Industrial activities have led to widespread chromium (Cr) contamination in the environment. Although Cr is an essential element for humans, the hexavalent form is toxic, mutagenic and carcinogenic. Consequently, the presence of Cr in the environment poses a serious threat to human and animal welfare. However, the toxicity of Cr is a function of oxidation state. For example, hexavalent Cr has a high solubility in soils and groundwater and, as a consequence, tends to be mobile in the environment. In contrast, a more reduced form of chromium, Cr(III), has limited hydroxide solubility and forms strong complexes with soil minerals. While trivalent Cr is relatively innocuous and immobile, hexavalent Cr is actively transported into cells by the sulfate transport system where it is capable of causing damage to DNA as well as indirectly generating oxygen radicals. Accordingly, reduction of Cr(VI) to Cr(III) is an important means by which the harmful effects of this toxin are mitigated. This general process forms the fundamental basis of a large number of technologies currently being tested for remediation of chromium-contaminated soils. Researchers from Stanford University's Department of Geological and Environmental Sciences are working on this problem using a combination of aqueous chemical measurements and x-ray absorption spectroscopy (XAS). This research is leading to a greater understanding of the solubility and reduction of Cr as well as to techniques that can be used to predict the ultimate solubility of Cr in mature, bioremediated systems.