An updated insight into the natural attenuation of As concentrations in Reigous Creek (southern France)

The removal of metals and metalloids occurring in acid mine drainage has been studied on different scales (years, days). Dissolved and particulate concentrations of Fe and As were monitored over a 4-a period along Reigous Creek, an acid mine drainage from a former Pb-Zn mine in southern France. Dissolved concentrations of Fe (12-25 mmol L-1), As (0.9-3.5 mmol L-1) and SO42- (10-70 mmol L-1) exhibited seasonal variations related to rainfall, with an increase during the driest months. About 30% of the As initially present in solution as As(III) was coprecipitated with Fe oxides in the first 40 m of Reigous Creek. The corresponding As removal rate was 3.58 x 10(-7) mol L-1 s(-1). The mineralogy of resultant precipitates varied spatially and seasonally. Over the first 40 m, amorphous As(V)-Fe(III) phases and tooeleite, were formed. Sediments deposited in the bed of the creek close to the spring contained both types of solid phases. Laminated concretions, which consist of precipitates around bacterial structures, were mainly constituted of tooeleite. Further downstream, these Fe-oxide phases were replaced by schwertmannite and ferrihydrite. On a daily basis, concentrations of dissolved Fe and As have been shown to vary up to 10% during the day as a result of photoreduction of Fe-oxide phases