Dynamic transport of antibiotics and antibiotic resistance genes under different treatment processes in a typical pharmaceutical wastewater treatment plant.

The propagation of antibiotic resistance is a challenge for human health worldwide, which has drawn much attention on the reduction of the resistance genes. To understand their occurrence during different treatment processes, in this study, four classes of antibiotics (tetracyclines, sulfonamides, quinolones, and macrolides), eight antibiotic resistance genes (ARGs) (tetB, tetW, sul1, sul2, gyrA, qepA, ermB, and ermF), and two mobile elements (int1 and int2) were investigated in a typical pharmaceutical plant. The total concentrations of antibiotics were detected in the range of 2.6 × 102 to 2.5 × 103 ng/L in the treatment processes, and the high abundance of ARGs was detected in the biological treatment unit. The dynamic trend analysis showed that antibiotics were partially removed in the anaerobic/aerobic processes, where ARGs were proliferated. The abundance of tetB and gyrA genes was positively correlated with pH and EC (p < 0.05), and the tetW, sul1 and sul2 genes were significantly correlated with TOC, TN, and DO (p < 0.05), indicating the influence of physicochemical properties of the solution on the levels of ARG subtypes. The phylogenetic analysis showed that the tetW clones had high homology with some pathogenic microorganisms, such as Klebsiella pneumonia and Neisseria meningitides, which would threaten human health. Results indicated that the horizontal transfer acted as a major driver in the ARGs evolution.