Microplastic Effects on Soil Aggregation in Sterilized and Non‐Sterilized Soils

ABSTRACT The adverse impact of soil microplastics on aggregation is generally attributed to the potential toxicity to soil microorganisms. However, there have been few studies that use sterile soil as a control environment for comparison with regular soils to test this hypothesis. Consequently, this study conducted soil incubation with oven‐heated sterilized soils to explore the effects of polyethylene (PE) and polypropylene (PP) microplastics (at sizes of 0.595, 0.089, and 0.009 mm) on the soil aggregate stabilities. The aim was to determine if their primary mode of action is through biogenic interactions with soil microorganisms. The microplastics reduced 49% and 82% water‐stable aggregates of 0.5–1 and 1–2 mm fractions in Tianjin soils, respectively. The effects of microplastics were particularly pronounced in the non‐sterilized soils during the initial month of incubation. Additionally, microplastics increased the surface roughness of aggregates by an average of 39%, yet microplastics did not significantly affect the aggregate mechanical stability in either soil type. This study suggests that interactions between soil microplastics and microorganisms work crucially on soil aggregation, but microplastics could also possibly affect soil aggregation through non‐biogenic pathways.