The pollutant Cr^VI is known to be very carcinogenic. In conditions of excess of Cr^VI, oxidation of D-galacturonic acid (Galur), the major metabolite of pectin, yields D-galactaric acid (Galar) and Cr^III. The redox reaction takes place through a multistep mechanism involving formation of intermediate Cr^II/IV and Cr^V species. The mechanism combines one- and two-electron pathways for the reduction of Cr^IV by the organic substrate: Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III. This is supported by the observation of the optical absorption spectra of Cr^VI esters, free radicals, CrO₂²⁺ (superoxoCr^III ion) and oxo-Cr^V complexes. Cr^IV cannot be directly detected; however, formation of CrO₂²⁺ provides indirect evidence for the intermediacy of Cr^II/IV. Cr^IV reacts with Galur much faster than Cr^V and Cr^VI do. The analysis of the reaction kinetics via optical absorption spectroscopy shows that the Cr^IV–Galur reaction rate inversely depends on [H⁺]. Nevertheless, high [H⁺] still does not facilitate accumulation of Cr^IV in the Cr^VI–Galur mixture. Cr^VI and the intermediate Cr^V react with Galur at comparable rates; therefore the build-up and decay of Cr^V accompany the decay of Cr^VI. The complete rate laws for the Cr^VI, Cr^V and Cr^IV–Galur redox reaction are here derived in detail. Furthermore, the nature of the five-co-ordinated oxo-Cr^V bischelate complexes formed in Cr^VI–Galur mixtures at pH 1–5 is investigated using continuous-wave and pulsed electron paramagnetic resonance (EPR) and density functional theory (DFT).