Spatial distribution of radioactive cesium fallout on grasslands from the Fukushima Daiichi Nuclear Power Plant in 2011

Large releases of radionuclides from the Fukushima Daiichi Nuclear Power Plant have resulted in serious radioactive pollution of a wide region of Eastern Japan, and the livestock industry has suffered serious damage as a result. In this study, the distribution of deposited radioactive cesium (Cs) and its transfer to vegetation were surveyed on a pasture and a meadow in Iwate Prefecture. Air radiation dose rates measured at a height of 1 cm in μSv h–1 were used to estimate the deposited radioactive Cs contamination in kBq m–2. The means and coefficients of variation (CV) of deposited radioactive Cs were higher in the pasture (163 kBq m–2, CV = 38.7%) than in the meadow (67 kBq m–2, CV = 10.2%). In the pasture, high radioactive Cs contamination was observed at the southeastern edge, demonstrating the heterogeneous nature of radioactive fallout. In both the pasture and the meadow, Cs contamination was higher in the low elevation area compared to the high elevation area. The part of the meadow to which potassium chloride and lime were applied showed higher radioactive Cs contamination compared to surrounding areas. Application of potassium and lime may reduce absorption of radioactive Cs by plants. High radioactive Cs levels were observed in pasture vegetation in the area with relatively high radioactive Cs contamination. Further studies are necessary to clarify the relationship between radioactive Cs contents in vegetation and soil/land dependent parameters such as radioactive Cs level, soil soluble K concentration, pH, clay and organic matter contents.