Accumulation of 137Cs in Brazilian soils and its transfer to plants under different climatic conditions

The spatial distribution and behaviour of the global fallout 137Cs in the tropical, subtropical and equatorial soil–plant systems were investigated at several upland sites in Brazil selected according to their climate characteristics, and to the agricultural importance. To determine the 137Cs deposition density, undisturbed soil profiles were taken from 23 environments situated between the latitudes of 02°N and 30°S. Sampling sites located along to the equator exhibited 137Cs deposition densities with an average value of 219 Bq m−2. Extremely low deposition densities of 1.3 Bq m−2 were found in the Amazon region. In contrast, the southern part of Brazil, located between latitudes of 20°S and 34°S, exhibited considerably higher deposition densities ranging from 140 Bq m−2 to 1620 Bq m−2. To examine the 137Cs soil-to-plant transfer in the Brazilian agricultural products, 29 mainly tropical plant species, and corresponding soil samples were collected at 43 sampling locations in nine federal states of Brazil. Values of the 137Cs concentration factor plant/soil exhibited a large range from 0.020 (beans) to 6.2 (cassava). Samples of some plant species originated from different collecting areas showed different concentration factors. The 137Cs content of some plants collected was not measurable due to a very low 137Cs concentration level found in the upper layers of the incremental soils. Globally, the soil-to-plant transfer of 137Cs can be described by a logarithmic normal distribution with a geometric mean of 0.3 and a geometric standard deviation of 3.9.