Science Magazine
31 October 2002

Conflict Brewing Over Herbicide's Link to Frog Deformities
Rebecca Renner

A witches' brew of controversy is bubbling up over the potential link between atrazine, one of the most widely used herbicides in the United States, and the decline of amphibians. The latest additions to the brew are new findings from developmental endocrinologist Tyrone Hayes's group at the University of California, Berkeley, suggesting that exposure to very low levels of atrazine in the wild is turning male frogs into hermaphrodites. But new experimental results in another frog species, to be presented by experimental toxicologist James Carr of Texas Tech University in Lubbock and other researchers at a meeting later this month, cast doubt on such low-dose effects. At stake could be continued regulatory approval for atrazine. [Renner does not note that Carr and his co-authors are funded by atrazine's producer for their research.]

Earlier this year Hayes set the kettle boiling when he reported in the Proceedings of the National Academy of Sciences that in the lab, male tadpoles exposed to low levels of atrazine developed into hermaphrodites or had other reproductive-organ deformities, apparently due to disruptions in their endocrine system (Science, 19 April, p. 447). The study used African clawed frogs (Xenopus laevis), known as the "lab rat" of amphibian toxicology studies. Now he's extended the finding to a native species, the leopard frog (Rana pipiens), in both lab and wild populations. Counterintuitively, the lowest doses of atrazine appear to be the bitterest pill for frogs. But other teams, including Carr's, say that they have been unable to replicate Hayes's original Xenopus findings.

Atrazine is used throughout the world in countries that are major corn growers, according to Timothy Pastoor, head of global risk assessment for Syngenta, a major producer of atrazine. Several countries in Europe have banned the compound but not directly due to health concerns. The countries have a policy of banning any questionable pesticide that occurs in drinking water at levels higher than 0.1 parts per billion (ppb).