Self-sensitized photochlorination of benzo[a]pyrene in saline water under simulated solar light irradiation.

Chlorinated organic compounds are ubiquitously detected in saline waters. The photochlorination of organic compounds is one possible source, and chlorine radicals originating from other photosensitive substances have been reported to be responsible for organic compounds chlorination in previous reports. In this study, benzo[a]pyrene (BaP) chlorination in 10% acetonitrile/NaCl aqueous solution was initiated by self-sensitization of BaP, while chlorine radicals were not involved in the reaction. After 45 min of photoreaction in four seawater samples, chlorinated product (6-ClBaP) accounted for 10-17% of the fraction of transformed BaP, which was higher than that previously reported. The influences of Cl-, pH, humic acid, electron donors, and particulate matter on the formation of chlorobenzo[a]pyrene were systematically investigated. A self-sensitized photochlorination reaction mechanism was proposed as follow: photoexited BaP was activated to singlet state and then transformed to triplet state through inter-system crossing. Then the excited triplet state and oxygen formed [3BaP*-3O2] or [BaP-1O2] complex, which further reacted with Cl- to produce 6-ClBaP.