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Integrated Field Lysimetry and Porewater Sampling for Evaluation of Chemical Mobility in Soils and Established Vegetation
Published on: July 4, 2014
Changes in arsenic speciation through a contaminated soil profile: a XAS based study
1Institut de Minéralogie et de Physique des Milieux Condensés, UMR CNRS 7590, Université Pierre et Marie Curie, Université Denis Diderot, IPGP, 140 rue de Lourmel, 75015 Paris, France. benjamin.cances@univ-reims.fr <benjamin.cances@univ-reims.fr>
The Science of the Total Environment
|April 15, 2008
Summary
Arsenic speciation in French soil varies with depth, with arseniosiderite in topsoil transitioning to iron oxides deeper down. This transformation impacts arsenic mobility and environmental fate near industrial waste sites.
Area of Science:
- Environmental Science
- Geochemistry
- Soil Science
Background:
- Industrial waste sites can contaminate surrounding soils with heavy metals like arsenic (As).
- Understanding arsenic speciation is crucial for assessing its environmental mobility and toxicity.
- Previous studies suggest arsenic contamination from arsenical pesticide manufacturing in Massif Central, France.
Purpose of the Study:
- To determine the chemical forms (speciation) of arsenic in impacted soil as a function of depth.
- To identify the sources and mineralogical hosts of arsenic contamination.
- To investigate the transformation of arsenic species within the soil profile.
Main Methods:
- X-ray Diffraction (XRD) for mineral identification.
- Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS) and Electron Probe Microanalysis (EPMA) for elemental and mineralogical analysis.
- Selective chemical extractions.
- Synchrotron-based X-ray Absorption Spectroscopy (XAS), including X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS).
Main Results:
- Arsenic concentrations decreased significantly with soil depth (8780 mg kg(-1) to 150 mg kg(-1)).
- Topsoil (0-5 cm) contained arseniosiderite and As(V)-bearing Fe(III)-(hydr)oxides.
- Deeper soil layers (>15 cm) primarily contained As(V) associated with amorphous Fe oxides, with minimal arseniosiderite.
- XANES confirmed arsenic existed exclusively as As(V) throughout the profile.
Conclusions:
- Arsenic speciation changes with soil depth, influenced by mineral transformations.
- Arseniosiderite, formed from primary arsenopyrite oxidation, progressively dissolves and is replaced by amorphous Fe oxides deeper in the soil.
- Amorphous Fe oxides are the main arsenic hosts in deeper, well-aerated soil layers, influencing arsenic's environmental fate.
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