A FIGHT over frogs could sway the fate of one of the world鈥檚 most widely used herbicides. A team of toxicologists is claiming that the chemical atrazine is emasculating wild frogs across the US, increasing fears that it could be contributing to amphibians鈥� decline worldwide. But another team of researchers, funded by one of the herbicide鈥檚 makers, is disputing the team鈥檚 earlier findings.
Atrazine accounts for 40 per cent of all herbicide applied in the US, and is sprayed over three-quarters of the country鈥檚 corn crop. Despite this, the Environmental Protection Agency (EPA) is considering whether to restrict the chemical鈥檚 use.
Endocrinologist Tyrone Hayes of the University of California, Berkeley, first warned of the dangers of atrazine earlier this year. Hayes鈥檚 team found that male frogs are feminised by a dose of atrazine that is just 1/30th the EPA safe drinking water standard. Affected males grow ovaries and multiple testes and have shrunken voice boxes. But critics charged the work was limited, as frogs used were an African species (Xenopus laevis) specially bred for the lab.
Advertisement
Now Hayes鈥檚 group has gathered data on wild frogs native to the US that suggest atrazine is every bit as nasty as the Xenopus study hinted, and may indeed be affecting many amphibian species worldwide. In papers in Nature (vol 419, p 895) and Environmental Health Perspectives (DOI:10.1289/ehp.5932), the team reports that atrazine damages gonads and makes male northern leopard frogs (Rana pipiens) hermaphrodites.
In lab tests, the gonadal problems were actually worse at ultra-low doses than at higher ones, perhaps because the endocrine system is attuned to minute concentrations of chemicals that mimic hormones. Hayes鈥檚 team also correlated the abnormalities in leopard frogs with atrazine concentrations along a 2200-kilometre transect across the US agricultural heartland. The frogs commonly breed in ditches and pools next to corn fields during the peak season for pesticide application.
But a panel of academic scientists funded by Syngenta, one of the companies that makes atrazine, questions the results. The panel will present talks at next month鈥檚 environmental toxicology conference in Utah that challenge the notion that atrazine harms amphibians. A study led by panel member James Carr of Texas Tech University in Lubbock, to be published in Environmental Toxicology and Chemistry in January, finds no effect on Xenopus voice-box muscles and no low-dose effect on gonads.
Some biologists suspect industry pressure, but Carr defends the work, and points out that it doesn鈥檛 let atrazine off the hook completely. 鈥淲e鈥檙e not saying atrazine does not cause gonadal abnormalities; our data shows it does,鈥� Carr says. Just at concentrations 250 times higher than Hayes found.
The EPA is reviewing the risks posed by atrazine, but such reviews often take years. If Hayes is right, and effects occur at doses too low to regulate, then only an outright ban will be effective. And if a ban is imposed in the US, the EPA would simply be following many European countries, which outlawed the chemical years ago.