Explaining the variation in 137Cs aggregated transfer factor for wild edible plants as a case study on Koshiabura (Eleutherococcus sciadophylloides) buds

Abstract

The aggregated transfer factor (Tag) is commonly used to represent the actual transfer of radiocesium from soil to wild edible plants, but the values have shown substantial variation since the Fukushima nuclear accident. To elucidate the factors causing this variation, we investigated the effects of spatial scale and vertical 137Cs distribution in the soil on the variation of Tag-137Cs values for one of the most severely contaminated wild edible plants, Eleutherococcus sciadophylloides Franch. et Sav. (Koshiabura). The variation in Tag-137Cs values was not reduced by direct measurement of 137Cs deposition in soil samples from the Koshiabura habitat, as a substitute for using spatially averaged airborne survey data at the administrative district scale. The 137Cs activity concentration in Koshiabura buds showed a significant positive correlation with the 137Cs inventories only in the organic horizon of soil from the Koshiabura habitat. The ratio of 137Cs inventories in the organic horizon to the total 137Cs deposition in soil exhibited substantial variation, especially in broad-leaved deciduous forests that Koshiabura primarily inhabits. This variation may be the cause of the wide range of Tag-137Cs values observed in Koshiabura buds when calculated from the total 137Cs deposition in soil.

Exploring simple ways to avoid collecting highly 137Cs-contaminated Aralia elata buds for the revival of local wild vegetable cultures

“…elata buds. Although T ag is generally rather variable (and thus often represented with GM and GSD) [ 8 , 21 , 22 ], the positive relationship may become observable under the current soil conditions more than 10 years after the contamination event.…”

“…elata buds, while the soil layer was assumed to possess abundant bioavailable 137 Cs that can be transferred to plants [ 30 ]. For example, Eleutherococcus sciadophylloides (Koshiabura, the Queen of sansai ), which develops extensive roots in the interface between the organic and mineral soil layers [ 32 ] exhibit one of the highest bud 137 Cs concentrations among Japanese wild vegetables [ 6 – 8 ]. In addition, 137 Cs activity concentrations in E .…”

“…In addition, 137 Cs activity concentrations in E . sciadophylloides are well correlated with 137 Cs inventories in the organic soil layer [ 8 ]. Thus, 137 Cs in the organic soil layer is still notable to understand 137 Cs transfer from the soil to wild vegetables.…”

“…Collecting various wild vegetables is restricted in some contaminated areas due to radiocesium concentrations exceeding the Japanese reference level (100 Bq/kg) [ 4 , 5 ]. Among the vegetables, the buds of Koshiabura ( Eleutherococcus [ Chengiopanax ] sciadophylloides [Araliaceae]), which is known as the “Queen of sansai ,” exhibits particularly high radiocesium concentrations compared to other wild vegetables [ 6 – 8 ]. Consequently, commercial shipping of this species is restricted in 113 municipalities in Japan [ 9 ].…”