Study on the Effect and Mechanism of PE Microplastics on Cadmium Adsorption in Soil.

Microplastics affect the sorption of heavy metals by soils and alter their migration and transformation in soils. In this paper, the changes in the soil adsorption performance of cadmium (Cd) in the presence of polyethylene microplastics (PE-MPs) with different particle sizes (13, 48, 150 μm) were investigated, to explore the related mechanisms with the help of scanning electron microscopy-X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The results showed that the effect of PE-MPs on soil adsorption of Cd²⁺ was manifested as inhibiting the adsorption of Cd²⁺ and promoting the desorption of Cd²⁺; this effect was more obvious when the dose of PE-MPs was higher or the particle size was larger. Regardless of the presence or absence of PE-MPs, the sorption process of Cd²⁺ by soil was more consistent with quasi-secondary kinetics and the Freundlich model, indicating that the processes were multilayer sorption controlled mainly by chemisorption. The adsorption mechanism of Cd²⁺ by soil is mainly surface complexation and precipitation. PE-MPs can cover the active sites on the soil surface and interfere with the interaction of Cd²⁺ with oxygen-containing functional groups in the soil, thus weakening the chemisorption of Cd²⁺ by soil. It can be seen that PE-MPs can enhance the mobility of Cd in soil and increase the risk of Cd pollution to the soil ecosystem. [ABSTRACT FROM AUTHOR]