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Castillejos Sepúlveda A, Metzger E, Littmann S, Taubner H, Chennu A, Gatti L, de Beer D, Klatt JM. Two-Dimensional Mapping of Arsenic Concentration and Speciation with Diffusive Equilibrium in Thin-Film Gels. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:8107-8117. [PMID: 37190938 DOI: 10.1021/acs.est.3c00887] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We present a new approach combining diffusive equilibrium in thin-film gels and spectrophotometric methods to determine the spatial distribution of arsenite, arsenate, and phosphate at submillimeter resolution. The method relies on the simultaneous deployment of three gel probes. Each retrieved gel is exposed to malachite green reagent gels differing in acidity and oxidant addition, leading to green coloration dependent on analyte speciation and concentration. Hyperspectral images of the gels enable mapping the three analytes in the 2.5-20 μM range. This method was applied in a contaminated brook in the Harz mountains, Germany, together with established mapping of dissolved iron. The use of two-dimensional (2D) gel probes was compared to traditional porewater extraction. The gels revealed banded porewater patterns on a mm-scale, which were undetectable using traditional methods. Small-scale correlation analyses of arsenic and iron microstructures in the gels suggested active iron-driven local redox cycling of arsenic. Overall, the results indicate continuous net release of arsenic from contaminant particles and deepen our understanding of arsenate transformation under anaerobic conditions. This study is the first fine-scale 2D characterization of arsenic speciation in porewater and represents a crucial step toward understanding the transfer and redox cycling of arsenic in contaminated sediment/soil ecosystems.
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Affiliation(s)
| | - Edouard Metzger
- Laboratoire de Planétologie et Géosciences, Université d'Angers, Nantes Université, Le Mans Université, CNRS UMR 6112, Angers 49045, France
| | - Sten Littmann
- Biogeochemistry Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, Bremen 28359, Germany
| | - Heidi Taubner
- MARUM Center for Marine Environmental Science and Faculty of Geosciences, Organic Geochemistry Group, University of Bremen, Leobener Str. 8, Bremen 28359, Germany
| | - Arjun Chennu
- Data Science and Technology, Leibniz Centre for Tropical Marine Research, Fahrenheitstr. 6, Bremen 28359, Germany
| | - Lais Gatti
- Microsensor Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, Bremen 28359, Germany
| | - Dirk de Beer
- Microsensor Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, Bremen 28359, Germany
| | - Judith M Klatt
- Microsensor Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, Bremen 28359, Germany
- Microcosm Earth Center, Max Planck Institute for Terrestrial Microbiology and Philipps-Universität Marburg, Marburg 35032, Germany
- Center for Synthetic Microbiology (SYNMIKRO), Marburg 35032, Germany
- Biogeochemistry Group, Department of Chemistry, Philipps-Universität Marburg, Marburg 35032, Germany
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