Pollution from a common herbicide might be causing die-offs in stream salamanders, according to biologists who say findings from their long-term study raise concerns over the role of atrazine in global amphibian declines.
The results also suggest that while impacts of the herbicide, atrazine, may not show up in short-term studies, even extremely low concentrations of the chemical may be deadly to amphibians in the long run.
"We are concerned that most studies used to make pesticide registration decisions and to derive safe concentrations last for about four days," said Jason R. Rohr, research associate at the Penn State Institutes of Energy and the Environment. "They often do not consider recovery processes, persistent effects of chemical exposure, or interactions among individuals within and between species that can affect our estimates of safe chemical concentrations."
Atrazine is one of the most widely used pesticides in the United States, and possibly the world. It is relatively long-lived and is even found at the poles. According to the U.S Environmental Protection Agency, it is one of the most common contaminants in ground and surface water.
Rohr and his colleagues Timothy M. Sesterhenn, doctoral candidate, Brent D. Palmer, associate professor, and Tyler Sager, doctoral candidate, all at the University of Kentucky, Lexington, exposed streamside salamander larvae to either 4, 40, or 400 parts per billion of atrazine until metamorphosis, the stage where the water-dwelling salamanders lose their gills and develop lungs that enable them to breathe in air. Scientists then tracked their survival to near reproductive age.
Results from the study, which lasted about 500 days, indicated that the two highest concentrations increased salamander mortality during exposure. However, this mortality benefited the survivors who experienced lower competition-related mortality after metamorphosis.