Fractionation of 137Cs and 60Co in soils by sequential extractions

Abstract

Comparison of six sequential extraction schemes either widely used or specifically developed for speciation of 137Cs and 60Co in two types of soil (Chromic Luvisol and Eutric Fluvisol) is presented. The results from the comparison show that extractable radiocesium in Chromic Luvisol (14%) is about three times lower than in Eutric Fluvisol (39%). For Chromic Luvisol the total extractable radiocobalt varies from 42 to 78% while the variation for Eutric Fluvisol is not so substantial (55–83%). The results show that BCR and NIST schemes developed for heavy metals are not efficient for radiocesium fractionation, but give very good results in the case of radiocobalt. The efficiency of a scheme is dependant not only on the type of radionuclide but on the type of soil as well. The best reagent for evaluation of bioavailable cesium is NH4NO3 or other NH+ 4-salt. Practically most of the radiocobalt is in extractable form in both soils (about 83%) and major part of radiocesium (more than 60% depending on the soil type) is strongly bound in the soils and not extractable.