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Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France |
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| Authors: | Farid Juillot Delphine Jouvin Philipe Telouk Philippe Ildefonse Steve Sutton Gordon E Brown Jr |
| Institution: | a Institut de Mineralogie et de Physique des Milieux Condenses (IMPMC), Université Pierre et Marie Curie, Université Paris-Diderot, IPGP, UMR-CNRS 7590, Campus Boucicaut, 140 rue de Loumel, 75015 Paris, France b Laboratoire PaleoEnvironnements et PaleobioSphere (PEPS), Departement de Sciences de la Terre, Université Lyon 1, UMR-CNRS 5125, 2 rue Dubois, 69622 Villeurbanne Cedex, France c Laboratoire de Geochimie des Eaux (LGE), Université Paris Diderot, IPGP, UMR-CNRS 7154, 2 place Jussieu, 75252 Paris Cedex 05, France d Laboratoire de Sciences de la Terre, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France e Consortium for Advanced radiation Sources, University of Chicago, Chicago, IL, USA f Department of Geological & Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA g Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025, USA |
| Abstract: | Zinc isotopes have been studied along two smelter-impacted soil profiles sampled near one of the largest Pb and Zn processing plants in Europe located in northern France, about 50 km south of Lille. Mean δ66Zn values along these two soil profiles range from +0.22 ± 0.17‰ (2σ) to +0.34 ± 0.17‰ (2σ) at the lowest horizons and from +0.38 ± 0.45‰ (2σ) to +0.76 ± 0.14‰ (2σ) near the surface. The δ66Zn values in the lowest horizons of the soils are interpreted as being representative of the local geochemical background (mean value +0.31 ± 0.38‰), whereas heavier δ66Zn values near the surface of the two soils are related to anthropogenic Zn. This anthropogenic Zn occurs in the form of franklinite (ZnFe2O4)-bearing slag grains originating from processing wastes at the smelter site and exhibiting δ66Zn values of +0.81 ± 0.20‰ (2σ). The presence of franklinite is indicated by EXAFS analysis of the topsoil samples from both soil profiles as well as by micro-XANES analysis of the surface horizon of a third smelter-impacted soil from a distant site. These results indicate that naturally occurring Zn and smelter-derived Zn exhibit significantly different δ66Zn values, which suggests that zinc isotopes can be used to distinguish between geogenic and anthropogenic sources of Zn in smelter-impacted soils. In addition to a possible influence of additional past sources of light Zn (likely Zn-sulfides and Zn-sulfates directly emitted by the smelter), the light δ66Zn values in the surface horizons compared to smelter-derived slag materials are interpreted as resulting mainly from fractionation processes associated with biotic and/or abiotic pedological processes (Zn-bearing mineral precipitation, Zn complexation by organic matter, and plant uptake of Zn). This conclusion emphasizes the need for additional Zn isotopic studies before being able to use Zn isotopes to trace sources and pathways of this element in surface environments. |
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