Selenium isotope fractionation during reduction by Fe(II)-Fe(III) hydroxide-sulfate (green rust)

Geochimica et Cosmochimica Acta
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We have determined the extent of Se isotope fractionation induced by reduction of selenate by sulfate interlayered green rust (GRSO4), a Fe(II)-Fe(III) hydroxide-sulfate. This compound is known to reduce selenate to Se(0), and it is the only naturally relevant abiotic selenate reduction pathway documented to date. Se reduction reactions, when they occur in nature, greatly reduce Se mobility and bioavailability. Se stable isotope analysis shows promise as an indicator of Se reduction, and Se isotope fractionation by various Se reactions must be known in order to refine this tool. We measured the increase in the 80Se/76Se ratio of dissolved selenate as lighter isotopes were preferentially consumed during reduction by GRSO4. Six different experiments that used GRSO4 made by two methods, with varying solution compositions and pH, yielded identical isotopic fractionations. Regression of all the data yielded an instantaneous isotope fractionation of 7.36 ± 0.24‰. Selenate reduction by GRSO4 induces much greater isotopic fractionation than does bacterial selenate reduction. If selenate reduction by GRSO4 occurs in nature, it may be identifiable on the basis of its relatively large isotopic fractionation.

Publication type Article
Publication Subtype Journal Article
Title Selenium isotope fractionation during reduction by Fe(II)-Fe(III) hydroxide-sulfate (green rust)
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/S0016-7037(02)01137-7
Volume 67
Issue 3
Year Published 2003
Language English
Publisher Elsevier
Contributing office(s) Toxic Substances Hydrology Program
Description 7 p.
First page 413
Last page 419
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