Bioaerosol emission characteristics and potential risks during composting: focus on pathogens and antimicrobial resistance

In this study, we analyzed bioaerosol emission characteristics and potential risks of antimicrobial resistance (AMR) during composting using the impaction culture method and metagenomic sequencing. The results showed that the highly saturated water vapor in the emission gas mitigated particulate matter emission during the thermophilic period. About the bioaerosols, the airborne aerobic bacterial emissions were suppressed as composting enters the mature period, and the airborne fungi are usually present as single-cell or small-cell aggregates (< 3.3 μm). In addition, the microbial community structure in bioaerosols was stable and independent of composting time. Most importantly, the PM_2.5 in bioaerosols contained large amounts of antibiotic resistance genes (ARGs), potential pathogens, and multidrug resistant pathogens, which were diverse and present in high concentrations. Among them, ARGs concentrations encoding 21 antibiotics ranged from –4.50 to 0.70 ppm/m³ (Log₁₀ ARGs). Among the 89 potential human pathogens detected, Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, and Staphylococcus aureus were the only culturable potentially multidrug resistant pathogens carrying multiple ARGs encoding resistance at high concentrations (–0.57 to 1.15 ppm/m³ (Log₁₀ ARGs)), and were more likely to persist and multiply in oligotrophic environments. Our findings indicate that composting technology can transfer AMR from solid compost to gas phase and increase the risk of AMR transmission.