Research questions popular herbicide’s effect on frogs

By Robert Sanders, Public Affairs

Abnormal gonads in a male Xenopus frog, resulting from exposure to the herbicide atrazine. The frog has become a hermaphrodite, with both male and female sex organs. Tyrone Hayes photo, courtesy PNAS

24 April 2002 | 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, raising concerns about heavy use of the herbicide on corn, soybeans and other crops in the Midwest and around the world.

A restricted herbicide, atrazine is used primarily on crops, not around the home, and can be purchased and applied only by certified applicators.

Developmental endocrinologist Tyrone Hayes reporting in the April 16 issue of Proceedings of the National Academy of Sciences, said 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.

“Atrazine-exposed frogs don't have normal reproductive systems,” said Hayes, an associate professor of integrative biology. “The males have ovaries in their testes and much smaller vocal organs,” which are essential in calling potential mates.

The herbicide has been in use for four decades in some 80 countries. The findings come at a time when the EPA is re-evaluating allowable levels of atrazine in drinking water.

More than 60 million pounds of the herbicide were applied last year in the United States alone. Manufacturer Syngenta estimates that farmers use the herbicide to control weeds on about two-thirds of all U.S. corn and sorghum acreage.