From Penn State News, "Study suggests link between agricultural chemicals and frog decline":
Around the world, amphibian populations are in decline, and scientists have not been able to figure out why. Now a study of leopard frogs in Pennsylvania has identified a possible culprit, and the ramifications are troubling, according to a Penn State ecologist.
Research conducted primarily at Penn State's Russell E. Larson Agricultural Research Center at Rock Springs in the summer of 2007 — described in a recently published article in the journal Nature — suggests that chemical pollution can increase often-deadly trematode (parasitic flatworm) infections in a declining amphibian species.
"Like canaries used to gauge the safety of air in coal mines, amphibians are thought to be the 'canaries' in our freshwater environments, and reductions in their health can warn that subsequent species declines might be in store," says Hunter Carrick, associate professor of aquatic ecology in Penn State's College of Agricultural Sciences, who was one of the lead investigators in the study.