Spatial distribution, transport patterns, and dynamic processes of microplastics in global rivers: A review

: Rivers serve as the principal pathway for transporting microplastics from land to the ocean, thereby playing an indispensable role in their global transport. This study conducted a bibliometric review based on 176 field-observation datasets and 323 mechanism-related publications spanning 2004-2026 to synthesise the spatial distribution, transport patterns and dynamic processes of microplastics in global river systems. Bibliometric analysis indicated that riverine microplastic research is growing rapidly but still accounts for only 11.16 % of total microplastic publications. Existing studies are dominated by occurrence surveys, while mechanistic research on transport and interfacial processes is relatively limited and represents the main emerging research frontier. Our dataset reveals that riverine microplastic pollution exhibits significant spatial heterogeneity worldwide. Africa possesses the highest microplastic concentrations in river water, while Europe suffers the most serious microplastic contamination in river sediments. Microplastic abundance hotspots are closely linked to urban areas, yet a marked spatial decoupling exists between hotspots in the water column and those in sediments. Small-sized particles, fibers/fragments, together with PE/PP dominate in both water and sediment phases. We conducted a comprehensive analysis of the transport patterns of riverine microplastics and their underlying theoretical foundations, including surface transport, suspended transport, bedload transport, turbidity current transport, hyporheic exchange, infiltration transport, and tidal-mediated alternate-flow transport. The findings further reveal six primary dynamic processes and associated driving factors governing riverine microplastic transport: diffusion, settling, resuspension, aggregation, eddy, and secondary current. The gap analysis reveals a substantial discrepancy between microplastic distribution patterns in complex natural environments and mechanistic understanding derived from controlled conditions, indicating that validation across a broader range of environmental conditions is needed to bridge laboratory findings and real-world river processes. These efforts will advance the prediction of microplastic fate and support targeted aquatic pollution mitigation.