Effect of sample drying and storage time on the extraction of fallout 239+240Pu, 137Cs and natural 210Pb as well as of stable Cs, Pb and Mn from soils

Abstract

Because substantial evidence exists that sample drying and storage may have an effect on the extractability of trace metals from soils and sediments, we have examined whether such effects are also present for the typical fallout radionuclides 137Cs and 239+240Pu, for natural 210Pb, as well as for the corresponding stable elements Cs and Pb. For comparison, stable Mn was also included, because for this element a clear effect of drying and storage has been demonstrated recently. The sequential extraction procedure of Tessier was applied to two soils (a typical mineral soil with a low organic matter content, and the top layer of a forest soil with a high organic matter content). No substantial effect of air-drying and subsequent sample storage up to 30 weeks was detectable for 137Cs, 239+240Pu and 210Pb as well as for stable Cs and Pb. A clear effect of drying and subsequent sample storage was observable for stable Mn extracted from the mineral soil into fraction I, where its concentration increased continually with storage time. This supports an earlier observation reported in the literature for a similar soil. Nevertheless, because we did not observe such an effect for the soil with the high organic matter content, one should be careful about generalizing this result. The results also suggest that isotopic equilibrium between 137Cs and stable Cs as well as between 210Pb and stable Pb in the two soils is approximately established.