A Potential Bioaerosol Source from Sewer Vent and its Health Risk Assessment

Bioaerosols are ubiquitous and can affect both air quality and public health. While natural sources are well-studied, anthropogenic sources, particularly emissions from sewer vents (SV) connected to indoor sanitation pipelines, remain insufficiently characterized. Such vents may episodically release fecal-associated microorganisms into ambient air during toilet flushing, yet their emission characteristics and exposure risks are not well quantified. Here we assess SV as a potential urban bioaerosol source and quantify inhalation exposure risks across four representative buildings: university dormitory, nursing home, residential community, and inpatient building. We monitored real-time particle emissions and simultaneously collected culturable bacteria and fungi at each SV and in the corresponding pedestrian zones (PZ) using two Andersen six-stage impactors. Chronic non-carcinogenic inhalation hazard quotients (HQs) were calculated based on estimated exposures. Results showed that culturable bacterial concentrations were higher at SV than PZ (ranging from 1.80 to 9.21 times) except the inpatient building, while fungal concentrations were opposite. Size-resolved measurements indicated that SV bacteria were dominated in particles >2.1 μm, while PZ bacteria had a larger coarse fraction, with 38% at >7 μm. Fungal aerosols at both locations were mainly at 1.1–4.7 μm range. Consistent with these patterns, bacterial HQs were higher at SV (0.15 males; 0.13 females) than at PZ (0.04 for both sexes). Fungal HQs exceeded bacterial HQs at both locations (SV: 0.20 males, 0.18 females; PZ: 0.21 males, 0.18 females), yet all HQs remained below commonly used reference thresholds. Ongoing work will apply high-throughput sequencing and SourceTracker to resolve microbial community composition and apportion SV contributions to PZ bioaerosols, informing targeted mitigation (e.g., filtration and UV sterilization) and supporting integration of sewer infrastructure into urban bioaerosol monitoring frameworks.

Keywords: bioaerosols; sewer vent; particle size distribution; culturable microorganisms; health risk assessment