Effects of solution chemistry and humic acid on the transport of polystyrene microplastics in manganese oxides coated sand

Microplastics as the emerging persistent pollutants have attracted more attention in the terrestrial environments. In this study, the transport behavior of polystyrene microplastics (PSMPs) in manganese oxides coated sand (MOCS) was examined under different pH, ionic strength (IS), cationic type and humic acid (HA) conditions. Compared with the transport behavior of PSMPs in the bare sand, the mobility of PSMPs in MOCS was significantly lower and less affected by pH, IS and cation type, which can be attributed to the existence of attractive electrostatic force and rougher collector surfaces of MOCS. Specifically, the transport of PSMPs was inhibited when cotransport with Cd2+. Furthermore, the HA significantly increased the transport of PSMPs in the MOCS, and the mobility increased with the increase of HA concentration ranged from 0 to 10 mg L−1. The results can contribute to the further understanding of the migration mechanism and fate of microplastics in the soil system.