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This article in SSSAJ

  1. Vol. 55 No. 6, p. 1597-1602
    Received: Dec 11, 1990

    * Corresponding author(s):
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Selenate Reduction in an Alluvial Soil

  1. Garrison Sposito ,
  2. Andrew Yang,
  3. Adrienne Mackzum and
  4. Rosemary H. Neal
  1. Dep. of Soil Science, Univ. of California, Berkeley, CA 94720
    California Dep. of Pesticide Regulation, Trailer 14, Univ. of California, Riverside, CA 92521



Recent studies of the mobility and solubility of Se in western San Joaquín Valley soils suggest that this potentially hazardous element can be managed by controlling its oxidation-reduction reactions. The soluble species, SeO4, which is highly mobile and toxic, can, in principle, be reduced to SeO3, which is strongly adsorbed, or to organoselenium species, which may volatilize under suitable conditions. Chemical thermodynamics predicts that the reduction sequence in soils should be: NO3 → SeO4 → MnO2 at pH >5. The objective of this study was to establish the position of SeO4 in the kinetic reduction sequence for a representative western San Joaquín Valley soil incubated in suspension with its own saturation extract. In a series of replications of an incubation experiment, it was observed that native NO3 (plus NO2) concentrations became undetectable after 100 h in the soil suspension without O2 supply. Soluble Se, either added as Na2SeO4 or indigenous to the soil, disappeared after 50 to 200 h. Native soluble Mn began to rise after 50 h and showed a sharp increase after 100 h of incubation. Retardation of SeO4 reduction in the presence of added NO3 was noted. The results indicated that, at native levels of NO3, effective microbial catalysis of SeO4 reduction occurred in the soil under the conditions of the experiments, in agreement with the recent isolation of bacterial species that can respire SeO4 while oxidizing organic acids typical of suboxic soil environments.

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