Beyond aerosolization: How antibiotic concentration and redox cycling amplify antibiotic resistance genes in wastewater treatment plant bioaerosols

Abstract Wastewater treatment plants are emission hotspots of airborne antibiotic resistance genes, yet the physicochemical drivers of their amplification remain unclear. Here, we quantified airborne antibiotics and oxidative potential (OP) in particulate matter above an aeration tank and a nearby reference site, linking these measurements to resistome profiles. Among the eleven targeted antibiotics, only erythromycin was detected in aerosols (250 ± 64 pg m − 3 ). Rapid droplet evaporation can concentrate dissolved antibiotics within aerosol microenvironments; however, the resulting aqueous-equivalent concentrations depend on aerosol water content and were not directly measured in this field campaign. Volume-normalized OP showed no site differences, but erythromycin abundance showed an exploratory positive co-variation with mass-normalized OP, suggesting co-variation between antibiotic loading and particle redox activity. Correspondingly, macrolide resistance genes were enriched in aerosols, while sulfonamide resistance genes showed no enrichment, reflecting the absence of sulfonamide partitioning. The dominance of stress-tolerant taxa such as Pseudomonas and Streptococcus is consistent with survival under atmospheric stressors at the aeration area. Together, these findings provide an exploratory framework in which aeration-driven aerosolization can concentrate dissolved constituents and co-occur with redox-active particulate matter, potentially shaping the airborne resistome. These results motivate expanded monitoring and mechanistic studies that explicitly include the air compartment when assessing environmental transmission of antibiotic resistance.