University of Pittsburgh researchers said the U.S. Environmental Protection Agency-approved pesticides, when mixed together, can decimate amphibian populations even if the concentration of the individual chemicals is within limits considered safe.

Such "cocktails of contaminants" are frequently detected in nature, the scientists said, noting their findings offer the first illustration of how a large mixture of pesticides can adversely impact the environment.

Associate Professor Rick Relyea, the study's lead author, exposed gray tree frog and leopard frog tadpoles to small amounts of the 10 pesticides -- insecticides carbaryl, chlorpyrifos, diazinon, endosulfan, and malathion, as well as five herbicides: acetochlor, atrazine, glyphosate, metolachlor, and 2,4-D.

He used each of the pesticides alone, the insecticides combined, a mix of the five herbicides, or all 10 of the poisons.

Relyea found a mixture of all 10 chemicals killed 99 percent of leopard frog tadpoles, as did the insecticide-only mixture.

The study is detailed in the online edition of the journal Oecologia.