Characteristics of a polluted artificial soil located along a motorway and effects of acidification on the leaching behavior of heavy metals (Pb, Zn, Cd)

Polluted artificial soils (average concentrations: Pb: 1460 ppm; Zn: 2830 ppm and Cd: 2.8 ppm) have been collected at the edge (less than 1 m) of the A-71 motorway in Sologne. These soils are characterized by XRD and a procedure of sequential extraction of Pb, Zn, Cd, Mn and Fe ( Tessier et al., 1979). Excepting for Fe, the “labile” fractions F I, F II and F III, respectively “exchangeable”, “carbonate-related” and “Fe-hydroxides-related” are dominant on the “residual” fraction F V. Fraction F IV “related to organic matter” is mostly significant for Pb. A study of the different size fractions indicates a strong metal enrichment in the finest one (Zn≫Pb, suggesting that in carbonate-free systems moderately acid rainstorms may leach Cd and a part of Zn from the border of the motorway, while Pb would remain fixed. A similar mobility scale has been derived from the study of other highly polluted materials related to motorways ( Lebreton and Thévenot, 1992; Colandini et al., 1995; Lee and Touray, 1997). When in addition Fe and Mn are considered, the mobility scale becomes Mn≅Cd>Zn≫Pb>Fe, for artificial soils as well as for suspensions, in spite of large differences in heavy metal contents and localizations. This is in agreement with the idea that most of the “acid labile” heavy metals from suspensions are localized within a highly polluted material, comparable to artificial soils and diluted by a large proportion of local Sologne soil.