Emission hotspots, health-relevant effects, and pathogen cytotoxicity of bioaerosols in an urban wastewater treatment plant

Urban wastewater treatment plants (WWTPs) are important sources of bioaerosols, yet their occupational health implications remain incompletely defined. We investigated a representative WWTP on the North China Plain using multi-matrix sampling (air, wastewater, sludge), microbial culture with 16S rRNA sequencing, in vitro exposure of bronchial epithelial cells, and host transcriptomics. Bioaerosol microbial concentrations ranged from 101 to 2.32 × 104 CFU m−3; particulate matter averaged 2052 μg m−3 and fine biological particles (<3.3 μm) accounted for 37.38% on average. Aerobic fermentation room and biological reaction tank were identified as emission hotspots. Light intensity, temperature, and humidity were primary environmental impact factors. Communities were dominated by Bacillus, with opportunistic pathogen such as Stenotrophomonas and Acinetobacter detected. Although BugBase estimated low community-level pathogenic potential (<5%), the occurrence of these taxa indicates a nontrivial exposure risk. Using Staphylococcus aureus and Streptococcus pneumoniae as representative respiratory bacterial models, cytotoxicity assays showed that both pathogens reduced epithelial viability in a dose- and time-dependent manner, yet through different ways: Streptococcus pneumoniae exhibited high adhesion, driving early colonization and sustained moderate inflammation with elevated IL-6 and IL-18; Staphylococcus aureus displayed greater invasiveness and robust pyroptosis, marked by Caspase-1 activation and early IL-1β induction. Transcriptomic profiling further revealed broad suppression of host metabolic pathways by Streptococcus pneumoniae, whereas Staphylococcus aureus preferentially activated immune and inflammation-related signaling. Together, these data provide an evidence base for risk assessment and the development of targeted controls, while further validation in primary-cell or in vivo models is needed to strengthen physiological relevance.