A comparative study on the degradation of iohexol and diatrizoate during UV/persulfate process: kinetics, degradation pathways and iodinated disinfection by-products

Abstract

Iodinated X-ray contrast media (ICM) are widely used in medical imaging due to their stable properties, but they cannot be effectively removed in wastewater treatment plants (especially hospital wastewater). Therefore, ICM have been widely detected in aquatic environments and may gradually accumulate and cause adverse effects to the creatures. In this paper, the degradation characteristics of two most commonly detected ICM, iohexol and diatrizoate, by ultraviolet/persulfate (UV/PS) were investigated. UV/PS can effectively degrade both ICM, with pseudo-first-order rate constants (k_obs) of 0.3641 min⁻¹ for iohexol and 0.3511 min⁻¹ for diatrizoate, and SO₄·^₋ played a major role in UV/PS degradation of both ICM. The presence of I⁻, Cl⁻, Br⁻, humic acid (HA), and alkaline conditions inhibited the degradation efficiency of both ICM. Less I-DBPs were formed from iohexol at low PS and high Br⁻ concentrations, but from diatrizoate at high PS and Br⁻ concentrations. The degradation pathways of iohexol and diatrizoate in the UV/PS process were proposed separately according to the detected degradation intermediates. This study can provide an essential theoretical basis for the UV/PS degradation of the two ICM.