(Beyond Pesticides, March 3, 2010)
A recently published study in the Proceedings of the National Academy of Sciences finds that male frogs exposed to the herbicide atrazine can become so completely female that they can mate and lay viable eggs. This latest study adds to the growing scientific evidence which shows that atrazine, one of the most common herbicides used in the U.S., disrupts the development and behavior of aquatic animals, and negatively effects their immune, hormone, and reproductive systems.
The study, “Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis),” led by Tyrone Hayes, PhD, at the University of California, Berkeley, demonstrates the reproductive consequences of atrazine exposure in adult amphibians. Dr. Hayes and other researchers examined a group of 40 African clawed frogs, all of which carried male chromosomes. As tadpoles, the frogs were put in water with 2.5 parts per billion (ppb) of atrazine — a concentration within federal drinking water standards. Atrazine-exposed males were both demasculinized (chemically castrated) and completely feminized as adults. Exposed genetic males developed into functional females that copulated with unexposed males and produced viable eggs. The eggs produced were all male offspring since both parents contributed male genes. When competing for female frogs’ attentions, atrazine-treated males frequently lost out to males that had not been treated. Atrazine-exposed males suffered from depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility. According to the researchers, these data are consistent with effects of atrazine observed in other vertebrate classes.
“It’s a chemical . . . that causes hormone havoc,” Dr. Hayes said. “You need to look at things that are affecting wildlife, and realize that, biologically, we’re not that different.”
Atrazine is the most commonly detected pesticide contaminant of ground, surface, and drinking water. Atrazine is also a potent endocrine disruptor that is active at low, ecologically relevant concentrations. Previous studies showed that atrazine adversely affects amphibian larval development. The U.S. Environmental Protection Agency (EPA), which re-approved the use of atrazine in 2006 concluding that there was no evidence atrazine was causing adverse impacts on the amphibians’ development, initiated a new evaluation of its potential health effects after well-publicized reports and a New York Times investigative piece found EPA’s regulations of atrazine in water to be insufficient. Even at levels considered “safe” by EPA drinking water standards, atrazine is linked to endocrine-disrupting effects. Other research by Dr. Hayes and others demonstrates that exposure to doses of atrazine as small as 0.1 parts per billion, turns tadpoles into hermaphrodites – creatures with both male and female sexual characteristics.
Atrazine has also been implicated in a study as a possible cause for male infertility, blocking the action of the male sex-hormone testosterone and could impact the development of male reproductive organs in humans. In yet another study last year by Rick Relyea, PhD, an associate professor of biological sciences in the University of Pittsburgh’s School of Arts and Sciences, a mixture of small amounts of ten of the most commonly used pesticides, including atrazine killed 99 percent of the leopard frog tadpoles that he was testing.
Studies from 2007, done by researchers at the Centers for Disease Control and Prevention (CDC), have determined that previous studies that assessed population-based exposure to atrazine were significantly and systematically underestimated. With the growing proof of the negative effects of atrazine, levels of exposure must be properly monitored and accounted for. Public health advocates have argued that exposure to atrazine should be eliminated entirely through its cancellation.
According to EPA, agency staff will evaluate the pesticide’s potential cancer and non-cancer effects on humans. Included in this new evaluation will be the most recent studies on atrazine and its potential association with birth defects, low birth weight, and premature births. Steve Owens, EPA’s Assistant Administrator for Prevention, Pesticides and Toxic Substances said, “Our examination of atrazine will be based on transparency and sound science, including independent scientific peer review, and will help determine whether a change in EPA’s regulatory position on this pesticide is appropriate.” During the new evaluation, EPA says it will consider the potential for atrazine cancer and non-cancer effects, and will include data generated since 2003 from laboratory and population studies. EPA will also seek advice from the Scientific Advisory Panel (SAP) established under the Federal Insecticide, Fungicide and Rodenticide Act.
In the Washington, DC region, atrazine has been found in the Potomac, Monocacy and Shenandoah rivers, where investigators are trying to determine whether it is related to male bass in the Potomac found to be growing eggs. Atrazine is already banned in Europe. Based on scientific evidence, there is no need to continue with the use of atrazine, especially with so many alternatives for pest management. For examples, see our Lawns and Landscapes page and our Organic Food page. For further information on this issue, please see our Threatened Waters page.
The Washington Post