Molecular perturbations of Daphnia magna in response to glyphosate - In laboratory medium and river water

Among the various emerging contaminants, glyphosate, a widely used active ingredient in herbicidal formulations, has become a pollutant of particular concern. Conventional water monitoring methods fall short in providing insights regarding the underlying toxicity mechanism of glyphosate. To bridge this gap, New Approach Methodologies can be more sensitive tools for pollution assessment. In this study, the effect of glyphosate in laboratory media and river water was assessed in neonates and two generations of daphnids. The 24 and 48 h LC₅₀ values for mortality in laboratory media were similar, 53 and 51 mg/l, respectively. Grazing activity was decreased after exposure to sublethal concentrations of glyphosate in laboratory media. Furthermore, key enzyme activities were used to determine the impact of glyphosate at a molecular level. Peptidase was the only enzyme with a decreased activity in acute exposures, while chronic (21-days) exposure resulted in an increase in the activities of acid phosphatase, lipase and glutathione S-transferase (GST) activity, and a decrease in the activity of β-galactosidase in laboratory media. However, GST was the only enzyme decreased in daphnids when exposed in acute or chronic scenarios to glyphosate in river water. Transgenerational exposures showed that the activities of peptidase and GST were increased in the second generation. Metabolic perturbations in amino acids were also assessed with a targeted approach in animals exposed in river water in the presence of glyphosate. Targeted analysis of river water for its chemical characteristics revealed only a few contaminants, including oxytetracycline, metformin, caffeine, fraxetin, esculetin, 2-Amino-3-methyl-imidazo[4,5-f]quinoline and 4'-aminoacetanilide. This offers a promising approach to improve next-generation risk assessment.