Canadian Forest Service Publications
Variation in amphibian response to two formulations of glyphosate-based herbicides. (Short Communication) 2014. Edge, C.; Gahl, M.; Thompson, D.; Hao, C.; Houlahan, J. Environmental Toxicology and Chemistry 33(11):2628-2632.
Issued by: Great Lakes Forestry Centre
Catalog ID: 36059
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Variation in toxicity among formulations and species makes it difficult to extrapolate resultsto all species and all formulations of herbicides. The authors exposed larval wood frogs (Lithobates sylvalicus) from 4 populations to 2 glyphosate-based herbicides, Roundup Weed and Grass Control1 and Roundup WeatherMax1 . The 96-h median lethal concentration values for both formulations varied among the populations (Roundup Weed and Grass Control, O.I4mg acid equivalents (a.e.yL to l.lOmg a.e./L; Roundup WeatherMax, 4.94 mg a.e./L to 8.26mg a.e./L), demonstrating that toxicity varies among the fonnulations and that susceptibility may differ among populations.
Plain Language Summary
We tested two glyphosate-based herbicides for their toxicity to larval wood frogs. Toxicity is known to differ among formulations, species, and populations and can be affected by environmental factors. Understanding these differences is very important in risk assessment, so that context-specific decisions can be made. We found that lethal concentration values for both formulations varied among the populations. Roundup WeatherMax® was approximately 5 times less toxic to larval wood frogs than Roundup Weed and Grass Control®. This difference in toxicity was likely due to differences in surfactants or adjuvants among formulations. Our results show that these variations along with differing susceptibility among populations make it difficult to extrapolate results to all species and all formulations of herbicides.