Decomposition of Iodinated Pharmaceuticals by UV-254 nm-assisted Advanced Oxidation Processes

Iodinated pharmaceuticals, thyroxine (a thyroid hormone) and diatrizoate (an iodinated X-ray contrast medium), are among the most prescribed active pharmaceutical ingredients. Both of them have been reported to potentially disrupt thyroid homeostasis even at very low concentrations. In this study, UV-254 nm-based photolysis and photochemical processes, i.e., UV only, UV/H₂O₂, and UV/S₂O₈^2-, were evaluated for the destruction of these two pharmaceuticals. Approximately 40% of 0.5μM thyroxine or diatrizoate was degraded through direct photolysis at UV fluence of 160mJcm^-2, probably resulting from the photosensitive cleavage of C-I bonds. While the addition of H₂O₂ only accelerated the degradation efficiency to a low degree, the destruction rates of both chemicals were significantly enhanced in the UV/S₂O₈^2- system, suggesting the potential vulnerability of the iodinated chemicals toward UV/S₂O₈^2- treatment. Such efficient destruction also occurred in the presence of radical scavengers when biologically treated wastewater samples were used as reaction matrices. The effects of initial oxidant concentrations, solution pH, as well as the presence of natural organic matter (humic acid or fulvic acid) and alkalinity were also investigated in this study. These results provide insights for the removal of iodinated pharmaceuticals in water and/or wastewater using UV-based photochemical processes.