(June 20, 2003) On June 18, 2003, The New York Times reported that scientists from the Environmental Protection Agency (EPA) say there is "sufficient evidence" to conclude that the country's most widely used pesticide, atrazine, causes sexual abnormality in frogs. They are recommending that the agency conduct more research to understand atrazine's mechanisms and its broader impact on frog populations.
The scientists noted that there had been six studies involving three species of frogs that show a variety of defects, including frogs with both multiple testes and multiple ovaries, when exposed to the chemical. "Over several studies and environmental conditions and species, atrazine exposure did appear to be having some impact on gonadal effects," Tom Steeger, a scientist with the environmental agency's pesticide office, said on Tuesday in a presentation to an independent scientific panel convened here to assess atrazine's impact on amphibians.
Scientists hired by Syngenta, a major manufacturer of atrazine, said they did not draw the same conclusions from available research. But EPA scientists said many of the industry-sponsored studies had a variety of problems, including testing conditions that led to high mortality in their frogs. The four-day hearing by the panel, which ends on Friday, is an extension of EPA's nine-year review of whether atrazine poses unacceptable risks to the environment and to public health. Later this year, the panel will make recommendations to the agency on how to proceed.
Atrazine is the most commonly used weed killer in North America and can be found in rainwater, snow runoff and ground water, according to Tyrone B. Hayes of the University of California at Berkeley, head of one of the research teams responsible for the studies cited by EPA. Atrazine has been banned in seven European countries.
Dr. Hayes' team found that frogs were affected by atrazine at doses as small as 0.1 parts per billion (ppb), though up to 3ppb is permitted in drinking water by EPA. As the amount of atrazine increased, up to 20 percent of frogs exposed during their early development produced multiple sex organs or had both male and female organs. Many also had small, feminized larynxes. When asked if atrazine is also a threat to people at low levels, Dr. Hayes said he did not know, adding that unlike frogs, we're not in water all the time. "I'm not saying its safe for humans. I'm not saying it's unsafe for humans. All I'm saying is it makes hermaphrodites of frogs," he said.
In another study, Pennsylvania State University researcher Joseph Kiesecker found that pesticides, including atrazine, play a role in frog leg deformities. His findings suggest that pesticides severely weaken the immune system, making frogs much more susceptible to parasitic infection and deformities such extra and missing legs. Dr. Keisecker's study not only linked atrazine with weakened immune systems in frogs, but slower development and smaller size. The levels of atrazine used by the researchers were below EPA-recommended levels for safe drinking water. Dr. Keisecker commented, "Amphibians have become an important model system. We have to consider that factors that influence infection rates in frogs may also play a role in human diseases."
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