Mineralization of Calcon, an azo dye, was carried out using UV254 in the presence of H2O2 (HP) and (NH4)(2)S2O8 (APS) as oxidants. Degradation is found to be pH dependent and with UV/HP system, it proceeds efficiently at pH 1 and 12.6 even though mineralization is efficient at pH 1. The mineralization efficiency is in the order: UV/APS > UV/HP in acidic to neutral medium and UV/HP > UV/APS in basic medium. Nevertheless, lowest mineralization is recorded at pH 7 and 9 for UV/HP and UV/APS systems respectively. Most importantly decay in degradation was not observed at higher concentrations of oxidants. Presence of anions exerts inhibition effect on the degradation process, which is in the order: Cl- > SO42- > NO3- and SO42- > Cl- > NO3- for HP and APS as oxidants respectively. Toxicity of the treated solutions was determined on the basis of E. coli growth and the detoxification efficiency of the systems was found to be in the order UV/APS > UV/HP. The solution after mineralization was completely detoxified by adjusting its pH to 7. Based on the results, it is recommended that APS is the most suitable oxidant for both mineralization and detoxification processes of Calcon. (C) 2011 Elsevier B.V. All rights reserved.