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Abstract :
[en] The total concentrations of trace elements in soils results from natural and anthropic factors. Knowledge of natural distribution (e.g. bio-geochemical background) helps assessing the impacts of human activities in terms of contaminations. But the processes generated by the modifications of the soil environment may also affect the form of a trace element, that is its distribution through various pools.
We investigated the chemical speciation of some metallic trace elements (Cu, Zn, Cr, Ni, Pb, Co, Cd) in soils from various land-use environment: “natural” soils under forest, “typical” cultivated soils, kitchen-garden soils, soils developped on geogenic anomalies and on contaminated areas. The analysis protocol aims at identifying different pools from their reaction to various extraction phases, ordered by increasing intensity in a single sequence. The different fractions are so-called soluble, linked to carbonates, to organic matter, to manganese oxides, to weakly cristallized Fe-Al oxides, to well-cristallized oxides, and residual. The “available” and total fractions have also been measured.
The results stress the fact that the comparisons are difficult from one situation to another because each one represents a particular case of human activity without a common logic. The relationships with the classical pedological parameters are therefore difficult to generalize. However some relationships between elements have been found inside the various types of land use, which could be usefull in the risk assesment of transfers from soils to plants.
