The metal elements traces dregs with the unstable fraction of the sediment of Sebou which risk?

In forms dissolved and/or fixed at the particles the metal elements traces can accumulate in the sedimentary zones and constitute important stocks of pollutants. These contaminants can be remaining in the dissolved phase and become biodisponible under the effect of the physicochemical conditions and could act as a long-term source of pollution. To understand the mobility and the reactivity of these stocks is an important issue for the management of the quality of the hydrosystèmes. The exchangeable or unstable fraction of the sediment corresponds to the metal ions being adsorbed on the surface of the particles constituting the sediment (clays, oxide iron…), or mobility and the biodisponibility are high in this fraction because of the weak electrostatic interactions. The goal of this study and to characterize the sediments of Sebou and Fès Rivers and to evaluate the risk of toxicity of the elements metal traces related to the particulate phase by the method of spared digestion. Metals in these fractions are assumed to be more available than metals associated with residual fractions.
The results obtained show a strong mobilization of the elements related to the unstable fraction which reaches 100% for Pb and 70% for Cr. The sediments are composed of two mineralogical phases and they are also very rich in organic matter.