Sources, vertical distribution, and migration rates of 239,240Pu, 238Pu, and 137Cs in grassland soil in three localities of central Bohemia

The vertical distribution and sources of 239,240Pu, 238Pu and 137Cs were determined at three sites in undisturbed grassland soils. Using a compartment model, the migration rates of 239,240Pu originating from atmospheric nuclear tests and Chernobyl-derived 137Cs in soil were calculated for widely used convection and as well for diffusion transport processes. Deposition of small amounts of Chernobyl-derived plutonium (0.5–1.0 Bq m−2 238Pu and 1–2 Bq m−2 239,240Pu) was found at two sites. The migration rate of 239,240Pu at sites studied in convection transport increases with depth so that at a depth of 0–10 cm it is 0.21–0.38 and at a depth of 25–35 cm it is 0.60–1.56 cm yr−1. The migration rate of 137Cs increases with depth as well. Using the diffusion transport model the resulting migration rates of 239,240Pu and 137Cs range from 0.65 to 0.94 and from 0.18 to 0.99 cm yr−1, respectively