Effect of microplastics on microbial dechlorination of a polychlorinated biphenyl mixture (Aroclor 1260)

Microplastics (MPs) and polychlorinated biphenyls (PCBs) generally coexist in the environment, posing risks to public health and the environment. This study investigated the effect of different MPs on the microbial anaerobic reductive dechlorination of Aroclor 1260, a commercial PCB mixture. MP exposure inhibited microbial reductive dechlorination of PCBs, with inhibition rates of 39.43%, 23.97%, and 17.53% by polyethylene (PE), polypropylene (PP), and polystyrene (PS), respectively. The dechlorination rate decreased from 1.63 μM Cl^- d^-1 to 0.99-1.34 μM Cl^- d^-1 after MP amendment. Chlorine removal in the meta-position of PCBs was primarily inhibited by MPs, with no changes in the final PCB dechlorination metabolites. The microbial community compositions in MP biofilms were not significantly different (P > 0.05) from those in suspension culture, although possessing greater Dehalococcoides abundance (0.52-0.81% in MP biofilms; 0.03-0.12% in suspension culture). The co-occurrence network analysis revealed that the presence of MPs attenuated microbial synergistic interactions in the dechlorinating culture systems, which may contribute to the inhibitory effect on microbial PCB dechlorination. These findings are important for comprehensively understanding microbial dechlorination behavior and the environmental fate of PCBs in environments with co-existing PCBs and MPs and for guiding the application of in situ PCB bioremediation.