Herbicide-Induced Physiological Changes in Myriophyllum verticillatum: Linuron and Nicosulfuron Exposure and Implications for Aquatic Ecosystem Health

Abstract Herbicides extensively applied in agricultural weed management can infiltrate aquatic ecosystems via runoff, leaching, and soil erosion, leading to unintended exposure of non-target organisms to phytotoxic compounds. This study investigated the physiological responses of Myriophyllum verticillatum, a submerged aquatic macrophyte, to varying concentrations (0, 0.01, 0.1, 1, and 10 ppm) of two widely used herbicides: Linuron (LIN) and Nicosulfuron (NS). Experimental treatments were conducted under controlled growth chamber conditions, with morphological observations recorded daily over six days. At harvest, biochemical analyses revealed that higher herbicide concentrations, particularly 10 ppm, induced visible toxicity symptoms such as chlorosis and necrosis. Quantitative measurements demonstrated significant reductions in photosynthetic pigments (chlorophyll-a, chlorophyll-b, carotenoids) and total protein content, indicating impaired photosynthetic capacity and metabolic disruption. Conversely, levels of non-protein sulfhydryl groups (NP-SH) and total phenolic compounds increased, suggesting activation of antioxidant defense mechanisms under chemical stress. Elevated hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations confirmed oxidative stress and lipid peroxidation. Correlation analyses highlighted statistically significant relationships between oxidative stress markers and physiological parameters, implying that reactive oxygen species (ROS) accumulation is a central driver of observed biochemical and morphological alterations. Overall, findings demonstrate dose-dependent phytotoxicity of LIN and NS on M. verticillatum, underscoring ecological risks associated with herbicide contamination in aquatic environments. These results emphasize the vulnerability of non-target aquatic plants to chemical stressors and highlight the need for environmentally sustainable weed management practices to mitigate herbicide-induced ecological impacts.