Uptake and distributions of 137Cs and stable Cs in rice plant components

The uptake and distributions of 137Cs and stable Cs were determined for rice plant components such as polished rice, rice bran, hull, straw and root components. The concentration of 137Cs in polished rice was 0.0048, and the soil-to-plant transfer factors in polished rice, rice bran and aboveground parts were 0.0011, 0.094 and 0.0038, respectively. The range of 137Cs concentrations in rice plant components was different by one order of magnitude, however the activity ratio for 137Cs/Cs showed a constant value and the distribution of 137Cs in rice plants was similar to that of stable Cs. This may be attributed to similar translocation rates for 137Cs and stable Cs in rice plants. On the other hand, the concentration ratios of Cs/K in leaves increased in older leaf blade positions, which meant that the translocation rate of stable Cs was slower than that of K. The edible component, polished rice, accounted for 34% of the dry weight, while the non-edible components accounted for 66%. Only 7% of Cs in the whole rice plant was found in polished rice, while 93% of Cs was present in the non-edible components. The percentage of 137Cs removed from the upper soil layer to the aboveground biomass of rice plants every year was calculated as 0.003%. Consequently, the distribution and translocation of stable Cs would serve as useful analogues in predicting the fate of 137Cs in an agricultural environment. (author)