[Show abstract][Hide abstract] ABSTRACT: Iodine occurs in multiple oxidation states in aquatic systems in the form of organic and inorganic species. This feature leads to complex biogeochemical cycling of stable iodine and its long-lived isotope, (129)I. In this study, we investigated the sorption, transport, and interconversion of iodine species by comparing their mobility in groundwaters at ambient concentrations of iodine species (10(-8) to 10(-7) M) to those at artificially elevated concentrations (78.7 μM), which often are used in laboratory analyses. Results demonstrate that the mobility of iodine species greatly depends on, in addition to the type of species, the iodine concentration used, presumably limited by the number of surface organic carbon binding sites to form covalent bonds. At ambient concentrations, iodide and iodate were significantly retarded (K(d) values as high as 49 mL g(-1)), whereas at concentrations of 78.7 μM, iodide traveled along with the water without retardation. Appreciable amounts of iodide during transport were retained in soils due to iodination of organic carbon, specifically retained by aromatic carbon. At high input concentration of iodate (78.7 μM), iodate was found to be reduced to iodide and subsequently followed the transport behavior of iodide. These experiments underscore the importance of studying iodine geochemistry at ambient concentrations and demonstrate the dynamic nature of their speciation during transport conditions.
[Show abstract][Hide abstract] ABSTRACT: Anthropogenic 129 I is found in the environment mainly due to releases from fuel reprocessing facilities, with smaller amounts from atmospheric bomb testing (1945À1970s) and natural production (1 and references therein). Due to its long half-life (1.6 Â 10 7 yrs), high inventories, and high mobility, 129 I accidentally released from fuel reprocessing facilities has migrated into groundwaters. For example, groundwater within several areas of the Savannah River Site (SRS) in South Carolina is contaminated with 129 I and other radionuclides. 2 The F-Area Seepage Basins plume has the highest concentrations of 129 I in the United States, with numerous wells having concentrations 10À100 times the drinking water standard (1 pCi/L). The highest concentration reported so far in 2009 is 1060 pCi/L in a well adjacent to the down gradient side of the largest basin. 3 For both iodine isotopes, 127 I and 129 I, iodide (I À), iodate (IO 3 À), and organo-iodine are the dominant forms in aquatic environments. In seawater, iodate is the dominant species due to the relatively high concentration of oxygen, whereas iodide is often the main species in freshwater, as well as coastal and estuarine environments (1, 4 and references therein). As a bio-philic element, iodine in mammals is almost entirely concentrated
Journal of Environmental Science and Technology 01/2011; 45:5543–5549.