Distribution of cesium-bearing microparticles in the paddy field and their effect on transfer factor of radioactive cesium for brown rice

Radioactive cesium-bearing microparticles (CsMPs) were insoluble glassy matrixes derived from Fukushima Daiichi Nuclear Power Plant accident. CsMPs may locally increase radioactive cesium (RCs) concentration of soils and crops. Furthermore, RCs in the CsMPs is included in insoluble grassy particle, it is considered that it may be difficult for crops to absorb. Transfer factor (TF) is used to evaluate transfer of RCs from soils to crops. However, the conventional TF is a simple ratio of RCs concentrations between them. This suggests that conventional TF may not be able to accurately assess RCs transfer from soils to crops when CsMPs are in the soil. Since there are many contaminated forests in Fukushima Prefecture, Japan, there are concerns about secondary contamination due to the inflow of CsMPs. In this study, we investigated the deposition of CsMPs in the paddy field located within specified reconstruction and revitalization base area in the first year of resumed cultivation following the accident. Furthermore, we evaluate the impact of CsMPs on RCs concentration in the soil and TF of brown rice.

The accumulation of RCs and CsMPs in our study field was not observed. RCs concentration of brown rice was less than the shipping limit defined by Japanese government. These suggested that the impact of secondary contamination was not large, and cultivation can be done safely. However, because there are many contaminated sites in the surrounding area, and it is necessary to continue to monitor the effects of radiation in the future. Furthermore, the proportion of CsMPs on RCs concentration in the soil was less than 10%. Therefore, CsMPs may not have a significant effect on transfer factor of RCs for brown rice.