State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, School of Environment, Northeast Normal University, Changchun, 130117, China.
Heilongjiang Province Key Laboratory of Geographical Environment Monitoring and Spatial Information Service in Cold Regions, Heilongjiang Province Collaborative Innovation Center of Cold Region Ecological Safety, School of Geographical Sciences, Harbin Normal University, Harbin, 150025, China.
Chemosphere. 2023 Sep;334:138968. doi: 10.1016/j.chemosphere.2023.138968. Epub 2023 May 19.
Insecticides are widely used in crop protection against insects and frequently detected in aquatic environment. Photolysis kinetics are directly related with exposure assessment and risk assessment. However, the photolysis mechanism of neonicotinoid insecticides with different structures has not been studied and compared systematically in the literature. In this paper, the photolysis rate constants in water were determined for eleven insecticides under irradiation of simulated sunlight. At the same time, the photolysis mechanism and effect of dissolved organic matter (DOM) on their photolysis were studied. The results showed that photolysis rates of eleven insecticides vary in a large range. The photolysis rates of nitro-substituted neonicotinoids and butenolide insecticide are much faster than that of cyanoimino-substituted neonicotinoids and sulfoximine insecticide. The ROS scavenging activity assays reveal that direct photolysis dominates the degradation of seven insecticides and, on the other hand, self-sensitized photolysis dominates four insecticides. The shading-effect from DOM can reduce the direct photolysis rates, on the other hand, ROSs generated by triplet-state DOM (DOM*) can also accelerate photolysis of insecticides. According to the photolytic products identified from HPLC-MS, these eleven insecticides have different photolysis pathways. Six insecticides are degraded from the removal of nitro group from their parent compounds and four insecticides are degraded through ·OH reaction or singlet oxygen (O) reaction. QSAR (quantitative structure-activity relationship) analysis showed that photolysis rate was directly related to the energy gap between the highest occupied molecular orbital to the lowest unfilled molecular orbital (E = E-E) and dipole moment (δ). These two descriptors reflect the chemical stability and reactivity of insecticides. The pathways developed from identified products and the molecular descriptors of QSAR models can well verify the photolysis mechanisms of eleven insecticides.
杀虫剂广泛用于防治农作物虫害，并经常在水生环境中检测到。光解动力学与暴露评估和风险评估直接相关。然而，不同结构的新烟碱类杀虫剂的光解机制在文献中尚未得到系统的研究和比较。在本文中，在模拟阳光照射下，测定了 11 种杀虫剂在水中的光解速率常数。同时，研究了溶解有机物（DOM）对其光解的光解机制和影响。结果表明，11 种杀虫剂的光解速率差异很大。硝基取代的新烟碱类和丁烯酸酯类杀虫剂的光解速率远快于氰基亚胺取代的新烟碱类和亚砜亚胺类杀虫剂。ROS 清除活性测定表明，直接光解主导着七种杀虫剂的降解，另一方面，自敏化光解主导着四种杀虫剂的降解。DOM 的遮光效应会降低直接光解速率，另一方面，DOM 的三重态（DOM*）产生的 ROS 也可以加速杀虫剂的光解。根据 HPLC-MS 鉴定的光解产物，这 11 种杀虫剂具有不同的光解途径。六种杀虫剂是从母体化合物中去除硝基得到降解，四种杀虫剂是通过·OH 反应或单线态氧（O）反应得到降解。QSAR（定量结构-活性关系）分析表明，光解速率与最高占据分子轨道与最低未占据分子轨道之间的能量差（E=E-E）和偶极矩（δ）直接相关。这两个描述符反映了杀虫剂的化学稳定性和反应性。从鉴定的产物和 QSAR 模型的分子描述符中开发的途径可以很好地验证 11 种杀虫剂的光解机制。
