Photodegradation kinetics of iopamidol by UV irradiation and enhanced formation of iodinated disinfection by-products in sequential oxidation processes

• Iopamidol can be degraded by UV irradiation with pseudo-first order kinetics.
• Effect of pH was negligible during UV degradation of iopamidol.
• Destruction pathways of iopamidol during UV irradiation were proposed.
• Iodide released from the stepwise deiodination of iopamidol was verified.
• Formation of I-DBPs were enhanced in UV and sequential oxidation of iopamidol.

The photochemical degradation of iopamidol with low-pressure UV lamps and the formation of iodinated disinfection by-products (I-DBPs) during sequential oxidation processes including chlorine, monochloramine and chlorine dioxide were investigated in this study. Iopamidol can be effectively decomposed by UV irradiation with pseudo-first order reaction kinetics. The evaluated quantum yield was found to be 0.03318 mol einstein−1. Results showed that iopamidol degradation rate was significantly increased by higher UV intensity and lower initial iopamidol concentration. However, the effect of solution pH was negligible. Degradation of iopamidol by UV photolysis was subjected to deiodination and hydroxylation mechanisms. The main degradation products including –OH substitutes and iodide were identified by UPLC-ESI-MS and UPLC-UV, respectively. Increasing the intensity of UV irradiation promoted the release of iodide. Destruction pathways of iopamidol photolysis were proposed. Enhanced formation of I-DBPs were observed after iopamidol photolysis followed by disinfection processes including chlorine, monochloramine and chlorine dioxide. With the increase of UV fluence, I-DBPs formation were significantly promoted.

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