Popular weed killer feminizes native leopard frogs across Midwest

of these feminized tadpoles. "In my opinion, this is an unacceptable risk."

Hayes and his colleagues sampled leopard frog tadpoles in eight separate ponds, ditches, rivers and streams in the Midwest during the summer of 2001 and found feminized male frogs at every site with measurable levels of atrazine. The current laboratory detection limit is 0.1 parts per billion (ppb).

The sites were scattered through the Corn Belt and beyond, including in Utah, Wyoming, Nebraska and near the Iowa-Illinois border. Several ponds chosen as controls because they are in nonagricultural areas also had measurable levels of atrazine and feminized frogs, while only one, in Utah, had neither detectable atrazine nor affected frogs.

The site with the highest concentration of feminized frogs was along the North Platte River in Wyoming. There, 92 percent of male frogs showed sex reversal. This area of Wyoming reports little use of atrazine, but the river is fed by streams that carry runoff from Colorado farms, which do use significant amounts of the herbicide.

Earlier this year, Hayes and his colleagues reported that a common laboratory frog, the African clawed frog (Xenopus laevis), became demasculinized when raised in lab tanks with concentrations of atrazine of 0.1 ppb or higher. The current allowable limit set by the Environmental Protection Agency for atrazine in drinking water is 3 ppb, and the proposed chronic exposure limit for aquatic life is 12 ppb.

The new experiment, reported in the Oct. 31 issue of Nature, is a repeat of these experiments using the leopard frog . The new report also contains a summary of Hayes' survey of Midwestern frog ponds.

A field study by another group showed similar gonadal abnormalities in atrazine-exposed northern cricket frogs (Acris crepitans).

Just as in Hayes' earlier experiment, the male tadpoles developed female characteristics in their sex organs, or gonads. Up to 29 percent of males de

Contact: Robert Sanders
University of California - Berkeley

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