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This article in JEQ

  1. Vol. 27 No. 4, p. 836-843
    Received: Mar 7, 1997

    * Corresponding author(s): william.frankenberger@vcr.edu
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Microbial Oxidation and Solubilization of Precipitated Elemental Selenium in Soil

  1. M. E. Losi and
  2. W. T. Frankenberger Jr. *
  1. Dep. of Soil and Environmental Sciences, Univ. of California, Riverside.



Oxidation of elemental selenium (Se0) leads to increased solubilizalion and enhanced bioavailability. In this work, laboratory microcosm experiments were conducted to study oxidation of Se0 in soil and liquid cultures. Major objectives were to examine the oxidation rates of four San Joaquin Valley, California soils, and to assess the contribution of biological vs. chemical processes. For these experiments, red, crystalline Se0 was prepared by both chemical and biological synthesis, and its presence was confirmed by synchrotron-based x-ray absorption spectroscopy. The amount of Se0 oxidized over 125 d was from 1 to 10% of Se0 in soils spiked to 250 mg Se0 kg−1 and approximately half that in soils spiked to 100 mg Se0 kg−1. First order rate constants for oxidation of Se0 were from 0.05 to 0.32 yr−1 and 0.04 to 0.39 yr−1 at 250 and 100 mg Se0 kg−1 soil, respectively. The amount of Se0 oxidized was generally correlated with prior exposure of the soil lo Se. Products included either selenite (SeO2−3), or both SeO2−3 and selenate (SeO2−4). Biotic processes were shown to be of major importance. Both heterotrophic and autotrophic oxidation were observed, and an inorganic C source (NaHCO3) was favored relative to glucose. This study demonstrates that Se0 oxidation in soils is largely biotic in nature, occurs at relatively slow rates and yields both SeO2−3 and SeO2−4.

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