Toxic metals in urban runoff: physico-chemical mobility assessment using speciation schemes

International audiencePhysico-chemical characterization of lead, zinc and cadmium has been carried out on eight samples from both separate and combined sewers. Dissolved and particulate total metal levels have been determined. A speciation scheme has been used ta further divide these phases in two dissolved fractions, bioavailable and stable, and five particulate fractions, ion-exchangeable, acid-soluble, reducible, oxidizable and residual. TotaJ dissolved lead concentrations were found ta be largely below European Community (EC) directives for drinking water production. Lead was represented by stable forms while zinc and cadmium were mainly bioavailable. Particulate concentrations were higher than naturallevels found in the Seine-Nolmandie basin. Zinc was characteristic for municipal effluents, and lead and cadmium were more concentrated in separate sewers. Correlations have been observed between particulate heavy metals and volatile matter on the ring highway, or with iron at the Savigny site. The particulate meral speciation scheme has demonstrated the important dependence of heavy metal distribution on the sampling site, as weil as the potentially more mobile nature of zinc and cadmium, compared to that of lead. The structural modifications undergone by solids during their transport along the sewer networks had a significant impact on particulate metal mobility. This has been clearly noted for lead, whose mobility decreased from upstream ta downstream in the studied system