Processes affecting land-surface dynamics of 129I impacted by atmospheric 129I releases from a spent nuclear fuel reprocessing plant

• Published in: The Science of the total environment Vol. 704; p. 135319
• Main Authors: Ota, Masakazu, Terada, Hiroaki, Hasegawa, Hidenao, Kakiuchi, Hideki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20-02-2020
• Subjects: Foliar adsorption; Foliar uptake; Methylation; Radioiodine; Root uptake; Radioiodine; Foliar uptake; Root uptake; Methylation; Foliar adsorption
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.135319

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•A field near a spent nuclear fuel reprocessing plant was contaminated with 129I.•Leaf contamination was caused by foliar adsorption of 129I due to wet deposition.•Foliar uptake of 129I2 via stomata and root uptake of soil 129I had less impact.•For soil 129I, root uptake was more influential than volatilization by methylation.
Terrestrial environments impacted by atmospheric releases of 129I from nuclear plants become contaminated with 129I; however, the relative importance of each land-surface 129I-transfer pathway in the process of the contamination is not well understood. In this study, transfers of 129I in an atmosphere-vegetation-soil system are modeled and incorporated into an existing land-surface model (SOLVEG-II). The model was also applied to the observed transfer of 129I at a vegetated field impacted by atmospheric releases of 129I (as gaseous I2 and CH3I) from the Rokkasho reprocessing plant, Japan, during 2007. Results from the model calculation and inter-comparison of the results with the measured environmental samples provide insights into the relative importance of each 129I-transfer pathway in the processes of 129I contamination of leaves and soil. The model calculation revealed that contamination of leaves of wild bamboo grasses was mostly caused by foliar adsorption of inorganic 129I (81%) following wet deposition of 129I. In contrast, accumulation of 129I in the leaf due to foliar uptake of atmospheric 129I2 (2%) was lesser. Root uptake of soil 129I was low, accounted for 17% of the 129I of the leaf. The low root-uptake of 129I in spite of the 129I contained in the soil was ascribed to the fact that the most fraction (over 90%) of the soil 129I existed in “soil-fixed” (not plant-available) form. Regarding the 129I-transfer to the soil, wet deposition of 129I was ten-fold more effective than dry deposition of atmospheric 129I2; however, the deposition of 129I during the year represented only 2% of the model-assumed 129I that pre-existed in the soil; indicating the importance of long-term accumulation of 129I in terrestrial environments. The model calculation also revealed that root uptake of inorganic 129I can be more influential than volatilization by methylation in exportation of 129I from soil.