Chemical speciation analysis of 129I in seawater and a preliminary investigation to use it as a tracer for geochemical cycle study of stable iodine

A method was developed for the determination of the 129I and 127I in iodide and iodate species in seawater. Iodide and iodate were first separated by anion exchange method from seawater; the separated fractions of various chemical species of iodine were further concentrated by solvent extraction and then converted to LiI irradiation target. The concentrations of 129I and 127I in various fractions were determined by neutron activation analysis using nuclear reactions of 129I (n, γ)130I and 127I(n, γ) 128I, respectively. Surface and bottom seawater samples from three locations in the Kattegat and Baltic Sea were analyzed for 129I and 127I in both iodide and iodate species and total inorganic iodine. Levels as low as 2.3×10−15 M 129I and 7 nM 127I were measured. The possibility of using this method to study the geochemical cycle of iodine in the ocean was investigated. The preliminary results indicate that this is possible, and that this method can be also used for the investigation of the transport, dispersion and mixture of water masses by using 129I discharged from reprocessing facilities as a tracer.