Short-term effects of glyphosate and Roundup Transorb® formulation on the cyanobacteria Synechococcus elongatus

Abstract

Glyphosate is an active ingredient used in herbicide formulations worldwide. However, besides glyphosate, these formulations have other components to facilitate glyphosate absorption by plants. These include the surfactants such as polyoxyethylene amine (POEA) present in the Roundup Transorb® (RT) formulation. Glyphosate formulations are potentially more toxic to non-target organisms than the pure active ingredient. In this work, we evaluated the toxicity (72 h) of pure glyphosate and RT for the cyanobacterium Synechococcus elongatus, based on biomass growth and cell viability. The formulation proved more toxic than pure glyphosate for both parameters analysed, with an IC50 (Inhibition concentration mean) based on biomass measured by optical density (750 nm) that was sixty times lower. Cell viability was not as sensitive as the biomass because, of the few cells left in the culture, most were viable. This indicates that there is a variation in tolerance between the cyanobacteria present in the inoculum. Thus, cell viability may underestimate the results of glyphosate and RT toxicity and be useful only in low concentrations of exposure.