Iodine isotopes in precipitation: Four-year time series variations before and after 2011 Fukushima nuclear accident

摘要

Rainwater samples were collected monthly from Fukushima, Japan, in 2012-2014 and analysed for I-127 and I-129. These are combined with previously reported data to investigate atmospheric levels and behaviour of Fukushima-derived I-129 before and after the 2011 nuclear accident. In the new datasets, I-127 and I-129 concentrations between October 2012 and October 2014 varied from 0.5 to 10 mu g/L and from 1.2 x 10(8) to 6.9 x 10(9) atoms/L respectively, resulting in I-129/I-127 atomic ratio ranges from 3 x 10(-8) to 2 x 10(-7). The I-129 concentrations were in good agreement with those in the previous period from March 2011 to September 2012, whereas the I-129 concentrations and I-129/I-127 ratios followed declining trends since the accident. Although I-129 concentrations in five samples during the period of 2013-2014 have approached the pre-accident levels, I-129 concentrations in most samples remained higher values in winter and spring-summer. The high I-129 levels in winter and spring-summer are most likely attributed to local resuspension of the Fukushima-derived radionuclide-bearing fine soil particles deposited on land surfaces, and re-emission through vegetation taking up I-129 from contaminated soil and water, respectively. Long-term declining rate suggests that contribution of the Fukushima-derived I-129 to the atmosphere would become less since 2014. (C) 2016 Elsevier Ltd. All rights reserved.