John Wiley & Sons, Ltd.

Role of sediments in modifying the toxicity of two roundup formulations to six species of larval anurans

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The role of sediment in modifying the toxicity of the original formulation of Roundup® and Roundup WeatherMAX® was examined in aqueous laboratory tests. Six species of anurans (Bufo fowleri, Hyla chrysoscelis, Rana catesbeiana, R. clamitans, R. sphenocephala, and R. pipiens) were exposed at Gosner stage 25 to concentrations of the 2 herbicide formulations in 96‐hour, static, non‐renewal experiments in the presence and absence of sediment. All species tested had lower LC50 values in water‐only exposures of both formulations compared to exposures with sediment. Sediment significantly altered the potency slopes in all tests with the exception of H. chrysoscelis and R. clamitans when exposed to the original formulation of Roundup® and H. chrysoscelis and R. sphenocephala in Roundup WeatherMAX® exposures. Thresholds were significantly different in all tests, including those where potency slopes did not differ. Based on water‐sediment exposures of the original formulation of Roundup®, all 6 species tested had a margin of safety when compared to the predicted environmental concentration of the highest label application rate. Five of 6 species had a margin of safety when exposed to Roundup WeatherMAX®. During incidental exposures in the field, sediments and organic matter present in aquatic systems provide significant sources of environmental ligands. If used according to label instructions, both herbicides should pose minimal risk to Anuran amphibians in actual field applications. Environ Toxicol Chem © 2014 SETAC

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