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  April 11,  2005
Volume 83, Number 15
p. 11


  Common Herbicide Kills Tadpoles
Biologist finds that low doses of Roundup are lethal to some amphibian species

AT RISK Tadpoles of the gray tree frog (shown) are killed by Roundup in experimental tanks.


The herbicide Roundup is lethal to some tadpole species, says a University of Pittsburgh researcher who tested the compound in experimental tanks. The surfactant used in the formulation appears to be the culprit. Roundup, manufactured by Monsanto, is the second most commonly applied herbicide in the U.S. and has been considered relatively nontoxic to animals.

Rick A. Relyea, an assistant professor of biology, examined how a pond's entire community--25 species including crustaceans, insects, snails, and tadpoles--responded to the addition of manufacturer-recommended doses of two insecticides, carbaryl and malathion, and two herbicides, Roundup (glyphosate) and 2,4-D.

He found that the insecticides indirectly increased the tadpole populations by decreasing predators, that 2,4-D had no effect, but that Roundup completely eliminated leopard frog and gray tree frog tadpoles and nearly eliminated wood frog and toad tadpoles. Spring peeper tadpoles were not affected (Ecol. Appl. 2005, 15, 618).

"The most shocking insight coming out of this was that Roundup, something designed to kill plants, was lethal to amphibians," says Relyea, who conducted the research at Pitt's laboratory of ecology. "We added Roundup to outdoor tanks simulating real ponds, and the next day we looked in the tanks and there were dead tadpoles all over the bottom."

Relyea concludes from previous research conducted in Australia that the lethal chemical is probably not glyphosate, the active ingredient in Roundup, but polyethoxylated tallowamine (POEA), the surfactant in the product that allows glyphosate to penetrate leaves.

About 10 years ago, scientists found that pure glyphosate is not very toxic to some Australian tadpole species, Relyea says. But they discovered that both Roundup and pure POEA are quite toxic to these same species. Now, to protect frogs, Roundup Bioactive, a glyphosate formulation that does not contain POEA as a surfactant, is used as the primary weed killer in Australia.

Eric S. Sachs, director of scientific affairs at Monsanto, says Roundup is not approved for use over water and that applicators avoid spraying it on water bodies that could support tadpoles.

Relyea points out, however, that in fields and forests, it is the temporary, shallow bodies of water--depressions only a few inches deep and 10 or 20 feet long--that produce most of the amphibians in this country. "Anyone spraying pesticides from an airplane would probably not avoid such puddles because they appear to be inconsequential," he says.

These new Roundup findings could provide a possible cause for the global decline of amphibians, Relyea says. His work, which is funded by the National Science Foundation, does not imply that all glyphosate formulations are toxic to tadpoles, but he concludes that those containing POEA are.

EPA says it will review Relyea's study and determine whether any additional regulatory actions are appropriate.

  Chemical & Engineering News
ISSN 0009-2347
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