Aging of PVC pipes induces release of microplastics: Insight into the role of the hydrophilicity of pipe inner surface

Microplastic pollution in drinking water pipelines has received growing attention in recent years. However, the mechanisms underlying microplastic release from pipe materials remain unclear. In this study, PVC pipes were artificially aged using potassium permanganate (KMnO 4 ), sodium hypochlorite (NaClO), and ultraviolet (UV) irradiation. The aged pipes were then subjected to hydraulic scouring to evaluate microplastic release behavior. Results showed that KMnO 4 - and UV-aged pipes predominantly released microplastics smaller than 100 μm, whereas NaClO-aged pipes tended to release larger particles. Aging reduced the contact angle of the pipe inner surface, indicating increased hydrophilicity. Pipes with similar hydrophilicity levels exhibited comparable microplastic release quantities, and greater hydrophilicity was associated with higher release. A regression analysis revealed a strong negative correlation between contact angle and microplastic release, identifying hydrophilicity as a key factor influencing release under hydraulic scouring. This study introduces hydrophilicity as a novel and significant factor in the analysis of microplastic release from aged pipes, offering new insights into the release mechanisms and providing a theoretical foundation for further research.