Microplastics alter the migration and transformation of vanadium in the riverine sediment environment.

Microplastics (MPs, size <5 mm) have emerged as environmental hazards and are widespread in the environment. They can significantly alter the reactivity and mobility of co-occurring elements. Vanadium, a strategic resource, was witnessed rising in the environment because of extensive anthropogenic activities. Nevertheless, the impact of MPs on the migration and transformation of vanadium has yet been investigated. This study therefore investigated the vanadium behavior in riverine sediment and overlying river water in the presence of MPs. 1.5 g representative non-degradable MPs (polyamide, polyethylene terephthalate) and biodegradable MPs (polybutylene succinate, polyhydroxyalkanoates) were separately amended into the reactors, which contained 50 mg vanadium-rich sediment. After incubation for 60 days, vanadium in the sediments decreased substantially, while vanadium increased in the overlying water, especially in reactors amended with biodegradable MPs. The biodegradable and non-degradable MPs were found to influence vanadium behavior through distinct mechanisms. The amendment of non-degradable MPs did not substantially impact humification process, during which the mobile and reducible vanadium passively leached out from the riverine sediment and migrated into overlying water. Conversely, amendment of biodegradable MPs significantly enriched several microbial genera (e.g., Massilia) in the MPs biofilm. These genera confer heavy metal resistance and synthetic polymer degradability, and were significantly correlated with specific sediment organic matter components (C3, Ex/Em = 270/352; C4, Ex/Em = 280(370)/504). The microbial community was found to alter sediment DOM when biodegradable MPs were introduced. These changes in microbial dynamics and sediment chemistry subsequently influenced the bioavailability and mobility of vanadium within the riverine sediment.