Indirect photodegradation of pharmaceutical and personal care products in dissolved black carbon solution: The role of microheterogeneous distribution of hydroxyl radical and sorption.

Dissolved black carbon (DBC) with a hyperconjugated structure is ubiquitous in nature, and plays a crucial role in the migration and transformation of environmental contaminants due to its prominent properties of accepting electrons and sorption. However, little is known about the DBC-induced phototransformation of pharmaceutical and personal care products (PPCPs) in natural waters. Herein, the photodegradation kinetics of PPCPs were investigated in DBC solution under simulated solar irradiation and compared with those in Suwannee River natural organic matter (SRNOM) solution. The decay rates for the positively charged PPCPs (mean 1.484 ± 0.041 h-1) were significantly higher than those for the negatively charged PPCPs (mean 0.014 ± 0.002 h-1) in DBC solution due to the charge interaction. Moreover, the decay rates for the positively charged PPCPs in DBC solution were approximately 3-16 times of those in SRNOM solution due to the discrepant sorption and ability to produce bonded HO•. Finally, a microheterogeneous photodegradation mechanism of HO•-labile PPCPs in DBC solution involving the sorption and subsequent reaction with bonded HO• in the DBC microphase was proposed, which was verified using isopropanol and isopropamide as selective HO• scavengers. This work will provide useful insights into the photochemistry of DBC and also the DBC-involved phototransformation of PPCPs in aquatic environments.