Photodegradation of Chlorinated Persistent Organic Pollutants (Cl-POPs) in Pearl River Suspended Particulate Matter–Water Systems: Kinetics, Quantitative Structure–Activity Relationship (QSAR) Development, and Mechanism

Chlorinated persistent organic pollutants (Cl-POPs) are highly hydrophobic and are easily adsorbed to solid particulate matter after being released into the water column, thus affecting the transformation process and environmental fate. This study investigated the photodegradation behavior of 16 Cl-POPs in the Pearl River suspended particulate matter (SPM)-water system. The photodegradation rates of polychlorinated biphenyls (PCBs) were generally higher than those of dioxins and increased with substitution numbers of Cl atoms. A QSAR model correlating photodegradation rate constants of Cl-POPs and their structural parameters was established by using multiple linear regression (MLR) analysis and machine learning. The model results showed that soil-water partition coefficient (K_OC), morgan fingerprint (mf_1747), and nucleophilicity index (NI) were the main factors affecting the photodegradation of Cl-POPs, confirming that the photodegradation of Cl-POPs with higher hydrophobicity and larger nucleophilic reactivity proceeded faster. According to the quenching experiment and theoretical calculation results, ^•O₂^- in the hydrophobic region contributed more to the strongly hydrophobic Cl-POPs, while the contribution of ^•OH was mainly concentrated in the weakly hydrophobic Cl-POPs. This study provided valuable insights into photolysis-related environmental persistence and fate of Cl-POPs in the SPM-water system.