Aerosolization of Azithromycin, Ofloxacin, and Co-occurring Antibiotic Resistance Genes during Municipal Wastewater Treatment

To effectively combat antibiotic resistance, it is critical to understand antibiotic usage patterns and their environmental dissemination. Wastewater treatment plants (WWTPs) are well-documented sources of antibiotics discharged into aquatic environments, but their role in releasing antibiotics via bioaerosols has not previously been investigated. In this study, seasonal air and liquid samples were collected throughout 2019 from a midsize WWTP employing both mechanical surface agitation and fine bubble aeration of activated sludge. Azithromycin and ofloxacin were detected in bioaerosols collected near aeration tanks at concentrations ranging from below detection limits up to 29 pg L^-1 air, suggesting that bioaerosols may represent a previously underappreciated route of environmental and occupational antibiotic exposure. Metagenomic analysis confirmed the co-occurrence of antibiotic resistance genes (ARGs) conferring resistance to macrolides and fluoroquinolones in both air and liquid samples. These findings highlight bioaerosols as an important yet overlooked pathway for the dissemination of antibiotics and ARGs, emphasizing the necessity of integrating airborne pathways into environmental antibiotic resistance surveillance programs, especially given the global scale of WWTP operations.