4 August 2005

Roundup™ Super-Toxic For Frogs As Well As Tadpoles

by Kate Melville

The disappearance of frogs and other amphibians around the world continues unabated, but a new study may shed some light on what's happening to our slimy friends. Conducted by Rick Relyea, from the University of Pittsburgh, the new study has built on his previous research examining the effects of the herbicide Roundup™ on frogs and tadpoles.

Published in the journal Ecological Applications, the findings showed that Roundup™ was deadly to tadpoles at lower concentrations than previously tested and that the presence of soil did not dilute the chemical's effects. While his previous research showed that Roundup™ was deadly to tadpoles, this study found that the product kills frogs in addition to tadpoles. Previous research established it is the product's surfactant (polyethoxylated tallowamine), added to make the herbicide penetrate plant leaves, and not the active herbicide (glyphosate), that is lethal to amphibians.

The figures from the study show just how deadly the herbicide is. Even when applied at concentrations that are just one-third of the maximum concentrations expected in nature, Roundup™ still killed more than 70 percent of tadpoles raised in outdoor tanks. Relyea examined whether the presence of soil in the tanks could mitigate the effects of the herbicide but found that it made no difference. In tanks with soil, after exposure to the maximum concentration expected in nature, nearly all of the tadpoles from three species had died.

For grown-up tadpoles, the results were no less worrying. The researchers found that the recommended application of Roundup™ killed up to 86 percent of terrestrial frogs after only one day. "The most striking result from the experiments was that a chemical designed to kill plants killed 98 percent of all tadpoles within three weeks and 79 percent of all frogs within one day," Relyea concluded.