Radioiodine concentrated in a wetland.
Most subsurface environmental radioactivity contamination is expected to eventually resurface in riparian zones, or wetlands. There are a number of extremely sharp biogeochemical interfaces in wetlands that could alter radionuclide speciation and promote accumulation. The objective of this study was to determine if a wetland concentrated (129)I emanating from a former waste disposal basin located on the Savannah River Site (SRS) in South Carolina, USA. Additionally, studies were conducted to evaluate the role of sediment organic matter in immobilizing the radioiodine. Groundwater samples were collected along a 0.7-km transect away from the seepage basin and in the downstream wetlands. The samples were analyzed for (129)I speciation (iodide (I(-)), iodate (IO3(-)), and organo-I). Groundwater (129)I concentrations in many locations in the wetlands (as high as 59.9 Bq L(-1)(129)I) were greatly elevated with respect to the source term (5.9 Bq L(-1)(129)I). (129)I concentration profiles in sediment cores were closely correlated to organic matter concentrations (r(2) = 0.992; n = 5). While the sediment organic matter promoted the uptake of (129)I to the wetland sediment, it also promoted the formation of a soluble organic fraction: 74% of the wetland groundwater (129)I could pass through a 1 kDa (<1 nm) membrane and only 26% of the (129)I was colloidal. Of that fraction that could pass through a 1 kDa membrane, 39% of the (129)I was organo-I. Therefore, while wetlands may be highly effective at immobilizing aqueous (129)I, they may also promote the formation of a low-molecular-weight organic species that does not partition to sediments. This study provides a rare example of radioactivity concentrations increasing rather than decreasing as it migrates from a point source and brings into question assumptions in risk models regarding continuous dilution of released contaminants.
Savannah River National Laboratory (SRNL), Aiken, SC, USA. Electronic address: daniel.kaplan@srnl.doe.gov.
Daniel I
DI
Kaplan
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Saijin
S
Zhang
Savannah River National Laboratory (SRNL), Aiken, SC, USA.
Kimberly A
KA
Roberts
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Kathy
K
Schwehr
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Chen
C
Xu
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Danielle
D
Creeley
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Yi-Fang
YF
Ho
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Hsiu-Ping
HP
Li
Los Alamos National Laboratory (LANL), Los Alamos, NM, USA.
Chris M
CM
Yeager
Department of Marine Science, Texas A&M University at Galveston, TX 77554, USA.
Peter H
PH
Santschi
D019015:Geologic Sediments / Q000032:analysis; D060587:Groundwater / Q000032:analysis; D007457:Iodine Radioisotopes / Q000032:analysis*; D011834:Radiation Monitoring; D013022:South Carolina; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D053833:Wetlands
D007457:Iodine Radioisotopes; D014875:Water Pollutants, Radioactive
Iodate; Iodide; Natural organic matter; Radioiodine; Speciation; Wetlands