Determination of chemical form of iodine with IC-ICP-MS system and its application to the environmental samples

Iodine-129 is one of the important radionuclides possibly released into the environment from nuclear weapons testing and from the nuclear facilities such as nuclear fuel reprocessing plants. Because of its long half-life (1.57 x 107 y), knowing its long-term behavior in the environment is a major concern. As I-129 is expected to act together with stable iodine (I-127) in the environment after long time, the biogeochemical cycling of stable iodine in the environment can be used for the reliable safety assessment of I-129. Chemical form is the one of the important factors controlling the 'iodine behavior in the environment. Iodide (I-) and iodate (IO3-) are known to be the major chemical form in the aqueous solution. However, the information on the chemical form of iodine in the environmental sample is limited because of lack of reliable analytical technique for trace level of iodine in the environment. In this study, the analytical system by using ion chromatograph (IC) followed by inductively coupled plasma mass spectrometry (ICP-MS) was developed for the separate determination of I- and IO3- in the aqueous solution. The IC with anion exchange column (EXCELPAK ICS-A23) was used for the separation of I- and IO3- with 30 mM (NH4)2CO3 as eluent. Separated iodine was determined with ICP-MS on line. with the detection limit 0.1 - 1 μg/L. The total iodine concentration was also measured by the direct determination with ICP-MS. The iodine in the several environmental samples such as irrigation water in paddy field was successfully determined with information of chemical form. In incubation experiment with flooded soil, the change of the chemical form of iodine in the soil solution with change of Eh was observed. Detailed data will be discussed in the presentation.