Measurement of stable iodine in crops and soils as an analogue of iodine-129

Long-life iodine-129 (half-life: 1.57x10^7 y) is the most critical radionuclide to be managed for the safe disposal of nuclear fuel waste. Its fate in the environment would be the same as that of stable iodine (I). Thus we measured stable I as an analogue of I-129 especially focusing on the soil-to-plant transfer in agricultural systems. Stable I concentrations were measured in 142 crop samples and associated agricultural field soil samples collected throughout Japan. We also measured bromine (Br) for comparison. The average I/Br concentration ratio in agricultural soil samples was about 0.5, while that in crop samples was about 0.01; the difference was possibly due to the different mobilities of these elements in soil as well as the different plant root uptake behaviors. We also calculated soil-to-crop transfer factors (TFs) of 25 crop species/parts. The highest TF for I, 0.48, was obtained for lettuce, and the lowest TF was 4.5x10^-4 for brown rice. The TF data from stable I observation for crops collected in agricultural fields were close to or within those of radiotracer experiments so that we judged the data would be applicable for dose estimation from I-129.Waste Management Symposium 201