Gamma irradiation-induced removal of sulfadiazine (SD) under different conditions was investigated. The results show that SD can be effectively degraded using gamma irradiation. The removal efficiencies of low-concentration SD can be remarkably improved in an acid solution, and SD degradation was in accordant with the pseudo-first-order kinetic model. The additives, such as H2O2 and Fenton reagent. were favorable for removing SD during gamma irradiation. However. SD removal was restrained with the addition of Na2CO3. Adding CH3OH in solution, we found that SD removal was restrained at low-irradiation dose while markedly promoted at high-irradiation dose. Based on the results of quantum chemical calculations and LC-MS analysis, SD degradation using gamma irradiation in aqueous solution is mainly ascribed to (OH)-O-center dot oxidation and the direct decomposition of SD molecules. (c) 2012 Elsevier B.V. All rights reserved.