Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France) - GéoHydrosystèmes COntinentaux - EA6293 Accéder directement au contenu
Article Dans Une Revue Journal of Soils and Sediments Année : 2019

Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France)

Cécile Grosbois
Alexandra Courtin-Nomade

Résumé

Purpose The threat of trace elements (TE) stored in sediments depends on total concentrations, their chemical form, and also on the type of TE–particle association and their resultant stability. The presentstudy aimed at identifying the major TE-bearing phases in river sediments and quantifying their in situ concentrations once total concentrations of TE had been determined in order to understand potential TE mobility and ensuing environmental risk during early diagenesis mechanisms and the sediment cascade. Materials and methods Several TE-enriched layers of sediment cores were selected in a polymetallic-contaminated river basin (Loire basin, France). Selected samples were taken from up- and downstream areas far from sites of specific mining, or heavy industrial or urban activities. They thus represent non-site-dependent sediments which were not modulated or controlled by specific mineralogy or anthropogenic activities. Detailed microscale investigation techniques (SEM, EPMA, andμSXRD) were used to characterize directly the complex TE–solid phase association within river sediments. Despite Bi, Cd, and Hg representing the highest enrichment of the studied sediment layers, these elements were not detected at a microscale and only ubiquitous TEsuch as As, Cu, Pb, and Zn could be quantified on polished thin sections (EPMA quantification limit = 1000 mg kg−1,n= 111). Results and discussion Three mineralogical groups were evidenced by PCA, EPMA, and μSXRD data. (i) Fine-grained aggregates of aluminosilicates were frequently detected, appearing multiphased in organic matrices. They were mostly enriched with Zn and Pb without any As or Cu. (ii) (Mn, Ti)-rich Fe oxyhydroxides were predominantly SEM observed, either as isolated grains, silicate coatings, or included in aggregates. They represented the highest detected in situ concentrations for all the studiedTE. And finally, (iii) Mn-rich particles were not frequently observed with SEM but when present were characterized by the highest TE concentrations. Phosphates, carbonates, and S-rich particles (sulfides and/or sulfates) were also determined by PCA as a potential mineralogical group. However, due to their very low TE concentrations and frequency, they could not be considered representative of a TE-bearing mineralogical group. Conclusions This fine sorting classification, combining different techniques at the particle scale, was used to visualize and quantify complex mineralogy and particle associations of TE-bearing phasesin river bed sediments under no specific mineralogical control. It represents an interesting approach to understand TE mobility during sediment cascade and post-depositional processes in sediments.
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Dates et versions

hal-02377282 , version 1 (23-11-2019)

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Cécile Grosbois, Alexandra Courtin-Nomade. Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France). Journal of Soils and Sediments, 2019, ⟨10.1007/s11368-019-02355-x⟩. ⟨hal-02377282⟩
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