The vertical transport and fate of MPs-oil composite pollutants in nearshore environment

MPs-oil composite pollutants interact with particles to form MPs-oil-particles aggregates (MOPAs) in nearshore environment. In this study, we investigated vertical transport and fate of MPs-oil composite pollutants mediated by particles under various time scales, proposed and elucidated associated mechanisms. Majority of MPs with -CH2 suspended in water columns and particles with Si-O and O-H adsorbed MPs-oil composite pollutants in sediment phase, which caused differences in morphology structure and composition. The MOPAs with spherical or irregular three-dimensional in water columns can transport to sediment phase, resulting in more than 79 % lamellar MOPAs and more than 63 % oil in sediment phase. Besides, we demonstrated that degraded small-sized MPs-oil composite pollutants can resuspend into water columns. The mass of n-alkanes in sediment phase (< 45 mu g) was lower than in water columns (< 120 mu g) during degradation process. More importantly, during the intermediate stage of degradation, the size of oil droplets on surface of MPs decreased and particles trapped them to sediment phase, resulting in a V-shaped curve of mass changes of C-14-C-35 in water columns. Our research fills the gap in the field of MPs-oil composite pollutants in water columns and sediment phase, which can provide theoretical support for their disposal.