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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]

Abstract: Soil cores and rainwater were sampled under canopies of Cryptomeria japonica in four montane areas along an atmospheric depositional gradient in Kanto, Japan. Soil cores (30cm in depth) were divided into 2-cm or 4-cm segments for analysis. Vertical distributions of elemental enrichment ratios in soils were calculated as follows: (X/Al)i/(X/Al)BG (where the numerator and denominator are concentration ratios of element-X and Al in the i- and bottom segments of soil cores, respectively). The upper 14-cm soil layer showed higher levels of Cu, Zn, As, Sb, and Pb than the lower (14–30cm) soil layer. In the four areas, the average enrichment ratios in the upper 6-cm soil layer were as follows: Pb (4.93)≥Sb (4.06)≥As (3.04)>Zn (1.71)≥Cu (1.56). Exogenous elements (kg/ha) accumulated in the upper 14-cm soil layer were as follows: Zn (26.0)>Pb (12.4)>Cu (4.48)≥As (3.43)≥Sb (0.49). These rank orders were consistent with those of elements in anthropogenic aerosols and polluted (roadside) air, respectively, indicating that air pollutants probably caused enrichment of these elements in the soil surface layer. Approximately half of the total concentrations of As, Sb, and Pb in the upper 14-cm soil layer were derived from exogenous (anthropogenic) sources. Sb showed the highest enrichment factor in anthropogenic aerosols, and shows similar deposition behavior to NO3 −, which is a typical acidic air pollutant. There was a strong correlation between Sb and NO3 − concentrations in rainfall (e.g., in the throughfall under C. japonica: [NO3 −]=21.1 [dissolved Sb], r =0.938, p <0.0001, n =182). Using this correlation, total (cumulative) inputs of NO3 − were estimated from the accumulated amounts of exogenous Sb in soils, i.e., 16.7t/ha at Mt. Kinsyo (most polluted), 8.6t/ha at Mt. Tsukuba (moderately polluted), and 5.8t/ha at the Taga mountain system (least polluted). There are no visible ecological effects of these accumulated elements in the Kanto region at present. However, the concentrations of some elements are within a harmful range, according to the Ecological Soil Screening Levels determined by the U.S. Environmental Protection Agency. [Copyright &y& Elsevier]

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]