Hexavalent chromium compounds are genotoxic carcinogens. Due to its structural similarity to sulfate, chromate (a typical form of chromium(VI) at neutral pH) is transported into cells via sulfate channels.[7] Inside the cell, hexavalent chromium(VI) is reduced first to pentavalent chromium(V) then to trivalent chromium(III) without the aid of any enzymes.[7][8] The reduction occurs via direct electron transfer primarily from ascorbate and some nonprotein thiols.[7] Vitamin C and other reducing agents combine with chromate to give chromium(III) products inside the cell.[7] The resultant chromium(III) forms stable complexes with nucleic acids and proteins.[7] This causes strand breaks and Cr–DNA adducts which are responsible for mutagenic damage.[7] According to Shi et al., the DNA can also be damaged by hydroxyl radicals produced during reoxidation of pentavalent chromium by hydrogen peroxide molecules present in the cell, which can cause double-strand breakage.[8]