Transfer of 90Sr to rice plants after its acute deposition onto flooded paddy soils

The transfer of 90Sr to rice plants following its acute ground deposition was examined experimentally in a greenhouse. Lysimeters were flooded after being filled with the soil monoliths from 12 paddy fields. A solution of 90Sr was applied to the standing water in the flooded lysimeters at the pre-transplanting stage or booting stage. Applied 90Sr was mixed with the topsoil only after the pre-transplanting application (PTA). The transfer was quantified with the areal transfer factor (TFa, m2 kg−1-dry) defined as the ratio of the plant concentration to the initial ground deposition. In the PTA, the first-year TFa values in the 12 soils were in the range of 8.2 × 10−3–2.1 × 10−2 and 1.7 × 10−4–3.6 × 10−4 for the straws and hulled seeds, respectively. The TFa values from the booting-stage application (BSA) were higher than those from the PTA by a factor of up to four. The ratios of the seed TFa to the straw TFa were, on the whole, higher in the BSA. The 90Sr TFa in the PTA was negatively correlated with the soil pH and, to a lesser degree, the exchangeable Ca content. In the second year, the TFa in the PTA reduced to 53–90% of that in the first year. A more significant reduction, in general, occurred in a sandier soil. Based on the four consecutive years' transfer data, an overall half-time of the 90Sr TFa was estimated to be 2.2 years.