The environmental impacts and remediation strategies of microplastics in aquatic sediments

Microplastics, defined as synthetic polymer particles smaller than 5 mm, have become pervasive contaminants in aquatic sediments worldwide, where they function as long-term repositories that integrate multiple environmental stressors. Sediment concentrations are commonly three to five orders of magnitude higher than those measured in overlying water, reflecting continuous inputs from both primary microplastics intentionally produced at small sizes and secondary microplastics formed through fragmentation of larger plastic debris. This review synthesizes a current understanding of microplastic sources, transport processes, and ecological implications in sedimentary environments, while highlighting key barriers to effective management. Microplastics reach sediments through point sources such as wastewater treatment plants and industrial discharges, as well as diffuse pathways including atmospheric deposition and stormwater runoff. Their transport and accumulation are governed by polymer density, particle size, biofilm development, and hydrodynamic conditions. Once deposited, microplastics interact with surrounding sediments by sorbing persistent organic pollutants and trace metals, thereby modifying contaminant partitioning and potential bioavailability. Benthic deposit-feeding organisms are directly exposed through sediment ingestion, although field evidence linking sediment contamination to bioaccumulation and trophic transfer remains limited. Despite growing recognition of risk, major knowledge gaps persist. Methodological inconsistency in sampling, extraction, and polymer identification limits comparability among studies, while limited temporal monitoring constrains understanding of disturbance-driven redistribution. These scientific challenges are compounded by unequal monitoring capacity and regulatory development across regions, creating data-poor areas where contamination burdens may be substantial. Addressing sediment microplastic contamination requires coordinated progress in analytical standardization, advanced monitoring technologies, interdisciplinary collaboration, and integrated mitigation strategies that prioritize source reduction alongside technological and nature-based solutions.