Variability of edaphic conditions in metal-contaminated sites at multiple scales. Two case studies in temperate and tropical environments

In numerous places, mining and ore treatment activities have generated environmental contaminations which endanger ecosystem viability and/or human health. In some places, the ecological pressure induced by the metal contaminations allowed the development a specific flora, fromwhich candidates for phytoremediation may be selected. A survey of edaphic conditions prevailing for plant growing in contaminated areas around metal smelters has been conducted in belgian calaminary sites (Zn, Pb, Cd contaminations) and in the Katanga province of RDC (Cu contaminations). As the processes generated by the modifications of the soil environment may affect the form of a trace element, that is its distribution through various pools, we investigated physical and chemical fractionation of some metallic trace elements (Cu, Zn, Pb, and Cd) in soils and compared temperate and tropical cases. The results stress the need for a typology of the contaminations that takes into account the classical pedological parameters, even if contaminated sites are far from classical soil environment. The variability of edaphic properties that can occur within small distances is also an important point to consider when planning rehabilitation operations