Toxic hexavalent chromium Cr(VI) in the form of potassium dichromate was radiolytically reduced to nontoxic trivalent chromium Cr(III) in N2O-saturated aqueous solutions containing formate. This reduction by the electron donor (CO2H center dot/CO2 center dot-) produced by continuous radiolysis of water, was a linear function of the absorbed dose. This reaction was pH and dose rate dependent. pH was an important parameter in the reduction, as it affects both chemical speciation of Cr(VI) and formate. Possible mechanisms related to dose rate dependence of removal of Cr(VI) are presented. At pH 3 a decrease in the radiation induced reduction of Cr(VI) was observed with increasing hydrogen peroxide concentration. A mechanism to account for this variation is proposed. These findings suggest that irradiation of Cr(VI) solutions in presence of formate can be effective, economical and simple means for treatment of waste water contaminated with hexavalent Cr(VI). (C) 2012 Elsevier B.V. All rights reserved.