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.