Selenium and Chromium Stable Isotopes and the Fate of Redox-Active Contaminants in the Environment

Abstract

In the second part of this study, I developed the chromium stable isotope system as a biogeochemical indicator and monitoring tool. After initial work designing the techniques, I measured chromium stable isotope fractionation in laboratory experiments and natural waters. I observed that the products of Cr(VI) reduction had delta53Cr values that were 3.4 +/- 0.1‰ less than that of the reactant. The 53Cr/ 52Cr ratios in water samples from three chromium-contaminated sites ranged from 1.1‰ to 5.8‰, relative to the standard and indicate the extent of reduction, a critical process that renders toxic Cr(VI) immobile and less toxic. Finally, I show that Cr stable isotope fractionation during sorption on alumina and goethite in laboratory experiments is insignificant and variations in 53Cr/52Cr values can be used to determine extent of reduction in natural waters.