文摘
In order to investigate the distributions and speciation of 129I (and 127I) in a contaminated F-Area groundwater plume of the Savannah River Site that cannot be explained by simple transport models, soil resuspension experiments simulating surface runoff or stormflow and erosion events were conducted. Results showed that 72鈥?7% of the newly introduced I鈥?/sup> or IO3鈥?/sup> were irreversibly sequestered into the organic-rich riparian soil, while the rest was transformed by the soil into colloidal and truly dissolved organo-iodine, resulting in 129I remobilization from the soil greatly exceeding the 1 pCi/L drinking water permit. This contradicts the conventional view that only considers I鈥?/sup> or IO3鈥?/sup> as the mobile forms. Laboratory iodination experiments indicate that iodine likely covalently binds to aromatic structures of the soil organic matter (SOM). Under very acidic conditions, abiotic iodination of SOM was predominant, whereas under less acidic conditions (pH 鈮?), microbial enzymatically assisted iodination of SOM was predominant. The organic-rich soil in the vadose zone of F-Area thus acts primarily as a 鈥渟ink,鈥?but may also behave as a potentially important vector for mobile radioiodine in an on鈥搊ff carrying mechanism. Generally the riparian zone provides as a natural attenuation zone that greatly reduces radioiodine release.