The management of stormwater sediment is a key issue for local authorities due to their pollution load and important tonnages. In view of reuse, e.g. for embankment, the environmental evaluation of these highly aggregated sediments requires studying trace metals fractionation and mobility. The distribution of trace metals (Cd, Cr, Cu, Ni, Pb, Zn) and their level of lability in three French stormwater sediments was determined using sequential and kinetic extractions (EDTA reagent) associated with mineralogical analysis and SEM observations. Using microanalysis, new data were acquired on the evolution of aggregate state during extractions and on its significant role in trace metals retention. Trace metals were, in particular, observed to be very stable in small aggregates (10-50 µm). The comparison of the two extraction methods pointed out that EDTA extraction was not convenient to evaluate the stable fraction of Cr, Ni and Zn. Moreover, the results were relevant for basins presenting similar trace metals sources, whatever the physicochemical conditions in basins. The results suggest that the management of stormwater sediments could be improve by a better knowledge of metal mobility, as far as chemical extractions could highlight the localisation of the mobile trace metals fraction. Treatment could be therefore avoided or specific treatment could be applied to a reduced volume of sediments.
