Biogeochemical behavior of 137Cs and 60Co in tropical soils

Results of a sequential chemical extraction procedure for 137Cs in an acidic Oxisol showed that 3 years after the contamination, 40 % of total concentration was considered readily bio-available, 20 % bound to organic matter and 40 % bound to Fe and Mn oxides. Four years after, the 137Cs distribution in this soil have been changed as a consequence of changes in soil properties : 8 % bio-available, 16 % bound to organic matter, 43 % bound to Fe and Mn oxides and 33% strongly bound to soil compounds. Changes in the 137Cs distribution in this soil were followed by reductions in soil to plant transfer factor (TF) : TFOxisol1996= 2,21 ± 1,30 (n=3) and TFOxisol2000 = 1,63 ± 0,38 (n=6). During the same period, the soil properties of a basic Oxisol remained almost the same, consequently the geochemical distribution and soil to plant transfer factor for 137Cs did not change in this soil. The geochemical distribution in an acidic Alfisol showed that Mn oxides are the main sink for this element and no 60Co was detected in the readily bio-available phase. In this soil, four years after contamination with 60Co, it was not detected in plants.