Co-exposure of microplastics and polychlorinated biphenyls strongly influenced the cycling processes of typical biogenic elements in anoxic soil.

The co-exposure of microplastics (MPs) and polychlorinated biphenyls (PCBs) in soil is inevitable, but their combined effect on cycles of typical biogenic elements (e.g. C, N, Fe, S) is still unclear. And the co-exposure of MPs and PCBs caused more severe effects than single exposure to pollution. Therefore, in this study, a 255-day anaerobic incubation experiment was conducted by adding polyethylene microplastics (PE MPs, including 30 ± 10 µm and 500 µm) and PCB138. The presence of PE MPs inhibited the PCB138 degradation. Also, PE MPs addition (1%, w/w) enhanced the methanogenesis, Fe(Ⅲ) reduction, and sulfate reduction while inhibited nitrate reduction and the biodegradation of PCB138. And PCB138 addition (10 mg·kg-1) promoted the methanogenesis and Fe(Ⅲ) reduction, but inhibited sulfate reduction and nitrate reduction. Strikingly, the presence of PE MPs significantly reduced the impact of PCB138 on the soil redox processes. The abundance changes of special microbial communities, including Anaeromyxobate, Geobacter, Bacillus, Desulfitobacterium, Thermodesulfovibrio, Metanobacterium, etc., were consistent with the changes in soil redox processes, revealing that the effect of PE MPs and/or PCB138 on the cycle of typical biogenic elements was mainly achieved by altering the functional microorganisms. This study improves the knowledge of studies on the impact of MPs and combined organic pollutants to soil redox processes, which is greatly important to the stabilization and balance of biogeochemical cycling in ecology.