Global weapons' fallout 137Cs in soils and transfer to vegetation in south-central Chile

The contamination and depth distribution of Cs-137 in soil due to the fallout from atmospheric weapons' tests were measured at 29 sites in the 9th and 10th administrative regions in Chile located in the 40degrees latitude in the southern hemisphere. The depth distribution in most of the sites follows no systematic pattern in the upper few centimetres, but below this depth an exponential decline could be deduced. The calculated relaxation depth appears to be a good indicator for estimating the long-term Cs-137 distribution in these soil profiles. It ranges from 4.4 +/- 1.9 cm in Palehumults to 8.4 +/- 4.4 and 9.7 +/- 5.1 cm in Hapludands and Psamments, respectively. For these soil types the value for the relaxation depth tends to increase with decreasing clay content and increasing volume of coarse pores. Cs-137 activity densities at the selected sites ranged from 450 to 5410 Bq m(-2) and correlate significantly (r-0.791(**)) with the mean annual rainfall rate of the sampling sites. Cs-137 concentration ratios of prairie plants/soil were found to be in the range 0.008-2.3 and could be related to relaxation depths in undisturbed soils. (C) 2002 Elsevier Science Ltd. All rights reserved.