Antimony isotopic composition in river waters affected by ancient mining activity.

In this study, antimony (Sb) isotopic composition was determined in natural water samples collected along two hydrosystems impacted by historical mining activities: the upper Orb River and the Gardon River watershed (SE, France). Antimony isotope ratio was measured by HG-MC-ICP-MS (Hydride Generation Multi-Collector Inductively Coupled Plasma Mass Spectrometer) after a preconcentration and purification step using a new thiol-cellulose powder (TCP) procedure. The external reproducibility obtained for δ(123)Sb measurements of our in-house Sb isotopic standard solution and a certified reference freshwater was 0.06‰ (2σ). Significant isotopic variations were evident in surface waters from the upper Orb River (-0.06‰≤δ(123)Sb≤+0.11‰) and from the Gardon River watershed (+0.27‰≤δ(123)Sb≤+0.83‰). In particular, streams that drained different former mining sites exploited for Sb or Pb-Zn exhibited contrasted Sb isotopic signature, that may be related to various biogeochemical processes occurring during Sb transfer from rocks, mine wastes and sediments to the water compartment. Nevertheless, Sb isotopic composition appeared to be stable along the Gardon River, which might be attributed to the conservative transport of Sb at distance from mine-impacted streams, due to the relative mobile behavior of Sb(V) in natural oxic waters. This study suggests that Sb isotopic composition could be a useful tool to track pollution sources and/or biogeochemical processes in hydrologic systems.