Association of Plutonium isotopes with natural soil particles of different size and comparison with 137CS

Information on how plutonium (Pu) isotopes associate with natural soil particles of different size is very important for the interpretation involved in the application of Pu isotopes as soil erosion tracers. This work investigated the association of Pu isotopes with different particle size fractions of natural soils and compared it with that of Cs-137. Ten bulk soils collected from two different areas were separated into different particle size fractions by a combination of wet sieving and centrifugation techniques and the sub-samples were analyzed for Cs-137, Pu-239 and Pu-240. Results showed that the concentrations of both (239+24) Pu and Cs-137 increase with decreased particle sizes and are closely related to the specific surface areas of soil particles, which demonstrated a similar preferential association of Pu with finer soil particles as Cs-137. The activity ratios of Pu239+24/(CS)-C-137 in soil fractions increasing with increased particle size further indicated a less preferential transport of Pu with fine particles compared to Cs-137. These results not only highlight the suitability of Pu isotopes as soil erosion tracers, but also provide useful information for assessing the migration behavior of Pu in contaminated environments.