ASSOCIATION OF FALLOUT PU-239+240 AND AM-241 WITH VARIOUS SOIL COMPONENTS IN SUCCESSIVE LAYERS OF A GRASSLAND SOIL

The association of Pu-239+240 and Am-241 from the global fallout with various soil components was investigated in six successive layers of an undisturbed grassland soil (Alfisol) from Oto 30 cm by a sequential extraction procedure. In this way, the fractions readily exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to organic matter, and residual (mineral) were determined. The results revealed that these radionuclides are in most soil layers primarily attached to the soil organic matter (in general >57%) but to a considerable extent also attached to oxides and minerals. As a result, the readily exchangeable fraction of these actinides 30-40 years after their deposition is rather low (for Pu, <1%). Significant differences between the partitioning of Pu and Am are observed for all fractions, even though they are rather small for the bound to organic matter fraction [with the exception of the 5-10-cm layer in the A(h) horizon, where much more Pu (67%) than Am (18%) is associated with organic matter]. In the fraction bound to oxides, more Am is found than Pu; in the residual fraction (minerals) of most soil layers, more Pu than Am is present. In all soil layers, the readily exchangeable fraction of Am is significantly higher than that of Pu (on average by a factor of 7). The results are also discussed in relation to the long-term vertical migration rates as determined recently for both radionuclides in the same soil and with respect to possible soil reclamation procedures.