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
(KOC), 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.