Sequestration and remobilization of radioiodine (I) by soil organic matter and possible consequences of the remedial action at Savannah River Site

Xu, C.*; Miller, E. J.*; Zhang, S.*; Li, H.-P.*; Ho, Y.-F.*; Schwehr, K. A.*; Kaplan, D. I.*; Otosaka, Shigeyoshi  ; Roberts, K. A.*; Brinkmeyer, R.*; Yeager, C. M.*; Santschi, P. H.*

In order to investigate accumulation process of iodine-129 (I) in a contaminated F-Area groundwater plume of the US Savannah River Site, soil resuspension experiments simulating surface runoff and erosion events were conducted. Results showed that 7277% of the newly-introduced iodide was irreversibly sequestered into the organic-rich soil, while the rest was transformed into colloidal and dissolved organo-iodine by the soil. Laboratory iodination of the soil indicated a preferential incorporation of inorganic iodine into soil organic matter (SOM) at acidic pH (34), except for the iodination catalyzed by lactoperoxidase, which favors more alkaline conditions. From this result, we concluded that under very acidic conditions, abiotic iodination of SOM was predominant, while under less acidic conditions (pH 5), microbial enzymatically-assisted iodination took over.