Distribution and Transport of Iodine Species In the Environment

Understanding the fate and transport of iodine in the environment is very important because of the large production and release (from either natural or anthropogenic sources) of 129I that has a long half-life (1.57 × 107 years), its complex geochemical behavior, and its role in regulating thyroid gland for human health and nutrition. Iodine has a unique and complex chemistry in the environment, and its fate and transport in aqueous environment is dictated by its chemical speciation. In reducing environments, iodine usually occurs as the presumably mobile iodide anion (I-). Under more oxidizing conditions, the more reactive iodate anion (IO3-) is predominant, which could lead to its retarded transport from its interaction with clays and organic matter. Co-existing of both inorganic and organic iodine species, with different proportions, has been reported in different environments. However, there is mixed reports regarding the mobility and environmental behavior for inorganic iodine and little results available for organic iodine chemicals. This work is to examine the iodine speciation in groundwaters and geological samples collected from several complexes of the U.S. Department of Energy, and to investigate sorption and transport behavior of both inorganic and organic iodine species in the geological samples that include Savannah River Site in South Carolina and Hanford Site in Washington. The results showed that the transport of iodine species in three samples from Savannah River Site at different depths exhibited different behavior, which was related to the difference in organic matter and clay mineralogy.