Hermaphrodite Frogs Caused By Popular Weed Killer?

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"Tyrone's work shows the lack of sensitivity of current testing protocols," says Theo Colborn, a senior scientist at the World Wildlife Fund. "We really don't know how to test chemicals properly. Tyrone's work shows that low dose exposure during development can have insidious hidden effects that can change the chemistry of the animal and significantly affects its development."

"Frogs are vertebrates like us and have similar endocrine systems—that is they use the same hormones to control development," says David Wake, an amphibian biologist at Berkeley. "Hayes' work is excellent. We must assume that his findings have relevance for us."

It is too early to say whether atrazine is responsible for the global decline in amphibian populations, but both Colborn and Wake agree that it is an angle that needs to be pursued.

"What is most disturbing," adds Wake, "is that the effects are manifested at extraordinarily low concentrations of atrazine—almost what you get from rainwater."

Atrazine can be as high as 21 ppb in groundwater, 102 ppb in river basins in agricultural areas, and 224 ppb in streams in the Midwest. There is virtually no atrazine-free environment, says Hayes, who adds that the herbicide has been used for 40 years in over 80 countries.

But not everyone agrees with Hayes' results.

"We have repeated Hayes' work and have seen effects only at levels of 25 ppb," says Ernest Smith, a biologist at the Institute of Environmental and Human Health at Texas Tech University. Smith says that at concentrations below 25 ppb neither he nor his colleagues observed abnormal numbers of testes or ovaries. And at no levels did they see any effects on the larynx.

In contrast with Hayes' study, Smith found that tadpoles exposed to 25 ppb atrazine caused abnormalities in only 4 or 5 percent of adults.

"Dr. Hayes' study is what it is," says John Giesy, an aquatic toxicologist at Michigan State University. Giesy is currently examining the effects of atrazine on adult frogs and investigating whether the pesticide affects their survival, growth and reproductive capabilities.

Both Smith and Giesy's studies were partially funded by Syngenta, the manufacturer of the herbicide. Syngenta also funded Hayes' studies until November 2000, when he decided to pursue the work independently.

Field studies have begun in regions of South Africa where atrazine has been used, and also planned for Michigan and Iowa where the herbicide is used extensively on corn and sorghum crops.

Both Giesy and Smith were present at a panel discussion held today by the EPA to review recent research on atrazine and re-evaluate allowable levels in drinking water. The EPA is required to make a final decision on the regulation of atrazine by August 5, 2002.

This story will be reported on National Geographic Today tonight.

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