Résumé
Antimony (Sb) is a contaminant of increasing concern; its sources and fate in the environment require particular attention and its isotopes could be useful geochemical tracers. In this study, Sb isotopic composition was investigated along two rivers impacted by mining and smelting activities in the city of Oruro (Bolivia). Antimony concentration and isotope ratio were measured in water, suspended particulate matter and sediments during two contrasted seasons along a gradient of pH (from 1.6 to 6.5) and Sb concentration (from 8057 to 7 µg.L -1 ). Antimony isotopic composition varied over a range of ~1 ‰ considering all sample types (-0.09 ≤ δ123Sb ≤ +0.93 ‰). The main stream impacted by acid mine drainage showed a progressive increase of δ123Sb in the dissolved phase (+0.42 to +0.70 ‰), concomitant to Fe precipitation and Sb concentration decrease. This suggested that natural Sb attenuation by sorption onto neoformed Fe oxyhydroxysulphates was involved as this process favours light isotopes in the solid (Δ123Sbwater-sediments averaged +0.3 ‰). Smelting-impacted tributary exhibited lighter dissolved Sb (+0.29 ≤ δ123Sb ≤ +0.36 ‰). Lake Uru-Uru which receives both rivers exhibited a δ123Sb value of +0.28 ‰ in the wet season and +0.55 ‰ in the dry season, which might reflect different contributions of the AMD-and smelter-impacted rivers. The study reveals, for the first time, the impact of two distinct anthropogenic sources on antimony (Sb) isotopic composition on a water body and provides new insights into the ability of antimony isotopes to trace sources and processes in contaminated aquatic systems.