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.
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.
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," said Dr. Fenton, a reproductive endocrinologist.
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.
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.
Atrazine has been banned in Europe, even in Switzerland, the home of manufacturer Syngenta.