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 (C60) in seawater-saturated columns packed with natural sand as affected by the mass concentration ratio of NPs/C60 and the hydrochemical characteristics. In seawater with 35 practical salinity units (PSU), NPs could remarkably enhance C60 dispersion with a NPs/C60 ratio of 1. NPs behaved as a vehicle to facilitate C60 transport by decreasing colloidal ζ-potential and forming stable primary heteroaggregates. As the NPs/C60 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 C60 rather than NPs. Under this condition, the transport trend of binary suspensions was similar to that of single C60 suspension, which was characterized by a ripening phenomenon. Seawater salinity is another key factor affecting the stability and associated transport of NPs and C60. In seawater with 3.5 PSU, NPs and C60 (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/C60 resembled those of single NPs suspension. This work demonstrated that the cotransport of NPs/C60 strongly depended on their mass concentration ratios and seawater salinity.