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Transport of polystyrene microplastics in bare and iron oxide-coated quartz sand: Effects of ionic strength, humic acid, and co-existing graphene oxide
Summary
Researchers investigated how graphene oxide nanoparticles and humic acid influence the transport of polystyrene microplastics through sand columns, comparing bare quartz sand with iron oxide-coated sand. They found that iron oxide-coated sand strongly retained microplastics regardless of other factors, while graphene oxide significantly promoted microplastic transport by increasing surface charge and creating steric barriers. The study suggests that the co-presence of nanomaterials and organic matter in the environment can significantly alter how microplastics move through soil and groundwater systems.
This research explored the effects of widely utilized nanomaterial graphene oxide (GO) and organic matter humic acid (HA) on the transport of microplastics under different ionic solution strengths in bare sand and iron oxide-coated sand. The results found transport of polystyrene microplastics (PS) did not respond to the presence of HA in sand that contains large amounts of iron oxide. Compared to bare quartz sand, ionic strength had little effect: <20 % of PS passed through Fe sand columns. There was a significant promotion of PS transport in the presence of GO, however, which can be attributed to the increased surface electronegativity of PS and steric hindrance. Moreover, GO combined with HA significantly promoted the transport of PS in the Fe sand, and transport further increased when the concentration of HA increased from 5 to 10 mg/L. Interestingly, the degree of this increase exactly corresponded to the change in the surface charge of the microplastics, demonstrating that electrostatic interaction dominated the PS transport. Further results indicated that co-existing pollutants had significant impacts on the transport of microplastics under various conditions by altering the surface characteristics of the plastic particles and the spatial steric hindrance within porous media. This research will offer insights into predicting the transport and fate of microplastics in complex environments.