Effects of Biotic and Abiotic Factors on the Vertical Migration of Microplastics in Soil Driven by Earthworms

As a new pollutant, microplastics pollution has become a global environmental issue. Agricultural soils contaminated with microplastics pose a potential threat to the food chain and terrestrial ecosystems. This study utilized a mesocosm device to simulate changes of different biotic (springtail, earthworm density, plant roots) and abiotic (type and aging of microplastics, exposure time, flooding) factors in agricultural soils and explored their effects on the vertical migration of microplastics in the soil driven by earthworms. Results show that the vertical migration of microplastics decreased with increasing soil depth, and was positively influenced by springtail and high densities of earthworms. The growth of plant roots tended to retain microplastics in the surface soil layer and reduce the vertical migration of microplastics by earthworms. The type of microplastics also had an impact on vertical migration in the order of PE > PS > PET. Short-term aging had no significant effect on the vertical migration of microplastics in soil, but exposure time and flooding promoted the migration of microplastics to deeper soil layers. This study provides a scientific basis for understanding the vertical migration patterns and influencing factors of microplastics in agricultural soils under earthworm activities.