Occurrence, risk, and treatment of ciprofloxacin and clarithromycin in drainage

Abstract

The widespread occurrence of antibiotics in the environment is a global problem, but their occurrence and spatiotemporal distribution, as that of their associated antibiotic-resistant genes and bacteria in Hong Kong estuaries and coast, are poorly understood or documented. Here, the long-term influences of ciprofloxacin (CIP) and clarithromycin (CLR) along the Kai Tak River (KTR) nullah, a man-made channel transporting treated effluents from two wastewater treatment plants, were monitored from December 2019 to April 2021. The results revealed that these antibiotics were widely distributed, exhibiting seasonal variations around median concentrations of 1693.8 ng L−1 for CIP and 632.1 ng L−1 for CLR. The ecological risk assessment indicated that ciprofloxacin and clarithromycin are the predominant ecological risk contributors to aquatic organisms in KTR water. The antibiotic resistance genes (ARGs) of acrB-1, acrA-2, mexF, acrA-1, and mexE persist in the sampled water along with CIP, CLR, and CIP/CLR-resistant bacteria. In addition, a PbO2 thin film electrode of superb stability and electrochemical activity was fabricated by an electrodeposition method and used for the electrochemical oxidation of antibiotic water pollutants. As a result, CIP and CLR were rapidly removed and degraded within fifteen minutes by electron transfer and reactive oxygen species, thus, mitigating ARG contamination in the nullah.