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The Environmental Protection Agency today reversed its stance on the potential hazards of atrazine, one of the most commonly-used herbicides in the country, saying it will re-examine how the chemical affects human health.

EPA officials said in a statement that the agency will take a close look at the weed-killer’s potential to cause cancer, as well as birth defects, low birth weight, and premature births. Agency scientists also will conduct research for the first time examining whether atrazine interferes with the hormone and reproductive systems of humans and amphibians.

The announcement marks a departure from the agency’s policies on atrazine during the Bush administration, when officials said that the concentrations of the herbicide measured in drinking water did not endanger public health. As recently as June, Steve Bradbury, deputy office director of the EPA’s office of Pesticide Programs, told the Huffington Post Investigative Fund “we have concluded that atrazine does not cause adverse effects to humans or the environment.”

Today, EPA spokesman Dale Kemery told the Investigative Fund, “This administration is taking a hard look at the atrazine decision made by the previous administration.”

As the Investigative Fund reported in a series of articles in August, the EPA failed to notify the public about data it had collected showing that atrazine has been found at levels above the federal safety limit in drinking water in at least four states. After the Investigative Fund analyzed and published the data, the EPA posted its data online and said it would continue to update it.

Atrazine, manufactured by the Swiss firm Syngenta, is primarily sprayed on cornfields and other major crops. The European Union has banned the use of atrazine, saying there was not enough information to prove its safety, and the EPA has long fielded criticism from environmental activists for allowing the chemical to remain on the market.

The EPA’s announcement of its new atrazine study follows a private September meeting between the EPA’s senior staff and the Senate Environmental and Public Works Committee, led by Sen. Barbara Boxer (D-Calif.) According to a senior staffer on the committee, Boxer’s team encouraged the EPA to open a new analysis of the risks of atrazine and to keep the public informed about the levels of the weed-killer in drinking water.

The committee plans to hold a hearing on atrazine and the EPA later this year, the staff member said.

The EPA said it will announce its specific plan for evaluating the effects of atrazine next month, and that the study would conclude in September 2010. Officials said the report also will include results from a National Cancer Institute Agricultural Health Study due next year.

“I think it is important for the EPA to evaluate the effects of atrazine on humans and I am very pleased to see that they are emphasizing transparency in this evaluation process,” said Jason Rohr, a specialist in ecotoxicology at the University of South Florida who served on the EPA’s atrazine panel this past spring. “Given atrazine’s consistent effects on freshwater vertebrates, it would not surprise me if a weight-of-evidence approach also revealed consistent effects on humans.”

In September, Rohr and colleagues published an article in the journal Environmental Health Perspectives examining more than 100 scientific studies of the weed-killer. They concluded that the chemical affected the developmental, behavioral, immune, hormone, and reproductive systems of aquatic animals.

That contrasted with an EPA statement in July, when the agency updated its Web site to say: “atrazine does not adversely affect amphibian gonadal development… and EPA believes that no additional testing is warranted to address this issue.”

“At the very least,” Rohr said, “the public should be notified when atrazine levels in their drinking water exceed the maximum contaminant level set by the EPA.”

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