PITTSBURGH-As amphibians continue to mysteriously disappear worldwide,a University of Pittsburgh researcher may have found more pieces of thepuzzle. Elaborating on his previous research, Pitt assistant professorof biological sciences Rick Relyea has discovered that Roundup(r), themost commonly used herbicide in the world, is deadly to tadpoles atlower concentrations than previously tested; that the presence of soildoes not mitigate the chemical's effects; and that the product killsfrogs in addition to tadpoles.
In two articles published in the August 1 issue of the journalEcological Applications, Relyea and his doctoral students NancySchoeppner and Jason Hoverman found that even when applied atconcentrations that are one-third of the maximum concentrationsexpected in nature, Roundup(r) still killed up to 71 percent oftadpoles raised in outdoor tanks.
Relyea also examined whether adding soil to the tanks wouldabsorb the Roundup(r) and make it less deadly to tadpoles. The soilmade no difference: After exposure to the maximum concentrationexpected in nature, nearly all of the tadpoles from three species died.
Although Roundup(r) is not approved for use in water, scientists havefound that the herbicide can wind up in small wetlands where tadpoleslive due to inadvertent spraying during the application of Roundup(r).
Studying how Roundup(r) affected frogs after metamorphosis,Relyea found that the recommended application of Roundup(r) Weed andGrass 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 achemical designed to kill plants killed 98 percent of all tadpoleswithin three weeks and 79 percent of all frogs within one day," Relyeawrote.
Previous studies have determined that it is Roundup(r)'s surfactant(polyethoxylated tallowamine, or POEA, an "inert" ingredient added tomake 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'sMcKinley Fund, and the Pennsylvania Academy of Science.
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