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Most Common Corn Herbicide Causes Sex Changes in Frogs
Field study finds deformed frogs
UC Berkeley prof's research links pesticide to abnormalities

San Francisco Chronicle
October 31, 2002

The most widely used pesticide in the United States appears to be causing developmental defects in a common Midwestern frog, according to a new study that has sparked a high-stakes debate over a chemical long considered environmentally safe.

Led by UC Berkeley biologist Tyrone B. Hayes, the study is the first evidence from field studies to show a link between the controversial weed killer, called atrazine, and health problems in a native species of amphibian in the United States.

The research, a summary of which appears today in the journal Nature, is generating some fierce reactions from other scientists in the field.

In an unusual step, scientists on an industry-financed panel assembled to asses the latest research issued a written challenge this week to a longer version of Hayes' study appearing in the journal Environmental Health Perspectives.

For his part, Hayes said scientists who had been criticizing his work were motivated in part by their own financial interests, because many work as paid consultants or have had research financed by atrazine's manufacturer, the Swiss agribusiness giant Syngenta.

Observers say the battle may just be getting started and could seriously complicate a federal regulatory review of atrazine's safety.

"This is a classic scientific debate where the stakes are kind of high," said Richard Wenning, senior manager at Environ, a risk-assessment consulting firm in Emeryville that has advised the Swiss company. "Atrazine is such a huge product. So people are shooting at each other."

WEED KILLER WIDELY USED

Atrazine has been used commercially in the United States since the late 1950s. In 1999, an estimated 80 million pounds were applied to U.S. corn and soybean crops, as well as golf courses, orchards and lawns.

A long line of research suggests the chemical breaks down quickly in the environment and posed no particular danger, when used properly, to humans or animal health. Now, environmentalists are questioning the consensus view that atrazine is safe. The U.S. Environmental Protection Agency is reviewing the technical and regulatory issues.

Hayes, an associate professor of integrative biology at UC Berkeley, first gained wide attention in April when he reported laboratory findings that atrazine could disrupt hormones and alter the sexual traits of certain male frogs.

Citing that evidence, Hayes said the popular farm chemical might be causing some of the widely observed declines in U.S. amphibian populations. But other scientists noted that Hayes had only looked at one species of African clawed frog, which is not native to North America.

In the latest study, Hayes and colleagues went out into the field. They drew a straight line on the map from Iowa to Utah, sampling for atrazine levels in the environment and testing native leopard frogs (Rana pipiens) taken from eight locations along the line.

The researchers say they found high numbers of feminized male frogs in watersheds even lightly contaminated with atrazine. In the most extreme case, 92 percent of the male frogs had abnormal gonads in water with just 0.1 part per billion of the farm chemical. The EPA allows 3 parts per billion in drinking water.

Hayes speculates that lower doses of the chemical may actually be more harmful than higher doses. Heavy exposures may trigger biological defenses, he said, that allow the frogs to adapt, and in some cases thrive in watersheds contaminated with concentrated farm runoff.

This makes it difficult to find a conclusive cause-and-effect pattern in Hayes' data. Other scientists appear to be having difficulties replicating the Berkeley scientist's experiments.

RESEARCH CALLED PIONEERING

Some independent experts say Hayes deserves credit for pioneering research into the role of chemicals in aquatic environments -- even though his studies leave many important questions unanswered.

For example, natural hermaphrodites have been identified in some species of amphibians as early as the 1920s, decades before atrazine was introduced. And there is no clear evidence yet to show that the defects Hayes reported cause reproduction problems and population declines.

"These are preliminary papers that are setting the tone for other studies," said Andrew Blaustein, an ecologist at Oregon State University. "This is a wake-up call, one of the early wake-up calls. But his experiments are very well done and backed up with really good field survey data."

But biologist James A. Carr of Texas Tech University in Lubbock, Texas, and others on the industry-financed panel raised "serious concerns" about the Hayes study design and conclusions, including flawed statistical analysis and "major inconsistencies in the data."

Asked for comment on the latest study, a Syngenta spokeswoman said, "We concur with the panel's opinions."

An EPA official, who spoke on condition of anonymity, said the Hayes study was being examined along with continuing, mostly unpublished research at eight other universities. A special EPA science advisory panel is being convened sometime next year to examine all the evidence.

"We're in the middle of it," the EPA official said. "The Hayes study isn't the only thing we are looking at."

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