Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site

Schwehr, K. A.*; Otosaka, Shigeyoshi  ; Merchel, S.*; Kaplan, D. I.*; Zhang, S.*; Xu, C.*; Li, H.-P.*; Ho, Y.-F.*; Yeager, C. M.*; Santschi, P. H.*; ASTER Team*

A new, accurate and simple pH-dependent solvent extraction method combined with accelerator mass spectrometry (AMS) measurement for I/I isotopes and iodine speciation (iodide, iodate, and organo-I) quantification in liquids of any ionic strength has been developed. We then validated the AMS method for activity concentration measurements with a recently developed gas chromatography mass spectrometry method for I concentrations of 1 Bq/L or higher. This technique was applied to I-contaminated groundwater from the Savannah River Site, USA, and demonstrated changes of I and I concentrations and speciation along a pH, redox potential, and organic carbon gradient. The data suggest that I/I and species distribution is strongly pH dependent. The new method can now be applied to a wide range of chemically-diverse aquatic systems, including uncontaminated environments.