Speciation of 137Cs and 129I in soil after the Fukushima NPP accident

Abstract

We evaluated the migration of radionuclides (131I, 129I, 134Cs, 136Cs, 137Cs, and 132Te) in the surface soil after the Fukushima nuclear accident. The radionuclides in the soil collected late March in 2011 were barely leached with ultrapure water, indicating that these are insoluble. We observed the chemical behavior of 137Cs and 129I in soil: (1) 137Cs was predominantly adsorbed within a depth of 2.5 cm from the ground surface; (2) 137Cs was hardly released from soil by the water leaching experiments that lasted for 270 days; (3) approximately, more than 90 % of 137Cs was adsorbed on organic matters and the residual fractions, while 129I was mainly fixed on the Fe-Mn oxide and organically bounded fraction. Therefore, we conclude that 137Cs and 129I in soil seldom leach into the soil water and migrate downward because of the irreversible adsorption. The shallow groundwater which residence time is short.