40K, 137Cs and 226Ra Soil and Plant Content in Seminatural Grasslands of Central Argentina

JURI AYUB, J., VELASCO, R.H., RIZZOTTO, M., QUINTANA, E. AND AGUIAR, J.

AIP CONFERENCE PROCEEDINGS

American Institute of Physics

Lugar: New York; Año: 2007

0094-243X

Activity concentrations of gamma emitting radionuclides have been determined in soil and plant samples, collected in permanent grassland in central Argentina. Two near areas (A1 and A2) under field conditions with soil undisturbed at least in the last four decades were selected. The soil is a sandy type with low clay content. The dominant vegetation in these areas consists of herbaceous gramineous, which is used for the feeding of cattle. The 40K inventories are similar in both areas and range from 143 kBq·m-2 to 197 kBq·m-2. For 137Cs the inventories are 0.56±0.06 kBq·m-2 and 0.52±0.2 kBq·m-2, for A1 and A2, respectively. Nevertheless, 137Cs activity concentration has a maximum for layers 5-10 cm depth in A1 and 10-15 cm depth in A2. For deeper layers (>10 cm) both areas show similar activity concentrations. The diffusion coefficient (Ds) and convection velocity (vs) are estimated with a convection-diffusion model. Ds values are in the range reported in the bibliography, while vs values are one order of magnitude higher. After 40 years most 137Cs fallout is still in the layer 10-15 cm depth. The great penetration of 137Cs (25 cm) in these soils may be the result of a high sand and low fine materials content. For 226Ra the inventories are similar in both areas and range from 13 kBq·m-2 to 18 kBq·m-2. 137Cs and 226Ra were not detected in grass samples. Activity concentration of 40K in vegetal samples ranges from 116 Bq·kg-1 to 613 Bq·kg-1 and the TF ranges from 0.05 to 0.42.