Effects of microplastics on the hydraulic properties and pore characteristics of compacted soil

As emerging persistent pollutants, microplastics have become widely distributed in natural environments. Current research primarily focuses on the effects of microplastics on uncompacted or lightly compacted soils. However, the effects of microplastics on compacted soils remain unclear and require an urgent investigation. Therefore, this study used polyethylene particles as microplastics to investigate their effects on the hydraulic properties (saturated hydraulic conductivity, water retention capacity, and water stability) and pore characteristics (porosity and pore size distribution) of compacted clayey soil. As the concentration of microplastics increased, the saturated hydraulic conductivity of compacted soil decreased, while the water retention capacity and water stability increased. The addition of microplastics reduced the porosity of compacted soil, decreasing the volume of inter-aggregate pores and increasing the volume of intra-aggregate pores. The percentage of macropores (>4 μm) decreased, while the percentage of micropores (<0.04 μm) increased. The changes in the hydraulic properties of compacted soil were mainly due to the alteration of its pore characteristics by microplastics. Overall, large-sized microplastics exhibited a greater impact than small-sized microplastics. In contrast to uncompacted or lightly compacted soils, the properties of compacted soils were significantly affected by microplastics at the environmentally relevant concentrations (0.5 wt%). This study reveals the mechanisms by which microplastics affect the hydraulic properties and pore characteristics of compacted soil, providing insights into the potential impacts and risks of microplastic pollution in the soil environment. • Microplastics reduce the saturated hydraulic conductivity of compacted soil. • Microplastics increase water retention and water stability of compacted soil. • Microplastics reduce inter-aggregate pores and increase intra-aggregate pores. • Higher concentrations and larger sizes of microplastics have pronounced effects. • Compacted soil is significantly affected at environmentally relevant concentration.