Professor Finds Chemical Causes Developmental Problem in Frogs

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A UC Berkeley professor has concluded that the agricultural chemical atrazine may disrupt frog development at concentrations 30 times lower than those currently allowed by the Environmental Protection Agency.

More than 60 million pounds of the popular weed killer were applied to crops in the United States last year. Many countries in Europe have banned the chemical.

"There are people who say, 'Oh, it's just frogs,' because atrazine is such a big seller," said Tyrone Hayes, a UC Berkeley integrative biology professor and lead project scientist. "But it reduces biological diversity, and any aquatic organism might be at risk."

The chemical disrupts a key step in the normal sexual development cycle of frogs.

Such disruption led an alarming number of frogs in Hayes' experiment to mature with both male and female sex traits.

"(In females), testosterone is converted into estrogen by an enzyme," Hayes said. "Normally, a male would make testosterone and release it into the blood. When male frogs are exposed to atrazine, enzyme activity is induced that converts testosterone to estrogen and demasculinizes the frogs."

It is unknown whether these abnormalities affect fertility and birthrates among frogs.

The experimental findings were replicated 51 times to ensure their accuracy before they were published in yesterday's issue of the Proceedings of the National Academy of Sciences.

Atrazine has been used widely for years because its solubility in water makes it relatively harmless to humans.

"If you drank a jar full of atrazine, you would probably flush it all out," Hayes said.

But amphibians, which may live immersed in atrazine-contaminated water, are sensitive to an amount of the chemical smaller than one thousandth of a grain of salt.

EPA guidelines limit atrazine concentrations to 3 parts per billion in human drinking water. But they do not protect organisms like frogs, which may be sensitive to atrazine concentrations as low as 0.1 parts per billion.

"This is very important and

elegant work," said Theo Colburn, a World Wildlife Fund scientist, in a press release. "Tyrone's work demonstrates the need to do research on the safety of chemicals in the field where the animals live and at the levels to which they are exposed."

Initially, work done by Hayes and his team was funded by Syngenta, the maker of atrazine, at the EPA's behest. The recently published findings, however, were funded independently.

Three undergraduates were listed as co-authors of the atrazine study, underscoring the potential impact of such research opportunities on the Berkeley campus.

"This was my first research experience, and it was really rewarding working with Professor Hayes," said undergraduate researcher Melissa Lee. "When I came here, I knew he did developmental research, but I wasn't looking for frogs specifically. I sort of stumbled onto frogs."

Hayes and his research group are already beginning to look for future research directions.

"The next step is to look at fertilization and functional implications," Hayes said. "We're also looking at other species and mixtures of other compounds. The final step is to identify the genes involved in this process."


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