Microplastics in constructed wetland ecological systems: Behavior, fate and environmental risks

Microplastics (MPs) have emerged as pervasive contaminants in aquatic environments and are increasingly recognized as a critical stressor in constructed wetlands (CWs). To systematically evaluate the behavior and fate of MPs, this review followed PRISMA guidelines, retrieving and screening over 405 peer-reviewed publications from 2019 to 2025 across Web of Science, Scopus, and Google Scholar. Using a rigorous inclusion criterion based on data quality and experimental relevance, 131 key studies were selected for in-depth synthesis and comparative analysis. Beyond serving as effective physical barriers that consistently achieve removal efficiencies exceeding 90%, CWs function as dynamic biogeochemical reactors where MPs undergo extensive aging, transformation, and biofilm colonization, thereby triggering complex long-term ecological risks. The roles of plants, substrates, microorganisms, and animals in MPs retention and transformation are critically evaluated, together with the influence of MPs properties (polymer type, size, and morphology) and wetland configurations on removal efficiency. Furthermore, the ecological responses of CWs under MPs exposure are comprehensively discussed. MPs exposure was found to significantly alter microbial community diversity, potentially inhibiting nitrogen removal and promoting greenhouse gas (CH₄ and N₂O) emissions. Particular attention is given to the aging behavior of MPs, additive release, pollutant adsorption, and their coupled ecological risks. Current challenges, such as the lack of standardized extraction methods and insufficient understanding of MPs-induced clogging, are identified. Finally, future research directions are proposed to enhance MPs management in CWs, aiming to balance pollutant removal performance, ecological safety, and long-term sustainability of wetland systems.