As amphibians continue to mysteriously disappear worldwide, a University of Pittsburgh researcher may have found more pieces of the puzzle. Elaborating on his previous research, Pitt assistant professor of biological sciences Rick Relyea has discovered that Roundup®, the most commonly used herbicide in the world, is deadly to tadpoles at lower concentrations than previously tested; that the presence of soil does not mitigate the chemical's effects; and that the product kills frogs in addition to tadpoles.

In two articles published in the August 1 issue of the journal Ecological Applications, Relyea and his doctoral students Nancy Schoeppner and Jason Hoverman found that even when applied at concentrations that are one-third of the maximum concentrations expected in nature, Roundup® still killed up to 71 percent of tadpoles raised in outdoor tanks.

Relyea also examined whether adding soil to the tanks would absorb the Roundup® and make it less deadly to tadpoles. The soil made no difference: After exposure to the maximum concentration expected in nature, nearly all of the tadpoles from three species died.

Although Roundup® is not approved for use in water, scientists have found that the herbicide can wind up in small wetlands where tadpoles live due to inadvertent spraying during the application of Roundup®.

Studying how Roundup® affected frogs after metamorphosis, Relyea found that the recommended application of Roundup® Weed and Grass Killer, a formulation marketed to homeowners and gardeners, 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 wrote.

Previous studies have determined that it is Roundup®'s surfactant (polyethoxylated tallowamine, or POEA, an "inert" ingredient added to make the herbicide penetrate plant leaves) and not the active herbicide (glyphosate) that is lethal to amphibians.

This research was funded by the National Science Foundation, Pitt's McKinley Fund, and the Pennsylvania Academy of Science.

Relyea, R.A. (2005) The lethal impact of Roundup® on aquatic and terrestrial amphibians. Ecol. Appl., In Press

The global decline in amphibian diversity has become an international environmental problem with a multitude of possible causes. There is evidence that pesticides may play a role, yet few pesticides have been tested on amphibians. For example, Roundup® is a globally-common herbicide that is conventionally thought to be nonlethal to amphibians. However, Roundup® has been tested on few amphibian species, with existing tests conducted mostly under laboratory conditions and on larval amphibians. Recent laboratory studies have indicated that Roundup® may be highly lethal to North American tadpoles, but we need to determine whether this effect occurs under more natural conditions and in post-metamorphic amphibians. I assembled communities of three species of North American tadpoles in outdoor pond mesocosms that contained different types of soil (which can absorb the pesticide) and I applied Roundup® as a direct overspray. After 3 wks, Roundup® killed 96-100% of larval amphibians (regardless of soil presence). I then exposed three species of juvenile (post-metamorphic) anurans to a direct overspray of Roundup in laboratory containers. After 1 d, Roundup killed 68-86% of juvenile amphibians. These results suggest that Roundup®, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines.

More on Dr. Relyea (http://www.pitt.edu/~biohome/Dept/Frame/Faculty/relyea.htm)