Otosaka Shigeyoshi, Satoh Yuhi, Suzuki Takashi, Kuwabara Jun, Nakanishi Takahiro
Research Group for Environmental Sciences, Nuclear Science and Engineering Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki, 319-1195, Japan.
Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Aomori, 039-3212, Japan.
J Environ Radioact. 2018 Dec;192:208-218. doi: 10.1016/j.jenvrad.2018.06.025. Epub 2018 Jul 4.
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 I and 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 I in seabed sediment recovered from offshore Fukushima in 2011 ranged between 0.02 and 0.45 mBq kg, with I/Cs activity ratios of (1.9 ± 0.5) × 10 Bq Bq. The initial deposition of I to the seafloor in the study area was 0.36 ± 0.13 GBq, and the general distribution of sedimentary I was established within 6 months after the accident. Although iodine is a biophilic element, the accident-derived I negligibly affects the benthic ecosystem. Until October 2013, a slight increase in activity of 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 Cs. The preferential increase of the I concentrations in the shelf-edge sediments was presumed to be affected by the re-deposition in the shelf-edge sediments of I desorbed from the contaminated coastal sediment. The results obtained from this study indicate that I/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.
在本研究中，于2011年3月福岛第一核电站事故后的两年内，从距福岛第一核电站（FDNPP）160公里范围内的26个站点采集了海床沉积物，并测量了其中碘和铯的浓度。通过比较这两种放射性核素在环境中的不同地球化学行为的分布情况，探讨了事故衍生放射性核素在海底附近的迁移情况。2011年从福岛近海采集的海床沉积物中碘的浓度在0.02至0.45毫贝克勒尔/千克之间，碘/铯活度比为(1.9±0.5)×10贝克勒尔/贝克勒尔。研究区域内碘向海底的初始沉积量为0.36±0.13吉贝克勒尔，事故发生后6个月内沉积碘的总体分布格局得以确立。尽管碘是一种亲生物元素，但事故衍生的碘对底栖生态系统的影响可忽略不计。直到2013年10月，在陆架边缘区域（海底深度：200 - 400米）的表层沉积物中观察到碘的活度略有增加，而铯未观察到这种趋势。陆架边缘沉积物中碘浓度的优先增加被推测是受从受污染海岸沉积物中解吸出来的碘在陆架边缘沉积物中的再沉积影响。本研究获得的结果表明，海洋颗粒中的碘/铯是追踪事故衍生物质，特别是亲生物放射性核素从海岸到近海区域二次迁移的有用指标。
