Effects of physicochemical factors on the transport of aged polystyrene nanoparticles in saturated porous media

Plastic debris, particularly nanoplastics, have attracted substantial attention as an emerging pollutant of global concern. The aging process caused by UV could dramatically alter the physicochemical properties of polystyrene plastics and affect their fate and transport in the subsurface environment. We researched the effects of diverse factors, including flow rate, ionic strength (IS), and cation valence on the transport of aged polystyrene nanoparticles (PSNPs) in saturated porous media and found that their mobility was greatly enhanced by the aging process at all other experimental conditions except coexistence with Al3+. Interestingly, we found that the aged PSNPs were polymerized due to the coexistence with Al3+, which led the aged PSNPs to exhibit weaker mobility than the pristine. Zeta potential and particle size measurements, FTIR spectroscopy, and XPS were employed to characterize the PSNPs, and the results suggest that UV radiation provides O-containing functional groups for the PSNPs. The experimental results correspond well with the ADR model and the values of Smax and k closely reflect the deposition of the PSNPs in sand columns. Moreover, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theoretical calculation accurately reflects the interaction of the pristine and aged PSNPs and quartz sand. Overall, due to the processes that PSNPs possibly undergo in the environment, their mobility may fluctuate dramatically. These findings help remedy knowledge deficiency regarding nanoplastic mobility being affected by aging processes, further underscore the critical influence of the aging process on the potential risks and environmental fates of nanoplastics. [Display omitted] •Aged PSNPs transport easier than the pristine in NaCl, CaCl2, and MgCl2 solutions.•The mobility of aged PSNPs in AlCl3 solution is lower than the pristine.•UV-radiation provides O-containing functional groups with the PSNPs.•DLVO theory explains the transport behaviors of pristine and aged PSNPs accurately.