Distribution and retention of Cs radioisotopes in soil affected by Fukushima nuclear plant accident

There was a large release of radio-cesium (¹³⁴Cs and ¹³⁷Cs) to the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, and contaminated the soil, over a vast area, due to fallout activity. Therefore, studies on the behaviour of radio-cesium especially migration in soil and its retention on soil particles is very important for external dose assessment and root uptake. We have determined the sorption coefficient (K_d) for Cs using the laboratory batch method in soil samples collected from a contaminated area affected by the FDNPP accident, and the effect of various soil parameters on the K_d value has been studied. We have noticed that Cs sorption is mostly influenced by cation exchange process and Cs is sorbed on the surface of clay particles. From vertical depth profile of Cs in soil, it is found that most of it is retained on the top layer within a 5-cm thickness. Sequential extraction of soil using various reagents may be helpful to understand better the mechanism of Cs retention.