Rice Uptake and Leaching of Tc in Different Paddy Soils Contaminated According to Two Contrasting Scenarios

Four different paddy soils collected around the Gyeongju nuclear site were treated with TcO4 solution under the assumption of two contrasting contamination scenarios. Scenario I (SN-I) is for a pre-transplanting deposition of Tc followed by plowing, whereas SN-II is for its deposition onto the water surface shortly after transplanting. Rice plants were grown in lysimeters in a greenhouse. Plant uptake of Tc was quantified with the TFarea (m·kg-dry). The SN-II TFarea values for straws and brown rice, having been generally higher than the SN-I values, were within the ranges of 6.9x10~4.1x10 and 5.2x10~7.3x10, respectively. Sorption onto clay seems to have decreased Tc uptake in SN-I, whereas it may have had an insignificant effect in SN-II. A phenomenon characteristic of submerged paddy soil, i.e., the development of a thin oxic surface layer may have greatly affected the rice uptake of SN-II Tc. The surface-water concentrations of Tc were much higher in SN-II than in SN-I. For the percolating water, however, the opposite was generally true. At most 1.3% of the applied Tc were leached through such percolation. The use of empirical deposition time-dependent TFarea values was considered desirable in assessing the radiological impact of a growing-season deposition of Tc onto paddy fields.