Reductive and oxidative degradation of iopamidol, iodinated X-ray contrast media, by Fe(III)-oxalate under UV and visible light treatment

• Published in: Water research (Oxford) Vol. 67; pp. 144 - 153
• Main Authors: Zhao, Cen, Arroyo-Mora, Luis E., DeCaprio, Anthony P., Sharma, Virender K., Dionysiou, Dionysios D., O'Shea, Kevin E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15-12-2014; Elsevier
• Subjects: Anions; Applied sciences; Byproducts; Chromatography, Liquid; Contrast media; Contrast Media - chemistry; Degradation; Drinking water and swimming-pool water. Desalination; Environmental Restoration and Remediation - methods; Exact sciences and technology; Fenton and photo-Fenton; General purification processes; Hydroxyl radical; Hydroxyl Radical - chemistry; Hydroxyl radicals; Iopamidol - chemistry; Kinetics; Light; Mass Spectrometry; Oxalic Acid - chemistry; Oxidation; Oxidation-Reduction; Photochemical; Photochemical Processes; Pollution; Reduction; Superoxide anion radical; Superoxides - chemistry; Ultraviolet Rays; Wastewaters; Water treatment and pollution; X-ray contrast media; X-ray contrast media; Superoxide anion radical; Fenton and photo-Fenton; Hydroxyl radical; Advanced oxidation processes; Water treatment; Reactive oxygen species; Hydrogen peroxide; Chemical reduction; Organic iodine compounds; Visible radiation; Hydroxyl radicals; Iopamidol; Fenton reaction; Oxidation; Contrast media; Organic compounds; Photochemical degradation; Drinking water treatment; Ultraviolet radiation; Iron III Compounds; Organic salt; Physicochemical purification; Superoxide radicals; Waste water purification; Photooxidation
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2014.09.009

Iopamidol, widely employed as iodinated X-ray contrast media (ICM), is readily degraded in a Fe(III)-oxalate photochemical system under UV (350 nm) and visible light (450 nm) irradiation. The degradation is nicely modeled by pseudo first order kinetics. The rates of hydroxyl radical (OH) production for Fe(III)-oxalate/H2O2/UV (350 nm) and Fe(III)-oxalate/H2O2/visible (450 nm) systems were 1.19 ± 0.12 and 0.30 ± 0.01 μM/min, respectively. The steady-state concentration of hydroxyl radical (OH) for the Fe(III)-oxalate/H2O2/UV (350 nm) conditions was 10.88 ± 1.13 × 10−14 M and 2.7 ± 0.1 × 10−14 M for the Fe(III)-oxalate/H2O2/visible (450 nm). The rate of superoxide anion radical (O2−) production under Fe(III)-oxalate/H2O2/UV (350 nm) was 0.19 ± 0.02 μM/min with a steady-state concentration of 5.43 ± 0.473 × 10−10 M. Detailed product studies using liquid chromatography coupled to Q-TOF/MS demonstrate both reduction (multiple dehalogenations) and oxidation (aromatic ring and side chains) contribute to the degradation pathways. The reduction processes appear to be initiated by the carbon dioxide anion radical (CO2−) while oxidation processes are consistent with OH initiated reaction pathways. Unlike most advanced oxidation processes the Fe(III)-oxalate/H2O2/photochemical system can initiate to both reductive and oxidative degradation processes. The observed reductive dehalogenation is an attractive remediation strategy for halogenated organic compounds as the process can dramatically reduce the formation of the problematic disinfection by-products often associated with oxidative treatment processes.
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•Fe(III)-oxalate photochemical treatment of iopamidol under UV and visible light irradiation.•Evaluation of hydroxyl radical and superoxide anion radical generation.•Contribution of both reduction and oxidation degradation pathways.