In this study, an electromagnetic induction electrodeless lamp (EIEL) was first introduced into UV advanced oxidation processes (AOPs) for photodegradation of Diatrizoate (DTZ), which was the most persistent iodinated X-ray contrast medium (ICM), and traditional Hg lamps were taken as references. Direct photolysis rate of DTZ under EIEL irradiation was 1.34 times as that under Hg irradiation, but the electric energy consumption was 0.87 times. In this sense, the combination of EIEL and oxidants (O-2, H2O2 and S2O82-(PS)) was further investigated. The remarkably increased photodegradation rates were observed in UV/PS system due to primary contribution rate of SO4 center dot- (62.5%) based on the results of radical concentrations and second-order rate constants of DTZ with SO4 center dot- and center dot OH. Inorganic ions influencing the photodegradation process were investigated. The effect of natural organic materials (NOMs) in UV/PS system was studied based on contribution ratios of light screening effect and squenching. Transformation mechanisms of DTZ in UV/PS system included deiodination, intramolecular cyclization, decarboxylation, deacetylation and deamination, which were further confirmed by frontier electron density calculations. The study indicated that UV/PS with EIEL irradiation has the potential to remove pharmaceuticals in contaminated aquatic environments. (C) 2017 Elsevier B.V. All rights reserved.