title: Iodine-129 and iodine-127 speciation in groundwater at the Hanford site, US: iodate incorporation into calcite.
abstract: The geochemical transport and fate of radioiodine depends largely on its chemical speciation that is greatly affected by environmental factors. This study reports, for the first time, the speciation of stable and radioactive iodine in the groundwater from the Hanford Site. Iodate was the dominant species and accounted for up to 84% of the total iodine present. The alkaline pH (pH ∼ 8) and predominantly oxidizing environment may have prevented reduction of the iodate. In addition, groundwater samples were found to have large amounts of calcite precipitate which were likely formed as a result of CO2 degassing during removal from the deep subsurface (>70m depth). Further analyses indicated that between 7 and 40% of the dissolved (127)I and (129)I that was originally in the groundwater had coprecipitated in the calcite. Iodate was the main species incorporated into calcite and this incorporation process could be impeded by elevating the pH and decreasing ionic strength in groundwater. This study provides critical information for predicting the long-term fate and transport of (129)I. Furthermore, the common sampling artifact resulting in the precipitation of calcite by degassing CO2, had the unintended consequence of providing insight into a potential solution for the in situ remediation of groundwater (129)I.
authors.affiliation: Department of Marine Science, Texas A&M University at Galveston , Texas 77554, United States. zhangs@tamug.edu
authors.forename: Saijin
authors.initials: S
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Xu
authors.forename: Danielle
authors.initials: D
authors.lastname: Creeley
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Ho
authors.forename: Hsiu-Ping
authors.initials: HP
authors.lastname: Li
authors.forename: Russell
authors.initials: R
authors.lastname: Grandbois
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Schwehr
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaplan
authors.forename: Chris M
authors.initials: CM
authors.lastname: Yeager
authors.forename: Dawn
authors.initials: D
authors.lastname: Wellman
authors.forename: Peter H
authors.initials: PH
authors.lastname: Santschi
mesh_terms: D002119:Calcium Carbonate / Q000032:analysis / Q000737:chemistry*; D002254:Carbonates / Q000032:analysis; D004784:Environmental Monitoring; D008401:Gas Chromatography-Mass Spectrometry; D060587:Groundwater / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007452:Iodates / Q000032:analysis / Q000737:chemistry*; D007455:Iodine / Q000032:analysis*; D007457:Iodine Radioisotopes / Q000032:analysis; D010100:Oxygen / Q000032:analysis; D014861:Washington; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002254:Carbonates; D007452:Iodates; D007457:Iodine Radioisotopes; D014875:Water Pollutants, Radioactive; D007455:Iodine; D002119:Calcium Carbonate; D010100:Oxygen