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PITTSBURGH—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.
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