Scavenging of polystyrene microplastics by sediment particles in both turbulent and calm aquatic environments

Microplastic particles (MP) are emerging pollutants ubiquitously distributed in all aquatic environments, remaining in suspension in the water column or deposited in sediment beds. MP are suspended in the water column along with other particles with whom they might interact. The current study presents the results of slow-settling MP (Polystyrene) scavenged by fast-settling sediment particles. The study covers a wide range of salinities (from freshwater to saltwater) and shear rates (from calm to mixing ecosystems). In calm regions, the scavenging by fast-settling sediment particles produces the greatest removal of MP from the water column (42 % of MP in suspension), thus increasing the MP pollution of sediment beds. In contrast, turbulence reduces the settling of MP and sediment particles (72 % of MP remain in suspension), causing more pollution than in calm regions. Although salinity increased the buoyancy of MP, the scavenging by sediment has been found to overcome the increase in buoyancy. Consequently, MP are transported to the sediment bed independently on the salinity. Therefore hotspots of MP contamination in aquatic environments need to consider both the MP and sediment interaction and the local mixing of the water column.