Commonly Used Herbicide May Cause Frog Mutation

By DAVID P. HAMILTON
Staff Reporter

Is one of the most common herbicides in the U.S. turning frogs into hermaphrodites in the wild?

New data from a field study conducted by Tyrone Hayes, a professor of integrative biology at the University of California at Berkeley, suggest that low residues of the herbicide atrazine in agricultural runoff may be seriously disrupting the sexual development of leopard frogs across the central and western U.S.

The research report, to be published Thursday in Nature, adds fresh evidence to a controversy over whether atrazine is an "endocrine disruptor," a chemical that can interfere with reproduction and development by altering hormonal balances in a variety of organisms.

A group of researchers funded by Syngenta Crop Protection Inc., a maker of atrazine and a unit of Syngenta AG of Switzerland, immediately denounced the Hayes study, charging that it drew sweeping conclusions from limited and inconsistent data. Atrazine is undergoing a regularly scheduled "re-registration" review of its health and ecological effects at the Environmental Protection Agency.

Leopard Frog

Even if atrazine eventually proves to be an endocrine disruptor in amphibians, it may not pose a risk to humans. Frogs are especially vulnerable to water-borne chemicals because they develop to maturity while immersed in water. Humans, by contrast, appear to rapidly purge atrazine from the body in their urine. Still, frogs share some important reproductive traits with humans. Early pregnancy tests, in fact, involved exposing female frogs to a woman's urine because a human hormone associated with pregnancy can cause the frogs to ovulate.

Last July, Dr. Hayes and several students, accompanied by an 18-wheel freezer truck, set out to collect samples of leopard frogs and ground water from Utah to Iowa. At each location, the team gathered 100 frogs, immediately killing them and preserving them in ethanol, as well as 100 milliliters of nearby ground water, which they froze.

When they returned, the researchers sent the water samples to two outside laboratories to analyze atrazine concentrations. Then they examined the frogs' gonads, determining that 10% to 92% of male frogs from seven of the eight sample sites were actually hermaphrodites whose testes produced egg cells.

The team also found that the highest rate of sexual deformities came from the North Platte River area in Wyoming, far from direct agricultural runoff. Water-sample tests revealed a low but measurable level of 0.4 part per billion of atrazine there. By contrast, at a cornfield in Polk County, Iowa -- the site with the highest level of atrazine exposure -- fewer than 20% of male frogs had developmental problems.

The field results lend support to Dr. Hayes's earlier lab studies. After applying measured doses of atrazine to aquariums in which frogs grew up from tadpoles, his group found that atrazine concentrations as low as 0.1 part per billion were sufficient to produce reproductive abnormalities.

Other endocrine disruptors also have more significant developmental effects at lower concentrations. In the case of leopard frogs, Dr. Hayes suggests that higher atrazine levels may short-circuit developmental circuitry in the pituitary gland, shutting down reproductive-organ development before hermaphroditism can develop.

"The implications are disastrous," says David Sassoon, a molecular developmental biologist with the Mt. Sinai School of Medicine in New York. "Something like this has been suspected for quite some time. It has just been difficult to figure out what it is."

But other researchers caution that the Hayes report doesn't prove that atrazine is solely responsible for the developmental problems in amphibians. Joe Thornton, the author of a book on endocrine disruptors, says the Nature study should be replicated on a larger scale at different sites before the findings can be considered conclusive. Nevertheless, he said, "We now have enough information to be very concerned about atrazine's effects on wildlife, and possibly people."

Opposing scientists levy harsher criticisms, charging that Dr. Hayes overlooked the fact that hermaphroditism in juvenile leopard frogs is common in the wild. The Atrazine Endocrine Ecological Risk Assessment Panel, a group of eight researchers funded by Syngenta via a consulting firm, released a detailed two-page critique of the study.

Dr. Hayes once served on that panel. He resigned more than a year ago, citing disagreements with the panel and Syngenta over the direction of his research.

Write to David P. Hamilton at david.hamilton@wsj.com