RESEARCH TRIANGLE PARK, North Carolina - Male rats exposed before birth to low doses of the weedkiller atrazine are more likely to develop prostate inflammation and to go through puberty later than non-exposed animals, finds a new study conducted by federal government scientists.

Atrazine is sprayed on an Iowa cornfield. (Photo credit unknown) One of the most common agricultural herbicides in the United States, some 80 million pounds of atrazine are applied across the country every year to control broadleaf and grassy weeds in crops such as corn and sugar cane. It is the main ingredient in about 40 name-brand herbicides.

"Atrazine is a staple product for producers, who use it as a critical tool for weed control in growing the vast majority of corn, sorghum and sugarcane in the United States. Use of atrazine fights weed resistance, reduces soil erosion and increases crop yield," according to the Triazine Network, an association of growers and researchers.

But atrazine and its byproducts are known to be endocrine disrupters that are persistent in the environment, making their way into both surface water and groundwater supplies.

This study on how atrazine affects male rats was led by Suzanne Fenton, PhD, and Jason Stanko, PhD, of the National Institute of Environmental Health Sciences, part of the National Institutes of Health. The scientists tested male rats using atrazine concentrations close to the regulated levels in drinking water sources.

The current maximum contamination level of atrazine allowed in drinking water is three parts per billion.

"We didn't expect to see these kinds of effects at such low levels," Fenton said, releasing the findings Tuesday.

Dr. Fenton, a reproductive endocrinologist, will be presenting the research findings in September to the U.S. Environmental Protection Agency, as part of its ongoing reassessment of atrazine.

In 2009, the EPA began a comprehensive new evaluation of atrazine to determine its effects on humans. At the end of this process, in September 2010, the agency has said it will decide whether to revise its current risk assessment of atrazine and whether new restrictions are necessary to better protect public health.

This is the third time since the early 1990s the EPA has evaluated atrazine. In each of the two previous reviews the EPA ruled in atrazine's favor, most recently in 2006 after considering 6,000 studies and 80,000 public comments.

"We hope that this information will be useful to the EPA, as it completes its risk assessment of atrazine," said Linda Birnbaum, Ph.D., director of the National Institute of Environmental Health Sciences and the National Toxicology Program.

Fenton began the work as a researcher at the EPA, but completed the research at NIEHS, working closely with NIEHS pathologists. Both agencies provided financial support for the study.

The researchers found that the incidence of prostate inflammation went from 48 percent in the control group of rats to 81 percent in the male offspring who were exposed to a mixture of atrazine and its breakdown products before birth. The severity of the inflammation increased with the strength of the doses.

"It was noteworthy that the prostate inflammation decreased over time, suggesting the effects may not be permanent," said David Malarkey, DVM, PhD, an NIEHS pathologist and co-author on the paper.

The scientists also found that puberty was delayed in the animals who exposed to atrazine.

This new study is Fenton's second paper showing low dose effects of atrazine metabolite mixtures.

Fenton was the senior author on a 2007 paper which demonstrated low doses of the atrazine mix delayed mammary development in female siblings from the same rat litters used in this current study.

Fenton points out that these findings may extend beyond atrazine alone, and may be relevant to other herbicides found in the same chlorotriazine family, including propazine and simazine. All three of the herbicides create the same set of breakdown products.

Fenton says more research is needed to understand the mechanism of action of the chlorotriazines and their metabolites on mammary and prostate tissue.

"These tissues seem to be particularly sensitive to the effects of atrazine and its breakdown products," Fenton said. "The effects may be due to the stage of fetal development at the time the animals were exposed."

Another point of view on the safety of atrazine and the related chemicals comes from the Triazine Network. A five-person executive committee leads the network: Jere White, chairman, Kansas Corn Growers and Kansas Grain Sorghum Producers Associations; Dan Botts, Florida Fruit and Vegetable Association; Joel Nelsen, California Citrus Mutual, Stephanie Whalen, Hawaii Agriculture Research Center, and Gary Marshall, Missouri Corn Growers Association.

In a letter to EPA Administrator Lisa Jackson, the Triazine Network argues that atrazine is safe and necessary to growers.

The growers say they are "increasingly concerned by the serious irregularities in the EPA's current re-review of the herbicide atrazine."

"No one cares more about the safety of the herbicide atrazine than those of us who use it in the fields where we raise our families," says the letter, signed by White. "We drink the local water. We swim and fish in local lakes, rivers, and ponds. We look forward to passing our way of life onto our children and grandchildren. Simply stated, we care about keeping our environment healthy and our foods safe and abundant."

"Atrazine and its companion triazine herbicides have a 50-year history as safe and effective weed-control products used on more than 30 commodities in over 40 states and 60 countries," the growers state in their letter.

"Five decades of continued and rigorous EPA testing has shown time and again that atrazine poses no danger to public health. Over the last half century, more than 6,000 atrazine studies have been submitted to EPA. These studies confirmed, and EPA agreed, that atrazine does not affect human health," the letter asserts.

"EPA's current 3 parts per billion limit for lifetime exposure or the 298 ppb limit for short-term exposure, are standards that are more than 1,000 times safer than a level shown to have no effect," maintains the Triazine Network.

But Professor Tyrone Hayes in the Department of Integrative Biology at the University of California, Berkeley, who specializes in the study of atrazine, calls the chemical, "a potent endocrine disruptor with ill effects in wildlife, laboratory animals and humans."

"Atrazine chemically castrates and feminizes wildlife and reduces immune function in both wildlife and laboratory rodents," says Hayes, who has published research showing that exposure to atrazine caused male tadpoles to turn into hermaphrodites - frogs with both male and female sexual characteristics.

"Atrazine induces breast and prostate cancer, retards mammary development and induces abortion in laboratory rodents," Hayes warns. "Studies in human populations and cell and tissue studies suggest that atrazine poses similar threats to humans."

Other scientists support the use of atrazine when it is used correctly. Purdue University weed scientist Bill Johnson says, "Farmers need to understand both the rate restrictions of atrazine for different soil types and the setbacks from water sources. Like any chemical, they shouldn't apply atrazine right before a big rain in order to prevent runoff."

Other safe-handling techniques include establishing 66-foot grass buffer strips along bodies of water and ditches to help filter out atrazine from water flowing across fields and choosing crops that don't require the use of atrazine when planting near water sources.

"There are a lot of herbicides labeled for corn, but only a select few control as many weeds at as low a cost as atrazine," Johnson said. "Herbicides with more narrow spectrums drive up costs and eliminate the simplicity atrazine offers."

But in March, 16 communities in six Midwestern states filed a federal lawsuit seeking to force atrazine manufacturer, the Swiss company Syngenta, to pay for removal of the herbicide from their drinking water. The class action lawsuit was filed in U.S. District Court for the Southern District of Illinois by 16 towns and villages in Kansas, Illinois, Indiana, Ohio, Missouri, and Iowa.

Atrazine has been banned in Europe, even in Switzerland, the home of manufacturer Syngenta.

Click here for more information about the EPA risk assessment.