Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors

Abstract

Glyphosate-based herbicides (e.g. Roundup ®) are extensively used in the aquatic environment, but there is a paucity of data on the toxicity of the formulated products and the influences by environmental factors. In this study, the acute toxicity of technical-grade glyphosate acid, isopropylamine (IPA) salt of glyphosate, Roundup ® and its surfactant polyoxyethylene amine (POEA) to Microtox ® bacterium ( Vibrio fischeri), microalgae ( Selenastrum capricornutum and Skeletonema costatum), protozoa ( Tetrahymena pyriformis and Euplotes vannus) and crustaceans ( Ceriodaphnia dubia and Acartia tonsa) was examined and the relative toxicity contributions of POEA to Roundup ® were calculated. The effects of four environmental factors (temperature, pH, suspended sediment and algal food concentrations) on the acute toxicity of Roundup ® to C. dubia were also examined. Generally, the toxicity order of the chemicals was: POEA > Roundup ® > glyphosate acid > IPA salt of glyphosate, while the toxicity of glyphosate acid was mainly due to its high acidity. Microtox ® bacterium and protozoa had similar sensitivities towards Roundup ® toxicity (i.e. IC50 from 23.5 to 29.5 mg AE/l). In contrast, microalgae and crustaceans were 4–5 folds more sensitive to Roundup ® toxicity than bacteria and protozoa. Except photosynthetic microalgae, POEA accounted for more than 86% of Roundup ® toxicity and the toxicity contribution of POEA was shown to be species-dependent. Increase in pH (6–9) and increase of suspended sediment concentration (0–200 mg/l) significantly increased the toxicity of Roundup ® to C. dubia, but there were no significant effects due to temperature change and food addition.