Fate of antibiotics and antibiotic resistance genes in home water purification systems

Abstract

Home water purification systems (HWPSs) are utilized worldwide to obtain clean drinking water. However, the reliability of HWPSs in providing safe water is unknown or not well-proven. In this study, the occurrences of antibiotics and antibiotic resistance genes (ARGs) in tap water, effluents, and filters of HWPSs were investigated in twenty-six houses and one laboratory. The levels of antibiotics and ARGs were between less than the limit of detection (LOD) and 7.9 ng/L and between less than LOD and 3.45 × 105 copies/L, respectively, in tap water. HWPSs with fresh filters had a high efficiency in removing antibiotics and ARGs, with removal rates of 91–92% and 0.46–2.43 log, respectively. However, after long-term operation (e.g., more than three months), some HWPSs had low removal rates of antibiotics and ARGs (3–79% and 0.03–0.15 log, respectively) and some HWPSs released antibiotics and ARGs into the effluents leading to higher levels of antibiotics and ARGs in the effluents than those in the influents. Biofilms were observed on many filters of the investigated HWPSs. ARGs were detected on the filters with relative abundances (the ratio of the abundance of ARGs to the abundance of 16S rRNA) of 2.56 × 10−8–2.89 × 10−2. High-throughput sequencing analysis showed that Proteobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes were the dominant phyla, and Alphaproteobacteria and Gammaproteobacteria were the dominant classes. The abundances of Cyanobacteria, Patescibacteria, Bacteroidetes, and Proteobacteria were significantly positively correlated with the abundances of ARGs. Microbial growth and enrichment commonly observed in HWPSs can accelerate the exposure risk posed by antibiotics and ARGs to the consumers of water from these appliances.