ObjectiveAs one of the typical forces in the process of erosion and migration, sediment abrasion can accelerate the fragmentation of microplastics, thereby affecting microplastic migration and redistribution within the watershed. However, how sediment abrasion affects the fragmentation behavior of microplastics is still unclear. Therefore, the objective of this study was to investigate the effect of sediment abrasion on the fragmentation of microplastics.MethodIn this study, topsoil was collected from a mulched cornfield in the Wangdonggou small watershed of the Loess Plateau and the abundance, type, and morphology of microplastics were analyzed using a laser infrared imaging system after different treatments. The different treatments include air-dried original soil, sediment standstill, and sediment abrasion with three concentrations of 560 kg·m^-3, 800 kg·m^-3 and 930 kg·m^-3.ResultThe results showed that: (1) PU, Polytetrafluoroethylene (PTFE), and Rubber (RB) were the main microplastics in the study area, mostly in the form of fragments with a diameter of 10~50 μm.(2) The average area of microplastic was largest in the air-dried soil treatment (5, 234 μm²) and the smallest (2, 067 n·kg^-1) was in the sediment standstill treatment. The microplastics after sediment abrasion treatments had the greatest average abundance (14, 400 n·kg^-1) and the smallest average area (2, 868 μm²). (3) The average abundance and area of microplastic under the three sediment abrasion treatments were significantly different. The average abundance of microplastic followed the pattern: moderate sediment concentration (18, 300 n·kg^-1) > low sediment concentration (13, 730 n·kg^-1) > high sediment concentration (8, 667 n·kg^-1), whilst the average area of microplastic showed: low sediment concentration (3, 932 μm²) > moderate sediment concentration (2, 472 μm²) > high sediment concentration (2, 099 μm²).ConclusionOverall, this study demonstrates that sediment abrasion significantly increased the microplastic abundance and reduced their areas, but the average abundance of microplastic reached the maximum at the moderate sediment concentration abrasion intensity. The sensitivity of different microplastic types to sediment abrasion was different, providing guiding information for the risk assessment of soil microplastic fragmentation and migration in eroding settings.