Common Weedkiller Causes Feminization of Frogs, Study Says

Male frogs exposed to atrazine, an herbicide commonly found in U.S. waters, can become completely feminized by the time they are adults, a new study says. The hormonal reversal can be so complete, in fact, that these frogs can mate with other male frogs and lay eggs, according to the report published in the Proceedings of the National Academy of Sciences. The weed killer, produced by Swiss-based Sygenta, was re-approved for use by the U.S. Environmental Protection Agency in 2006. But recent studies show the chemical may interfere with the hormone systems of fish, birds, rats, and frogs. The most recent research, conducted by scientists at the University of California at Berkeley, examined the effects on 40 African clawed frogs exposed to the chemical as tadpoles. While all of the frogs carried male chromosomes initially, about 10 percent became “functionally female” as they developed, and were able to produce viable eggs after mating, said Tyrone Hayes, the lead author. The other 90 percent retained male characteristics, but often had lower testosterone levels. “It’s a chemical… that causes hormone havoc,” Hayes said.