The control of Cr and U mobility by redox processes in natural waters
The environmental speciation and mobility of highly toxic Cr and U is controlled primarily by redox processes. In oxidising environments, soluble and bioavailable Cr6+ and U6+ species predominate, but under reducing conditions these partition to highly insoluble Cr3+ and U4+ oxides. Redox-induced shifts in Cr and U stable isotopic composition in natural and contaminated land systems have not yet been defined.
We will determine the isotopic fractionation that occurs during redox cycling by reacting Cr and U with a range of key Fe and Mn minerals (e.g. Fe304) and a range of natural sediments (i.e. microcosms). We will then compare this lab data to Cr and U isotope data from natural and contaminated sites to understand how stable isotope measurements can be used to quantify the biochemical processes controlling the speciation of Cr and U. This, in turn, could be used to inform risk assessment for contaminated land sites and/or models for the global cycle of U and Cr.