Article pubs.acs.org/est
X-ray Absorption Fine Structure Evidence for Amorphous Zinc Sulfide as a Major Zinc Species in Suspended Matter from the Seine River Downstream of Paris, Ile-de-France, France Cindy Priadi,† Pierre Le Pape,†,‡ Guillaume Morin,*,§ Sophie Ayrault,† Fabien Maillot,§ Farid Juillot,§ Rebecca Hochreutener,§ Isabelle Llorens,⊥ Denis Testemale,¶ Olivier Proux,∥ and Gordon E. Brown, Jr.#,∇ †
Laboratoire des Sciences du Climat et de l’Environnement (LSCE/IPSL), UMR 1572 (CEA/CNRS/UVSQ), Domaine du CNRS, Avenue de la Terrasse, bat 12, 91198 Gif-sur-Yvette, France ‡ UMR IDES 8148, CNRS, Université Paris-Sud, bât. 504, 91405 Orsay, France § Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR 7590, CNRS, UPMC−Université Paris 7-IPGP, case 115, 4 Place Jussieu, 75252 Paris, Cedex 05, France ⊥ CEA INAC/SP2M/NRS, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France ¶ Institut Néel MCMF, CNRS, 38042, Grenoble France ∥ Observatoire des Sciences de l’Univers de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France # Surface & Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, United States ∇ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 69, Menlo Park, California 94025, United States S Supporting Information *
ABSTRACT: Zinc is one of the most widespread trace metals (TMs) in Earth surface environments and is the most concentrated TM in the downstream section of the Seine River (France) due to significant anthropogenic input from the Paris conurbation. In order to better identify the sources and cycling processes of Zn in this River basin, we investigated seasonal and spatial variations of Zn speciation in suspended particulate matter (SPM) in the oxic water column of the Seine River from upstream to downstream of Paris using synchrotron-based extend X-ray absorption fine structure (EXAFS) spectroscopy at the Zn K-edge. First-neighbor contributions to the EXAFS were analyzed in SPM samples, dried and stored under a dry nitrogen atmosphere or under an ambient oxygenated atmosphere. We found a sulfur first coordination environment around Zn (in the form of amorphous zinc sulfide) in the raw SPM samples stored under dry nitrogen vs an oxygen first coordination environment around Zn in the samples stored in an oxygenated atmosphere. These findings are supported by scanning electron microscopy and energy dispersive X-ray spectrometry observations. Linear combination fitting of the EXAFS data for SPM samples, using a large set of EXAFS spectra of Zn model compounds, indicates dramatic changes in the Zn speciation from upstream to downstream of Paris, with amorphous ZnS particles becoming dominant dowstream. In contrast, Zn species associated with calcite (either adsorbed or incorporated in the structure) are dominant upstream. Other Zn species representing about half of the Zn pool in the SPM consist of Zn-sorbed on iron oxyhydroxides (ferrihydrite and goethite) and, to a lesser extent, Zn−Al layered double hydroxides, Zn incorporated in dioctahedral layers of clay minerals and Zn sorbed to amorphous silica. Our results highlight the importance of preserving the oxidation state in TM speciation studies when sampling suspended matter, even in an oxic water column.
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INTRODUCTION Received: Revised: Accepted: Published:
Zinc is one of the most widespread trace metals (TMs) in Earth surface environments because of anthropogenic and natural inputs over millennia.1 Among anthropogenic inputs to surface © 2012 American Chemical Society
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dx.doi.org/10.1021/es2041652 | Environ. Sci. Technol. 2012, 46, 3712−3720
Environmental Science & Technology
Article
of urban environments on metal speciation in such rivers, knowledge of which is essential for establishing reliable water monitoring methods.
waters, urban runoff has been recognized as a major source of TMs.2 In such aqueous media, speciation of TMs in the dissolved and particulate phases is a key parameter that directly influences the mobility and bioavailability of TMs. In particular, the mode of association of TMs with mineral or organic host phases (surface complexation, incorporation in mineral structures, association with natural organic matter) directly influences their solubility. However, the speciation of TMs in riverine suspended matter is difficult to determine accurately because supended solids occur at very low concentrations in rivers (typically a few mg/L), and their speciation can be potentially sensitive to changes in redox conditions during sampling and analysis, as previously observed for dredged river sediments.3 In addition, distinguishing between soluble TMs and TMs associated with particulate matter is difficult because mineral and organic colloidal materials often occur in natural waters and may bind or incorporate TMs. For instance, Rozan et al.4 showed that Cu, Zn, Fe, and polysulphide complexes in the dissolved fraction (
