Radiocesium and 40K distribution of river sediments and floodplain deposits in the Fukushima exclusion zone. (December 2018)

• Record Type: Journal Article
• Authors: Somboon, S.; Kavasi, N.; Sahoo, S.K.; Inoue, K.; Arae, H.; Tsuruoka, H.; Shimizu, H.; Fukushi, M.
• Is Part Of: Journal of environmental radioactivity. Volume 195(2018)
• Page Start: 40
• Page End: 53
• Publication Date: 2018-12
• Subjects: Fukushima accident -- Particle size distribution -- Radiocesium -- 40K -- Riverbed sediment -- Floodplain deposit; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2018.09.003
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: In this study, radiocesium and 40 K analysis were accomplished for samples of riverbed sediments and floodplain deposits collected from five rivers in the vicinity (<20 km) of the damaged Fukushima Daiichi Nuclear Power Plant after seven years of the accident. Sediment particle size distribution and major oxide content were determined also for six selected samples to understand the retention and migration process of radiocesium in river environments. The radiocesium activity concentration varied from 103 ± 6 Bq·kg −1 to 22, 000 ± 500 Bq·kg −1 in riverbed sediments and from 92 ± 5 Bq·kg −1 to 117, 000 ± 2000 Bq·kg −1 in floodplain deposits. The 134 Cs/ 137 Cs ratio (decay corrected to 15 March 2011) was 1.02 in the both samples. Compared to monitoring results in 2011, it was proved that the radiocesium distribution pattern had been changed remarkably during seven years. The radiocesium was primarily attached to fine clay particles but its sorption on sand and coarse sand particles was also considerable. The sorption process of radiocesium was not affected by the presence of water and moreover, after seven years of the Fukushima accident, a significant radiocesium migration cannot be expected without particle migration. Consequently, radiocesium will remain for a long time in the river environments and its redistribution is mainly affected by the erosion process of the sediments. The average 40 K activity concentration of riverbed sediment and floodplain deposit samples was 640 ± 152 Bq·kg −1 changing from 319 ± 18 Bq·kg −1 to 916 ± 41 Bq·kg −1 . In the river estuary zones, significant activity concentration decrements were observed for both radionuclides. This suggests that seawater intrusion has a decreasing effect on both natural and artificial radionuclides via wash-out of particulate radiocesium and 40 K, and desorption of these radionuclides, but to reveal the detail of this process further investigations are required. The analysis of 40 K can help in a simple and easy way to reveal the mineral composition differences of sediment samples. Highlights: Radiocesium activity concentration in Fukushima riverbed sediments varied from 103 ± 6 Bq·kg −1 to 22, 000 ± 500 Bq·kg −1 . Fukushima river floodplain deposits for radiocesium were from 92 ± 5 Bq·kg −1 to 117, 000 ± 2000 Bq·kg −1 . Radiocesium was attached to fine clay particles whereas sorption on sand and coarse sand particles was also significant. The radiocesium remains in the river environments after seven year of FDNPP accident.