For decades, farmers, lawn care workers and professional green thumbs have relied on the popular weed killer atrazine to protect their crops, golf courses and manicured lawns.
But atrazine often washes into water supplies and has become among the most common contaminants in American reservoirs and other sources of drinking water.
Recent studies suggest that, even at concentrations meeting current federal standards, the chemical may be associated with birth defects, low birth weights and menstrual problems.
Laboratory experiments suggest that when animals are exposed briefly to atrazine before birth, they may become more vulnerable to cancer later.
An investigation by The New York Times has found that in some towns, atrazine concentrations in drinking water have spiked, sometimes for longer than a month. But the reports produced by local water systems for residents often fail to reflect those higher concentrations.
EPA cites studies
Representatives of the Environmental Protection Agency and Syngenta, the company that manufactures most of the atrazine sold, say that current federal standards are based on hundreds of studies showing Americans are safe. In a written statement, the EPA said that it applied large safety buffers in regulating atrazine and continued to monitor emerging science.
But the head of another government agency voiced apprehension.
"I'm very concerned about the general population's exposure to atrazine," said Dr. Linda S. Birnbaum, director of the National Institute of Environmental Health Sciences, a division of the Department of Health and Human Services. "We don't really know what these chemicals do to fetuses or prepubescent children."
Atrazine, which is sold under brand names including AAtrex, is most commonly used on corn. But it can also be found on lawns, gardens, parks and golf courses.