Coupled behaviors of antibiotics and antibiotic resistance genes in constructed wetlands: Mechanisms and impacts on nitrogen and phosphorus removal.

Abstract

Constructed wetlands (CWs) are widely used for wastewater treatment, but the coupled responses of antibiotic fate, antibiotic resistance genes (ARGs), and nutrient-removal stability under mixed-antibiotic exposure remain unclear. Here, we investigated antibiotic partitioning, ARG profiles, microbial communities, functional genes, nutrient removal, and residual risks in gravel, zeolite, and iron-carbon (Fe-C)/zeolite horizontal subsurface-flow CWs exposed to 19 antibiotics. Antibiotics preferentially accumulated in inlet zones, plant roots, and filler-associated biofilms. Zeolite-based systems reduced aqueous antibiotic residues but increased filler-surface retention and multidrug efflux pump genes, indicating a decoupling between antibiotic removal and resistance responses. Filler type also shaped microbial and functional responses. The Fe-C/zeolite system maintained stable total nitrogen removal and enhanced ammonia nitrogen and total phosphorus removal, indicating greater functional resilience. Partial least squares path modeling showed that nutrient removal was primarily associated with functional microorganisms and nutrient-cycling genes, with R2 values of 0.82 for total nitrogen and 0.51 for total phosphorus removal. Human health risks were negligible (HQ < 1), whereas ecological and antimicrobial resistance selection risks persisted, with maximum RQeco and RQAMR values of 31.90 and 11.56, respectively. Overall, this study highlights the need for risk-oriented design of CWs to balance antibiotic removal, resistance control, and nutrient-removal resilience.