Use of carbon stable isotopes to monitor biostimulation and electron donor fate in chromium-contaminated groundwater.

Hexavalent chromium Cr(VI) is a common inorganic contaminant in industrial areas and represents a serious threat to human health due its toxicity. Here we report experimental results from a field-scale investigation of Cr(VI) bio-immobilization at Hanford 100H reservation, a U.S Department of Energy facility (Washington State, USA).

Reoxidation of Chromium(III) Products Formed under Different Biogeochemical Regimes.

Hexavalent chromium, Cr(VI), is a widespread and toxic groundwater contaminant. Reductive immobilization to Cr(III) is a treatment option, but its success depends on the long-term potential for reduced chromium precipitates to remain immobilized under oxidizing conditions. In this unique long-term study, aquifer sediments subjected to reductive Cr(VI) immobilization under different biogeochemical regimes were tested for their susceptibility to reoxidation.

Physiological and transcriptional studies of Cr(VI) reduction under aerobic and denitrifying conditions by an aquifer-derived pseudomonad.

Cr(VI) is a widespread groundwater contaminant that is a potent toxin, mutagen, and carcinogen. In situ reductive immobilization is a favored approach for Cr(VI) bioremediation, and Cr(VI) reduction has been reported in a variety of aerobic, facultative, and anaerobic bacteria, including a number of pseudomonads. However, studies comparing Cr(VI) reduction under aerobic and denitrifying conditions in the same organism are not available.

Molecular analysis of phosphate limitation in Geobacteraceae during the bioremediation of a uranium-contaminated aquifer.

Nutrient limitation is an environmental stress that may reduce the effectiveness of bioremediation strategies, especially when the contaminants are organic compounds or when organic compounds are added to promote microbial activities such as metal reduction. Genes indicative of phosphate-limitation were identified by microarray analysis of chemostat cultures of Geobacter sulfureducens. This analysis revealed that genes in the pst-pho operon, which is associated with a high-affinity phosphate uptake system in other microorganisms, had significantly higher transcript abundance under phosphate-limiting conditions, with the genes pstB and phoU upregulated the most.

Application of a high-density oligonucleotide microarray approach to study bacterial population dynamics during uranium reduction and reoxidation.

Reduction of soluble uranium U(VI) to less-soluble uranium U(IV) is a promising approach to minimize migration from contaminated aquifers. It is generally assumed that, under constant reducing conditions, U(IV) is stable and immobile; however, in a previous study, we documented reoxidation of U(IV) under continuous reducing conditions (Wan et al., Environ.

Colloid formation at waste plume fronts.

Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U.S. Department of Energy (DOE) facilities such as the Hanford Site (Washington state).

pH neutralization and zonation in alkaline-saline tank waste plumes.

At the Hanford Site in Washington State, the pH values of contaminant plumes resulting from leaking of initially highly alkaline-saline radioactive waste solutions into the subsurface are now found to be substantially neutralized. However, the nature of plume pH neutralization has not previously been understood. As a master geochemical variable, pH needs to be understood in order to predict the fate and transport of contaminants carried by the waste plumes.