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Environmental Processes
Antimonite Binding to Natural Organic Matter: Spectroscopic Evidence from a Mine Water Impacted Peatland Johannes Besold, Anne Eberle, Vincent Noël, Katharina Kujala, Naresh Kumar, Andreas C Scheinost, Juan S. Lezama-Pacheco, Scott Fendorf, and Britta Planer-Friedrich Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b03924 • Publication Date (Web): 22 Aug 2019 Downloaded from pubs.acs.org on August 22, 2019
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Environmental Science & Technology
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“Antimonite Binding to Natural Organic Matter:
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Spectroscopic Evidence from a Mine Water
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Impacted Peatland”
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Johannes Besold1, Anne Eberle1, Vincent Noël2, Katharina Kujala3, Naresh Kumar4,5,
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Andreas C. Scheinost6, Juan Lezama Pacheco7, Scott Fendorf 7 and Britta Planer-
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Friedrich*1
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Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), Bayreuth University, 95440 Bayreuth, Germany Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, United States Water Resources and Environmental Engineering Research Unit, University of Oulu, FI90014, Oulu, Finland Department of Geological Sciences, School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305, USA. Department of Environmental Geosciences, University of Vienna, 1090 Vienna, Austria
The Rossendorf Beamline (ROBL) at ESRF, 38043 Grenoble, France and HelmholtzZentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, Bautzner Landstraße 400, 01328 Dresden, Germany Department of Earth System Science, School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305, USA
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ABSTRACT
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Peatlands and other wetlands are sinks for antimony (Sb), and solid natural organic
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matter (NOM) may play an important role in controlling Sb binding. However, direct
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evidence of Sb sequestration in natural peat samples is lacking. Here, we analyzed solid
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phase Sb, iron (Fe), and sulfur (S) as well as aqueous Sb speciation in three profiles up
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to a depth of 80 cm in a mine water impacted peatland in northern Finland. Linear
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combination fittings of extended X-ray absorption fine structure spectra showed that Sb
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binding to Fe phases was of minor importance and observed only in the uppermost layers
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of the peatland. Instead, the dominant (to almost exclusive) sequestration mechanism
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was Sb(III) binding to oxygen-containing functional groups, and at greater depths,
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increasingly Sb(III) binding to thiol groups of NOM. Aqueous Sb speciation was
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dominated by antimonate, while antimonite concentrations were low, further supporting
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our findings of much higher reactivity of Sb(III) than Sb(V) towards peat surfaces.
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Insufficient residence time for efficient reduction of antimonate to antimonite currently
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hinders higher Sb removal in the studied peatland. Overall, our findings imply that Sb(III)
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binding to solid NOM acts as an important sequestration mechanism under reducing
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conditions in peatlands and other high-organic matter environments.
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TOC
Sb(III)-S-Corg
Sb C R
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Sb(III)-O-Corg
Sb(III/V)-O-Fe
Depth
Fitted Sb fractions
Sb
O C R
S
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INTRODUCTION
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Wetlands span more than 6% of the global ice-free land area1 and among those,
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peatlands, with ~3% land cover, are the dominant group.2 Peatlands have important
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ecological functions including long-term carbon storage, niche for threatened animal and
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plant species or regulation of the water budget.2 In addition, they are also increasingly
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recognized as sinks for potentially toxic trace metal(loid)s3-7 and therefore are an
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important factor controlling surface water and groundwater quality.
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Antimony (Sb) is a potentially toxic trace element, which has received increasing
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attention only during the last decades due to increased mining activities8,9 as well as
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increased industrial use10-12 and proposed toxicity similar to arsenic (As).13,14 Moreover,
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Sb is a redox-active trace metalloid that prevails at environmentally relevant pH values
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as pentavalent aqueous antimonate (Sb(OH)6−) under mostly oxic and as trivalent
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aqueous antimonite (Sb(OH)3) under mostly anoxic conditions.15 At high dissolved sulfide
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concentrations and neutral to alkaline pH, also thiolated Sb can form.16-18
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The natural Sb background concentrations in soils and sediments (
