1-2 weeks.

The fact that endosulfan can disperse widely and persist in the environment has long raised concerns about its effects on wildlife. Research on its impacts on amphibians in the Sierra Nevada indicates that endosulfan is detectable in Pacific treefrog populations (Pseudacris regilla) throughout the range and is toxic to amphibians at extraordinarily low concentrations. However, a just-published study indicates that concentrations in frog tissues are generally well below levels that would cause direct or indirect impacts. 

Overall, the effects of endosulfan on Sierran amphibians is likely relatively minor compared to those caused by trout introductions and the amphibian chytrid fungus (Batrachochytrium dendrobatidis). But given its broad toxicity to wildlife and humans the ban on endosulfan use was nonetheless long overdue. 

The following publications provide additional information on the effects of pesticides on amphibians in the Sierra Nevada:

Bradford, D. F., E. M. Heithmar, N. G. Tallent-Halsell, G.-M. Momplaisir, C. G. Rosal, K. E. Varner, M. S. Nash, and L. A. Riddick. 2010. Temporal patterns and sources of atmospherically deposited pesticides in alpine lakes of the Sierra Nevada, California, U.S.A. Environmental Science and Technology 44:4609-4614.

Bradford, D. F., K. Stanley, L. L. McConnell, N. G. Tallent-Halsell, M. S. Nash, and S. M. Simonich. 2010. Spatial patterns of atmospherically deposited organic contaminants at high elevation in the southern Sierra Nevada mountains, California, USA. Environmental Toxicology and Chemistry 29:1056-1066.

Davidson, C. and R. A. Knapp. 2007. Multiple stressors and amphibian declines:  dual impacts of pesticides and fish on yellow-legged frogs. Ecological Applications 17:587–597.

Davidson, C., H. B. Shaffer, and M. R. Jennings. 2002. Spatial tests of the pesticide drift, habitat destruction, UV-B, and climate-change hypotheses for California amphibian declines. Conservation Biology 16:1588-1601.

McConnell, L. L., J. S. Lenoir, S. Datta, and J. N. Seiber. 1998. Wet deposition of current-use pesticides in the Sierra Nevada mountain range, California, USA. Environmental Toxicology and Chemistry 17:1908-1916.

Sparling, D. W. and G. Fellers. 2009. Toxicity of two insecticides to California, USA, anurans and its relevance to declining amphibian populations. Environmental Toxicology and Chemistry 28:1696–1703.

Back to The Mountain Yellow-legged Frog Site.


  1. For those of us less adept at finding the publications, can you point us to a repository or two where we can read the publications?

    Also, does Bd follow the same upslope blow-in pattern of migration?



  2. Hi Russ. You can get PDFs of most publications using Google Scholar ( Just paste the author names and title into the Google Scholar search box and you'll generally find what you need. For papers for which a PDF is not accessible via Google Scholar email the corresponding author and request one.

    As for the pattern of spread by Bd, it is similar to that for pesticides. Bd arrived at sites in the western Sierra Nevada first (in the 1970s) and it has been spreading eastward every since. I'm working on a paper describing that spread pattern right now so hopefully that will be available before too long.