Degradation of iopamidol by UV365/NaClO: Roles of reactive species, degradation mechanism, and toxicology

Congwei Luo; Ming'an Li; Xiaoxiang Cheng; Daoji Wu; Fengxun Tan; Zhiquan Li; Yongkai Chen; Fan Yu; Qiao Ma

doi:10.1016/j.watres.2022.118840

Degradation of iopamidol by UV₃₆₅/NaClO: Roles of reactive species, degradation mechanism, and toxicology

Water Res. 2022 Aug 15:222:118840. doi: 10.1016/j.watres.2022.118840. Epub 2022 Jul 9.

Authors

Congwei Luo¹, Ming'an Li², Xiaoxiang Cheng³, Daoji Wu¹, Fengxun Tan², Zhiquan Li², Yongkai Chen², Fan Yu², Qiao Ma⁴

Affiliations

¹ School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan, 250101, P. R. China; Resources and Environment Innovation Institute, Shandong Jianzhu University, Jinan, 250101, P. R. China.
² School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan, 250101, P. R. China.
³ School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan, 250101, P. R. China. Electronic address: cxx19890823@163.com.
⁴ National Engineering Lab of Coal-Fired Pollution Emission Reduction, School of Energy and Power Engineering, Shandong University, Jinan 250061, P. R. China.

PMID: 35858527
DOI: 10.1016/j.watres.2022.118840

Abstract

The degradation of iopamidol (IPM) was investigated using a UV₃₆₅/NaClO system. The reactive species (HO·, ClO·, ozone, Cl·, and Cl₂^-·) in the system were identified, and the changing trends of the percentage contributions of these reactive species to IPM removal under various conditions were systematically evaluated. The results showed that ClO· and HO· played the most significant roles in the apparent pseudo-first-order rate constants of IPM degradation (k_obs, min^-1) in the control experiment, and their percentage contributions to k_obs were 41.31% and 34.45%, respectively. In addition, Cl· and Cl₂^-· together contributed 22% to the k_obs. Furthermore, the contribution of ozone to the IPM removal could be neglected. The concentrations of these species increased significantly when the concentration of NaClO was increased from 50 µM to 200 µM, while the percentage contribution of ClO· to k_obs was greatly increased. The concentrations and percentage contributions of HO· and ClO· decreased significantly as the solution pH increased from 5 to 9, with Cl₂^-· playing a greater role in the degradation of IPM under alkaline conditions. While Cl^- or HCO₃^-/CO₃^2- significantly promoted the generation of Cl₂^-· or CO₃^-·, neither had an obvious effect on k_obs, suggesting that Cl₂^-· and CO₃^-· should have a certain reactivity with IPM. Compared with that of Cl₂^-·, the percentage contribution of ClO· and Cl· to k_obs was more likely to be inhibited by NOM. In addition, the organic and inorganic oxidation products of IPM were detected. The oxidation mechanisms of IPM degradation in the UV₃₆₅/NaClO system, such as the H-extraction reaction, deiodination, substitution reaction, amide hydrolysis, and amine oxidation, were proposed according to the obtained 15 organic products. No effect on acute toxicity towards Vibrio fischeri and Photobacterium phosphoreum was detected during the oxidation of IPM by the UV₃₆₅/NaClO system. Furthermore, the engineering feasibility of the oxidation system was demonstrated, by the effective degradation of IPM in actual water. However, HOI rapidly accumulated during the removal of IPM in the UV₃₆₅/NaClO system, which poses certain environmental risks and will needs to be investigated.

Keywords: Iopamidol; Kinetic; NaClO; Radical; Toxicity; Ultraviolet.

MeSH terms

Chlorine
Iopamidol
Kinetics
Oxidation-Reduction
Ozone*
Ultraviolet Rays
Water Pollutants, Chemical* / analysis
Water Purification* / methods

Substances

Water Pollutants, Chemical
Chlorine
Ozone
Iopamidol