Soil samples collected from three forest sites within the 30-km zone around the Chernobyl reactor were analyzed for 239Pu and 240Pu by ICP-MS. The average 240Pu/239Pu atom ratio in contaminated surface soil samples, values of which are scarce in the literature, was 0.408. There were almost no differences in the 240Pu/239Pu ratios between the individual samples analyzed, although the 239+240Pu levels varied very widely (i.e. from 6.3 to 1430 Bq kg-1 dry weight) depending on the distance from the reactor and on the soil layers investigated. This result corresponded to area-related activities for 239+240Pu between 1.1 kBq m-2 and 13.3 kBq m-2. It was estimated that about half of the Pu migrated from the organic layers to the underlying mineral layers. The 240Pu/239Pu ratio observed in the Chernobyl area was much higher than that attributed to weapons fallout (ca. 0.18). The high ratio was related to the high burn-up grade of the reactor fuel. The 240Pu/239Pu ratio observed might be used as a “fingerprint” in...