Catalytic ozonation of iohexol with α-Fe_0.9Mn_0.1OOH in water: Efficiency, degradation mechanism and toxicity evaluation

Iohexol, a widely used iodinated X-ray contrast media, is difficult to completely degrade with the traditional water treatment process. Catalytic ozonation with synthesized α-Fe_0.9Mn_0.1OOH as the catalyst can significantly promote the degradation of iohexol relative to that with ozonation alone. Hydroxyl radicals play a predominant role during the degradation of iohexol. The effect of various factors, including catalyst dose, ozone dose, iohexol concentration and water matrix factors, on the catalytic performance were investigated. The presence of α-Fe_0.9Mn_0.1OOH in the catalytic system can significantly promote the removal of iohexol and mineralization of the dissolved organic carbon in real water samples. The intermediate products were determined by high-resolution liquid chromatography, and the reaction site was predicted by frontier electron density (FED) calculations. The degradation mechanism of iohexol followed the processes of H-abstraction, amide hydrolysis, amide oxidation, and ·OH substitution. Higher exposure concentrations of iohexol had a negative effect on the survival and hatching rates in the development of zebrafish embryos. The autonomic movement process and heartbeat rate of the zebrafish larvae showed significant differences as the exposure concentration of iohexol increased. The catalytic ozonation process with α-Fe_0.9Mn_0.1OOH can decrease the toxicity of iohexol containing water.