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News Release 08-188

Researcher Links Agricultural Chemicals to Infections in a Declining Amphibian Species

A fertilizer and herbicide are partly to blame

Photo of an adult leopard frog.

An adult leopard frog.

October 29, 2008

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.

Amphibians around the world are on the decline from disease. In an article in this week's issue of the journal Nature, Jason Rohr of the University of South Florida (USF) and colleagues revealed that chemical pollution can increase often deadly trematode (parasitic flatworm) infections in the northern leopard frog, 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. "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 (NSF) and U.S. Department of Agriculture grants.

According to Rohr, identifying the main risk factors and predictors for disease in amphibians is important.  This 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 of subsequent species declines and degradation of ecosystem services.

"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 spread of infectious disease and loss of biodiversity are each a serious challenge to scientists seeking a fundamental understanding of ecological systems, and to policy makers charged with protecting the environment," said Alan Tessier, an NSF program director. "Rohr and his colleagues demonstrate how both of these phenomena are linked to the widespread use of a common agrochemical in the case of a declining amphibians species. This work illustrates how predicting anthropogenic impacts requires a fundamental understanding of the complexity of species interactions embedded within food webs."


Media Contacts
Lara Wade, University of South Florida, (813) 974-9060, email:
Lily Whiteman, National Science Foundation, (703) 292-8310, email:

Program Contacts
Alan Tessier, National Science Foundation, (703) 292-7198, email:

Principal Investigators
Jason Rohr, University of South Florida, (813) 974-0156, email:

The U.S. National Science Foundation propels the nation forward by advancing fundamental research in all fields of science and engineering. NSF supports research and people by providing facilities, instruments and funding to support their ingenuity and sustain the U.S. as a global leader in research and innovation. With a fiscal year 2020 budget of $8.3 billion, NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and institutions. Each year, NSF receives more than 40,000 competitive proposals and makes about 11,000 new awards. Those awards include support for cooperative research with industry, Arctic and Antarctic research and operations, and U.S. participation in international scientific efforts.

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