Effects of Nano- and Microplastic Particles (NMPs) on the Transport of PFOA in Natural Sediment

Per- and polyfluoroalkyl substances (PFAS) ubiquitously coexisted with nano- and microplastic particles (NMPs) in natural sediment. The divergent physiochemical characteristics of nanoplastics (NPs) and microplastics (MPs) may differentially modulate PFOA transport and associated environmental risks by serving as distinct vectors, yet, the magnitude and mechanisms of these effects remain poorly elucidated. Here, column experiments were conducted to investigate the impacts of polystyrene (PS) NPs (0.1 μm) and MPs (5 μm) on the transport of perfluorooctanoic acid (PFOA) in saturated natural sediment under two pH conditions (4.7 and 6.0). Results showed the individual transport of PS NMPs and the adsorption affinity of PFOA to these particles collectively governed the overall impact on PFOA transport in sediment. Smaller PSNPs had an insignificant influence on PFOA mobility under both pH conditions, yielding effluent recoveries > 90.55 ± 2.20% versus 91.92 ± 1.00% ~ 93.97 ± 0.48% in a single-solute system. This was likely due to the high mobility capacity of both PSNPs and potential PSNPs-PFOA complex in the sediment. In contrast, despite the majority of PFOA remaining unbound to the PSMPs surface (> 91.13%), larger sized PSMPs can act as a vehicle to slightly enhance the retention of PFOA due to its high retention in sediment across both pH conditions. This study underscored the necessity of distinguishing between NPs and MPs when evaluating PFOA transport risks in natural sediment environments.