Fate of antibiotic-resistant bacteria and antibiotic resistance genes in the electrokinetic treatment of antibiotic-polluted soil

Abstract

In this study, we investigated the fate of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) during the electrokinetic treatment of antibiotic-polluted soils (EKA). Tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), were used as template chemicals. Electrokinetic treatment of blank soil (EKS) and antibiotic-polluted soil without an electric field (NOE) served as controls. Polarity reversal every 12 h ensured a suitable pH in the electrolytes and soil. The average removal rates of TC, OTC, and CTC after 7 days reached 39.5%, 34.5%, and 36.7% with EKA, respectively; this was mainly attributed to direct or indirect electrochemical reactions as well as indigenous biological processes. The abundance of total bacteria and ARB with NOE was statistically greater than that with EKA and EKS. For the soil at 0–2 cm, the abundance of anti-MIX bacteria (MIX means the three antibiotics combined) was 8.60 × 105 CFU g−1 soil with EKA and 1.72 × 106 CFU g−1 with NOE. And as to the specific types, the abundance of ARB was uniformly in the order OTC > TC > CTC > MIX. Compared with NOE, tetC, tetG, tetW, and tetM was reduced with EKA by an average ratio of 55.5%, 12.4%, 47.1%, and 61.2%, respectively. Finally, positive correlations were found between ARGs and TC concentrations. TetM and tetW showed higher correlations with TC concentration than tetC and tetG. These findings suggest that electrokinetic treatment is a promising technology for the removal of emerging contaminants such as antibiotics and more persistent ARGs in soil.