Aging Dynamics of Polyvinyl Chloride Microplastics in Three Soils with Different Properties

Microplastic (MP) contamination in soil has been of great concern, but the dynamic aging process and potential pathways of MPs in natural soil systems remain poorly understood. Herein, poly(vinyl chloride) microplastics (5% w/w) were weathered for 12 months in sandy soil, silty clay, and silt loam. The results showed that the continuous increase of C═O and O-H groups (rate constant, k = 0.080-0.424 m^-1) with time was observed on the surface of MPs aging in sandy soil due to the leading role of ^•OH induced by light irradiation. In the loam soil, the abundant coating of aluminosilicates and iron oxides on the MP surface by the formation of mineral-hydroxyl groups inhibited the generation of the C═O group (k < 0.165 m^-1). The k of the characteristic bond C-Cl during the first 9 months was 9.51 and 1.93 times higher in clay compared to that in sandy and loam soil, respectively, revealing that dechlorination triggered the first step of the aging process for MPs in clay owing to the participation of degrading bacteria (Phenylobacterium and Caulobacteraceae). The results provide important insights into the aging dynamics of MPs in environmentally realistic circumstance, which account for understanding the different aging processes of MPs in different soils.