Organo-lodine Formation in Soils and Aquifer Sediments at Ambient Concentrations

摘要

One of the key risk drivers at radioactive waste disposal facilities is radioiodine, especially ~(129)l. As iodine mobility varies greatly with iodine speciation, experiments with ~(129)l-contaminated aquifer sediments from the Savannah River Site located in Aiken, SC, were carried out to test iodine interactions with soils and aquifer sediments. Using tracer ~(125)I~-r and stable ~(127)I~- additions, it was shown that such interactions were highly dependent on I~- concentrations added to sediment suspensions, contact time with the sediment and organic carbon (OC) content, resulting in an empirical particle-water partition coefficient (K_dl that was an inverse power function of the added I~-concentration. However, K_d values of organically bound ~(127)I were 3 orders of magnitude higher than those determined after 1-2 weeks of tracer equilibration, approaching those of OC. Under ambient conditions, organo-iodine (0l) was a major fraction (67%) of the total iodine in the dissolved phase and by implication of the particulate phase. As the total concentration of amended l~- increased, the fraction of detectable dissolved OI decreased. This trend, attributed to OC becoming the limiting factor in the aquifer sediment explains why at elevated I~-concentrations OI is often not detected.