August 15, 2005: 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
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(r) 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,"
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.