Nagasaki sediments reveal that long-term fate of plutonium is controlled by select organic matter moieties

Journal Article · 02 May 2019 · Science of the Total Environment

DOI: https://doi.org/10.1016/j.scitotenv.2019.04.375 · OSTI ID:1659203

Lin, Peng ^[1]; Xu, Chen ^[1]; Kaplan, D. I. ^[2]; Chen, Hongmei ^[3]; Yeager, Chris Michael  ^[4]; Xing, Wei ^[1]; Sun, Luni ^[1]; Schwehr, Kathleen ^[1]; Yamazaki, Hidro ^[5]; Saito-Kokubu, Yoko ^[6]; Hatcher, Patrick ^[3]; Santschi, Peter H. ^[1]

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1. Texas A & M Univ. at Galveston, TX (United States)
2. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
3. Old Dominion Univ., Norfolk, VA (United States)
4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
5. Kindai Univ. (Japan)
6. Japan Atomic Energy Agency, Izumichu (Japan)

Forecasting the long-term fate of plutonium (Pu) is becoming increasingly important as more worldwide military and nuclear-power waste is being generated. Nagasaki sediments containing bomb-derived Pu that was deposited in 1945 provided a unique opportunity to explore the long-term geochemical behavior of Pu. Through a combination of selective extractions and molecular characterization via electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS), we determined that 55±3% of the bomb-derived 239,240Pu was preferentially associated with more persistent organic matter compounds in Nagasaki sediments, particularly those natural organic matter (NOM) stabilized by Fe oxides (NOMFe-oxide). Other organic matter compounds served as a secondary sink of these bomb-derived 239,240Pu (31±2% on average), and <20% of the 239,240Pu was immobilized by inorganic mineral particles. In a narrow, 239,240Pu-enriched layer of only 9-cm depth (total core depth was 600 cm), N-containing carboxyl aliphatic and/or alicyclic molecules (CCAM) in NOMFe-oxide and other NOM fractions immobilized the majority of 239,240Pu. Among the cluster of N-containing CCAM moieties, hydroxamate siderophores, the strongest known Pu chelators in nature, were further detected in these “aged” Nagasaki bomb residue-containing sediments. While present long-term disposal and environmental remediation modeling assume that solubility limits and sorption to mineral surfaces control Pu subsurface mobility, our observations suggest that NOM, which is present in essentially all subsurface systems, undoubtedly plays an important role in sequestrering Pu. Ignoring the role of NOM in controlling Pu fate and transport is not justified in most environmental systems.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: 89233218CNA000001; ER65222-1038426-0017532; ER64567-1031562-0014364; AC09-08SR22470
• OSTI ID: 1659203
• Alternate ID(s): OSTI ID: 1545405
• Report Number(s): LA-UR-19-30249
• Journal Information: Science of the Total Environment, Vol. 678; ISSN 0048-9697
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English