J. Phys. IV France 107 (2003) 735
DOI: 10.1051/jp4:20030406

Biogeochemical cycle and speciation of As and Cr in an acid mine environment : The case of Carnoulès Creek, France

I. Le Hécho¹, C. Pecheyran¹, S. Charles¹, M. Monperrus¹, M.-P. Pavageau¹, C. Casiot², M. Potin-Gautier¹, M. Leblanc^{2, 2} and O.F.X. Donard<sup>1

1</sup>  Laboratoire de Chimie Analytique Brio-inorganique et Environnement, UMR 5034 du CNRS, Hélioparc Pau-Pyrénées, 2 avenue du Président Angot, 64053 Pau cedex 9, France
²  Laboratoire Hydrosciences, UMR 5569, Université de Montpellier 2, Case 57, place E. Bataillon, 34095 Montpellier cedex 05, France

Abstract
The aim of the work was to understand the biogeochemical cycles of two pollutants of interest found in the Carnoulès Creek : arsenic and chromium. The data for dissolved chromium speciation showed that this element is rather homogeneously distributed along the seepage water with 70-80% of Cr (VI); in particles collected from the same samples. chromium is totally present under the trivalent form. These results are consistent with the fact that hexavalent chromium is much more mobile fhan Cr (III).

According to the results of dissolved arsenic speciation-arsenite was thé oniy species found. In the particles. As (V) and As (III) were deteeted and arsenate was the predominant fonn. A spatial evolution was evidenced with a global increase of As (V) percentage from the tailing basis to the river. This evolution can be explained by an oxidation phenomenon. Speciation analyses were also performe in solid samples : sediments and bacteria films taken in the seepage water. In sediments, more than 80% of As was under the pentavalent form whereas only 65% of arsenate is found in bacterial films.

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