Biogeochemical behavior of ¹³⁷Cs and ⁶⁰Co in tropical soils

¹ Instituto de Radioproteçao e Dosimetria, IRD/CNEN, Av. Salvador Allende s/n, Recreio, Rio de Janeiro RJ, Brasil
² Centro Nacional de Pesquisa de Solos, CNPS/EMBRAPA, Rua Jardim Botánico, 1024 Jardim Botánico, Rio de Janeiro, Brasil

Abstract

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) : TF_Oxisol1996= 2,21 ± 1,30 (n=3) and TF_Oxisol2000 = 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.