The Efficiency of Moldboard Plowing upon Deactivation and Rehabilitation of Radioactively Contaminated Pastures in the North of Japan

摘要

The nuclear disaster at the Fukushima-1 nuclear power plant resulted in the widespread contamination of agrocenoses with radiocesium (_(134)Cs and_(137)Cs) on the Honshu Island. Our study was performed on four agricultural fields located on gentle slopes of southern aspect 150 km to the northwest from the nuclear power plant. Three plots were tilled in different periods (in 2012–2013), and one plot remained untilled. The density of soil contamination and the specific activity of radiocesium in plants (June 2014) on tilled plots appeared to be permissible. Thus, the density of soil contamination varied within the range of 1.3–6.5 kBq/m_(2), and the specific radioactivity of plants did not exceed 100 Bq/kg in plants. Such areas may be used as pastures without restrictions. At the same time, an increased density of the soil contamination (13–32 kBq/m_(2)) and the concentration of radiocesium in plants (up to 138 Bq/kg) were detected in some areas not subjected to reclamation works. Such fallow lands are suitable as pastures only for feeding cattle for meat and for milk with their obligatory subsequent processing. On all the plots, the concentration of radiocesium in soils decreased down the soil profile. In general, radiocesium was accumulated on the middle and lower parts of slopes, which is associated with the development of water erosion and initial distribution of radiocesium during the snowmelt season. The air dose rate on the studied plots did not exceed the permissible safety level (0.2 μSv/h) and varied within the range 0.05–0.10 μSv/h. The maximum level of γ-radiation was determined on the fallow (untilled) plot. On tilled plots, γ-radiation was 30–50% lower. Therefore, soil moldboard plowin tillage to the depth of 20 cm with or without shallow cultivation is an efficient measure to reclaim agricultural lands with the initially low level of radiocesium contamination (up to 32 kBq/m_(2)).