Photoformation of EPFRs during phototransformation of polycyclic aromatic hydrocarbons (PAHs) on particles in an aqueous solution: The hydrogenation of PAHs and effect of co-existing water matrix factors

<title>Abstract</title> Environmentally persistent free radicals (EPFRs) generated on particles under irradiation in water have attracted particular attention and their formation mechanisms are not well understood. This study investigated the photoformation of EPFRs on both actual samples collected from an oil production plant in Panjin, Liaoning, China and Fe(III)-montmorillonite simulated samples in water. EPFRs detected on actual samples are not easily generated compared with those in the soil or in the air based on the concentrations of identified PAHs. EPR signals at the range of 10¹⁷ to 10¹⁸ spin/g were detected on Fe(III)-montmorillonite simulated samples. Their g factors were smaller than 2.0030, which indicated the generation of carbon centered EPFRs. The primary byproducts were identified by chromatography-mass spectrometer (GC-MS) and a possible EPFR formation pathway during PAH degradation was proposed. Hydrogenation of PAHs during the photoformation of EPFRs was observed and might be due to catalysis of the simulated particles and the interaction of the intermediates. Meanwhile, effects of typical anions (NO₂⁻ and Cl⁻) and surfactant (TWEEN ® 80 and sodium dodecyl sulfate) were investigated, indicating the phototransformation process and adsorption process would affect the formation of EPFRs. Overall, our study provided useful information to understand the photoformation of EPFRs in aqueous environments.