Effect of low-level H2O2 and Fe(II) on the UV treatment of tetracycline antibiotics and the toxicity of reaction solutions to zebrafish embryos

Abstract

The pollution of tetracyclines (TCs) in waters has caused public concern and scientific interest. This study investigates the effect of low-level hydrogen peroxide (H2O2) and ferrous ion (Fe(II) concentrations on the UV treatment of four TCs: oxytetracycline (OTC), tetracycline (TC), chlorotetracycline (CTC), and doxycycline (DXC). The optimum addition of Fe(II) (0.05 mM) and H2O2 (0.5 mM) promoted the attenuation and mineralization of test TCs, and a higher pH was conducive to their attenuation. Environmental-level water constituents (CO32−, HCO3−, NO3−, SO42−, NH4+, fulvic acid (FA), and humic acid (HA)) promoted test TCs attenuation under UV treatment, but inhibited their attenuation under H2O2/UV and Fe(II)/UV treatments (with the exception of HCO3− and FA). The attenuation of test TCs was attributed to UV and DOM* under UV treatment, UV, DOM*, H2O2, and ·OH under H2O2/UV treatment, and UV, DOM*, Fe-complexation, and ·OH under Fe(II)/UV treatment. A tentative degradation pathway of test TCs was proposed based on the detected intermediates and the degradation mechanisms. Additionally, an evaluation of the toxicity of treated solutions to zebrafish embryos showed that, solutions treated by only Fe(II) or H2O2 caused great toxicity, and Fe(II) or H2O2 combining with UV treatment could decrease the toxicity but required a longer irradiation time (>4h). Overall, our findings provide a scientific assessment of UV-based methods to remove antibiotics from aquatic systems.