Permeable pavement systems for microplastic mitigation: Critical insights on transport, retention, detection and...

Microplastics (MPs) in urban stormwater are emerging contaminants of increasing concern due to their persistence, mobility, and potential impacts on ecosystems and human health. Permeable pavement systems (PPS) have gained attention as stormwater control measures capable of intercepting MPs; however, their long-term performance and associated uncertainties remain poorly understood. This paper synthesises current evidence on MP transport, retention, detection, and removal in PPS based on twenty-eight peer-reviewed studies published between 2000 and May 2026. The evidence indicates a rapidly emerging field, with most studies published during the past six years and annual output peaking in 2025. Reported short-term MP retention efficiencies range from 89% to 99.6% under controlled and field conditions. However, meaningful comparison among studies is constrained by substantial variation in pavement configurations, hydraulic loading, MP characteristics, and analytical methodology. Retention occurs predominantly within surfaces, joints, bedding, and geotextile layers, whereas fragment-shaped MPs (<100 µm) are most frequently detected in effluent. Emerging design innovations, including drinking water treatment sludge, cured carbon fibres, recycled e-polycarbonate aggregates, and tyre- or plastic-derived materials, show potential for enhancing retention and hydraulic or mechanical performance. Nevertheless, their long-term durability, remobilisation potential, secondary MP generation, and life-cycle implications remain largely unresolved. Overall, current evidence provides stronger support for short-term MP interception than sustained environmental risk reduction. Future research should prioritise harmonised monitoring and analytical protocols, long-term field validation, improved detection of tyre wear particles, mass-balance assessment, and evaluation of MP remobilisation under realistic hydraulic, climatic, and maintenance conditions to strengthen confidence in PPS as sustainable stormwater treatment technologies.