Degradation of diclofenac in aqueous solution by ionizing radiation in the presence of humic acid

Abstract Diclofenac (DFC) is becoming a ubiquitous pollutant and pose a risk to ecosystem and human beings, which is usually used as a nonsteroidal anti-inflammatory drug for treating painful diseases. In this study, the degradation of DFC in aqueous solution by ionizing radiation was investigated in the presence of various concentrations of humic acid, due to its wide existence in water matrix as natural organic matter (NOM). The experimental results showed that the removal efficiency of DFC was 80.8% at 0.8 kGy absorbed dose and initial concentration of 30 mg/L. The DFC degradation by ionizing radiation could be described by pseudo first-order kinetics model. Humic acid had negative influence on the degradation efficiency of DFC, which decreased from 80.8% to 62.9% when humic acid concentration was 30 mg/L, mainly due to the competition between humic acid and DFC for OH radicals. Several intermediate products were identified by LC-MS analysis during DFC degradation process, and a possible degradation pathway of DFC by ionizing radiation was proposed.