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Atmospheric Direct Uptake and Long-term Fate of Radiocesium in Trees after the Fukushima Nuclear Accident

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ABSTRACT

Large areas of forests were radioactively contaminated by the Fukushima nuclear accident of 2011, and forest decontamination is now an important problem in Japan. However, whether trees absorb radioactive fallout from soil via the roots or directly from the atmosphere through the bark and leaves is unclear. We measured the uptake of radiocesium by trees in forests heavily contaminated by the Fukushima nuclear accident. The radiocesium concentrations in sapwood of two tree species, the deciduous broadleaved konara (Quercus serrata) and the evergreen coniferous sugi (Cryptomeria japonica), were higher than that in heartwood. The concentration profiles showed anomalous directionality in konara and non-directionality in sugi, indicating that most radiocesium in the tree rings was directly absorbed from the atmosphere via bark and leaves rather than via roots. Numerical modelling shows that the maximum 137Cs concentration in the xylem of konara will be achieved 28 years after the accident. Conversely, the values for sugi will monotonously decrease because of the small transfer factor in this species. Overall, xylem 137Cs concentrations will not be affected by root uptake if active root systems occur 10 cm below the soil.

No MeSH data available.


Radial distribution of 137Cs and 40K measured in annual tree rings in the trunk disc for each of the four different cardinal compass directions.Results for (a) konara and (b) sugi. Solid squares represent the 137Cs concentration and open circles the 40K concentration. Red, navy blue, olive and turquoise blue indicate the sides of the trunks facing east, north, west and south, respectively.
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f2: Radial distribution of 137Cs and 40K measured in annual tree rings in the trunk disc for each of the four different cardinal compass directions.Results for (a) konara and (b) sugi. Solid squares represent the 137Cs concentration and open circles the 40K concentration. Red, navy blue, olive and turquoise blue indicate the sides of the trunks facing east, north, west and south, respectively.

Mentions: We harvested two Japanese common trees (konara: Quercus serrata Murray, a deciduous broadleaf tree and sugi: Cryptomeria japonica D. Don, an evergreen coniferous tree) to investigate the distribution of 137C, 134Cs and 40K in tree rings in 2012 (Supplementary Table S1). The distributions of 137Cs and 134Cs are almost the same in the rings of both trees. We also measured the concentrations of stable isotopes of Cs and K in tree rings (Supplementary Table S2). We show the distribution of 137Cs and 40K in the xylem in trees divided into four cardinal compass directions in Figs. 2a and 2b. We also demonstrate a directional distribution of 137Cs concentration compared with 40K concentration for konara (Fig. 3a) and a non-directional distribution for sugi (Fig. 3b). In addition, we summarize the directional distribution of radiocesium concentration in the sapwood region of trunk discs in four different directions, verified using the χ2-test, in Table 1.


Atmospheric Direct Uptake and Long-term Fate of Radiocesium in Trees after the Fukushima Nuclear Accident
Radial distribution of 137Cs and 40K measured in annual tree rings in the trunk disc for each of the four different cardinal compass directions.Results for (a) konara and (b) sugi. Solid squares represent the 137Cs concentration and open circles the 40K concentration. Red, navy blue, olive and turquoise blue indicate the sides of the trunks facing east, north, west and south, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382682&req=5

f2: Radial distribution of 137Cs and 40K measured in annual tree rings in the trunk disc for each of the four different cardinal compass directions.Results for (a) konara and (b) sugi. Solid squares represent the 137Cs concentration and open circles the 40K concentration. Red, navy blue, olive and turquoise blue indicate the sides of the trunks facing east, north, west and south, respectively.
Mentions: We harvested two Japanese common trees (konara: Quercus serrata Murray, a deciduous broadleaf tree and sugi: Cryptomeria japonica D. Don, an evergreen coniferous tree) to investigate the distribution of 137C, 134Cs and 40K in tree rings in 2012 (Supplementary Table S1). The distributions of 137Cs and 134Cs are almost the same in the rings of both trees. We also measured the concentrations of stable isotopes of Cs and K in tree rings (Supplementary Table S2). We show the distribution of 137Cs and 40K in the xylem in trees divided into four cardinal compass directions in Figs. 2a and 2b. We also demonstrate a directional distribution of 137Cs concentration compared with 40K concentration for konara (Fig. 3a) and a non-directional distribution for sugi (Fig. 3b). In addition, we summarize the directional distribution of radiocesium concentration in the sapwood region of trunk discs in four different directions, verified using the χ2-test, in Table 1.

View Article: PubMed Central - PubMed

ABSTRACT

Large areas of forests were radioactively contaminated by the Fukushima nuclear accident of 2011, and forest decontamination is now an important problem in Japan. However, whether trees absorb radioactive fallout from soil via the roots or directly from the atmosphere through the bark and leaves is unclear. We measured the uptake of radiocesium by trees in forests heavily contaminated by the Fukushima nuclear accident. The radiocesium concentrations in sapwood of two tree species, the deciduous broadleaved konara (Quercus serrata) and the evergreen coniferous sugi (Cryptomeria japonica), were higher than that in heartwood. The concentration profiles showed anomalous directionality in konara and non-directionality in sugi, indicating that most radiocesium in the tree rings was directly absorbed from the atmosphere via bark and leaves rather than via roots. Numerical modelling shows that the maximum 137Cs concentration in the xylem of konara will be achieved 28 years after the accident. Conversely, the values for sugi will monotonously decrease because of the small transfer factor in this species. Overall, xylem 137Cs concentrations will not be affected by root uptake if active root systems occur 10 cm below the soil.

No MeSH data available.