Transfer of 137Cs from various paddy soils to rice seeds after its application at different times

In order to study the transfer of accidentally deposited radiocesium from different types of paddy soil to rice seeds, soil blocks were collected into small lysimeters from 18 paddy fields located within 5 km radii of Kori, Yonggwang and Ulchin NPPs and carried to a greenhouse. An aqueous solution of 137Cs was applied to the surface of standing water in the lysimeter before transplanting rice seedlings and during the plant growth. After the pre-transplanting application, the topsoil was mixed with 137 Cs under the flooded condition. Transfer factors (m2 kg-1 -dry hulled seeds) of 137Cs applied before transplanting varied with soils by a factor of about 15. The regional mean was 9.8x10-5 for Kori site, 1.2x10-4 for Yonggwang site and 1.8x10-4 for Ulchin site. The 137Cs applications at the early tillering stage and at booting stage resulted in 2-3 and 10-30 times, respectively, higher transfer factors compared with the pre-transplanting application. A highly significantly positive correlation was found between soil organic matter content and transfer factor. The present result can be used for predicting the root uptake concentration of radiocesium in rice seeds at the time of its acute deposition onto paddy fields at different times of the year