Owing to the earthquake and the resulting tsunami occurred on March 2011 in central-eastern Japan, the Fukushima Dai-ichi Nuclear Power Plant was damaged by several hydrogen explosions. This accident released a vast amount of radionuclides, including caesium 134 and 137 (ca. ratio 1:1). Initial fallout contaminated cultivated soils, forests, water bodies, residential areas, asphalt and concrete surfaces. Afterwards, a variety of decontamination practices has been done, reducing the ambient dose rates.
In a recent study, published in Environmental Pollution (available online since April 19, 2018 ►) and conducted by Prof. Yuichi Onda (University of Tsukuba, Japan ►) and Dr. Manuel López-Vicente (EEAD-CSIC, Soil Management and Global Change Group ►), eight decontamination practices have been evaluated in a forest plantation of Japanese cedar located 16 km southwest to the Power Plant and within the exclusion area. Radiocesium (Cs-137) concentrations and activities were calculated in soil and litter samples, during 27 months (May 2013 – July 2015), in 10 experimental plots and after decontamination practices. Differences were statistically significant and four homogeneous groups were distinguished. Tree thinning and litter removal greatly reduced the radioactivity. Tree thinning, clearcutting with litter removal, and litter removal also had higher discharge rates than those rates in the control plots. We only observed low rates in the two plots with matting (soil conservation practice). The temporal variability was explained by (i) the different rainfall depths registered during the measurement intervals (with heavy rainfall events and typhoons); and (ii) the fluctuations of the total ground coverage (canopy and surface). The decrease trend in radiocesium concentration was high in 2013, moderate in 2014 and low in 2015 owing to the vegetation recovery after the countermeasures, thus reducing the possibility of the second pollution of the neighbouring areas. The average proportions of contribution of Cs-137 discharge by soil and leaf fraction were 96.6% and 3.4%.
This research was funded by the project “Development of techniques for migration control against radioactive substances in forests (2012-2016)” of the Japanese Forestry Agency; and was carried out by Dr. Manuel López-Vicente during his postdoctoral stays at the University of Tsukuba (Prof. Onda Laboratory) in 2015 (Research Fellowships Program of the Canon Foundation in Europe, call 2014) and 2016.
López-Vicente M, Onda Y, Takahashi J, Kato H, Chayama S, Hisadome K. Radiocesium concentrations in soil and leaf after decontamination practices in a forest plantation highly polluted by the Fukushima accident. Environmental Pollution 239, 448-456 (2018)
DOI: 10.1016/j.envpol.2018.04.045 ►