Abstract
The Great East Japan Earthquake on 11 March 2011, caused the release of radioactive materials from the Fukushima Daiichi Nuclear Power Plant (FDNPP), contaminating eastern Japan, particularly in part of Fukushima Prefecture. In 2012 and 2014, the radiocaesium concentration in brown rice did not exceed regulatory levels in Minamisoma City, Fukushima. However, in 2013, some radiocaesium concentrations in brown rice exceeded regulatory levels. In this work, autoradiograms showed that high radioactivity was present as contaminated spots on the panicles of rice and in brown rice in 2013. We evaluate the contribution of direct contamination to the radiocaesium concentration in brown rice and discuss the origin of radiocaesium contamination in brown rice using the 134Cs/137Cs radioactivity ratio. Here, we show that the main cause of the unexplained radiocaesium contamination of brown rice in Minamisoma City in 2013 is the adherence of radioactive materials to the rice panicles, and these radioactive materials are associated with reactor units 2 or 3 of FDNPP.
Highlights
Produced in a limited area of Minamisoma City[4]
We evaluate the effect of the direct contamination on the radiocaesium concentration in brown rice in Minamisoma City during 2013 and discuss the origin of the radiocaesium contamination of brown rice by examining the 134Cs/137Cs radioactivity ratio
The central area of Minamisoma City coincided with the southern limit of the area north of FDNPP available for farming rice for human consumption
Summary
Produced in a limited area of Minamisoma City[4]. In this area, the radiocaesium concentration in brown rice did not exceed 100 Bq kg−1 in 2012 and 20144,5. To evaluate the effect of the direct contamination on the radiocaesium concentration in brown rice in Minamisoma City in 2013, the grains of the brown rice samples with high radiocaesium concentrations in the southern area were divided into highly contaminated grains and less contaminated grains after 2 weeks of exposure on an imaging plate.
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