Occurrence, Removal, and Risk Assessment of Antimicrobials and Their Transformation Products in Effluent from Australian Wastewater Treatment Plants.

Despite Australia's high antimicrobial use, their residues in wastewater and their impacts on receiving waters remain largely unknown. This study assessed the occurrence, removal, and risk for antimicrobial resistance (AMR) of 102 antimicrobial substances and selected transformation products (TPs) in wastewater effluent from 47 wastewater treatment plants (WWTPs) across Australia. Thirty-two antimicrobials and 13 TPs were detected, with 14 analytes occurring at >80% frequencies. Ampicillin, penicillin V, penicilloic V acid, fluconazole, and tazobactam M1 were observed with high median concentrations of >0.2 μg/L. Collectively, the WWTPs released 5.4 kg/day or 0.54 g/day/1000 inhabitants of antimicrobials/TPs into natural waters, with β-lactams, quinolones, nitroimidazoles/azoles, and sulfonamides comprising high volumes, which was correlated with the population's socioeconomic statuses. Thirty-seven analytes were removed at rates >80% post-treatment, whereas quinolones, nitroimidazoles/azoles, lincosamides, and macrolide TPs were observed with poor removal efficiencies, which were affected by treatment processes and regional climate. Comparing measured concentrations with the predicted no-effect concentrations for AMR selection (PNECAMR), 7 antimicrobials exerted selection risk for resistant bacteria. Concerningly, ciprofloxacin posed medium/high risk in most of the assessed WWTPs. The accumulative effects of antimicrobial classes and certain TPs might further aggravate adverse impacts on AMR development. Our study provides insights into the presence and AMR implications of antimicrobials in treated wastewater, aiming to safeguard public health and ecosystems.