Microplastic pollution characteristics, transport, and control in urban stormwater runoff

Microplastics (MPs) have received increasing attention as emerging pollutants posing substantial ecological risks. Urban stormwater runoff is an important pathway by which MPs are transported into soil and aquatic environments, where they adversely affect organisms and ecosystem functions. This review synthesises the occurrence, sources, environmental behaviour, and control strategies of MPs in urban runoff. Research indicates that these particles primarily originate from discarded plastic fragmentation, tyre and road wear, and atmospheric deposition. Their abundance is significantly influenced by land-use types, antecedent dry periods, and rainfall intensity. The migration of MPs across media is a complex process governed by intrinsic particle properties (size and density) and extrinsic factors like topography and hydrology. Current management focuses on source reduction through street cleaning and interception by way of stormwater infrastructure and low-impact development facilities, such as bioretention systems and wetlands. While these methods effectively capture larger fragments, gaps remain regarding the long-term fate of nanoplastics and their synergistic toxicity with other pollutants. Future research should prioritise developing intelligent monitoring networks and standardised policies to enhance the resilience of urban ecosystems against MP pollution.