Resuspension of Micro- and Nanoplastics Trapped in Coastal Sediments: Insights into Their Cross-Interface Transport and Environmental Fate in Transitional Zones

Changes in environmental conditions may drive the transfer of micro- and nanoplastics (MNPs) between sediment layers and overlying waters, yet their resuspension behavior in coastal transitional waters and the underlying mechanisms remain unclear. This study comprehensively investigated the resuspension dynamics of MNPs from sediments with different properties, as well as the effects of aquatic environmental conditions, including salinity, sediment water content, and hydrodynamics, on MNP resuspension. Sediment grain size and mineralogical composition played a dominant role in governing MNP resuspension. Differences in resuspension behavior between microplastic and nanoplastic particles were identified. MNP resuspension showed a nonlinear response to salinity, with increasing salinity generally suppressing resuspension. Resuspension was highly sensitive to salinity changes within the low-salinity range. A U-shaped pattern was observed in PSNP resuspension, with the resuspension rate initially decreasing as sediment water content declined and then increasing as sediments became drier. Positive correlations between MNP resuspension and fluid shear rate were observed, while sediment-trapped MNPs exhibited distinct sensitivities to hydrodynamic disturbances between freshwater and marine conditions. Trapped MNPs were more susceptible to hydrodynamic disturbance under freshwater conditions. These findings offer valuable insights into MNP resuspension and advance understanding of their vertical transport and overall environmental fate in coastal regions.