USF Researcher Links Agricultural Chemicals to Amphibian Declines

TAMPA, Fla. (Oct. 29, 2008) – Around the world, amphibians are on the decline from disease. 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.

According to Rohr, identifying the main risk factors and predictors for disease in amphibians is important. Their 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.”

Like canaries used to gauge the safety of air in coal mines, 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.”

The University of South Florida is one of the nation's top 63 public research universities and one of 39 community-engaged, four-year public universities as designated by the Carnegie Foundation for the Advancement of Teaching. USF was awarded more than $360 million in research contracts and grants in FY 2007/2008. The university offers 219 degree programs at the undergraduate, graduate, specialist and doctoral levels, including the doctor of medicine. The university has a $1.8 billion annual budget, an annual economic impact of $3.2 billion, and serves more than 46,000 students on campuses in Tampa, St. Petersburg, Sarasota-Manatee and Lakeland. USF is a member of the Big East Athletic Conference.

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