Researcher Links Agricultural Chemicals to Amphibian Declines

USF biologist Jason Rohr and colleagues, revealed that chemical pollution can increase often deadly trematode (parasitic flatworm) infections in a declining amphibian species.

Amphibians are on the decline around the world. In a recently released article in the journal Nature (Vol. 455 No. 7217 pp. 1235-1239), USF biologist Jason Rohr and colleagues, revealed that chemical pollution can increase often deadly trematode (parasitic flatworm) infections in a declining amphibian species. “The combination of atrazine, a widely used herbicide, and phosphate, a primary ingredient in fertilizers, accounted for 74 percent of the variation in larval trematode abundance in the frogs,” said Rohr, an assistant professor in the USF Department of Integrative Biology. “These agrochemicals increase trematode infections by augmenting snail intermediate hosts – the source of trematodes that infect amphibians – and suppressing amphibian immune responses.” The research was funded by National Science Foundation, the U.S. Department of Agriculture and Environmental Protection Agency grants. The task of identifying the main risk factors and predictors for disease in amphibians is important. The study showed that atrazine and phosphate concentrations in the Minnesota wetlands they investigated were the best of over 240 plausible predictors of trematode abundance in frogs. In a manipulative experiment conducted in outdoor, 300 gallon tanks, Rohr and colleagues verified that atrazine increased snail abundance, caused amphibian immuno-suppression and elevated amphibian trematode loads. “At concentrations commonly occurring in freshwater ecosystems, atrazine and phosphate can be drivers of amphibian trematode infections, raising concerns about the role of these chemicals in amphibian declines” concluded Rohr. “Reducing atrazine and phosphate inputs to wetlands might remediate these often debilitating amphibian trematode infections.” Amphibians are thought to be the “canaries” in our freshwater environments; reductions in their health can warn that subsequent species declines and degradation of ecosystem services might be in store. “Atrazine and fertilizers might not be the only chemicals affecting disease risk,” says Rohr. “Many chemicals can be immuno-suppressive and standard toxicity tests used to register chemicals in the United States and Europe are conducted on isolated individuals, ignoring interactions with other species, such as their parasites. Thus, our findings are likely the tip of the iceberg for pollution-induced disease emergence in both humans and wildlife.”