Atrazine is a widely used herbicide. Its use is controversial due to widespread contamination in drinking water and its associations with birth defects and menstrual problems when consumed by humans at concentrations below government standards. Although it has been banned in the European Union, it is still one of the most widely used herbicides in the world. An international team of researchers has reviewed the evidence linking exposure to atrazine — an herbicide widely used in the U.S. and more than 60 other nations — to reproductive problems in animals. The team found consistent patterns of reproductive dysfunction in amphibians, fish, reptiles and mammals exposed to the chemical. The researchers looked at studies linking atrazine exposure to abnormal androgen (male hormone) levels in fish, amphibians, reptiles and mammals and studies that found a common association between exposure to the herbicide and the feminization of male gonads in many animals.
Atrazine is used to stop pre- and post-emergence broadleaf and grassy weeds in major crops. The compound is both effective and inexpensive, and thus is well-suited to production systems with very narrow profit margins, as is often the case with maize.
Its effect on yields has been estimated from 6% to 1%, with 3-4% being the conclusion of one review. In another study looking at combined data from 236 university corn field trials from 1986—2005, atrazine treatments showed an average of 5.7 bushels more per acre than alternative herbicide treatments.
Atrazine was banned in the European Union in 2004 because of its persistent groundwater contamination. In the United States, however, atrazine is one of the most widely used herbicides, with 76 million pounds of it applied each year, in spite of the restriction that used to be imposed. Its endocrine disruptor effects, possible carcinogenic effect, and epidemiological connection to low sperm levels in men has led several researchers to call for banning it in the US.
Beasley’s lab was one of the first to find that male frogs exposed to atrazine in the wild were more likely to have both male and female gonadal tissue than frogs living in an atrazine-free environment. And in a 2010 study, Tyrone Hayes, a professor of integrative biology at the University of California at Berkeley and lead author of the review, reported in the Proceedings of the National Academy of Sciences that atrazine exposure in frogs was associated with genetic males becoming females and functioning as females, Beasley said.
The new review describes the disruptions of hormone function and sexual development reported in studies of mammals, frogs, fish, reptiles and human cells exposed to the herbicide. The studies found that atrazine exposure can change the expression of genes involved in hormone signaling, interfere with metamorphosis, inhibit key enzymes that control estrogen and androgen production, skew the sex ratio of wild and laboratory animals (toward female) and otherwise disrupt the normal reproductive development and functioning of males and females.
"One of the things that became clear in writing this paper is that atrazine works through a number of different mechanisms," Hayes said. "It’s been shown that it increases production of (the stress hormone) cortisol. It’s been shown that it inhibits key enzymes in steroid hormone production while increasing others. It’s been shown that it somehow prevents androgen from binding to its receptor."
There also are studies that show no effects — or different effects — in animals exposed to atrazine, Beasley said. "But the studies are not all the same. There are different species, different times of exposure, different stages of development and different strains within a species." All in all, he said, the evidence that atrazine harms animals, particularly amphibians and other creatures that encounter it in the water, is compelling.
For further information: http://news.illinois.edu/news/11/1128atrazine_ValBeasley.html