title: Factors controlling mobility of 127I and 129I species in an acidic groundwater plume at the Savannah River Site.
abstract: In order to quantify changes in iodine speciation and to assess factors controlling the distribution and mobility of iodine at an iodine-129 ((129)I) contaminated site located at the U.S. Department of Energy's Savannah River Site (SRS), spatial distributions and transformation of (129)I and stable iodine ((127)I) species in groundwater were investigated along a gradient in redox potential (654 to 360 mV), organic carbon concentration (5 to 60 μmol L(-1)), and pH (pH 3.2 to 6.8). Total (129)I concentration in groundwater was 8.6±2.8 Bq L(-1) immediately downstream of a former waste seepage basin (well FSB-95DR), and decreased with distance from the seepage basin. (127)I concentration decreased similarly to that of (129)I. Elevated concentrations of (127)I or (129)I were not detected in groundwater collected from wells located outside of the mixed waste plume of this area. At FSB-95DR, the majority (55-86%) of iodine existed as iodide for both (127)I and (129)I. Then, as the iodide move down gradient, some of it transformed into iodate and organo-iodine. Considering that iodate has a higher K(d) value than iodide, we hypothesize that the production of iodate in groundwater resulted in the removal of iodine from the groundwater and consequently decreased concentrations of (127)I and (129)I in downstream areas. Significant amounts of organo-iodine species (30-82% of the total iodine) were also observed at upstream wells, including those outside the mixed waste plume. Concentrations of groundwater iodide decreased at a faster rate than organo-iodine along the transect from the seepage basin. We concluded that removal of iodine from the groundwater through the formation of high molecular weight organo-iodine species is complicated by the release of other more mobile organo-iodine species in the groundwater.
authors.affiliation: Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, Building 3029, 200 Seawolf Parkway, Galveston, TX 77553, USA. otosaka.shigeyoshi@jaea.go.jp
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Otosaka
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Schwehr
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaplan
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Roberts
authors.forename: Saijin
authors.initials: S
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Xu
authors.forename: Hsiu-Ping
authors.initials: HP
authors.lastname: Li
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Ho
authors.forename: Robin
authors.initials: R
authors.lastname: Brinkmeyer
authors.forename: Chris M
authors.initials: CM
authors.lastname: Yeager
authors.forename: Peter H
authors.initials: PH
authors.lastname: Santschi
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007456:Iodine Isotopes / Q000032:analysis / Q000737:chemistry*; D007457:Iodine Radioisotopes / Q000032:analysis / Q000737:chemistry*; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry*; D014481:United States; D037041:United States Government Agencies; D014872:Water Movements
chemical_list: D007456:Iodine Isotopes; D007457:Iodine Radioisotopes