In atmospheric waters, oxidation of Cr(III) to Cr(VI) by OH center dot free radicals is a major environmental hazard since non-toxic species is transformed into toxic one. It is important to obtain some details concerning this oxidation reaction. In this study we simulated this oxidation by steady state radiolysis using Co-60 radioactive source and pulse radiolysis technique using a 2.5 MeV van de Graaff electron accelerator and investigated its kinetics in the pH range 1 to 9. Our findings showed that the reaction was highly pH dependant with a maximum yield at pH 4. The electron transfer proceeds via an inner sphere mechanism with (i) formation of the [OH center dot-Cr(III)] adduct with an equilibrium constant of 2.34 x 10(4) mol(-1) dm(-3) then (ii) followed by an electron transfer from Cr(III) to OH (center dot) within the adduct with a rate constant of 2.51 x 10(4) s(-1). The implication of this oxidation to atmospheric chromium contamination is discussed. (C) 2014 Elsevier B.V. All rights reserved.