Pitt research finds that low concentrations of pesticides can become tox...(d the bulk of leopard frog tadpoles. .....)

"Endosulfan appears to be about 1,000-times more lethal to amphibians than other pesticides that we have examined," Relyea said. "Unfortunately, pesticide regulations do not require amphibian testing, so very little is known about endosulfan's impact on amphibians, despite being sprayed in the environment for more than five decades."

For most of the pesticides, the concentration Relyea administered (2 to 16 parts per billion) was far below the human-lifetime-exposure levels set by the EPA and also fell short of the maximum concentrations detected in natural bodies of water. But the research suggests that these low concentrationswhich can travel easily by water and, particularly, windcan combine into one toxic mixture. In the published paper, Relyea points out that declining amphibian populations have been recorded in pristine areas far downwind from areas of active pesticide use, and he suggests that the chemical cocktail he describes could be a culprit.

The results of this study build on a nine-year effort by Relyea to understand potential links between the global decline in amphibians, routine pesticide use, and the possible threat to humans in the future. Amphibians are considered an environmental indicator species because of their unique sensitivity to pollutants. Their demise from pesticide overexposure could foreshadow the fate of less sensitive animals, Relyea said. Leopard frogs, in particular, are vulnerable to contamination; once plentiful across North America, including Pennsylvania, their population has declined in recent years as pollution and deforestation have increased.

Relyea published a paper in the Oct. 1 edition of Ecological Applications reporting that gradual amounts of malathionthe most popular insecticide in the United Statesthat were too small to directly kill developing leopard frog tadpoles instead sparked a biological chain of events that deprived them of thei
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