The Curious Case of Atrazine

Tyrone Hayes with one of his African clawed frogs. Photo by Peg Skorpinski.

By Jody Roberts

In 2003 the U.S. Environmental Protection Agency (EPA) concluded its reevaluation of atrazine, one of the most commonly used herbicides in the United States. The EPA ruled that the product required no new regulations on its manufacture or use but decided to extend its monitoring efforts to track where and how much of the chemical might be found in drinking sources. Ordinarily this event would not warrant much attention. However, in this case, the EPA decision came in the midst of a fierce debate regarding possible environmental and human health effects and over the data used to both support and dispute these claims.

At issue was the possible hormone-disrupting effect of atrazine. The EPA concluded that "[t]he revised assessment does not suggest that endocrine disruption [. . .] be regarded as a legitimate regulatory endpoint at this time." This ruling fuses two issues: the role of uncertainty in regulatory science and the toxicity models used for regulation. Thus, the issue here is not really about atrazine at all. The case is only one instance of where these two problems meet, but examining this case further gives us some idea of how the problems might be understood and, ideally, overcome.

Atrazine is manufactured by a Swiss firm, Syngenta. In 1998, the company hired EcoRisk, a small Seattle-based environmental and toxicology consulting firm, to test and analyze possible health effects associated with the herbicide. Tyrone Hayes was one of the scientists responsible for examining the effects of exposure on amphibians.

Hayes, a professor in the department of integrative biology at the University of California, Berkeley, created an experimental system for exposing African clawed frogs to various levels of atrazine. Hayes's research methods differ from conventional chemical exposure tests, which expose their subjects to increasingly large amounts of chemicals in order to define a lethal dose. Hayes instead tests chemicals at low doses, or “ecologically relevant” doses— similar to those that can be found in the everyday environment.

Hayes's initial results, gathered while under contract to EcoRisk, suggested that atrazine did in fact have developmental effects on his subjects at low-dose exposures. After a year spent garnering additional funds from the National Science Foundation, the Howard Hughes Medical Institute, the W. Alton Jones Foundation, and a number of other small foundations, Hayes repeated his initial research and in 2002 published his results in the Proceedings of the National Academies of Science and in Nature.

Hayes believed the results were clear: small doses of atrazine similar to levels found in the environment produced gonadal abnormalities (hermaphroditism) (at 0.1 ppb) and reduced laryngeal size (at 1 ppb) in developing frogs. These feminized traits, which can hinder the male frogs' ability to reproduce and/or attract mates, are attributed to atrazine-induced production of aromatase, an enzyme that converts testosterone to estrogen in vertebrates (a group that includes humans). Because we are all potentially exposed to ecologically relevant doses of atrazine in our everyday lives, Hayes believes humans, too, are at risk. Even in areas where the herbicide is not regularly used, atrazine concentrations can be as high as 21 ppb in groundwater and 1 ppb in rainwater.

Perhaps most importantly, Hayes's research suggests that EPA officials begin to use "endocrine-regulated endpoints" in their assessments of chemicals and the extent to which they should be regulated by the federal government. Contrary to the established models of toxicity, endocrine disrupters can have tremendous developmental effects even at small doses; they are also time specific and can have trans-generational effects. These chemicals require a new and different model of toxicity establishing regulatory standards.

Syngenta attempted to discredit Hayes's work by claiming that his results could not be reproduced because of flawed methods. Several additional studies were undertaken, but none were able to reproduce Hayes's published findings. The EPA, in its assessment, found design errors in these follow-up experiments; however, because of the Data Quality Act (DQA), Syngenta needed only to provide results that differed enough from Hayes’s to suggest a degree of uncertainty. The DQA, passed in December 2000, was designed to ensure and maximize the quality, objectivity, utility, and integrity of information disseminated by federal agencies and to provide a pathway for appeal to any group that feels that federal decisions are made on the basis of “unsound” science.

The DQA is an outgrowth of a much larger issue concerning the pesky notion of uncertainty in science and how this uncertainty affects the decision-making process. What should we do in the face of uncertainty? These questions involve the intersection of several disparate sectors of society—science, government, and business. The curious case of atrazine and its regulation serves as an example of what happens when scientific, political, and corporate cultures collide. Each of these groups functions in a culturally specific way. Finding a way to bridge these cultural differences is essential for ensuring the successful operation of our regulatory systems, and it may create a way to deal with the uncertainty inherent in science.

For Further Reading
Hayes, Tyrone B., et al. “Herbicides: Feminization of Male Frogs in the Wild.” Nature 419 (2002), 895–896.

Hayes, Tyrone B., et al. “Hermaphroditic, Demasculinized Frogs after Exposure to the Herbicide Atrazine at Low Ecologically Relevant Doses.” PNAS 99 (2002), 5476–5480.

Renner, Rebecca. “Controversy Clouds Atrazine Studies.” Environmental Science and Technology, Science News, 19 February 2004.

Renner, Rebecca. “Do Male Frogs Naturally Have Female Traits?” Environmental Science and Technology, Science News, 9 June 2005.

U.S. Environmental Protection Agency, “Consumer Factsheet on: Atrazine.” Ground Water and Drinking Water, updated 28 February 2006, www.epa.gov/safewater/dwh/c-soc/atrazine.html.

Weiss, Rick. "'Data Quality ' Law Is Nemesis of Regulation." Washington Post, 16 August 2004, p. A01.