Herbicide Scrambles Frogs' Sex Organs
Atrazine feminizes the amphibians
WEDNESDAY, Oct. 30, 2002 (HealthDayNews) -- When Froggy goes a courtin', he'd better hope there was no atrazine in his pond when he was a tadpole.
That's because the chemical, one of the world's most popular weed killers, scrambles the sexual development of male frogs, new research has found.
Atrazine stimulates the conversion of testosterone into estrogen, and has been shown to do this in not only amphibians but fish and mammals, too.
In earlier work, California scientists reported that atrazine exposure turned male African clawed frogs (Xenopus laevis) into hermaphrodites. This time, they repeated their experiment in wild leopard frogs (Rana pipiens), giving hatchlings various amounts of the pesticide.
"This is now a second species" in which the chemical causes sex organ changes, says Tyrone Hayes, a biologist at the University of California, Berkeley and leader of the research effort. In an upcoming paper, Hayes says, his group will demonstrate that exposure to atrazine "significantly" reduces fertility in African clawed frogs.
A report on the latest findings appears in tomorrow's issue of Nature.
Male leopard frog tadpoles exposed to atrazine developed egg cells in their testes, not true hermaphrodites but not normal, either. And they had stunted sex organs, too. None of the unexposed animals had egg cells in their testes, and only one had retarded gonad growth.
Taking to the field, Hayes' group found that frogs living in areas contaminated with atrazine were more likely to have reproductive anomalies than those where the pesticide wasn't present.
They saw no hermaphroditic frogs in locations where atrazine was absent, while sites with at least 0.2 parts per billion in water all had such creatures. In one area, 92 percent of the male leopard frogs collected had abnormal reproductive organs.
That site is on Wyoming's North Platte River, in a county that didn't record much sale of atrazine. However, the river is fed by streams rooted in Colorado that are tainted with the substance, the researchers say.
The U.S. Environmental Protection Agency (EPA) is in the process of reviewing atrazine's safety.
Theo Colborn, director of the wildlife and contaminants program at the World Wildlife Fund, says her group has been petitioning the EPA since the early 1990s to remove the chemical from the market because of its ability to addle hormones during species development.
Now, she says, the Berkeley group "has demonstrated here that there is definitely an interference with the hormonal instruction during development with these frogs."
The EPA's maximum safe threshold for atrazine in water is 3 parts per billion in tap water, 30 times higher than the level at which Hayes' group saw detrimental effects.
The EPA considers atrazine to be an unlikely carcinogen in humans. However, the agency has found evidence that short-term and long-term exposure to high amounts of the chemical may cause heart damage, eye trouble, muscle breakdown, weight loss and other health problems.
Farmers use more than 76 million pounds of atrazine a year in this country, covering roughly three-quarters of all U.S. corn acreage as well as other fields.
The Natural Resources Defense Council, an environmental group, says the herbicide has been banned in France, Germany and Italy because of its potential risks to people.
David Deegan, an EPA spokesman, says the agency is aware of Hayes' research on frogs and its scientists are reviewing the information as part of their risk assessment for atrazine. A preliminary draft of the document should be released in January, with a final version out in about a year, he says.
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