Common Weed Killer Impacts Wildlife

TAMPA, Fla. (Sept. 28, 2009) – An analysis of more than 100 scientific studies conducted on atrazine, one of the world’s most common and controversial weed killers, reveals the chemical’s consistent ill effects on the development, behavior, immune, hormone and reproductive systems of amphibians and freshwater fish, USF researchers have concluded in a new study.

In a study published in the journal, Environmental Health Perspectives, USF assistant professor Jason R. Rohr and postdoctoral fellow Krista A. McCoy say the body of scientific research on the chemical shows that while atrazine typically does not directly kill amphibians and fish, there is consistent scientific evidence that it is negatively impacting their biology.  The authors conclude that these non-lethal effects must be weighed against the benefit of using the weed killer.

Atrazine was banned in Europe in 2004, but is still widely used in the United States and 80 other nations, making it one of the most commonly used herbicides in the world. It is also used in the Southeast and Florida where it is often used on lawns, golf courses, and in sugarcane agriculture.

The risk posed by atrazine to aquatic systems is presently being re-evaluated by the U. S. Environmental Protection Agency.

“Much of the controversy has centered on atrazine’s effects on endocrine and reproductive systems,” Rohr said. “The weight-of-evidence, however, suggests that atrazine regularly causes reproductive abnormalities and is an endocrine disruptor.”

Rohr and McCoy’s research examines the large body of scientific literature of the chemical’s effects on fish and amphibians and identified consistent trends in those studies’ findings.

“The value of our research is that it points out trends and general patterns for the benefit of researchers and policymakers who might not have the time or resources to wade through the extensive scientific literature, which varies in quality, on atrazine effects,” Rohr said.

Among Rohr and McCoy’s findings are:

• Atrazine reduced size of amphibians at or near metamorphosis in 19 of 19 studies.
• Atrazine elevated amphibian and fish activity in 12 of 14 studies, reduced anti-predator behaviors in six of seven studies, and reduced olfactory abilities for fish but not for amphibians.
• Atrazine was associated with a reduction in 35 of 43 immune function endpoints and with an increase in 13 of 16 infection endpoints.
• Atrazine altered at least one aspect of male frogs’ reproductive development in eight of 10 studies, and consistently affected gonadal function, altering spermatogenesis in two of two studies and sex hormone concentrations in six of seven studies.
• Effects of atrazine on fish and amphibian reproductive success, sex ratios, gene frequencies, populations, and communities remain uncertain.

“Perhaps most striking were the highly consistent reductions in animal growth and changes in animal behavior associated with atrazine”, Rohr said.  “Importantly, atrazine exposure also seems to be tipping the balance towards parasites and pathogens.  Our findings revealed that atrazine exposure frequently increases infection risk.”

Rohr and McCoy, however, offer two important caveats.  First, they warn against extrapolating their findings to humans because human exposure to atrazine is likely very different than the exposure of fish and amphibians.

Second, Rohr and McCoy’s study draws no conclusions on whether the U.S. should tighten restrictions or impose new regulations on atrazine.  Rather, they encourage that any decision be based on the costs and benefits of atrazine use and alternative strategies to weed control.

Nevertheless, the consistent effects of atrazine on several vital systems of fish and amphibians call for more critical evaluation of atrazine use, the researchers said.