Aggregated transfer factor of 137 Cs in edible wild plants and its time dependence after the Fukushima Dai-ichi nuclear accident

We obtained the aggregated transfer factor ( T ag ) 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 ag 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 ag obtained from actual measurements agreed well with T ag 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 ag values showed substantial variation. The T ag 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 ag estimation for long-term potential ingestion dose in the future to the public because of the slow decline. The calculated T ag values of all species for 2014–2019 ranged from 6.1 × 10 −5 to 5.2 × 10 −3 m 2 /kg-fresh mass. The maximum T ag 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 ag than spermatophyte and pteridophyte perennials.