Cotransport of nanoplastics (NPs) with fullerene (C60) in saturated sand: Effect of NPs/C60 ratio and seawater salinity

Nanoplastics (NPs) have been identified as newly emerging particulate contaminants . In marine environments, the interaction between NPs and other engineered nanoparticles remains unknown. This study investigated the cotransport of NPs with fullerene (C 60 ) in seawater-saturated columns packed with natural sand as affected by the mass concentration ratio of NPs/C 60 and the hydrochemical characteristics. In seawater with 35 practical salinity units (PSU), NPs could remarkably enhance C 60 dispersion with a NPs/C 60 ratio of 1. NPs behaved as a vehicle to facilitate C 60 transport by decreasing colloidal ζ-potential and forming stable primary heteroaggregates. As the NPs/C 60 ratio decreased to 1/3, NPs mobility was progressively restrained because of the formation of large secondary aggregates. When the ratio continuously decreased to 1/10, the stability and transport of colloids were governed by C 60 rather than NPs. Under this condition, the transport trend of binary suspensions was similar to that of single C 60 suspension, which was characterized by a ripening phenomenon. Seawater salinity is another key factor affecting the stability and associated transport of NPs and C 60 . In seawater with 3.5 PSU, NPs and C 60 (1:1) in binary suspension exhibited colloidal dispersion, which was driven by a high-energy barrier. Thus, the profiles of the cotransport and retention of NPs/C 60 resembled those of single NPs suspension. This work demonstrated that the cotransport of NPs/C 60 strongly depended on their mass concentration ratios and seawater salinity.