Aging in soil increases the disturbance of microplastics to the gut microbiota of soil fauna

Microplastics (MPs) in the soil environment inevitably experience aging processes. However, how aging in soil affects MP toxicity to soil fauna remains poorly understood. In this study, two types of widely distributed MPs (polypropylene and tire wear particles) were aged in different soils, and their surface properties, morphology, leaching features of additives, biofilm colonization and toxicity to the typical soil fauna Enchytraeus crypticus were investigated. Results showed that aging in soil slightly changed the surface properties and morphology for both types of MPs, but significantly affected the release of additives, especially for those MPs aged in soil amended with manure. Moreover, a distinct and less diverse microbial community than the surrounding soils was formed on the surface of MPs, and MP type was a determinant of the biofilm microbial community. Exposure experiments indicated that aged MPs, especially those aged in soil with manure significantly affected the reproduction of soil worms with a more obvious disturbance to their gut microbiota, and biofilm features and changes in the leaching properties of MPs during aging were the main factors for these shifts. This study is the first attempt to reveal the role of aging in soil in MP toxicity to soil fauna.