Analysis of 129I and 127I in soils of the Chernobyl Exclusion Zone, 29 years after the deposition of 129I

The Chernobyl Exclusion Zone (CEZ) represents a unique natural laboratory that received significant I-179 contamination across a range of soils and land-use types in a short time period in 1986. Data are presented on I-129 and I-127 in soil samples collected from highly contaminated areas in the CEZ in 2015. The geometric mean (GM) total concentration of stable iodine (I-177) was 6.7 x 10(-7) g g(-1) and the (GM) total concentration of I-129 was 239 x 10(-13) g g(-1), equivalent to 1.56 mBq kg(-1). GM total I-177 concentration is below the European average soil concentration of 3.94 x 10(-6) g g(-1) , while I-179 is significantly higher than the pre-Chernobyl activity concentration for I-179 of 0.094 mBq kg(-1). Significant differences were found in the extractability of native, stable I-127 and I-129 almost 30 years after the introduction of I-129 to the soils. Both I-127 and I-129 were predominantly associated with alkaline-extractable soil organic matter, established using a three-step sequential extraction procedure. Whereas I-127 was significantly correlated with gross soil organic matter (measured by loss on ignition), however, I-129 was not. The ratio of I-179/I-177 was significantly lower in extracts of soil organic matter than in more labile (soluble and adsorbed) fractions, indicating incomplete equilibration of I-179 with native I-127 in soil humic substances after Corresponding 29 years residence time in the CEZ soils. The initial physicochemical form of I-119 in the CEZ soils is unknown, but the widespread presence of uranium oxide fuel particles is unlikely to have influenced the environmental behaviour of I-129. Our findings have implications for long-term radiation dose from I-129 in contaminated soils and the use of native, stable I-127 as a proxy for the long-term fate of I-129. (C) 2019 Elsevier B.V. All rights reserved.