Fibrous and Filmy Microplastics Exert Opposite Effects on the Mobility of Nanoplastics in Saturated Porous Media

Abstract

This study explored the influence of fibrous and filmy polyethylene terephthalate (PET) on the transportation of NPs in saturated porous media. With the strong electrostatic repulsion, the negatively charged PET fibers (-57.5 mV) improved the transport of NPs, and the mass percentage of NPs recovered from the effluent ( Meff ) increased from 69.3% to 86.7%. However, PET films (-49.7 mV) showed the opposite result, that is, Meff decreased from 69.3% to 57.0%. X-ray micro-computed tomography quantitatively revealed the change in effective porosity of porous media before and after adding various PET MPs. The addition of 10 mm fiber increased the porosity from 0.39 to 0.43, whereas the addition of 10×102   film reduced the porosity from 0.39 to 0.29. In addition, the variation in saturated hydraulic conductivity (K s) reflected the change in the ability of the porous system to transfer water. The fiber-facilitated transport of NPs is presumably due to the formation of new connected pores between fibers and sand grains, whereas the film-inhibited transport of NPs may be due to the partial truncation of transport path of NPs. Overall, the effect of coexisting MPs on the mobility of NPs strongly relies on the shape and size of MPs.

Keywords: Micro-CT analysis, Micro/nanoplastics, transport, Fibers, Films