Evaluation of the selectivity of sequential extraction procedures applied to the speciation of cadmium in soils

This study aimed at evaluating the selectivity of different extractants - and thus the efficiency of various extraction schemes - used to assess the Cd speciation in the soil of the Swiss Jura. For this purpose, three extractration schemes were selected and all were applied to three different soils. Each extraction scheme consisted of six steps intended to extract Cd bound to: (1) exchangeable, (2) carbonate, (3) Mn-oxides and amorphous compounds, (4) Fe-oxides, (5) organic matter and (6) residual fractions. The results showed that the selectivity of the extraction depended not only on the type of reagents used to extract each phase, but also on the order in which they were applied. In the final analysis, none of the tested schemes were totally satisfactory. The main reason for this is that soil is not a simple addition of pure components but rather the result of complex interactions between its basic constituents. However, one of the schemes would appear to be good enough to characterise adequately the Cd speciation In the soil of the Jura chain.