Chlorpyrifos and Chlorpyrifos‐Methyl Degradation by ˙ OH in the Atmosphere and in Water: Theoretical Calculations and Molecular Dynamic Simulations

As agriculture advances, organophosphorus pesticides (OPPs), renowned for their efficacy, are being extensively utilized. However, their residues pose significant risks to both the environment and human health. In this study, we employed computational methods in both gas and aqueous phases to investigate the ˙OH‐initiated oxidation mechanisms of two common pesticides, chlorpyrifos (CPY) and chlorpyrifos‐methyl (CPM). The calculations revealed that the reactions proceed primarily via addition and dehydrogenation. Addition at the phosphorus atom was found to be the most energetically favorable pathway, surpassing additions at the pyridine ring carbon atoms, followed by hydrogen abstraction from the methyl or ethyl group. In contrast, other abstraction reactions were less favorable. The reaction rate constants, atmospheric lifetimes, and half‐lives were calculated. Acute and chronic toxicity assessments were performed to estimate the toxicity levels of CPM and its degradation products. The neurotoxicity of these products was further investigated using molecular docking and molecular dynamics simulations. Compounds P15 and P26 exhibited the highest binding affinities with acetylcholinesterase (AChE), while P24 and P26 showed the strongest binding to butyrylcholinesterase (BChE). Finally, molecular dynamics simulations over a 100 ns timeframe demonstrated stable interactions between CPM degradation products and cholinesterases, identifying the degradation products that pose the greatest risk to the neurodevelopmental system. These results could provide theoretical support for the ˙OH‐initiated degradation of OPPs in engineering applications and are conducive to the development of new OPPs.