Antimony (Sb) is one of the most enriched elements in urban environments but also the least studied. Given its potential toxicity, it is therefore very important to identify the impact of Sb on the environmental compartments accumulating this emerging contamination. Despite the fact that significant enrichments were registered in urban environment samples, important scientific issues remain totally unexplored, such as the relative contributions of the different sources of Sb contamination, and Sb biogeochemical behavior within and between urban sedimentary reservoirs. In this context, providing information about Sb speciation and transfer pathways is of prime importance in order to control the environmental dissemination of this emerging contaminant in the critical zone. The pluri-disciplinary ANTIMONY project will provide innovative knowledge on the sources and chemical forms of Sb in an urban continuum, from sources to receiving environmental compartments and this up to a long-time range. It proposes a progressive strategy made necessary by the complexity of the processes involved and by the lack of knowledge about the sources and the fate of Sb in urban areas. ANTIMONY is built in such a way as to explore the mechanisms governing Sb behavior at the molecular scale in controlled batch experiments, and to progressively increase the time and space scales of the experiments up to the study of long-term trends and impacts of Sb contamination on urban areas. Task 1 will examine the mechanisms of Sb mobilization in controlled conditions (T1 batch experiments). The number of potential processes (sorption/desorption of Sb species, biotic and abiotic redox transformations) require laboratory experiments in which processes are singled out for study: Sb(V) reduction to Sb(III) by pure bacterial strains or reductants produced by microbial activity (Fe(II), sulfides), ligand exchange from oxygen to sulfur, and oxidative stibnite dissolution. This comprehensive approach will generate novel "fundamental" information concerning the isotope fractionation and mineralogical changes accompanying the environmental and microbial processes that Sb is involved in. Task 2 is dedicated to retention ponds located along roads, which stand as model systems to study Sb transfers from car traffic areas to the aquatic environment. The partition of Sb in these environments, the Sb isotope ratio and the mineralogy of the bearing phases will be documented. Mesocosm experiments with sediments representative of urban reservoirs will be designed to gain insights into the processes affecting Sb mobility and to elucidate the role of bacteria in Sb transfer between water and sediment compartments. We will also use ?123Sb measurements as a probe to monitor the mechanisms involved at the molecular scale (oxidation, reduction, ligand exchange), allowing us to draw hypotheses on the changes in Sb geochemistry observed in the environment. We will take opportunity of this task to carry out isolation of pure or simplified bacterial consortia involved in Sb reduction. Task 3 will explore the behavior of Sb in the ‘road to the pond’ continuum during a rain event to reveal the fast changes in Sb behavior during heavy rain events which are suspected to transport a large part of the road to pond Sb fluxes. The analysis of other than road Sb source samples (e.g. paints, plastics, lead artefacts) will document the isotopic and spectroscopic signature of these sources. In Task 4, sediment archives will be collected in the Seine River Basin to document the influence of source changes vs. post-depositional processes on the Sb contamination trajectory during the last century in relation with diagenesis and source changes. During its course, ANTIMONY will provide sediment and DNA banking material for future studies devoted to Sb biogeochemical cycles and to other emerging contaminants, related to road traffic or not.