Accelerated indirect photolysis of UV-328 within the hydrophobic microdomains of dissolved organic matter: the role of sorption and localized reactive intermediates

Abstract

UV-328 is a persistent, bioaccumulative, and toxic pollutant, whose environmental fate is critical for risk assessment. This study investigated its distribution and indirect photodegradation in dissolved organic matter (DOM)-water systems. Solubility enhancement experiments revealed strong partitioning of UV-328 onto various DOMs (log K_DOC = 5.08–5.90), positively correlated with DOM aromaticity. While direct photolysis of UV-328 was negligible, its degradation was significantly accelerated within the hydrophobic microdomains of DOM. Quenching and probe experiments identified photochemically produced reactive intermediates (PPRIs) as the driving force, with triplet-state DOM (³DOM*) and singlet oxygen (¹O₂) as the key species. Crucially, a dual-probe method confirmed the micro-heterogeneous distribution of PPRIs, with their elevated concentrations within the DOM phase accounting for the accelerated photolysis. Transformation pathways, including hydrolysis, side-chain cleavage, and hydroxylation, were proposed. ECOSAR predictions suggested that the resulting photoproducts had lower ecotoxicity than the parent compound. These findings underscore that the heterogeneous distribution of both pollutants and reactants is a decisive factor in the photochemical fate of hydrophobic contaminants, highlighting DOM-mediated phototransformation as a key environmental attenuation pathway.