Received: October 28, 2015; Revised: December 2, 2015 Accepted: December 4, 2015.
ABSTRACT
Four different paddy soils collected around the Gyeongju nuclear site were treated with 99TcO4? solution under the assumption of two contrasting contamination scenarios. Scenario I (SN-I) is for a pre-transplanting deposition of 99Tc 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 99Tc was quantified with the TFarea (m2·kg?1-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?3~4.1x10?2 and 5.2x10?6~7.3x10?5, respectively. Sorption onto clay seems to have decreased 99Tc 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 99Tc. The surface-water concentrations of 99Tc 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 99Tc 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 99Tc onto paddy fields.
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