Colloidal speciation of heavy metals in runoff and interstitial waters of a retention/infiltration pond

The thickness of non-saturated zone and physico-chemical conditions are important parameters to assess the impact of infiltration ponds on water resources with respect to heavy metals transfer. As changes in physico-chemical parameters of solutions have a strong impact on the mobility of colloidal phases in sediments and soils, the colloidal facilitated transfer of heavy metals has to be investigated. Therefore, this study focuses on the characterization of runoff, surface and interstitial waters in a retention/infiltration pond collecting runoff waters of a bridge near Nantes. Physico-chemical parameters and chemical analyses were performed on the waters during about one year. The separation of dissolved and colloidal fractions was carried out by filtration and ultrafiltration for one sample of surface and interstitial waters. Until now, the runoff waters were only filtered at 0.45 microm. The comparison of physico-chemical data shows that the minor variations of runoff water parameters are mitigated in basin and in soils but strong variations impact the composition of interstitial waters. High concentrations of zinc, copper and still of lead are measured in runoff. Lead and cadmium seem to be associated to colloidal and particulate fractions while zinc, copper, nickel and chromium are distributed in all fractions.