Particle-size speciation of Pu isotopes in surface soils from Inner Mongolia (China) and its implications for Asian Dust monitoring.

To study the applications of Pu isotopes in long-distance dust migration monitoring, Pu isotopes in surface soil of Inner Mongolia have been analyzed using SF-ICP-MS after size fractionation. 240 Pu/239 Pu atom ratios ranged narrowly (0.169-0.200) and indicated global fallout character, while 239+240 Pu activities increased with decreasing particle size. A spherical model could well simulate 239+240 Pu activities as a function of particle diameter when soil particle size was less than 600µm, and the soil particle surface sorption phenomenon of Pu isotopes in natural soil samples was revealed. Furthermore, 239+240 Pu activity in fine particles (sized less than 53µm) had good consistency with that in atmospheric depositions of Japan since the 2000s, suggesting new Asian Dust sources (i.e. central Inner Mongolia) other than the well-known Chinese deserts.