Effect of pre-oxidation on the release of brominated DBP precursors from microplastics and its fluorescence characteristics

Abstract

The widespread occurrence of microplastics (MPs) in aquatic environments has raised concerns about their interactions with water treatment processes, particularly through the release of microplastic-derived dissolved organic matter (MP-DOM) that may serve as precursors to toxic disinfection byproducts (DBPs). While the leaching of DBP precursors from MPs has been documented, the influence of halogenated plastic additives under oxidative weathering conditions remains poorly understood. This study investigates the effects of typical pre-oxidation treatments—ultraviolet (UV) irradiation, chlorination (Cl₂), and their combination—on the release and transformation of MP-DOM from polyethylene (PE) and polylactic acid (PLA), and its contribution to brominated DBP (Br-DBP) formation during subsequent chloramination. The roles of both inorganic bromide ions and a model brominated flame retardant (decabromodiphenyl ethane, DBDPE) were evaluated as bromine sources. UV-based treatments significantly enhanced the release of humic-like fluorescent components from MPs and increased Br-DBP formation by up to 100-fold, particularly in the presence of brominated additives. While bromide ions directly promoted Br-DBP generation, DBDPE acted as a latent bromine source, releasing reactive bromine only under oxidative conditions. PE-derived DOM exhibited stronger correlations between fluorescence properties and DBP formation metrics, including estimated cytotoxicity, compared to PLA-DOM. These findings underscore the need to monitor MP-DOM characteristics in water treatment systems, as oxidative pre-treatment can enhance the release of reactive DOM fractions and increase Br-DBP risks, particularly in the presence of brominated plastic additives.