Phototransformation Kinetics and Changes in the Antibacterial Activity of Antimicrobial Agents

Abstract

Incomplete removal of antibiotics and other antibacterial agents (AAs) in traditional wastewater treatment systems is a potential public health threat that leads to the spread of pollutants and resistance genes in the environment. Some of the common AAs have been shown to be effectively removed by UV₂₅₄ irradiation. However, whether it is effective under UV-LED and sunlight and whether phototransformed products retain antibacterial activity remain unclear. In this study, the photodegradation of 12 common AAs was investigated under irradiation by a low-pressure mercury lamp, an LED peaked at 275 nm, and a xenon lamp to simulate sunlight. Results show that the rates of ionizable AAs varied significantly under pH 5.4, 7.0, and 8.4, with overall increasing rates at higher pH conditions. The intrinsic photochemical parameters, integrated light absorbance and quantum yield, were strongly affected by the light wavelength, leading to significant difference in degradation rates. However, the rates and photochemical parameters were not directly correlated with their electrochemical properties. The growth inhibition test on Escherichia coli showed that most of the common AAs lose their antibacterial activity after light irradiation, except chlortetracycline. These results suggest that light irradiation of common AAs is effective to mitigate their antibacterial activity.