Interaction between Differentially Charged Microplastics Particles and Soils

Microplastics (MPs) have attracted increasing concern as emerging contaminants of global importance in recent years. Soil is considered an important sink for MPs. Due to environmental weathering, MP surfaces are often charged, but there are limited studies on the interaction of differentially charged MP with soils. This study constructed Derjaguin−Landau−Verwey−Overbeek (DLVO) potential energy profiles, investigated the interaction mechanism of MPs with positive (MP+) and negative (MP-) charges on nine typical soils through quantitative analysis of fluorescence intensity, and found that the attachment capacity of MP to soil was consistent with the predicted results of DLVO interaction energy calculation. The attachment of MPs to different soils fit the pseudo-second-order kinetic model well. The attachment isotherm data of MP+ fit the linear model better, while the MP- data fit the Langmuir model. The attachment capacity of MPs was significantly correlated with the zeta potential of soils. These results, as well as the Fourier transform infrared spectroscopy (FTIR) spectra and scanning electronic microscopy (SEM) images of soils, indicated that electrostatic interactions and physical trapping were the dominant mechanisms for MP attachment to soils. The high attachment capacity of soil for MPs is worrisome, as it could adversely impact soil health and ecosystems