Pesticides Linked to Disappearance of Amphibians

by Anne Sherrod

New research has shown that pollution of the air by ag­ricultural pesticides is a significant factor in the decline of amphibians.

Two pesticides used in the San Joachin Valley of California are being carried by wind into the Sierra Nevada Mountains. There they were found in the snow, water and soil – and in the amphibians – of the Sierra Nevada national parks.  

The study focused on the effects of endosulfan (an orga­nochlorine) and chlorpyrifos (an organophosphate), on Pacific tree frogs and foothill yellow-legged frogs. The researchers concluded that the use of these chemicals in the San Joachin Valley posed a serious risk to amphibians in the Sierra Ne­vada Mountains 50-75 miles away. Other pesticides were also found, and the toxicity of all the compounds together is much greater than any one kind. 

Pesticides can volatilize from the ground in warm agri­cultural areas, and be transported by wind until they fall to the ground again with rain or snow. This process, known as “glo­bal distillation,” is responsible for the presence of organochlo­rine compounds in the Arctic, where they are concentrated in the fat of wildlife and aboriginal people.  

Organochlorine pesticides, including endosulfan, have been found high in the Canadian Rocky Mountains, where winds most frequently come from agricultural regions in the Okanagan and Washington State. Samples from Mount Rev­elstoke Provincial Park and Yoho National Park indicate that “the highest pesticide concentrations are found in temperate mountain soils that are rich in organic matter and receive large amounts of cold precipitation” (Daly et al., 2007). The yellow-legged frogs of the Sierra Nevada have now been decimated by the deadly chytrid fungus. But the slide to­wards extinction started from other causes, including levels of pesticides too low to cause death; instead they caused chronic effects on reproduction and development and (who knows?) perhaps immunity.

This a warning bell for humans, who have pesticides invading their bodies not only from the food they eat, but also from water melting in snow packs high in the mountains. 



Daly, G.L., et al., “Pesticides in Western Canadian Moun­tain Air and Soil,” Environmental Science and Technology, 2007 Sept. 1; 41(17):6020-5. Available at Shen, L., et al., “Atmospheric distribution and long-range transport behaviour of organochlorine pesticides in North America,” Environmental Science and Technology, 2005 Jan 15; 39(2):409-20, Sparling, D.W., and Fellers, G.M., “Toxicity of two insecticides to California, USA, Anurans and its relevance to declining amphibian popula­tions,” Environmental Toxicology and Chemistry, Vol. 28, No. 8, 2009,…/Sparling%20&%20Fellers%20-%202009.pdf

[From WS September/October 2009]

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