Aggregated transfer factor of Cs in edible wild plants and its time dependence after the Fukushima Dai-ichi nuclear accident.

We obtained the aggregated transfer factor (T) for 10 common edible wild plant species (four perennial spermatophytes, bamboo shoot, two tree species, and three perennial pteridophytes) in northeastern Japan. Measurement of T was carried out in 2012-2019 and we also used publicly available data for 2012-2019: food monitoring data and total deposition data from an airborne survey. The T obtained from actual measurements agreed well with T values calculated from the publicly available data. The sampling locations were only identified at the municipal level and uncertainty of the deposition for the publicly available data, and thus T values showed substantial variation. The T of the perennial spermatophytes, including bamboo shoot, and perennial pteridophytes showed single exponential decline with effective half-lives of approximately 2 years, whereas those of tree species did not show distinct temporal change. These results imply that data since 2014 are applicable for T estimation for long-term potential ingestion dose in the future to the public because of the slow decline. The calculated T values of all species for 2014-2019 ranged from 6.1 × 10 to 5.2 × 10 m/kg-fresh mass. The maximum T value was observed for the tree koshiabura (Chengiopanax sciadophylloides) and the minimum value was observed for the perennial spermatophyte giant butterbur (Petasites japonica). Tree species showed higher T than spermatophyte and pteridophyte perennials.