The fate of antibiotic resistance genes in tertiary wastewater treatment works and their correlation with other contaminants

Antibiotic resistance genes (ARGs) in wastewater treatment works (WWTWs) represent a critical pathway for the dissemination of antimicrobial resistance into receiving aquatic environments, yet uncertainties remain regarding their persistence through current treatment stages and the factors influencing their removal. This study investigated selected ARGs' prevalence, removal efficiency, and fate in four WWTWs in the Hunter region of New South Wales, Australia, providing insight into the efficacy of treatment processes under existing operating conditions. Using quantitative PCR (qPCR), we quantified the absolute and relative abundance of five selected ARGs ( dfrA1, tetA, qnrS, vanB , and sul1 ), an integron marker gene ( intI1 ), and bacterial 16S rRNA gene across different wastewater treatment phases. Results revealed that all ARGs were present in influent samples, with tetA and intI1 being the most abundant. The tertiary treatment phase, particularly disinfection, significantly reduced ARG levels, with removal efficiencies ranging from 94.89% to 99.98%. However, tetA exhibited lower removal rates than other ARGs, particularly in Morpeth WWTW (83%), persisting at detectable levels in influent and final effluent. The study further explored the correlation between ARGs, nutrients, and trace metals, revealing a positive linear correlation with nitrate but largely negative correlations with phosphate and trace metals. These findings demonstrate the effectiveness of tertiary wastewater treatment in reducing the loads of the selected ARGs, certain resistance determinants can persist and potentially contribute to environmental dissemination. This study advances current understanding by identifying risks and environmental interactions that should be considered in WWTP design, monitoring frameworks, and public health risk assessments related to antimicrobial resistance. • Tertiary WWTWs achieved high ARG removal under real operating conditions. • Disinfection was the most effective treatment stage in removing ARGs. • ARGs correlated positively with nutrients (nitrate and phosphate). • Metals mainly exhibited a linear negative correlation with ARGs in WWTPs.