Distribution and fate of 129I in the seabed sediment off Fukushima. (December 2018)

• Record Type: Journal Article
• Authors: Otosaka, Shigeyoshi; Satoh, Yuhi; Suzuki, Takashi; Kuwabara, Jun; Nakanishi, Takahiro
• Is Part Of: Journal of environmental radioactivity. Volume 192(2018)
• Page Start: 208
• Page End: 218
• Publication Date: 2018-12
• Subjects: Fukushima Daiichi Nuclear Power Plant -- Radioiodine -- Seabed sediment -- Sinking particles -- Coastal environment; 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.2018.06.025
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: In this study, seabed sediment was collected from 26 stations located within 160 km from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) during the 2 years which followed the FDNPP accident of March 2011 and the concentrations of 129 I and 137 Cs were measured. By comparing the distribution of these two radionuclides with respect to their different geochemical behaviors in the environment, the transport of accident-derived radionuclides near the seafloor is discussed. The concentration of 129 I in seabed sediment recovered from offshore Fukushima in 2011 ranged between 0.02 and 0.45 mBq kg −1, with 129 I/ 137 Cs activity ratios of (1.9 ± 0.5) × 10 −6 Bq Bq −1 . The initial deposition of 129 I to the seafloor in the study area was 0.36 ± 0.13 GBq, and the general distribution of sedimentary 129 I was established within 6 months after the accident. Although iodine is a biophilic element, the accident-derived 129 I negligibly affects the benthic ecosystem. Until October 2013, a slight increase in activity of 129 I in the surface sediment along the shelf-edge region (bottom depth: 200–400 m) was observed, despite that such a trend was not observed for 137 Cs. The preferential increase of the 129 I concentrations in the shelf-edge sediments was presumed to be affected by the re-deposition in the shelf-edge sediments of 129 I desorbed from the contaminated coastal sediment. The results obtained from this study indicate that 129 I/ 137 Cs in marine particles is a useful indicator for tracking the secondary transport of accident-derived materials, particularly biophilic radionuclides, from the coast to offshore areas. Graphical abstract: Image 1 Highlights: Concentration of 129 I in seabed sediment off Fukushima is reported for the first time. Deposition of the FDNPP accident-derived 129 I to the seafloor was 0.36 ± 0.13 GBq Until October 2013, 129 I activity in sediment increased in the shelf-edge region. Remobilization of 129 I near the seafloor likely affected the sequential accumulation. The accident-derived 129 I is considered to negligibly affect the benthic ecosystem.