Comparison of two sequential extraction procedures for uranium fractionation in contaminated soils

Two sequential extraction procedures were carried out on six soils with different chemical properties and contamination history to estimate the partitioning of U between different soil fractions. The first method (method of Schultz) was specifically developed for actinides, while the second one (method of Rauret) was initially created for heavy metals. A soil-to-plant transfer experiment was carried out with ryegrass to verify if one of the extracted fractions efficiently predicted plant uptake. In artificially contaminated soils, most of the U was retrieved from the exchangeable and the carbonates fractions. In soils with high natural levels of U or contaminated by industrial activity, most of the U was found in the less available fractions. The highest U transfer factors (TF) were observed for artificially contaminated soils and the lowest for soils with high natural concentrations or industrial contamination. The U concentration in the roots and shoots and the soil-to-root TF are well correlated to the U concentration determined in the first extracted fractions from the method of Schultz. Conclusion: the extraction method according to Schultz should be preferably used for U, and the exchangeable fraction can be proposed as a potential indicator to evaluate plant uptake in soils.