Biodegradable and Nondegradable Microplastics Cause Distinct Impacts on the Microbial Vanadate Removal

The microplastics (MPs) were found to be ubiquitous and demonstrated distinct degradability in the environment. Vanadium, a strategic element with increasing production, has recently been identified as an environmental hazard. Because MPs can alter the mobility and transformation of vanadium, this study investigated the impact of biodegradable and nondegradable MPs on microbial vanadate [V(V)] removal. Polylactide (PLA), polyhydroxyalkanoate (PHA), polystyrene (PS), and polyvinyl chloride (PVC) MPs were separately amended into bioreactors containing vanadate. Distinct vanadate adsorption and removal were observed. Although pristine MPs exhibited comparable V(V) adsorption capacities, a substantial increase in adsorption was observed for MPs following exposure to the microbial vanadate removal experiment. Characterization of MPs revealed that surface morphology (e.g., groove) and functional groups (e.g., −C-O−) contributed to such a performance. Notably, biodegradable MPs significantly improved the vanadate removal efficiencies. Metagenomics results identified genes that are putatively affiliated with V(V) reduction and PHA as well as PLA MP depolymerization. The microbial-mediated process was elucidated, in which specific microorganisms (e.g., Comamonas, Rhodococcus) broke down PHA and PLA MPs. The monomers or intermediates were then taken up by other microorganisms, contributing to the vanadate removal. Beyond the well-studied microbial V(V) reduction pathways, such as those involving nitrite and nitrate reductase, additional mechanisms, including thioredoxin oxidation and sulfite reductase, have also been shown to mediate V(V) reduction. Because biodegradable and nondegradable MPs influenced the transformation and migration of vanadate, greater attention should be given to the management of plastic wastes.