Washington - A new study shows that male frogs exposed to the herbicide atrazine - commonly found in U.S. rivers and streams - can make a startling developmental U-turn, turning female so completely that they can mate with other males and lay viable eggs.
The study will focus new attention on concerns about atrazine, which is applied to an estimated 75 percent of American cornfields. Its manufacturer, the Swiss agricultural giant Syngenta, says the product is safe for wildlife, and for people who are exposed to small amounts in drinking water.
In recent years, however, some studies have seemed to show that atrazine can drive natural hormone systems haywire in fish, birds, rats and frogs. In some cases, male animals exposed to the chemical developed female characteristics.
The study led by Tyrone Hayes, a professor at the University of California, was published in the Proceedings of the National Academy of Sciences. It showed an even starker transformation: Among a group of male African clawed frogs raised in water tainted with atrazine, he said, a fraction grew up to look and act like females.
"Ten percent of the chromosomal males become completely, functionally female," Hayes said in a telephone interview. "They can lay eggs (and) they mate with other males."
The offspring of those unions were all male, he said, since both parents were genetically male. No female frogs were treated with atrazine in the study.
The other 90 percent of the exposed frogs retained some male features, Hayes said, but often showed signs of "feminization," including lower testosterone levels and fertility. When pitted head-to-head against males that had not been exposed to atrazine, the atrazine-treated males frequently lost out in competition for female frogs.
Hayes said the reason for these changes could be that atrazine, when absorbed through a frog's skin, helps produce an enzyme that converts an unusual amount of testosterone into estrogen.
Those findings run counter to the U.S. Environmental Protection Agency's pronouncement in 2007 that atrazine does not cause problems in amphibian development.
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Belongs to a large group of herbicides that were used in Europe, rather much, two to four decades ago or so.
I remember, we banned the last ones in Norway, in the early 1990'ies. So did the EU countries. It was toxicology for some of them, for others it was persistence in the environment. Of course, there are still residues in ground water, and soil. But, they have long since been taken out of use in Europe.
Do you still polute your environment with them?