-
[show abstract]
[hide abstract]
ABSTRACT: We studied Cr isotopic fractionation during Cr(VI) reduction by Pseudomonas stutzeri strain RCH2. Despite the fact that strain RCH2 reduces Cr(VI) cometabolically under both aerobic and denitrifying conditions and at similar specific rates, fractionation was markedly different under these two conditions (ε was ∼2‰ aerobically and ∼0.4‰ under denitrifying conditions).
Applied and environmental microbiology 01/2012; 78(7):2462-4. · 3.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The prevalence of calcium as a major cation in surface and oceanic environments, the necessity of calcium in the functioning
of living cells and bone growth, and the large spread in mass between calcium isotopes all suggest that calcium isotope biogeochemistry
can be an important avenue of insight into past and present biogeochemical cycling processes. In the following chapter, we
review the main areas of research where Ca isotope studies have been pursued and detail recent research results in biogeochemical
applications. In marine environments, biogenic fractionation of Ca isotopes during biomineralization produces predictable
offsets in some organisms, which facilitate the reconstruction of seawater δ44/40Ca over geologic timescales. In terrestrial studies, observed Ca isotope fractionation between soil and various components
of vegetation enables the construction of a local Ca budget and provides a partial explanation for the scale of Ca isotopic
variability within a single watershed. The research reviewed in this chapter provides a foundation for future investigations
into the macro- and microscopic processes and biochemical pathways dictating the distribution of this essential nutrient using
stable Ca isotope ratios.
12/2010: pages 105-124;
-
[show abstract]
[hide abstract]
ABSTRACT: During the last two decades, expanding industrial activity in east Asia has led to increased production of airborne pollutants that can be transported to North America. Previous efforts to detect this trans-Pacific pollution have relied upon remote sensing and remote sample locations. We tested whether Pb isotope ratios in airborne particles can be used to directly evaluate the Asian contribution to airborne particles of anthropogenic origin in western North America, using a time series of samples from a pair of sites upwind and downwind of the San Francisco Bay Area. Our results for airborne Pb at these sites indicate a median value of 29% Asian origin, based on mixing relations between distinct regional sample groups. This trans-Pacific Pb is present in small quantities but serves as a tracer for airborne particles within the growing Asian industrial plume. We then applied this analysis to archived samples from urban sites in central California. Taken together, our results suggest that the analysis of Pb isotopes can reveal the distribution of airborne particles affected by Asian industrial pollution at urban sites in northern California. Under suitable circumstances, this analysis can improve understanding of the global transport of pollution, independent of transport models.
Environmental Science & Technology 10/2010; 44(23):8911-6. · 4.80 Impact Factor
-
Boris Faybishenko,
Terry C Hazen,
Philip E Long,
Eoin L Brodie,
Mark E Conrad,
Susan S Hubbard,
John N Christensen,
Dominique Joyner,
Sharon E Borglin,
Romy Chakraborty, [......],
Jinsong Chen, Shaun T Brown,
Tetsu K Tokunaga,
Jiamin Wan,
Mary Firestone,
Darrell R Newcomer,
Charles T Resch,
Kirk J Cantrell,
Anna Willett,
Stephen Koenigsberg
[show abstract]
[hide abstract]
ABSTRACT: The results of a field experiment designed to test the effectiveness of a novel approach for long-term, in situ bioimmobilization of toxic and soluble Cr(VI) in groundwater using a hydrogen release compound (HRC)--a slow release glycerol polylactate--are described. The field experiment was conducted at the Hanford Site (Washington), a U.S. Department of Energy nuclear production facility, using a combination of hydrogeological, geophysical, geochemical, and microbiological measurements and analyses of water samples and sediments. The results of this experiment show that a single HRC injection into groundwater stimulates an increase in biomass, a depletion of terminal electron acceptors O2, NO3-, and SO4(2-), and an increase in Fe2+, resulting in a significant decrease in soluble Cr(VI). The Cr(VI) concentration has remained below the background concentration in the downgradient pumping/ monitoring well, and below the detection limit in the injection well for more than 3 years after the HRC injection. The degree of sustainability of Cr(VI) reductive bioimmobilization under different redox conditions at this and other contaminated sites is currently under study.
Environmental Science and Technology 12/2008; 42(22):8478-85. · 5.23 Impact Factor
