Computer Science
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.5716x&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 75, Issue 19, p. 5716-5735.
Computer Science
Scientific paper
129 I is one of the three major radiation risk contributors to the public as a consequence of past nuclear processing activities at Department of Energy (DOE) facilities. Elevated levels of 129 I are present in the surface soils of F-Area of Savannah River Site, which used to be an isotope separation facility for the production of nuclear weapons components. The 129 I in soils is thought to be bound predominantly to soil organic matter (SOM). Measurements of stable 127 I and radioactive 129 I in humic acids (HAs) and fulvic acids (FAs) obtained by five successive alkaline, two glycerol and one citric acid-alkaline extraction, demonstrated that these extractable humic substances (HS) together account for 54-56% and 46% of the total 127 I and 129 I in the soil, respectively. The remainder was likely bound to residual SOM. The iodine content (μg-I/g-C) generally decreased with each subsequent extract, while 129 I/ 127 I increased concurrently. The coincident variations in chemical compositions, aromaticity (estimated by UV spectroscopy), functional groups (e.g., aliphatic), degree of humification, relative migration in the hydrophobic interaction column, and molecular weight indicated that: (1) iodine in different HAs was bound to a small-size aromatic subunit (˜10 kDa); (2) the large-size subunit (˜90 kDa), which likely linked the small-size unit through some weak chemical forces (hydrogen bonds, hydrophobic or electrostatic interactions), determined the relative mobility of iodine bound to organic matter; (3) from the strong correlation between iodine content and aromaticity in the HAs, we suggested that iodine incorporation into the SOM via covalent aromatic C-I bond is the key mechanism controlling iodine behavior in this system. However, this relationship is not universal for all fractions of organic matter as evidenced from the different slopes of this relationship at the two sampling sites, as well as from the different relationships for HAs and FAs, respectively. These differences in iodination are due to different SOM molecular sizes, compositions, and availability of preferred iodination sites. 129 I in the soil downstream from the contaminated site and near a wetland abruptly dropped below our detection limit (0.5 pCi- 129 I/g-soil), which suggests that the high SOM in the plume soil around the 129 I-contaminated F-Area might be a natural barrier to scavenge radioiodine released from the nuclear waste repository by forming organo-iodine compounds. Soil resuspension experiments showed that mobile 129 I was mostly associated with a low average molecular weight amphiphilic organic carrier (13.5-15 kDa). SOM clearly behaves as a sink for iodine at the Savannah River Site F-Area. However, this work demonstrates that a small fraction of the SOM can also behave as a source, namely that a small fraction that may be readily dispersible under some environmental conditions and presumably release iodine in the organic-colloidal form. This radioiodinated organo-colloid likely can get into the groundwater through infiltration or surface runoff where it might migrate further into the wetlands. Results from this study provide the geochemical basis for future 129 I migration controls, remediation, and/or land-groundwater management strategies.
Brinkmeyer Robin
Ho Yi-Fang
Kaplan Daniel I.
Li Hsiu-Ping
Miller Eric J.
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