Study says herbicide causes frogs' sex change Science

A powerful and widely used herbicide called Atrazine changes the sex of many male frogs to females and emasculates three-quarters of others, according to research reported this week by a UC Berkeley professor and molecular toxicologist.

The findings were immediately assailed as "fundamentally flawed" by scientists with Syngenta, the international agribusiness company and the chemical's largest manufacturer.

The controversy has major political implications because the Environmental Protection Agency had approved Atrazine under the Bush administration after rejecting earlier findings, and agency scientists in the Obama administration are now reviewing that EPA rule. The European Union has already banned Atrazine after concluding that minute levels found in lakes and streams severely damaged amphibians.

Research by Tyrone Hayes and his colleagues in their Berkeley laboratory found that 10 percent of their male frogs changed to females after ingesting small doses of Atrazine.

The newly altered females remained genetically male, but proved capable of mating with other males, Hayes said. The offspring of those couples were all male frogs and perfectly capable of mating with normal females.

The new research from Hayes' laboratory at UC Berkeley is being published this week in the early online edition of the Proceedings of the National Academy of Sciences.

Hayes said in an interview Tuesday that because Atrazine has been used for many years on crop lands all over the world, there is a strong likelihood that the chemical may be playing a major role in the global decline of populations of other amphibians as well as frogs that has puzzled scientists and altered the ecology in many parts of the world.

"There is more and more evidence from other researchers," he said, "that Atrazine is also damaging the immune systems of fish, reptiles and birds."

The lab work by Hayes and his colleagues involved common laboratory frogs. They later studied wild African clawed frogs (Xenopus laevis) in the field and confirmed the results in the lab, Hayes said.

Frogs both in the laboratory and in the field were exposed to small doses of Atrazine as larvae, and then for two to three years during their growth from larvae to adulthood.

The herbicide has long been known as an endocrine disruptor - a chemical that alters the functioning of hormones. In the case of the frogs, the disruption showed up clearly as changing testosterone to estrogen in the bodies of the male frogs, Hayes said.

From 1997 to 2000, Hayes said, he was employed by Syngenta as a research biologist, but that when his work began to show dangers from the chemical, his contract was abruptly ended.

At the company's U.S. headquarters in Greensborough, N.C., Tim Pastoor, a toxicologist for the division called Syngenta Crop Protection, said he had examined Hayes's work and found it "basically and fundamentally flawed." He said Hayes' "results are not plausible."

Hayes said that similar research into Atrazine that he did under contract for an environmental firm in Ferndale, Wash., called Ecorisk between 1997 and 2000 was ended after he found the compound was indeed an endocrine disruptor.

Scott Ogle, an official at that company, said that he had never heard of Hayes.

This story has been corrected since in appeared in print.