This study investigated the effect of the herbicide metolachlor (MET) on the redox homeostasis of the freshwater green alga Pseudokirchneriella subcapitata. At low MET concentrations (≤40 μg L⁻¹), no effects on algal cells were detected. The exposure of P. subcapitata to 45–235 μg L⁻¹ MET induced a significant increase of reactive oxygen species (ROS). The intracellular levels of ROS were particularly increased at high (115 and 235 μg L⁻¹) but environmentally relevant MET concentrations. The exposure of algal cells to 115 and 235 μg L⁻¹ MET originated a decrease in the levels of antioxidants molecules (reduced glutathione and carotenoids) as well as a reduction of the activity of scavenging enzymes (superoxide dismutase and catalase). These results suggest that antioxidant (non-enzymatic and enzymatic) defenses were affected by the excess of MET. As consequence of this imbalance (ROS overproduction and decline of the antioxidant system), ROS inflicted oxidative injury with lipid peroxidation and damage of cell membrane integrity. The results provide further insights about the toxic modes of action of MET on a non-target organism and emphasize the relevance of toxicological studies in the assessment of the impact of herbicides in freshwater environments.

这项研究调查了除草剂甲草胺（MET）对淡水绿藻次生伪藻（Pseudokirchneriella subcapitata）的氧化还原稳态的影响。在低MET浓度（≤40μgL ^-1）下，未检测到对藻类细胞的影响。亚人参P.暴露于45–235μgL ^-1 MET会引起活性氧（ROS）的显着增加。在高浓度（115和235μgL ^-1）但与环境有关的MET浓度下，ROS的细胞内水平尤其增加。藻类细胞暴露于115和235μgL ^-1MET导致抗氧化剂分子水平的降低（减少的谷胱甘肽和类胡萝卜素）以及清除酶（超氧化物歧化酶和过氧化氢酶）活性的降低。这些结果表明抗氧化剂（非酶和酶）的防御受到过量MET的影响。这种不平衡的结果（ROS过度生产和抗氧化剂系统的下降）导致ROS发生脂质过氧化和细胞膜完整性受损的氧化损伤。结果提供了关于MET对非目标生物的毒性作用方式的进一步见解，并强调了毒理学研究在评估除草剂在淡水环境中的影响方面的相关性。