Enhancement of Mass Interception Coefficient Data of Radiostrontium by Leafy Crops Using Global Fallout ⁹⁰Sr and Naturally Occurring ⁷Be

Abstract

When artificial radionuclides are released into the atmospheric environment, one of the important processes by which they affect the human radiation dose is the direct deposition of the radionuclides onto crop surfaces. Because leafy vegetables are consumed while fresh and often raw, the mass interception coefficient [= concentration in food (Bq/kg dry mass (DM) or fresh mass)/total deposition (Bq/m2)] is a key parameter for estimating radionuclide concentrations in crops after the deposition of radionuclides on plant stands. However, such data are still sparse, especially for radiostrontium (89Sr and 90Sr). To enhance the mass interception coefficient data for leafy crops, we used global fallout 90Sr data in leafy crops harvested in 1963–1965 and the deposition data for the corresponding crop growing period. Geometric mean values of the mass interception coefficient of 90Sr for leafy crops were 2.8 m2 kg–1 DM for spinach, 0.60 m2 kg–1 DM for cabbage, and 1.3 m2 kg–1 DM for Chinese cabbage. For comparison, we measured naturally occurring 7Be in giant butterbur leaves, and the results showed that the data were similar to those of 90Sr for spinach. These data were similar to the previously obtained data by single spike radiotracer experiments. Therefore, in the case of nuclear emergency situations, mass interception coefficient data obtained using global fallout 90Sr and/or naturally occurring 7Be should be valuable to estimate radioactivity contamination levels of radiostrontium directly deposited on leafy crops.