Mechanism and kinetics studies of the atmospheric oxidation of p,p'-Dicofol by OH and NO3 radicals.

Abstract As an effective organochlorine pesticide, Dicofol has been extensively applied in more than 30 countries for protecting over 60 different crops. Considering its large consumption and potential adverse effect on human health (endocrine disrupting and carcinogenicity), the fate of Dicofol sprayed into the air is of public concern. In this study, we conducted a comprehensive study on the reaction mechanisms of p,p' -Dicofol with OH and NO 3 radicals using DFT method. Comparing the abstrations by OH and NO 3 radical, OH and NO 3 radical addition reactions are predominant due to the lower potential barriers and stronger heat release. The phenolic substances (P1 P5), epoxides (P11 and P15), dialdehyde (P13) and other species (P8, P9, P10 and P14) are generated by OH additions and their subsequent reactions while OH abstraction reactions produce DCBP, P7 and chlorphenyl radical. Particularly, NO 3 additions and their subsequent reactions yield dialdehydes (P16 and P17) and 2,8-DCDD, which is the first report of the generation of dioxin from atmospheric oxidation of p,p' -Dicofol. Additionally, based on the structure optimization and energy calculation, rate constants and Arrhenius formulas of the elementary reactions of p,p' -Dicofol with OH and NO 3 radicals were obtained over the temperature range of 280–380 K and at 1 atm. The rate constants for the reactions of p,p' -Dicofol with OH and NO 3 radicals are 1.51 × 10−12 and 8.88 × 10−14 cm3 molecule−1 s−1, respectively. The lifetime (τ Total) of p,p' -Dicofol determined by the reactions of OH and NO 3 radical is 5.86 h, indicating a potential long-range transport in the atmosphere. Graphical abstract Image 1 Highlights • We studied a comprehensive mechanism of the reactions between p,p' -Dicofol and OH/NO 3 radicals. • The lifetime (τ Total) of p,p' -Dicofol determined by the reactions with OH and NO 3 radical is 5.86 h. • NO 3 addition and its subsequent reactions yield 2,8-DCDD. [ABSTRACT FROM AUTHOR]