Microplastics generation from PVC pipes in drinking water distribution systems: Effects of aging and flow conditions

Microplastics (MPs) contamination in drinking water has raised increasing health concerns, yet the contributions of different aging and flow conditions on the release of MPs from plastic pipes remain insufficiently understood. This study examined the effects of external photoaging, internal chlorine aging, and their combination on MPs release from polyvinyl chloride (PVC) pipes under stagnant and flow conditions. In stagnant water, external photoaging showed no significant influence on MPs release from PVC pipe interiors. In contrast, internal chlorine aging and combined aging significantly increased MPs release, with no statistical difference between them, indicating that internal chlorine aging was the dominant factor responsible for MPs release. After internal chlorine aging at 1.7 mg/L as Cl₂ for 9, 27, 54, and 81 d, MPs counts released into stagnant water increased from 134 ± 10 to 314 ± 59 particles. In flowing water (5.5 L/min), MPs release was substantially higher, reaching 949 ± 102 particles after 81 d, in which MPs were primarily in the <10 μm size range (30-214 particles, 40-62%). Although the carbonyl index (CI) increased with aging duration for all aging scenarios, the smallest increase occurred under internal chlorine aging, suggesting that CI was not directly linked to MPs release. Scanning electron microscopy revealed progressive hole formation on the PVC inner surfaces due to chlorine attack. Positive correlations were observed between hole density and MPs release, indicating that physical deformation resulting from chlorine oxidation was a key factor associated with MPs release.