Background This study analyzes the effectiveness of gamma irradiation in removing diatrizoate contrast from different water matrices: ultrapure water, surface water, groundwater and wastewater. The use of gamma irradiation for degradation is influenced by coexisting substances in natural waters and wastewaters. The influence of the presence of anions Cl-,NO2-,NO3-,SO42-andCO32-/HCO3- on the degradation of diatrizoate by gamma irradiation was investigated. Results Study results indicate that: (1) diatrizoate radiolysis fits pseudo-first-order kinetics; removal of91.9% of the diatrizoate was achieved at a dose of 1000Gy; (2) diatrizoate degradation depends on the type of water matrix, with the radiolysis being affected by the presence of anions, as follows: (i) high concentrations of Cl- increase the efficacy of the process; and (ii) low concentrations of NO2- markedly decrease the degradation rate, because nitrite ions act as scavengers of eaq-, hydroxyl radical and hydrogen radical; (3) TOC values showed that diatrizoate does not mineralize at a dose of 1000Gy. Conclusions Radiolysis degrades diatrizoate by more than 90%; results obtained indicate that it is not mineralized, with TOC values remaining constant in all waters studied. (c) 2013 Society of Chemical Industry