Berkeley - 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 an article in the April 16 issue of Proceedings of the National Academy of Sciences, University of California, Berkeley, developmental endocrinologist Tyrone B. Hayes, associate professor of integrative biology, and his colleagues 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.
As Hayes later 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," Hayes said. "Because it is so widespread, aquatic environments are at risk."
Because the herbicide has been in use for 40 years in some 80 countries, its effect on sexual development in male frogs could be one of many factors in the global decline of amphibians, he added.
The findings come at a time when the EPA is re-evaluating allowable levels of atrazine in drinking water, which stand today at 3 parts
Contact: Robert Sanders
University of California - Berkeley