Theoretical study on the OH-initiated atmospheric reaction of 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT)

p,p′-DDT is a member of the widely used organochlorine pesticides. In this paper, the mechanism for the OH-initiated reaction of p,p′-DDT is studied at the MPWB1K/6–311 + G(3df,2p)//MPWB1K/6–31 + G(d,p) level. The OH addition reaction to the C2 atom and H abstraction reaction from alkyl are energetically favorable pathways in OH-initiated reactions of DDT. On the basis of the quantum chemical information, the Rice–Ramsperger–Kassel–Marcus (RRKM) theory is used to calculate the rate constants over the temperature range of 200–800 K. The OH addition reaction is dominant according to the branching ratio, and the atmospheric lifetime of p,p′-DDT is 7.9 days. This work provides a comprehensive understanding of the OH-initiated atmospheric degradation of p,p′-DDT which is helpful for experiments and risk assessment.

The branching ratio of each reaction among the OH-initiated reaction from 200 to 800 K (a: OH radical addition; b: H atoms abstraction; c: addition reaction vs abstraction reaction.Figure optionsDownload high-quality image (116 K)Download as PowerPoint slideHighlights
► The OH-initiated reactions include H-abstracted and OH addition reaction.
► The Non-Arrhenius formulas of rate constants with the temperature are fitted.
► The rate constant of DDT relative to OH radical is 1.50 × 10−12 cm3 molecule−1 s−1.