Monsanto’s weedkiller deadly to frogs and tadpoles alike

New research by Rick Relyea, assistant professor of biological sciences at Pittsburgh University, and published in the August edition of the Ecological Applications journal, found that the recommended application of Roundup Weed and Grass Killer, a common formulation marketed to homeowners and gardeners, killed up to 86 percent of terrestrial frogs after only one day.

Even when applied at concentrations of only one-third of the maximum expected in nature, Roundup still killed up to 71% of tadpoles raised in outdoor tanks.

Although the herbicide isn’t designed to be used near water, and instructions on the packaging make this clear, it is hard to keep such chemicals from leaching into water sources and pesticides and weedkillers are a major source of water pollution.

In addition, many amphibians live in shallow puddles so could easily be affected, while wetlands in fields and forests could be accidentally sprayed.

Last year a study by the IUCN – the Global Amphibian Assessment – found that roughly one third of all amphibians were under threat. Habitat loss is the greatest cause of their demise but their permeable skins also make them extremely susceptible to toxins in the environment.

Relyea’s study also examined whether soil would absorb the Roundup and make it less deadly. However, it made no difference and after exposure to the maximum concentration expected in nature nearly all of the tadpoles from three species of frog died.

“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.

In Europe, Monsanto sells Roundup Biactive, a version with a different surfactant that doesn’t harm amphibians. The question is why it doesn’t do the same in the US?

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

By David Hopkins