PITTSBURGH Ten of the world's most popular pesticides can decimate amphibian populations when mixed together even if the concentration of the individual chemicals are within limits considered safe, according to University of Pittsburgh research published Nov. 11 in the online edition of Oecologia. Such "cocktails of contaminants" are frequently detected in nature, the paper notes, and the Pitt findings offer the first illustration of how a large mixture of pesticides can adversely affect the environment.
Study author Rick Relyea, an associate professor of biological sciences in Pitt's School of Arts and Sciences, exposed gray tree frog and leopard frog tadpoles to small amounts of the 10 pesticides that are widely used throughout the world. Relyea selected five insecticidescarbaryl, chlorpyrifos, diazinon, endosulfan, and malathionand five herbicidesacetochlor, atrazine, glyphosate, metolachlor, and 2,4-D. He administered the following doses: each of the pesticides alone, the insecticides combined, a mix of the five herbicides, or all 10 of the poisons.
Relyea found that a mixture of all 10 chemicals killed 99 percent of leopard frog tadpoles as did the insecticide-only mixture; the herbicide mixture had no effect on the tadpoles. While leopard frogs perished, gray tree frogs did not succumb to the poisons and instead flourished in the absence of leopard frog competitors.
Relyea also discovered that endosulfana neurotoxin banned in several nations but still used extensively in U.S. agricultureis inordinately deadly to leopard frog tadpoles. By itself, the chemical caused 84 percent of the leopard frogs to die. This lethality was previously unknown because current regulations from the U.S. Environmental Protection Agency (EPA) do not require amphibian testing, Relyea said. His results showed that endosulfan was not only highly toxic to leopard frogs, but also that it served as the linchpin of the pesticide mixture that eliminate
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University of Pittsburgh