ORIGINAL ABSTRACT

The active ingredient (a.i.) glyphosate is frequently detected in waterways at relatively high concentrations, posing a risk to aquatic organisms including freshwater mussels, North America's most endangered animal group. This research aims to evaluate for the first time the effect of a glyphosate-based herbicide on a freshwater mussel (Unionid) using a battery of biomarkers. The mussel Elliptio complanata was exposed for 21 days to Credit® Xtreme (at 0, 50, 100, and 150 µg/L a.i. of glyphosate). An integrated biomarker response (IBRv2) was used to visualize the overall impact of each glyphosate-based herbicide concentration on mussels' health conditions. The biomarker results showed that glyphosate (used at 100 µg/L and 150 µg/L) induced lipid peroxidation in the gills and digestive gland and inhibited acetylcholinesterase in the foot and gills, indicating oxidative damage and neurotoxicity. Other biomarkers were influenced at the lowest concentration of glyphosate tested (50 µg/L): lipids (decrease), triglycerides (increase) and, to a lesser extent, vitellogenin (decrease). For the latter biomarkers, the sexes were not affected similarly, and they were only sensitive at 50 µg/L, only females showed a trend toward a decrease for vitellogenin and a decrease for lipids. Using IBRv2, we found a clear discrimination between concentrations, and the index values increased with glyphosate concentration, attesting to the deterioration in biomarker-defined mussel health when exposed to Credit® Xtreme at realistic glyphosate concentrations in agricultural rivers. This study shows that glyphosate-based herbicides can alter neurological function, induce oxidative damage, and selectively modify the E. complanata metabolism at relatively low concentrations.