The purpose of this study is to evaluate the contamination in As, Ba, Co, Cu, Mn, Ni, Sr, V, Zn and REE, in a high uranium activity (up to 21,000Bq∙kg(-1)) area, downstream of a former uranium mine. Different geochemical proxies like enrichment factor and fractions from a sequential extraction procedure are used to evaluate the level of contamination, the mobility and the availability of the potential contaminants. Pb isotope ratios are determined in the total samples and in the sequential leachates to identify the sources of the contaminants and to determine the mobility of radiogenic Pb in the context of uranium mining. In spite of the large uranium contamination measured in the soils and the sediments (EF≫40), trace element contamination is low to moderate (2

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Single and sequential extractions are current and useful tools for estimating the availability of metals in soils or sediments. Many chemical extraction procedures have been proposed in the literature, making the comparison difficult. This study compares the data consistency of the potential availability given by four chemical extractions commonly found in the literature: ➢ two single procedures (using dilute HCl or EDTA as reactant) ➢ two sequential procedures (the modified standardized 3-steps procedure of the Standards, Measurements and Testing Programme (SMTP), namely BCR-extraction, and the 7-steps procedure of Leleyter and Probst (1999), namely LP-extraction).The leaching procedures are all performed on the reference lake sediment CRM BCR-701, used as a reference to assess the accuracy of the modified standardized procedure of Rauret et al. (1999). The results show similar availabilities between HCl and EDTA single leaches for Zn, Cu, Cr and Pb and between HCl and the BCR procedures for Zn, Cu, Cr and Ni. The LP-extraction is the most aggressive of the four tested procedures (except for Pb extraction), mainly due to a better extraction of the exchangeable fraction, by a better dissolution of the acidosoluble phase and particularly to a better dissolution of the amorphous and crystalline Fe-oxides. The comparison between the four procedures reveals a major problem of Pb extraction, potentially due to the formation of lead precipitates during HCl and the LP-extractions, even if an overestimation of the lead availability by the BCR procedure cannot be excluded.

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