... do typical agricultural applications of glyphosate harm frog populations?
The study led by researchers at the University of Pittsburgh by Relyea found that exposure to the global herbicide Roundup caused increased mortality in tadpoles of a number of different frog species 8. This data has raised concerns about the impact of glyphosate-based herbicides on frogs and possible links to the global widespread decline of amphibian species in general.
However, detailed evaluations of this study, along with other studies by Relyea and co-workers 9,10,11 have revealed the unrealistic high dosages that were applied during the experiments. The herbicide concentrations in water that were found to be lethal to tadpoles greatly exceeded environmentally realistic field exposure levels and consequently are not indicative of risk to tadpole populations in natural waterbodies.
Shortly after the Relyea papers were published, the National Institute for Public Health and the Environment (RIVM) in the Netherlands reviewed these studies in the context of realistic environmental exposures and standard ecological risk assessments. RIVM concluded that the data does not provide convincing evidence that glyphosate herbicides pose a significant risk to frog populations in the Netherlands 12.
What do other toxicological studies on amphibians reveal?
The effects of around a dozen different glyphosate-based formulations have now been evaluated on almost 30 species of amphibians in acute and chronic amphibian toxicity studies 7, 14, 5, 1, 2, 6. Even when caged frogs were tested, no unusual adverse effects were noted following exposure to conservative but realistic environmental concentrations of glyphosate-based herbicides or to residues resulting from commercial forestry spray operations. Even in cases where an overspray of herbicides into the water had occurred, against the guidelines of Good Agricultural Practice (GAP), no acute toxic effects were observed.
Several chronic exposure studies have investigated the impact of formulated glyphosate on growth, development and survival of frog species and found no adverse effects at predicted environmental concentrations 3, 4. The absence of chronic effects was concluded to result from rapid dissipation of glyphosate and its surfactant from the water column. Surfactants are included in glyphosate-based formulations in order to increase the uptake of glyphosate into plants and improve the efficacy of the product. Surfactants are known to be toxic to aquatic organisms because they enhance the permeability of cellular membranes such as gills. This could potentially result in chronic effects at very high environmentally unrealistic concentrations.
However, previous work has demonstrated that the toxicity of surfactants in aquatic systems decreases rapidly because of rapid dissipation from water 13 and chronic effects in natural aquatic environments over long periods of time are therefore unlikely to occur.
Last update: 25 October 2012