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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. [ABSTRACT FROM AUTHOR]

Changes in 137Cs export over time following clearcutting were investigated in a Japanese forested catchment affected by the Fukushima nuclear accident. A total of 13% of the catchment area was clear-cut 2 years after the accident. Annual suspended solids (SS) export at the catchment outlet increased 1.4 to 2.0 times after clearcutting; however, 137Cs export increased slightly (up to 1.1 times), corresponding to 0.21% to 0.30% of the 137Cs inventory in the catchment. The smaller change in 137Cs export than in SS export was due to a rapid decrease in the activity concentration following clearcutting. This decrease was likely caused by both natural attenuation and SS derived from sources with a low activity concentration in the clear-cut area. Monitoring of the sediment transport from hillslopes in small-scale experimental plots showed that the 137Cs yield in the skid trail was 3.6 to 21 times greater than those in clear-cut and unlogged forest floors. This significant 137Cs transport was due to greater soil erosion (by up to two orders of magnitude) along the skid trail, despite the lower activity concentration than those in the other plots. This indicates that while skid trails were involved in the rapid decrease of the activity concentration of SS, they were a potential source of the increased export of 137Cs and SS. Net 137Cs export increased by clearcutting (the export excluding the decrease accompanied by natural attenuation) was estimated to account for only 0.092% of the inventory in the catchment for 2.5 years. These results imply that the impact of clearcutting on 137Cs export was temporary in this catchment. [ABSTRACT FROM AUTHOR]

Cryptomeria japonica trees in the area surrounding Fukushima, Japan, intercepted 137 Cs present in atmospheric deposits soon after the Fukushima nuclear accident in March 2011. To study the uptake and translocation of 137 Cs in C. japonica leaves, we analyzed activity concentrations of 137 Cs and the concentration ratios of 137 Cs to 133 Cs ( 137 Cs/ 133 Cs) in old and new leaves of C. japonica collected from a forest on Mount Tsukuba between 9 and 15 months after the accident. Both isotopes were also analyzed in throughfall, bulk precipitation and soil extracts. Water of atmospheric and soil origin were used as proxies for deciphering the absorption from leaf surfaces and root systems, respectively. Results indicate that 20–40% of foliar 137 Cs existed inside the leaf, while 60–80% adhered to the leaf surface. The 137 Cs/ 133 Cs ratios inside leaves that had sprouted before the accident were considerably higher than that of the soil extract and lower than that of throughfall and bulk precipitation. Additionally, more than 80% of 137 Cs in throughfall and bulk precipitation was present in the dissolved form, which is available for foliar uptake, indicating that a portion of the 137 Cs inside old leaves was presumably absorbed from the leaf surface. New leaves that sprouted after the accident had similar 137 Cs/ 133 Cs ratios to that of the old leaves, suggesting that internal 137 Cs was translocated from old to new leaves. For 17 species of woody plants other than C. japonica , new leaves that sprouted after the accident also contained 137 Cs, and their 137 Cs/ 133 Cs ratios were equal to or higher than that of the soil extract. These results suggested that foliar uptake and further translocation of 137 Cs is an important vector of contamination in various tree species during or just after radioactive fallout. [ABSTRACT FROM AUTHOR]

Chemical transport models played key roles in understanding the atmospheric behaviors and deposition patterns of radioactive materials emitted from the Fukushima Daiichi nuclear power plant after the nuclear accident that accompanied the great Tohoku earthquake and tsunami on 11 March 2011. However, model results could not be sufficiently evaluated because of limited observational data. We assess the model performance to simulate the deposition patterns of radiocesium (137Cs) by making use of airborne monitoring survey data for the first time. We conducted ten sensitivity simulations to evaluate the atmospheric model uncertainties associated with key model settings including emission data and wet deposition modules. We found that simulation using emissions estimated with a regional-scale (500 km) model better reproduced the observed 137Cs deposition pattern in eastern Japan than simulation using emissions estimated with local-scale (50 km) or global-scale models. In addition, simulation using a process-based wet deposition module reproduced the observations well, whereas simulation using scavenging coefficients showed large uncertainties associated with empirical parameters. The best-available simulation reproduced the observed 137Cs deposition rates in high-deposition areas (=10 kBq m-2) within 1 order of magnitude and showed that deposition of radiocesium over land occurred predominantly during 15-16, 20-23, and 30-31 March 2011. [ABSTRACT FROM AUTHOR]