Effects of the herbicides quizalofop-p-ethyl and quizalofop-ethyl on the physiology, oxidative damage, synthesis, and release of microcystin-LR in Microcystis aeruginosa

摘要

Quizalofop-Ethyl (QE) is a widely used phenoxy herbicide. It contains two enantiomers, and only its R-enantiomer quizalofop-p-ethyl (QpE) has herbicidal activity. Cyanobacterial blooms caused by Microcystis aeruginosa pose a threat to human health and aquatic environments, but the potential effects of chiral herbicides on M. aeruginosa are rarely studied. In this study, we carried out experiments using 0,0.5,1,2, and 5 mg/L of QE and QpE to explore the effects on the growth, metabolism, synthesis, and release of microcystin-LR (MC-LR) in M. aeruginosa, which is the dominant species of algal blooms and indicator organism of water contamination. The biomass and chlorophyll a and protein content were consistent, showing that QpE at high concentrations (2 and 5 mg/L) showed greater acute toxicity than QE. On the expression of photosynthesis-related genes psaB and psbD1, QpE at 2 and 5 mg/L showed a stronger inhibition effect than QE. The oxidative stress caused by QE and QpE indicated that 144 h of exposure increased the concentration of MDA and enhanced the activities of superoxide dismutase and catalase. The synthesis of intracellular MC-LR in M. aeruginosa was stimulated by 144 h of QpE and QE exposure, and QpE showed a stronger stimulation effect than QE at high concentrations. The content of extracellular MC-LR increased after 144 h of QpE exposure and remained stable under QE exposure compared with that in the control group. Moreover, the expression of MC-LR-related gene mcyH was upregulated by QpE (144 h exposure) but downregulated by QE. These results are helpful to understand the toxicological effects of chiral herbicides on nontarget aquatic organisms, thus providing a theoretical basis for the rational use and the ecological risk assessment of chiral pesticides.