Atrazine, a weed killer widely used in the Midwestern United States and other agricultural areas of the world, can chemically castrate" male frogs and turn some into females. New research suggests the herbicide may be a cause of amphibian declines around the globe, said biologists at the University of California-Berkeley. Researchers found that long-term exposure to low levels of atrazine - 2.5 parts per billion of water - emasculated three-quarters of laboratory frogs and turned one in 10 into females. Scientists believe the pesticide interferes with endocrine hormones, such as estrogen and testosterone. "The effects of atrazine in the long term have been shown to demasculinize or chemically castrate [frogs], combined with complete feminization of some animals," said lead researcher Tyrone B. Hayes, a biologist and herpetologist. Hayes found that 10 percent of the exposed genetic male frogs developed into functional females who copulated with unexposed males and produced viable eggs. The other 90 percent of the exposed male frogs expressed decreased libido, reduced sperm count and decreased fertility, among other findings. Tens of millions of pounds of atrazine are used each year in the United States. Syngenta estimates that 60 million pounds were used during 2008, most of it on corn. A 2006 study by the U.S. Geological Survey found atrazine in approximately 75 percent of stream water and about 40 percent of all groundwater samples from agricultural areas tested between 1992 and 2001.