Strontium-90 (90Sr) and cesium-137 (137Cs) were released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Strontium-90 concentration in environment was extremely lower than that of 137Cs in the soil after the FDNPP accident. However, 90Sr may induce higher risk of health effect to human than 137Cs by considering longer biological half-life of 90Sr than 137Cs. Moreover, there is not sufficient data on 90Sr horizontal and vertical distribution compared to 137Cs, which is important for predicting their long-term migration. In the present study, the distribution of 90Sr and 137Cs in the soils of Kawauchi and Fukushima paddy rice fields was investigated and the migration of 90Sr and 137Cs in Lake Ogi sediment and its forestry catchment area was studied. A rough relation between 90Sr and 137Cs levels in soil is shown and such insufficient correlation might be defined by the low 90Sr concentration and because of global fallout. Furthermore, 90Sr gave higher coefficient of variation in comparison to 137Cs, portraying that the movement of 90Sr is more affected by the environmental factors rather than 137Cs. The depth dependency of 90Sr and 137Cs in Lake Ogi forestry catchment area is shown for both radionuclides, and the activity concentration decreases with the increase of depth. However, the 90Sr infiltrates more to 10 cm soil profile in contrast to 137Cs, showing 90Sr faster vertical migration than 137Cs. Sediment to soil ratio for 90Sr reported a higher value than that of 137Cs, which possibly depicts more horizontal flowing of 90Sr from forest soil to lake sediment than 137Cs. Consequently, the higher mobility of 90Sr than 137Cs was proposed.
