Poisoning Frogs

Are People Next?

Despite new findings by the University of California, Berkeley, which link the pesticide atrazine to sexual mutations in frogs, the Environmental Protection Agency (EPA) is considering a three- to four-fold increase for atrazine standards in drinking water.

If passed, the acceptable level of atrazine could rise from three parts per billion (ppb) to as high as 12 ppb. This new level would be 120 times higher than the concentration that UC Berkeley developmental endocrinologist Tyrone B. Hayes has found to mutate frogs in the environment.

The pesticide atrazine turned African clawed frog tadpoles into hermaphrodites.© AP Photo / Daily Oklahoman / David McDaniel

The raise was proposed last year and was based on findings that atrazine, once classified as a human carcinogen, is not as dangerous as previously thought. Nationally, atrazine is the second most common pesticide found in private and community wells and has been a popular, affordable chemical among farmers since the 1960s.

In Hayes" study, African clawed frog tadpoles exposed to levels of atrazine commonly found in the environment were demasculinized and turned into hermaphrodites—creatures with both male and female genitalia. Atrazine also lowered male frogs" testosterone levels to below that of female frogs and reduced the size of their vocal chords, which are used to call potential mates. Sixteen percent of the animals experienced such effects at atrazine levels as low as .1 ppb. No control animals exhibited such abnormalities.

Hayes says these effects bring the environmental costs of atrazine into serious question. He says atrazine might be one of the factors contributing to the global decline of amphibians. Although he doubts atrazine has as severe an effect on humans, who do not spend their lives in the water, he says the pesticide might subtly affect human sex hormones.

Previous debate, centering on the notion that atrazine was a human carcinogen, stemmed from studies in which Sprague-Dawley rats developed mammary-gland tumors after being exposed to the pesticide. Amal Mahfouz, a chemical manager for atrazine with the EPA’s Office of Water, says that the mammary tumors were later found to be strain-specific to Sprague-Dawley rats, which are frail.

The EPA is just beginning to consider the Berkeley findings, with a regulatory decision expected by late January. Catherine Eiden, a risk assessor at the EPA Office of Pesticide Programs, says that although she does not know what effect the new data will have on the committee’s decision, "It certainly has gotten our attention."