SAN FRANCISCO--A series of high-profile papers this year showed that the herbicide atrazine can deform frogs, perhaps partly explaining the plague of amphibian deformities in North America. Now, the same research team shows that agricultural chemicals can greatly compound atrazine's deadly effects.
In a lab study published in April, developmental endocrinologist Tyrone Hayes of the University of California, Berkeley, and colleagues showed that low doses of atrazine can deform Xenopus laevis, a widely studied African frog (ScienceNOW, 15 April). In October, the team reproduced the effect in the leopard frog, native to North America, and found similar deformities in field sites contaminated with atrazine. But other researchers said that the field data were ambiguous and that more complex factors likely cause the deformities observed in the wild (ScienceNOW, 30 October).
Hayes's team has now added another layer of complexity to the atrazine puzzle. The team studied other herbicides and pesticides from the U.S. corn belt, where atrazine is widely used to control grassy weeds. They raised tadpoles in 3000 plastic deli tubs with various doses of atrazine, the herbicide metolachlor, and eight other insecticides and fungicides. They found that tadpoles exposed to 10 parts per billion (ppb) of atrazine metamorphosed into adults 10 days later than tadpoles not exposed to pesticides. Adding 10 ppb of metolachlor doubled that delay, while the full pesticide cocktail more than tripled it--an impact more severe than 1000 ppb of atrazine alone. Each dose also led to an increase in developmental abnormalities such as contorted limbs, although these data have not yet been fully analyzed. Hayes presented the study at the annual meeting of the American Society for Cell Biology here on 14 December.
Research on multiple contaminants is essential, says cell biologist David Epel of Stanford University in California. "The real world is mixtures," agrees toxicologist Michael McClure of the National Institute of Environmental Health and Safety in Research Triangle Park, North Carolina. To determine whether the effects he has seen are widespread in natural habitats, Hayes is teaming up with the U.S. Geological Survey on a nationwide survey. The researchers hope to finalize plans in the next few weeks--in time for the start of the frog breeding season in the southern United States.
With reporting by Rebecca Renner.