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Chlorination-driven leaching and characterization of dissolved organic matter from PVC microplastics
Summary
PVC plastic pipes are common in water systems, and this study found that chlorine (the disinfectant used to keep tap water safe) actually breaks down PVC microplastics faster, causing them to release more dissolved carbon-based compounds into the water, especially early on and at higher chlorine levels. This matters because it suggests the very process we use to disinfect drinking water may be speeding up plastic breakdown in pipes, potentially adding more tiny plastic particles and byproducts to the water we drink, though more research is needed to know exactly how this affects human health.
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), 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.