Chlorination-driven leaching and characterization of dissolved organic matter from PVC microplastics

Polyvinyl chloride (PVC) is one of the most widely used plastic polymers in drinking-water distribution systems. Despite its prevalence, the synergistic influence of chlorine disinfectants and environmental stressors on PVC degradation and the chlorination-driven release of dissolved organic matter (DOM) remains poorly quantified. Leaching experiments using PVC-microplastics (PVC-MPs) were conducted in both ultrapure-water and river-water media with various chlorine concentrations under water, thermal, and UV irradiation conditions to characterize chlorine- and leaching condition-dependent shifts in dissolved organic carbon (DOC), chromophoric DOM (CDOM), fluorescence excitation-emission matrices (EEMs), and other surface and optical properties, including size, Zeta-potential, spectral slope (S_275-295), specific-UV-absorbance at 254 nm (SUVA₂₅₄), and PARAFAC-derived fluorescent components. Significant morphological alterations on PVC-MPs surfaces were observed under all leaching conditions, demonstrating the susceptibility of PVC to oxidative and photolytic aging. Distinct patterns emerged across leaching conditions: water leaching consistently yielded the highest DOM release in both CDOM and DOC, particularly during early stages, characterized by higher molecular weight and greater aromaticity relative to thermally and UV-induced leaching. Fluorescence EEM spectra were dominated by protein-like and humic-like components, with fluorescence intensities increasing systematically with both chlorine concentration and leaching duration. Higher chlorine levels generally maintained DOM at nano-sizes below 400 nm. By integrating controlled chlorine exposure, multiple environmental stressors, natural water matrices, and advanced optical-fluorescence characterization, this study provides new insights into PVC-MPs degradation pathways and their implications for drinking-water disinfection practices, distribution system performance, and aquatic environmental quality.