Role of colloids in heavy metal transfer through a retention-infiltration basin.

Runoff waters from a main bridge near Nantes (France), surface waters and pore waters in the infiltration basin collecting runoff were analysed after filtration and ultrafiltration to investigate the role of colloids in the transfer of trace metals (Zn, Cu and Pb) from the road to the groundwater. The role of the basin in mitigation of the variations of physico-chemical parameters and chemical elements concentrations was confirmed. An increase of mobile colloidal phase by comparison with runoff and high concentrations of trace metals were observed in pore waters of the sediment. Up to 100% of Pb and 60% of Cu and Zn may be associated to compounds having a molecular weight above 5 kDaltons. Principal component analysis outlined the variability of the influence of the physico-chemical parameters on trace metals concentrations for the different waters. Speciation calculations pointed out the potential precipitation of Fe and Al oxyhydroxides in all kind of waters.

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.