Mechanistic and Kinetic Study of Atmospheric Oxidation of Chlordane Initiated by OH Radicals

Abstract

Chlordane, one of the extremely hazardous Persistent Organic Pollutants (POPs), was widely used as pesticides all over the world and its residues have been detected at high concentrations in many areas. As a species of Semi-Volatile Organic Compounds (SVOCs), chlordane exists mainly in the atmosphere where it can be migrated and transformed. Due to the carcinogenic and mutagenic properties, understanding its atmospheric fate is of great significance. In the present work, the oxidation mechanism of chlordane initiated by OH radicals under the atmospheric conditions was investigated by using Density Functional Theory (DFT). The geometrical structures were optimized at the M06- 2X/6-311+g(d,p) level and single-point energies were calculated at the M06-2X/6-311+g(3df,2p) level. The relevant rate constants of the key elementary reactions were calculated by using Rice-Ramsperger- Kassel-Marcus (RRKM) theory at 298 K and 1 atm. All of the energetically favorable pathways were discussed in detail, and theoretical results showed that the oxidation products are dichlorochlordene, hydroxychlrodane, cycloketone and dichloracyl. Combined with available experimental observation, this study can, therefore, help to clarify the atmospheric fate of chlordane.