Are free radicals actually responsible for enhanced oxidation of contaminants by Cr(VI) in the presence of bisulfite?

Recently, the technology for the remediation of Cr(VI) pollutant via bisulfite has been found to be effective for fast elimination of co-contaminants especially in acidic solution, where free radicals (i.e., sulfate and/or hydroxyl radicals) are proposed to act as dominant oxidants.