Microplastic types dominate the effects of bismuth oxide semi-conductor nanoparticles on their transport in saturated quartz sand

The transport of microplastics (MPs) is of great significance due to its potential threat to subsurface systems. The copresence of MPs and semi-conductor nanoparticles is quite common in practical environments (i. e. in electronic/electrical waste disposal sites). To date, the influence of bismuth oxide (BiO) semi-conductor nanoparticles on MPs transport in porous media has still been rarely and explicitly explored. Therefore, the effect of BiO on the transport of distinct types of MPs were investigated using column experiments. The MPs included 0.51 μm and 1.1 μm polystyrene (PS), 1 μm polyethylene terephthalate (PET) and 1 μm polyethylene (PE) MPs. Mechanisms for the differently altered transport of various MPs with BiO were further elucidated. It was verified that the deposited BiO on sand surfaces could contribute to the decreased transport of PET and PE MPs by column experiments with pre-treatment. Moreover, scanning electron microscopy (SEM), dynamic light scattering (DLS) measurements, and electrochemical Nyquist curves demonstrated that the interaction of PE and PET MPs with BiO was more pronounced than that of PS MPs, especially for PE MPs. In addition, density functional theory (DFT) calculations combined with adsorption experiments further confirmed that the adsorption between PE MPs and BiO was the strongest, which then contributed to the highest decrease of PE MPs transport. This study highlighted that the MPs types might be the major factor controlling its interaction with copresent substances, thereby affecting its fate and transport in soil systems.