The higher oxidation states of iron (Fe(VI) and Fe(V) in particular) have been shown to be strongly oxidizing in enzymatic systems, where they can carry out aliphatic hydrogen abstraction. In addition, they have been postulated as intermediates in Fenton-type systems. Fe(VI) itself is relatively stable and has been shown to have potential as an oxidant in the so-called ''green'' treatment of polluted waters. By contrast, Fe(V) is a relatively short-lived transient when produced in aqueous solution in the absence of strongly bonding ligands other than hydroxide, a feature that has limited studies of its reactivity. Fe(VI) has been proposed to be useful in battery design and a very interesting study suggested that ferrate may be able to oxidize insoluble chromium to chromate and thus serve to remove chromium contamination in the Hanford radioactive waste tanks
