Vertical distribution of 129I and radiocesium in forest soil collected near the Fukushima Daiichi Nuclear Power Plant boundary

Three soil core samples were collected from a forest located about 1.1 km south of the Fukushima Daiichi Nuclear Power Plant (FDNPP) boundary in 2017, and the vertical profiles of I-129 from the FDNPP accident were determined by the combination of TMAH (tetramethyl ammonium hydroxide) extraction and ICPMS/MS analysis. The humus layer above the soil layer was heavily contaminated with Cs-134 (1983-5985 Bq g(-1)) and Cs-137 (1947-5902 Bq g(-1)) (decay-corrected to March 11, 2011). The I-129 activity concentrations decreased sharply with the soil depth, from 1894 to 34.1, from 9384 to 78.9, and from 2536 to 51.3 mBq kg(-1), for the three sites. Downward migration of I-129 was slightly faster than the one of Cs-134. In addition, the cumulative I-129 inventories were observed to be 43.4 +/- 1.0, 71.7 +/- 1.8, and 56.5 +/- 1.8 Bq m(-2) , respectively. Subsequently, the cumulative I-131 inventories were estimated to be 1.76 +/- 0.06, 2.90 +/- 0.11, and 2.28 +/- 0.10 GBq m(-2) (decay-corrected to March 11, 2011), respectively. Finally, the total atmospheric deposition of I-129 on the land of Japan due to the FDNPP accident was estimated to be around 1.09 -1.71 kg (7.11-11.2 GBq). (C) 2019 Elsevier Ltd. All rights reserved.