B13A-0599
Organic matter controls on iodine and plutonium in atmospheric depositions, streams, and soils in the Fukushima Prefecture

Monday, 14 December 2015
Poster Hall (Moscone South)
Chen Xu1, Saijin Zhang1, Yuko Sugiyama2, Nobuhito Ohte3, Yi-Fang Ho1, Nobuhide Fujitake4, Daniel I Kaplan5, Chris M Yeager6, Kathleen A Schwehr1 and Peter H Santschi7, (1)Texas A & M University at Galveston, Galveston, TX, United States, (2)University of Hyogo, Himeji, Japan, (3)Kyoto University, Kyoto, Japan, (4)Kobe University, Division of Agroenvironmental Biology, Graduate School of Agriculture Science, Kobe, Japan, (5)Savannah River National Lab, Aiken, SC, United States, (6)Los Alamos National Laboratory, Los Alamos, NM, United States, (7)Texas A & M University College Station, College Station, TX, United States
Abstract:
In order to assess how environmental factors are controlling the distribution and migration of radioiodine and plutonium that were emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, we quantified iodine and 239,240Pu concentration changes in soil samples with different land uses (urban, paddy, deciduous forest and coniferous forest), as well as iodine speciation in surface water and rainwater. A ranking of the land uses by their stable 127I and by their 239,240Pu concentrations were quite distinct from that of 134,137Cs, indicating 137Cs might not be a good geochemical proxy for radioactive 129I or Pu in the long-term, post-FDNPP accident. Being a proxy for the long-term fate of 129I, soil 127I content was well correlated to soil organic matter (SOM) content, regardless of land use type, suggesting that SOM might be an important factor controlling iodine biogeochemistry. Other soil chemical properties, such as Eh and pH, had strong correlations to soil 127I content, but only within a given land use (e.g., within urban soils). Organic carbon (OC) and Eh were positively, and pH was negatively correlated to 127I concentrations in surface water and rain samples. It is also noticeable that 127I in the bulk deposition was concentrated along the rainwater passage likely due to plant evapotranspiration activity, with all inorganic iodine being completely converted to organo-iodine by plant organic matter. 239,240Pu activities of all soil samples were well within the global fallout range, but the Fukushima-derived 239,240Pu was detectable at a distance ~61 km away, NW of FDNPP. However, it is confined to the litter layer, even three years after the FDNPP accident-derived emissions. 239,240Pu activities were significantly correlated with soil OC and nitrogen contents, indicating Pu may be associated with nitrogen-containing SOM, similar to what has been observed at other locations in the United States, e.g., Savannah River Site (SRS) and Rocky Flats Environmental Technology Site (RFETS). Together, these finding suggest that NOM plays an key role in controlling the fate and transport of I and Pu and may warrant greater consideration for predicting long-term stewardship of contaminated areas and evaluating various remediation options in Japan.