Comparison of Methods for Assessment of Radionuclide Speciation in Soils

Abstract

A comparison of sequential extraction methods proposed by F.I. Pavlotskaya [1, 2] and A. Tessier [3] for fractionation of technogenic (¹³⁷Cs and ⁹⁰Sr) and natural (²²⁶Ra, ²³²Th, and ²³⁸U) radionuclides from soils was performed. It is shown that both methods provide comparable results in the extraction of various forms of occurrence of technogenic radionuclides. Furthermore, both methods indicate a significantly higher availability of ⁹⁰Sr to plants and its greater ability to migrate with downward soil solution flows in comparison with ¹³⁷Cs. However, when used for the assessment of the occurrence forms of natural heavy radionuclides, the two methods provide inconsistent results. The Tessier sequential extraction method indicates higher contents of compounds available to plants and mobile compounds in comparison with the Pavlotskaya method. A possible reason behind this may be the soil chemistry complexity of radionuclides such as ²³²Th and ²³⁸U that feature polyvalence and a strong tendency for hydrolysis and complex formation; in addition, their behavior may be affected by various carriers. These elements form a broad range of compounds that change one into another with changes in the chemical conditions; this complicates accurate comparison of the composition of their forms extracted by reagents used in the above methods.