tadpoles of the African clawed frog, Xenopus laevis--the lab rat of amphibians-in water with levels of atrazine varying from 0.01 to 200 parts per billion (ppb). The EPA standard is 3 ppb. At and above 0.1 ppb, 16% to 20% of the animals developed up to six gonads, including both testes and ovaries. In male adult frogs exposed to 25 ppb of atrazine, testosterone levels dropped 10-fold, to levels found in females. "This study is ground-breaking," says Val Beasley, an ecotoxicologist at the

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... ity of Illinois, Urbana-Champaign. It may well "give us an important piece of the puzzle of amphibian declines," adds James Collins of Arizona State University in Tempe. Atrazine concentrations used in the study are frequently encountered in the wild, affirms U.S. Geological Survey hydrologist William Battaglin. Atrazine is routinely present in streams, rivers, and reservoirs in the central portion of the United States at levels of 1 to 10 ppb in spring; peaks of 100 to 200 ppb have been recorded. Airborne atrazine is brought to earth in rainfall, sometimes at concentrations above 1 ppb. Because the herbicide is most often applied in the spring, its runoff peaks just as frogs are breeding and tadpoles developing-often in ditches and pools near agricultural fields. Because Hayes and colleagues found no effects on mortality, growth rate, or external appearance, they argue that endocrine abnormalities might easily occur in the wild unnoticed. But critics point out . e that the current study doesn't reveal whether the abnormalities affect reproductive ability. It's also not clear whether atrazine-induced damage would lead to decreases in amphibian numbers. EPA biologist William Rabert adds that wildlife studies must demonstrate negative effects on populations before the agency will consider regulatory action. As useful as Xenopus is in the lab, conservationists aren't trying to protect it, so Hayes and his group have been studying wild frogs in North America. Their unpublished data suggest that in northern leopard frogs the effects of atrazine are "even more dramatic than what we see in Xenopus," Hayes says. Lab work with this species has shown similar gonadal effects, and field collections across the United States reveal that frogs in areas of high atrazine use show more endocrine damage than those in areas devoid of the chemical, he says. Hayes and colleagues suggest that atrazine disrupts the endocrine system in a different way from compounds known to mimic hormones. They propose that atrazine activates the enzyme aromatase, which converts andro-tadpoles of the African clawed frog, Xenopus laevis--the lab rat of amphibians-in water with levels of atrazine varying from 0.01 to 200 parts per billion (ppb). The EPA standard is 3 ppb. At and above 0.1 ppb, 16% to 20% of the animals developed up to six gonads, including both testes and ovaries. In male adult frogs exposed to 25 ppb of atrazine, testosterone levels dropped 10-fold, to levels found in females. "This study is ground-breaking," says Val Beasley, an ecotoxicologist at the University of Illinois, Urbana-Champaign. It may well "give us an important piece of the puzzle of amphibian declines," adds James Collins of Arizona State University in Tempe. Atrazine concentrations used in the study are frequently encountered in the wild, affirms U.S. Geological Survey hydrologist William Battaglin. Atrazine is routinely present in streams, rivers, and reservoirs in the central portion of the United States at levels of 1 to 10 ppb in spring; peaks of 100 to 200 ppb have been recorded. Airborne atrazine is brought to earth in rainfall, sometimes at concentrations above 1 ppb. Because the herbicide is most often applied in the spring, its runoff peaks just as frogs are breeding and tadpoles developing-often in ditches and pools near agricultural fields. Because Hayes and colleagues found no effects on mortality, growth rate, or external appearance, they argue that endocrine abnormalities might easily occur in the wild unnoticed. But critics point out . e that the current study doesn't reveal whether the abnormalities affect reproductive ability. It's also not clear whether atrazine-induced damage would lead to decreases in amphibian numbers. EPA biologist William Rabert adds that wildlife studies must demonstrate negative effects on populations before the agency will consider regulatory action. As useful as Xenopus is in the lab, conservationists aren't trying to protect it, so Hayes and his group have been studying wild frogs in North America. Their unpublished data suggest that in northern leopard frogs the effects of atrazine are "even more dramatic than what we see in Xenopus," Hayes says. Lab work with this species has shown similar gonadal effects, and field collections across the United States reveal that frogs in areas of high atrazine use show more endocrine damage than those in areas devoid of the chemical, he says. Hayes and colleagues suggest that atrazine disrupts the endocrine system in a different way from compounds known to mimic hormones. They propose that atrazine activates the enzyme aromatase, which converts androgens to estrogen. "The testes have been coopted by atrazine to make the wrong thing," gens to estrogen. "The testes have been coopted by atrazine to make the wrong thing," NEWS OF THE WEEK Hayes explains. Reproductive biologist Louis Guillette of the University of Florida, Gainesville, and his students first demonstrated this mechanism in atrazine-exposed alligators, whose testes produced hormones as ovaries do, and it has since been shown or suggested in several other vertebrates. The new report, published in the 16 April issue of the Proceedings of the National Academy of Sciences, appeared the same week that EPA was to release its revised risk assessment for atrazine, a key step in its years-long process of reviewing the chemical's effects on humans, wildlife, and the environment. Although EPA officials refused to comment on the risk assessment before Science went to press, they confirmed that Hayes's results were forwarded to them before publication and were considered in the assessment. -JAY WITHGOTT Jay Withgott writes from San Francisco. _Ija_nHllO I1mgIPi0SM NEWS OF THE WEEK