Kinetics and mechanism of OH-initiated atmospheric oxidation of organophosphorus plasticizers: A computational study on tri-p-cresyl phosphate.

Understanding the atmospheric fate of organophosphorus plasticizers is important for their environmental risk assessment. However, limited information is available at present. In this study, density functional theory (DFT) calculations were performed to investigate the transformation mechanism and kinetics of tri-p-cresyl phosphate (TpCP) initiated by OH. Results show that the initial reactions are dominated by H-abstraction and OH addition to form TpCP-radical, TpCP-OH adducts and aryl phosphodiester. The H-abstraction pathways are more favorable than the OH addition pathways. The TpCP-radical and TpCP-OH adducts can further react with O2 in the atmosphere to finally form benzaldehyde phosphate, hydroxylated TpCP and bicyclic radicals. Based on the transition state theory, the calculated rate constant (kOH ) of TpCP with OH at T = 298 K is 1.9 × 10-12 cm3 molecule-1 s-1 with an atmospheric lifetime of 4.2 days, which demonstrates that gaseous TpCP is atmospherically persistent. This study provides a comprehensive investigation of the OH-initiated oxidation of TpCP, which is useful for understanding its mechanism of transformation and evaluating the risk in atmospheric environment.