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Title: Mapping of selenium concentrations in soil aggregates with synchrotron X-ray fluorescence microprobe

Abstract

The possible occurrence of reducing microsites in synthetic soil aggregates and their influences on the distribution of selenium species with redox-dependent mobilities was tested using the synchrotron X-ray fluorescence microprobe (SXRFM). Synthetic, effectively two-dimensional soil aggregates of diameters ranging from 10 to 30 mm were constructed, with and without inclusion of sections of Scirpus robustus and S. californicus root sections. Each aggregate was uniformly wetted with a saline solution containing 240 g m{sup {minus}3} Se [98% as Se(VI), and 2% as Se(IV)]. Gas-phase porosities varied between individual aggregates from 0.00 to 0.40 and were maintained relatively constant during the incubation period of up to 17 days. Exchanges of soil gases with atmospheric air occurred only along the periphery of the aggregates. Scanning of the aggregates using SXRFM demonstrated that Se was essentially homogeneously distributed in soils without Scirpus root sections, suggesting that Se remained primarily as the soluble Se(VI) species. The SXRFM results revealed large accumulations of total Se was measured in water-saturated soils within 1 to 4 mm of decomposing roots. These observations provide support for a model of localized reducing zones in which Se(VI) is reduced to less mobile Se(IV) and to insoluble Se(0), resulting in local accumulationmore » of total Se. The measured Se accumulation in one microsite compared reasonably well with a simple transient Se(VI) diffusion model. It is postulated that such mechanism may account for similar heterogeneities observable in some Se-contaminated soils at Kesterson Reservoir. Such heterogeneities in concentrations of Se and other constituents within individual soil aggregates have important implications with respect to reactivity and need to be included in any detailed mechanistic modeling of chemical cycling within soils. This work provides an example of the substantial capabilities of SXRFM in studies of soils. 45 refs., 11 figs.« less

Authors:
 [1]; ;  [2]
  1. Lawrence Berkeley Lab., CA (United States)
  2. Univ. of Chicago, IL (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
81122
DOE Contract Number:  
AC03-76SF00098; AC02-76CH00016
Resource Type:
Journal Article
Journal Name:
Soil Science
Additional Journal Information:
Journal Volume: 158; Journal Issue: 6; Other Information: PBD: 1994
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 44 INSTRUMENTATION, INCLUDING NUCLEAR AND PARTICLE DETECTORS; SELENIUM; MAPPING; ECOLOGICAL CONCENTRATION; SOILS; X-RAY FLUORESCENCE ANALYSIS; X-RAY FLUORESCENCE ANALYZERS; FEASIBILITY STUDIES

Citation Formats

Tokunaga, T.K., Sutton, S.R., and Bajt, S. Mapping of selenium concentrations in soil aggregates with synchrotron X-ray fluorescence microprobe. United States: N. p., 1994. Web. doi:10.1097/00010694-199415860-00004.
Tokunaga, T.K., Sutton, S.R., & Bajt, S. Mapping of selenium concentrations in soil aggregates with synchrotron X-ray fluorescence microprobe. United States. doi:10.1097/00010694-199415860-00004.
Tokunaga, T.K., Sutton, S.R., and Bajt, S. Sat . "Mapping of selenium concentrations in soil aggregates with synchrotron X-ray fluorescence microprobe". United States. doi:10.1097/00010694-199415860-00004.
@article{osti_81122,
title = {Mapping of selenium concentrations in soil aggregates with synchrotron X-ray fluorescence microprobe},
author = {Tokunaga, T.K. and Sutton, S.R. and Bajt, S.},
abstractNote = {The possible occurrence of reducing microsites in synthetic soil aggregates and their influences on the distribution of selenium species with redox-dependent mobilities was tested using the synchrotron X-ray fluorescence microprobe (SXRFM). Synthetic, effectively two-dimensional soil aggregates of diameters ranging from 10 to 30 mm were constructed, with and without inclusion of sections of Scirpus robustus and S. californicus root sections. Each aggregate was uniformly wetted with a saline solution containing 240 g m{sup {minus}3} Se [98% as Se(VI), and 2% as Se(IV)]. Gas-phase porosities varied between individual aggregates from 0.00 to 0.40 and were maintained relatively constant during the incubation period of up to 17 days. Exchanges of soil gases with atmospheric air occurred only along the periphery of the aggregates. Scanning of the aggregates using SXRFM demonstrated that Se was essentially homogeneously distributed in soils without Scirpus root sections, suggesting that Se remained primarily as the soluble Se(VI) species. The SXRFM results revealed large accumulations of total Se was measured in water-saturated soils within 1 to 4 mm of decomposing roots. These observations provide support for a model of localized reducing zones in which Se(VI) is reduced to less mobile Se(IV) and to insoluble Se(0), resulting in local accumulation of total Se. The measured Se accumulation in one microsite compared reasonably well with a simple transient Se(VI) diffusion model. It is postulated that such mechanism may account for similar heterogeneities observable in some Se-contaminated soils at Kesterson Reservoir. Such heterogeneities in concentrations of Se and other constituents within individual soil aggregates have important implications with respect to reactivity and need to be included in any detailed mechanistic modeling of chemical cycling within soils. This work provides an example of the substantial capabilities of SXRFM in studies of soils. 45 refs., 11 figs.},
doi = {10.1097/00010694-199415860-00004},
journal = {Soil Science},
number = 6,
volume = 158,
place = {United States},
year = {1994},
month = {12}
}