APPLICATION OF A SEQUENTIAL EXTRACTION PROCEDURE TO CALCAREOUS SOIL SAMPLES - PRELIMINARY STUDIES

The localization of trace metals in soils is usually performed by sequ ential extraction procedures. Our purpose was to study the fractioning of copper in calcareous soils, in order to predict its mobility, usin g the extraction procedure proposed by Tessier et al. This preliminary study is devoted to the improvements of this method applied to calcar eous soil samples. First, it was necessary to assess the experimental conditions allowing the complete solubilisation of the different compa rtments involved in the extraction procedure with their appropriate re agent (acetic acid-sodium acetate and carbonates, iron hydroxide and h ydroxylamine, organic matter and hydrogen peroxide, fluorhydric-perchl oric acid and residual fraction). The complete solubilisation of each compartment was tested by measuring the residual phase. Secondly, it w as necessary to study the analytical protocol for the determination of copper with electrothermal atomic absorption; an improvement of this determination was particularly necessary for the reagent used for the exchangeable fraction (sodium acetate at pH = 8.5). According to the e xperimental results, the quality (repeatability, concordance of the su m of fractions with the total content of copper determined with indepe ndent measurement) of the proposed protocol seems to be quite good. So me results of the fractioning of copper in calcareous soil samples are given; these samples are characterised by a high value of copper in t he residual fraction corresponding to a poor availability of this elem ent.