Speciation and mobility of particle-associated radiocesium in soils and pond sediments from Fukushima, Japan

Abstract

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident that occurred in March 2011 at the nuclear facilities of units 1, 2 and 3 in Japan resulted in the release of radioactive cesium (137Cs) containing particles. In this work, the speciation and mobility of particle associated radiocesium was investigated by sequential extraction, digital autoradiography and leaching experiment (with 0.16 M HCl) on contaminated soil and pond sediment samples collected from areas close (approximately 11 km) to the damaged reactors. Upon screening samples with digital autoradiography, very heterogeneous distributions of hotspots were encountered in all investigated samples, indicating the presence of radioactive particles. The number of particles reflects the direction of the plume from the reactors. In addition, the radioactive particles were found to exert certain influence on 137Cs mobility and bioavailability. The results from sequential extractions showed that 137Cs in soils and pond sediments remain largely irreversibly bound and is associated to inert fractions. Morevoer, upon subjecting a small soil and sediment samples to simulated gastrointestinal fluid (0.16 M HCl) extractions for 65 hours, < 3 % of 137Cs was leached indicating a low degree of potential mobility and bioavailability. From the study it was concluded that 137Cs in soils and pond sediments in the Fukushima area is of relatively low mobility and potential bioavailability.