Transcriptomic and metabolomic insights into the combined toxicity of acute glyphosate and copper exposure in water flea (Daphnia magna).

Copper (Cu) and glyphosate are ubiquitous contaminants in aquatic environments, with well-documented individual toxicological effects. However, the mechanisms underlying their combined toxicity and the dual role of glyphosate remain unclear. In this study, Daphnia magna (D. magna) was used as a model organism to investigate the effects of acute exposure to 10 μg L-1 Cu, 20 mg L-1 glyphosate, and their mixture. An integrated approach was employed, including physiological, histopathological, biochemical, transcriptomic, and metabolomic analyses. Results showed that glyphosate reduced Cu bioaccumulation in D. magna during 24-96 h of exposure, thereby alleviating Cu-induced toxicity. This mitigation was manifested as increased body length at 48-72 h, reduced intestinal damage and apoptosis, and modulated antioxidant enzyme activities. Additionally, glyphosate exerted independent molecular disturbances, including downregulation of genes involved in the neuroactive ligand-receptor interaction pathway and inhibition of amino acid metabolism. Co-exposure induced 1044 differentially expressed genes (DEGs), in contrast to 610 DEGs in the Cu-alone group and 859 DEGs in the glyphosate-alone group. These DEGs were significantly enriched in starch and sucrose metabolism and oxidative phosphorylation pathways. Metabolomic analysis further revealed that Cu partially reversed glyphosate-induced inhibition of amino acid metabolism. Collectively, these findings clarify the interactive effects between Cu and glyphosate, providing valuable insights for the risk assessment of aquatic co-pollutants.