The nation's top-selling weed killer, atrazine, disrupts the sexual development of frogs at concentrations 30 times lower than levels allowed by the Environmental Protection Agency (EPA), raising concerns about heavy use of the herbicide on corn, soybeans and other crops in the Midwest and around the world.
In the April 16 issue of Proceedings of the National Academy of Sciences, developmental endocrinologist Tyrone Hayes and colleagues from the University of California, Berkeley, report that atrazine at levels often found in the environment demasculinizes tadpoles and turns them into hermaphrodites creatures with both male and female sexual characteristics. The herbicide also lowers levels of the male hormone testosterone in sexually mature male frogs by a factor of 10, to levels lower than those in normal female frogs. The research was funded by the National Science Foundation (NSF).
"Researchers are investigating a number of possible causes for declining populations of amphibians, said William Zamer, program director in NSF's division of integrative biology and neuroscience, which funded the research. Hayes and colleagues appear to have identified another potential agent. Their findings indicate that atrazine has significant endocrinological effects on frogs at very low doses."
As Hayes discovered, many atrazine-contaminated ponds in the Midwest contain native leopard frogs with the same abnormalities. Atrazine-exposed frogs don't have normal reproductive systems," he said. "The males have ovaries in their testes and much smaller vocal organs," which are essential in calling potential mates. It is unclear whether these abnormalities lead to reduced fertility. Hayes now is trying to determine how the abnormalities affect the frogs' ability to produce offspring.
"The use of atrazine in the environment is basically an
uncontrolled experiment - there seems to be no atrazine-free environment," Ha
Contact: Cheryl Dybas
National Science Foundation