Radiocesium contaminations of 20 wood species and the corresponding gamma-ray dose rates around the canopies at 5 months after the Fukushima nuclear power plant accident

• Published in: Journal of environmental radioactivity 2013-01, Vol.115, p.60-68
• Main Authors: Yoshihara, Toshihiro, Matsumura, Hideyuki, Hashida, Shin-nosuke, Nagaoka, Toru
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; branches; canopy; Cesium Radioisotopes - analysis; Cycadopsida; Deciduous species; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; Evergreen species; Fukushima; Fukushima Nuclear Accident; Fundamental and applied biological sciences. Psychology; gamma radiation; Gamma Rays; Japan; leaves; Magnoliopsida; monitoring; nuclear power; Plant Leaves - chemistry; prediction; Radiation Dosage; Radiation Monitoring; Radioactive Pollutants - analysis; Radiocesium; soil; Wood; Woody plants
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2012.07.002

Radiocesium (134Cs + 137Cs) deposition from the Fukushima nuclear power plant accident was measured in 20 woody plants (12 evergreen and 8 deciduous species) grown in Abiko (approximately 200 km SSW from the NPP). Leaves (needles) and twigs were sampled from each of three foliar positions (top, middle, and bottom) in the plant canopy in early August 2011. At the time, soils around the plants were also sampled, and gamma radiation dose rates were measured at each sampling position. The average radiocesium activity in the observed leaves of the evergreen species was 7.7 times that in the leaves of the deciduous species. Among the observed evergreen coniferous species, the activity in pre-fallout-expanded leaves was 2.4 times that in the post-fallout-expanded leaves. Notably, a distinct variation in the activity among the evergreen coniferous species could be observed for the post-fallout-expanded leaves but not for the pre-fallout-expanded leaves. Although these differences depend on whether the leaves had expanded at the time of the fallout, it is probable that a considerable amount of radiocesium was translocated to newly developed leaves at a species-specific rate. In addition, it was demonstrated that dose rates around woody plants were not consistent with the prevailing prediction that general dose rates correspondingly decrease with monitoring height from the ground. Thus, the dose rates in the top foliar layer of the deciduous species decreased more than predicted, whereas those in the top foliar layer of the coniferous species did not decrease. This may be due to differences in the balance between the attenuation resulting from a shielding effect of the plant bodies and the higher radiocesium accumulation in the leaves. ► Radiocesium accumulations by the Fukushima accident were compared for 20 wood species. ► The foliar accumulations were higher in evergreen species than in deciduous species. ► The difference would be mainly from the life cycle and the related characteristics. ► The foliar Cs accumulation obviously influenced the dose rates around the plants.