Aggregated transfer factor of ¹³⁷Cs in wild edible mushrooms collected in 2016-2020 for long-term internal dose assessment use

Ingestion of edible wild mushrooms collected in areas contaminated with radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident may pose a risk of internal dose to their consumers. A species-specific aggregated transfer factor (T_ag), which is calculated using radiocesium concentration in a wild mushroom species (Bq kg^-1 wet mass [WM]) divided by the total concentration in the soil surface area (Bq m^-2), would be a useful tool to estimate the dose from wild mushrooms by ingestion. In this study, we especially focused on the T_ag data collected in 2016-2020 to use these values for a long-term dose assessment. We assumed that ¹³⁷Cs concentrations after that year were almost the same, thus the soil-mushroom system would be in an apparent steady-state condition. In all, we could obtain T_ag values of ¹³⁷Cs in 62 edible wild mushroom species native to Japan. The geometric mean (GM) values were 1.5 × 10^-3 m² kg^-1 WM using GMs of 13 saprobic type species and 5.0 × 10^-3 m² kg^-1 WM using GMs of 21 mycorrhizal type species (N > 2). On average, the GMs of species-specific T_ag values were 1.9 ± 0.9 times higher than those reported in a previous study of wild mushrooms made after the FDNPP accident, probably due to the different approaches for T_ag calculation.