Mass Interception Fractions and Weathering Half-lives of Iodine-131 and Radiocesium in Leafy Vegetables Observed after the Fukushima Daiichi Nuclear Power Plant Accident

Abstract

Background: This study was carried out to provide environmental transfer parameter values to estimate activity concentrations of these radionuclides in agricultural crops when direct contamination occurred. Materials and Methods: Mass interception fractions ( F B s) and weathering half-lives ( T w s) of 131 I and radiocesium were calculated using openly available monitoring data obtained after the Fukushima Daiichi Nuclear Power Plant accident. F B is the ratio between the initial radioactivity concentration of a radionuclide retained by the edible part of the plant (Bq ‧ kg -1 fresh weight [FW]) and the amount of deposited radionuclide in that area (Bq ‧ m -2 ). T w values can be calculated using activity concentrations of crops decreased with time after the initial contamination. Results and Discussion: Calculated F B and T w values for 131 I and radiocesium were mostly obtained for leafy vegetables. The analytical results showed that there was no difference of F B s between 131 I and radiocesium by t -test; geometric mean values for leafy vegetables cultivated under outdoor conditions were 0.058 and 0.12 m 2 ‧ kg -1 FW, respectively. Geometric mean T w value of 131 I in leafy vegetables grown under outdoor conditions was 8.6 days, and that of radiocesium was 6.6 days; there was no significant difference between T w values of these radionuclides by Wilcoxon rank sum test. Conclusion: There was no difference between 131 I and radiocesium for F B s and T w s. By using these factors, we would be able to carry out a rough estimation of the activity concentrations of 131 I and radiocesium in the edible part of leafy crops when a nuclear accident occurred.