Invasive species versus pollutants: Potential of Limnoperna fortunei to degrade glyphosate-based commercial formulations

Abstract

The intensive use of glyphosate in industrial agriculture may lead to freshwater contamination, encouraging studies of its toxic effect on non-target aquatic organisms. Glyphosate-based commercial formulations contain adjuvants, making them even more toxic than the active ingredient (a.i.) itself. The golden mussel Limnoperna fortunei is a freshwater invasive species which has been found to increase glyphosate dissipation in water and to accelerate eutrophication. The aim of this study is to evaluate the capability of L. fortunei to reduce the concentration of glyphosate in two commercial formulations, Roundup Max® and Glifosato Atanor®. Results were compared with the decay of the a.i. alone and in presence of mussels. Evasive response and toxicity tests were performed in a first set of trials to analyze the response of L. fortunei exposed to Roundup Max® and Glifosato Atanor®. Subsequently, we conducted a 21-day degradation experiment in 2.6-L microcosms applying the following treatments: 6 mg L−1 of technical-grade glyphosate (G), Glifosato Atanor® (A), Roundup Max® (R), 20 mussels in dechlorinated tap water (M), and the combination of mussels and herbicide either in the technical-grade (MG) or formulated form (MA and MR) (all by triplicate). Samples were collected at days 0, 1, 7, 14 and 21. No significant differences in glyphosate decay were found between treatments with mussels (MG: 2.03 ± 0.40 mg L−1; MA: 1.60 ± 0.32 mg L−1; MR: 1.81 ± 0.21 mg L−1), between glyphosate as a.i. and the commercial formulations, and between the commercial formulations, suggesting that the adjuvants did not affect the degrading potential of L. fortunei. In addition to the acceleration of glyphosate dissipation in water, there was an increase in the concentration of dissolved nutrients in water (N–NH4 + and P-PO4 3-) even higher than that caused by the filtering activity of the mussels, probably resulting from stress or from the degradation of glyphosate and adjuvants. We believe that a larger bioavailability of these nutrients due to glyphosate metabolization mediated by mussels would accelerate eutrophication processes in natural water bodies. The approach used here, where L. fortunei was exposed to two commercial formulations actually used in agricultural practices, sheds light on the potential impact of glyphosate decay on water bodies invaded by this species.