Microplastics and nanoplastics in stormwater management engineered porous media systems: a systematic review of their sources, transport, retention, and removal characteristics

Abstract

The widespread presence of microplastics and nanoplastics (MNPs) in stormwater poses significant risks to both ecological and human health, necessitating the development of effective and sustainable mitigation strategies. Stormwater management engineered porous media systems (SWMEPMS) have emerged as promising solutions, leveraging filtration processes to capture and retain MNPs while supporting Sustainable Development Goals (SDGs 6, 11, and 14). Despite their potential, research on the fate of MNPs within SWMEPMS remains limited. Most importantly, no prior study has systematically and comprehensively reviewed how SWMEPMS remove MNPs from stormwater, particularly in relation to removal mechanisms, porous media characteristics, and water chemistry, despite their growing application and relevance. To bridge this gap, the standardized PRISMA methodology was employed to review the sources, transport, retention, and removal characteristics of MNPs in SWMEPMS. Key findings of the review highlight that MNPs in stormwater runoff are predominantly composed of polymers, including polyethylene, polypropylene, polystyrene, and tire wear particles (TWPs). SWMEPMS demonstrate up to 100% removal efficiency through mechanisms like sedimentation, straining, entrapment, entanglement, accumulation, agglomeration, electrostatic interactions, and surface complexation. Engineered porous media characteristics, such as surface properties, particle size distribution, and porosity, play crucial roles in enhancing removal efficiency, with porous media like limestone and biochar demonstrating greater performance than sand. The presence of functional groups, such as carbonyl, hydroxyl, carboxyl, and amino groups, on either the media or MNPs enhanced the removal efficiency of SWMEPMS. This review synthesises existing knowledge, identifies gaps, and offers recommendations for future research to enhance this technology.