We monitored soil and rice radiocaesium concentrations in paddy fields in Minamisoma City, Fukushima Prefecture, Japan, from 2013 to 2016. As a result, brown rice samples collected in 2013 contained average 67 Bq/kg-dry weight (dw) of 137Cs. Five in the 9 samples exceeded 100 Bq/kg radiocaesium, which is the limit for food radioactive contamination in Japan. This is presumably due to radiocaesium fallout led by debris removal operations in the Fukushima Dai-ichi Nuclear Power Plant on 19 August 2013. 137Cs concentrations in the brown rice samples collected in 2014–2016 contained only 2–8 Bq/kg-dw. The soil and rice samples collected near water inlets of the paddy fields showed higher 137Cs concentrations than those collected at center and near water outlets. Transfer factors of 137Cs from soil to brown rice also tended to be higher at the water inlets except 2013, suggesting that irrigation water can affect on radiocaesium concentration in rice plants.
An investigation concerning the transfer of radioactive caesium from soil to ears of rice in the paddy fields of Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident has been carried out. Because the investigation in 2013 revealed relatively higher concentrations of radioactive 137Cs and 134Cs in the rice ears from one of the neighboring four contiguous fields, the aim of the present research carried out in 2014 and 2015 was to investigate the features of the paddy field where the contaminated rice ears were produced. It was revealed that the concentrations of radioactive 137Cs and 134Cs in the soil decreased with increasing depth, despite the fact that the cultivation was carried out in the preceding year. The Cs depth dependency was different among the fields. The 137Cs and 134Cs penetrated more deeply in the field where a relatively higher radioactive caesium concentration in ears of rice was observed. The difference depended on the variation of grain size distribution of soil, which affected the uptake of caesium in the rice ears. Four fields were cultivated in 2013 and 2014, although the upper two fields were not cultivated in 2015. Some locations showed relatively higher concentrations of radioactive 137Cs and 134Cs for rice ears in the two bottom fields in 2015, compared to the concentrations in 2013 and 2014, suggesting the possibility of a change of grain size distribution of soil.
To investigate the predictability of radiocaesium concentrations in the Japanese ripe pear fruits (Hosui and Kosui) based on those in the thinned-out pear fruits before the harvest, radiocaesium concentrations in thinned-out and ripe pear fruits were measured by γ-ray spectrometry. There was no significant difference in 137Cs concentrations of thinned-out and ripe pear fruits between Hosui and Kosui. The concentrations of 137Cs in ripe pear fruits (whole and flesh) were about quarter of those in thinned-out pear fruits. This finding suggests that the radiocaesium concentrations in ripe pear fruits could be predicted from those in thinned-out pear fruits.
18F-FBPA-PET is investigated as a method for prediction of therapeutic sensitivity of BNCT. Since microdistribution of BPA influences the biological effect of BNCT, if T/B (Tumor/Blood) and N/B (Normal tissue/Blood) ratios are similar in different tumors and normal tissues, the biological effect is not necessarily similar. Therefore, FBPA-PET is just a necessary condition and not a sufficient condition to select a candidate patient for BNCT. However, the usefulness of FBPA-PET can be evaluated by comparing local effect of BNCT in which absorbed dose is calculated by T/B or N/B ratio obtained from FBPA-PET, with the local effect by standard X-ray therapy. In this review, I will explain the implications and expectations of FBPA-PET which can be deduced from the consideration of CBE factor and human tumor radiobiology.