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Update:August 23, 2019

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A plant-available form of radiocesium in forest soil is rapidly decreasing


Article title

Six-year trends in exchangeable radiocesium in Fukushima forest soils

Author (affiliation)

Takuya Manaka (a), Naohiro Imamura (a), Shinji Kaneko (b), Satoru Miura (c), Hitomi Furusawa (a), Tsutomu Kanasashi (a)

(a) Department of Forest Soils, FFPRI, Tsukuba, Ibaraki, Japan.

(b) Kansai Research Center, FFPRI, Kyoto, Japan.

(c) Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, Japan.

Publication Journal

Journal of Environmental Radioactivity, 203:84-92, July 2019 DOI:10.1016/j.jenvrad.2019.02.014( External link )

Content introduction

The Fukushima Daiichi Nuclear Power Plant accident in 2011 led to the deposition of large amounts of radiocesium in the forests of Fukushima. Although radiocesium is mostly fixed on the surface of the soil, it has also been found in the internal tissues of trees. Using Fukushima forest soil samples collected annually for 6 years after the accident, we measured the proportion of exchangeable radiocesium(note), which is easily taken up by plants. The exchangeable radiocesium as a proportion of total radiocesium in organic as well as mineral soil layers was ≤10% about 5 months after the accident, and it showed an exponential decrease over 6 years. This indicates that radiocesium that is available for plants is rapidly decreasing. This result provides important clues for understanding the mechanism of radiocesium contamination of trees and predicting future dynamics of radiocesium in forest ecosystems.

Note: This form of radiocesium is electrostatically absorbed by negative charges on the surfaces of clay minerals and organic matter in forest soils and easily released into the soil water.

Figure: Gradual changes in the proportion

Figure: Gradual changes in the proportion of exchangeable radiocesium at the Japanese cedar site in Kawauchi.