Unraveling the combined impacts of pristine and aged polyethylene microplastics and the ciprofloxacin antibiotic on sediment microbial communities and ecological functions.

Microplastics (MPs) and antibiotics are pervasive pollutants in aquatic environments. However, the combined effects of aged MPs and antibiotics on ecological systems remain unclear. Through 16S rRNA sequencing, we confirmed that polyethylene microplastics (PE) and the ciprofloxacin antibiotic (CIP) significantly altered sediment microbial community structure and ecological function. Except for the sole addition of CIP, introducing single PE or combined contaminant treatments resulted in varying reductions in the edges, nodes, and average degree of the single-factor correlation network (1.52 %-18.83 %), ultimately destabilizing microbial communities through network simplification. This reduction in network complexity indicated that PE had a major impact on disrupting microbial interactions and community structure in combined pollution scenarios. Based on functional annotation of prokaryotic taxa analysis, PE and CIP were shown to significantly affect the Carbon-Nitrogen (C-N) cycle (p < 0.05), and combined contamination mitigated nitrogen cycle-related functions. In addition, ultraviolet-aged PE (p < 0.05) and CIP (p < 0.01), as well as key environmental factors pH (p < 0.01) and total nitrogen (p < 0.05), significantly affected the sediment community structure (p < 0.001). Our study can aid in exploring and assessing the combined risks of emerging contaminants.