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Effect of microplastics concentration and size on pollutants removal and antibiotic resistance genes (ARGs) generation in constructed wetlands: A metagenomics insight
Summary
Microplastics in constructed wetlands used for wastewater treatment reduced the removal of nitrogen, phosphorus, and antibiotics while promoting the spread of antibiotic resistance genes. This means microplastic contamination could undermine water treatment systems and contribute to the growing crisis of antibiotic-resistant bacteria, which poses a significant threat to public health.
The accrual of microplastics (MPs) and antibiotics poses synergistic threats to the environment. This study systemically examined the effect of environmental-level (μg/L) MPs (90-110 µm) and nanoplastics (NPs, 700 nm) on constructed wetlands (CWs) treating oxytetracycline-contaminated wastewater via metagenomics analysis. Polystyrene (PS) MPs notably hindered the removal of nitrogen, phosphorus, and oxytetracycline, particularly at high level (1000 μg/L), with removal rates of 73.34 %, 59.59 %, and 99.34 %, respectively. Among them, the removal of NH-N decreased the most in comparison to CK, at 15.26 %. Antibiotic resistance genes (ARGs) copies/16S rRNA ranged from 0.26 to 0.42 in CWs, exceeding that found in rivers by a factor of 1.5 to 2.5 times. The relative abundance of multidrug resistance genes (mdtB, acrB, mexF, mdtC, and mexT) and tetracycline resistance genes (txtA, tetG, and tetP) exhibited a pronounced increase under MPs exposure, ranging from 0.06 to 0.14 and 0.01 to 0.08 copies/16S rRNA, respectively. Redundancy and network analyses emphasized robust associations among contaminant reduction, ARG abundance, and microbial community. Partial least squares path modeling indicated MPs exerted a more profound influence on pollutant removal (coefficient = 0.8194), microbial community (coefficient = 0.3358) and ARGs dissemination (coefficient = 0.6566) compared to NPs. MPs concentrations significantly affects pollutants removal and ARGs proliferation, and MPs with larger sizes amplified ARG dissemination. This research highlights the influence of MPs on CW-mediated wastewater treatment and ARGs accumulation, offering valuable insights for developing ecological wastewater treatment strategies tailored to multi-pollutant scenarios. These insights are fundamental in developing sustainable solutions to the adverse impacts of MPs on ecosystems.