Dispersal and transport of microplastic particles under different flow conditions in riverine ecosystem

Microplastic (MP) pollution is a global issue owing to its potential threats to ecosystems and human health. MP pollution in river ecosystems is widely investigated, but the transport process under different hydrological conditions remain unclear. In this study, an approach of particle tracking in conjunction with hydrodynamic modeling was developed to investigate the dispersal and transport processes of microplastic particles in riverine ecosystem. The concentration and dispersal pattern of polyamide (PA), polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) particles under base flow and flood events with recurrence intervals of 10-year, 20-year and 50-year were identified. Results indicated that rainfall intensity had a significant impact on the microplastic transport in rivers. Higher suspension concentration and lower sedimented concentration were observed in high flow periods, and the sedimented concentration showed a slow increasing trend in the flood recession stage. High water velocity facilitated the microplastic particles to be migrated for a longer distance, and high water flow was conducive to transport more microplastics from source points. Besides, microplastic particles with high density had worse mobility in water and more prone to deposition. PET were likely to be transported for a relatively shorter distance, while PP had higher mobility and took less time to reach the same simulation point. This study put forward an effective approach to understand the transport of MPs in the river. The results obtained are useful to identify pollution hotspots and track pollution paths.