title: Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site.
abstract: A primary obstacle in understanding the fate and transport of the toxic radionuclide (129)I (a thyroid seeker) is an accurate method to distinguish it from the stable isotope, (127)I, and to quantify the various species at environmentally relevant concentrations (~10(-8) M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of (129)I/(127)I isotope ratios and iodine speciation (iodide (I(-)), iodate (IO3(-)), and organo-I (OI)) in aquatic systems. The method exhibited an overall uncertainty of 10% or less for I(-) and IO3(-), and less than 30% for OI species concentrations and enabled (129)I measurements as low as 0.001 Bq/L (1 Bq/L=10(-13) M). The method was used to analyze groundwater from the Savannah River Site (SRS), South Carolina, USA, along a pH, redox potential (Eh), and organic carbon gradient (8-60 μM DOC). The data confirmed that the (129)I/(127)I ratios and species distribution were strongly pH dependent and varied in a systematic manner from the strongly acidic source. While (129)I speciation in plume samples containing total I concentrations >1.7 Bq/L was similar whether measured by AMS or GC-MS ([I(-)]≫[IO3(-)]=[OI]), AMS enabled (129)I speciation measurements at much lower concentrations than what was possible with GC-MS. AMS analyses demonstrated that groundwater samples minimally impacted by the plume were still orders of magnitude higher than ambient (129)I concentrations typically found elsewhere in the USA groundwaters and rivers. This is likely due to past atmospheric releases of volatile (129)I species by SRS nuclear reprocessing facilities near the study site. Furthermore, the results confirmed the existence of (129)I not only as I(-), but also as OI and IO3(-) species.
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Schwehr
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States; Research Group for Environmental Science, Japan Atomic Energy Agency, Tokai Mura, Ibaraki 319 1195, Japan.
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Otosaka
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Merchel
authors.affiliation: Savannah River National Laboratory, Aiken, SC 29808, United States.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaplan
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Saijin
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Xu
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Hsiu-Ping
authors.initials: HP
authors.lastname: Li
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Ho
authors.affiliation: Los Alamos National Laboratory, Los Alamos, NM 87545, United States.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Yeager
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, OCSB 3029, 200 Seawolf Parkway, Galveston, TX 77553, United States.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Santschi
authors.affiliation: ASTER Team, Aix-Marseille University, CEREGE, CNRS-IRD UM 34, 13545 Aix-en-Provence, France.
mesh_terms: D004784:Environmental Monitoring; D007456:Iodine Isotopes / Q000032:analysis*; D045483:Rivers / Q000737:chemistry; D013022:South Carolina; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D007456:Iodine Isotopes; D014874:Water Pollutants, Chemical
keywords: Accelerator mass spectrometer (AMS) Iodine speciation; Iodate; Iodide; Organo-iodine; Radioiodine ((129)I)