The UC Berkeley scientists also showed that male leopard frogs raised in laboratory tanks contaminated with atrazine develop egg cells in their testes and essentially turn into hermaphrodites. These sexual abnormalities were observed at atrazine levels as low as 0.1 parts per billion (ppb), 30 times lower than the current allowable limit for atrazine in drinking water set by the Environmental Protection Agency.
These findings, added to earlier evidence that atrazine demasculinizes two other species of frog, suggest that the herbicide could be a factor in the decline of frogs and other amphibians in the United States and around the world, the authors say. Atrazine has been used on crops since 1956 and currently is the most widely used herbicide in the nation.
"These studies clearly indicate that atrazine is detrimental to amphibians," said study author Tyrone Hayes, associate professor of integrative biology at UC Berkeley.
At the least, he said, atrazine is altering amphibian populations in large areas of the United States. His field studies show that frogs seem to adapt, since leopard frogs (Rana pipiens) - the most common frogs in the Midwest - are often abundant in some of the corn growing areas region where atrazine is used most. Atrazine may feminize male tadpoles and turn them into female frogs, he said, or it may render some males infertile. Alternatively, atrazine may favor tadpoles that delay sexual differentiation until after they've turned into frogs and leave the contaminated water.
"Atrazine is potentially destroying biodiversity," said Hayes, now engaged in studies to determine the ultimate fate
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
30-Oct-2002