The acute toxicity of Daphnia magna to mixtures of herbicides (glyphosate, glufosinate-ammonium) and heavy metals (Cu, Cd) are concentration-dependent.

The widespread use of herbicides glyphosate (Gly) and glufosinate (Glu) has raised increasing concerns about their environmental toxicity. In aquatic systems, herbicide residues can form complexes or chelate with dissolved substances in water, thereby altering their bioavailability. This study examined the acute toxicity of Gly and Glu, as well as the modulatory effects of heavy metals (Cu and Cd) on Daphnia magna, a freshwater cladoceran. The study further investigated the combined effects of these compounds on D. magna, assessing endpoints including pollution stress response, heart rate, beat frequency, cellular apoptosis, and gene expression levels. Results indicate that the 48-h EC50 values for Gly and Glu on D. magna are 198 ± 1.29 and 1193 ± 89.2 mg/L, respectively, classifying them as low-toxicity pesticides. Co-exposure significantly reduced the heart rate and hopping frequency of D. magna, induced apoptosis, and upregulated related gene expression.Predictive analyses using CA and IA models indicated that low concentrations of Gly exhibited an antagonistic effect with both heavy metals, whereas the interaction between Cu and Gly in the IA model showed this trend but was not significant. Low concentrations of Glu and Cu, as well as high concentrations of Glu and Cd, all exhibited antagonistic effects. Overall, the addition of low-concentration herbicides to the binary mixture of heavy metals reduced the toxicity to D. magna. Nevertheless, as the concentration of the herbicide increased, the weakening of the toxicity effect observed in the low-concentration group was no longer significant.