WASHINGTON - The Environmental Protection Agency is embroiled in several fierce legal and scientific debates as it struggles to write new rules governing the use of atrazine, one of the nation's most widely used herbicides.
The chemical, used to banish weeds from cornfields in the Midwest and residential lawns in the Southeast, has been linked in studies to cancer in humans and to deformities in frogs that caused them to grow both testes and ovaries. It is banned in some European countries.
Now, the EPA acknowledges that the newly published research on frogs may force it to seek an extension of a court-ordered August deadline for issuing the rules.
Atrazine's major manufacturer, Syngenta AG of Switzerland, now says it will offer studies to rebut the frog research, and it continues to challenge many of the agency's findings as being too cautious. But environmental groups are making the opposite claim: that the agency is not being cautious enough.
Complicating matters further, a lawsuit against the company brought by factory workers who say they got prostate cancer after being exposed to the chemical has provided new ammunition for critics challenging the agency's decision two years ago to remove atrazine from its list of substances that probably cause cancer in humans.
One such group, the Natural Resources Defense Council, says it will file a petition with the EPA and the Justice Department tomorrow asking that the chemical be banned and that the company be investigated for not promptly disclosing the workplace cancers, as required by law.
"I think that the EPA has missed the boat on the cancer assessment completely, because they did not have available important information about its links to cancer," said Jennifer Sass, a senior scientist at the council, an advocacy group that specializes in litigation to enforce environmental laws.
Sass said that if the agency had considered those links, "there would be no safe levels" for use of atrazine.
Syngenta, which is the largest agribusiness company in the world, dismisses that argument. Tim Pastoor, who is in charge of global risk assessment for the company, said, "The notion that anyone would want to ban atrazine is silly." Pastoor said that scientific evidence proved atrazine to be safe as currently used and that the EPA, in its current reviews, was being far too conservative in its scientific approach. He said the reason so many workers at the company's factory were found to have prostate cancer was simply that the company intensively screens its workers for the disease.
The United States uses about 60 million pounds of atrazine a year, and its traces are found in the water supplies of many communities. But in preliminary reviews published this year, EPA scientists suggest that in most parts of the country people are not exposed to dangerous levels. That finding makes an outright ban unlikely.
But the EPA's top pesticide official, Stephen L. Johnson, said the research on frogs raised new issues, and added, "Given these conflicting results, we have to work through it."
The agency's critics say its scientific methods are fundamentally flawed and violate two federal laws - the Food Quality Protection Act and the Safe Drinking Water Act - that set strict standards and deadlines for reviewing the safety of hundreds of pesticides and other widely used chemicals.
Peter Lehner, chief of the environmental bureau in the New York state attorney general's office, said the state would file comments in June criticizing the agency's preliminary risk assessment and expressing concerns that the agency is not doing enough to protect the public from exposure. Public comments on the preliminary assessment are due by July 3.
"Legally, our concern is a pattern of EPA disregarding the science and the legal mandates of the federal statutes," said Lehner, adding that traces of the weedkiller had been found in 40 percent of the state's water supplies, 50 percent of those in Suffolk County and 75 percent of those in farming areas of the Hudson River valley.
Critics of atrazine note scientific evidence that infants and children may be especially vulnerable to developmental problems or to cancer if they or their nursing mothers are exposed even to relatively small amounts for a short time, as when spring rains wash the chemicals from newly tilled fields.
Syngenta replies that data on atrazine offer "reasonable certainty," as the law requires, that infants and children would suffer "no harm" from exposure to it. The EPA's health scientists, though, rejected that argument. Rather, while finding that in general most drinking water supplies appear safe, they identified dozens of towns, mostly in the Midwest, where infant exposures appeared likely to have exceeded the safety threshold. The towns were identified because in one year or another, seasonal rains had washed high levels of the chemical into streams, lakes and reservoirs used to supply drinking water.
The EPA's deliberations are especially complex because they are based on experiments with laboratory animals that imperfectly model the way chemicals like atrazine affect humans. Syngenta has been highly critical of the agency's use of the animal studies.
In the latest research to cause a stir, Tyrone B. Hayes, a scientist who had previously conducted research for the company that makes atrazine but who now works independently, has found that male frogs developed serious abnormalities after being exposed in his laboratory to levels of the herbicide much lower than the EPA considers safe in drinking water. Significant numbers of the frogs developed both male and female reproductive organs, a finding that he suggested might help explain declines in amphibian species around the world. His work was published in April in the Proceedings of the National Academy of Sciences.
Although several field studies have found associations between exposure to atrazine and similar herbicides and elevated incidence of several kinds of cancer, that kind of study alone does not prove cause and effect. The claims by workers that the chemical gave them cancer are hard to prove. Syngenta argues that the evidence of cancer among its workers was detected simply because the company provides complete screening for its work force.
Its studies on the workers' cancers were made public only recently, as a result of the litigation and of pressure on the EPA by the Natural Resources Defense Council, which learned of the studies from workers' attorneys.
Syngenta found that in the last several years 17 employees and contract workers, mostly at its plant in St. Gabriel, La., had developed prostate cancer. The workers' attorneys and the environmental group say that is much higher than should be expected, regardless of the screenings of workers.
An internal EPA review agreed with the company that screening "likely accounts for most, if not all, of the observed increase." But the EPA's scientists and two outside experts who examined the issue for the agency all found severe shortcomings in the company's studies, especially the lack of data provided on the exposure of workers to atrazine.