This study investigated the reaction mechanisms of toxic hexavalent chromium (Cr(VI)) with polysaccharide biopolymers, including cellulose, hemicellulose and chitin, to understand their roles in determining the Cr(VI) removal efficiencies of biomaterials containing these polymers. The Cr(VI) removal rates and capacities at pH 2 followed the order of hemicellulose > chitin >> cellulose. The Cr(VI) removals by these biopolymers were primarily due to the reduction of Cr(VI) to Cr(VI). The hydroxyl groups of these biomaterials were the predominant reactive sites for Cr(VI) reduction, and the oxidation of the hydroxyl groups by Cr(VI) led to the formation of carboxyl groups. In addition to the reactivity of functional groups toward Cr(VI), the accessibility of functional groups in different biopolymers may also determine the reduction rates of Cr(VI) by the biopolymers. (C) 2011 Elsevier B.V. All rights reserved.