Mechanism study on OH-initiated atmospheric degradation of the organophosphorus pesticide chlorpyrifos

Chlorpyrifos is a member of the organophosphorus class of insecticides. It has been regarded as an important atmospheric pollutant because of the high detection-frequency in the air and its potential adverse effects on humans and the environment. In this work, the reaction mechanism and possible degradation products for the OH-initiated atmospheric oxidation of chlorpyrifos were investigated at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31G(d) level. OH addition to P atom, H abstraction from the –CH2– moieties and the addition of OH to the C atom (C1) bonded with chlorine atom and nitrogen atom in the pyridyl ring are energetically favorable pathways for the reaction of chlorpyrifos with OH radicals. The theoretical study shows that the dominant products for OH-initiated atmospheric oxidation of chlorpyrifos are chlorpyrifos oxon, SO2, 3,5,6-trichloro-2-pyridinol (TCP) and O,O-diethyl phosphorothioate.