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

The aim of the work was to understand the biogeochemical cycles of two pollutants of interest found in the Carnoules Creek: arsenic and chromium. The data for dissolved chromium speciation showed that this clement 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 than Cr (III). According to the results of dissolved arsenic speciation, arsenite was the only species found. In the particles, As (V) and As (III) were detected and arsenate was the predominant form. 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 performed 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.