On the analysis of iodine-129 and iodine-127 in environmental materials byaccelerator mass spectrometry and ion chromatography

Based on a review of literature about the abundances of I-129 (T-1/2 = 15.7 Ma) in the environment we show that there is a severe lack of knowledge, i n particular about natural, pre-nuclear levels. Among the two analytical te chniques which are sensitive enough to investigate I-129 in environmental m aterials, namely radiochemical neutron activation analysis (RNAA) and accel erator mass spectrometry (AMS), only AMS is capable of covering the natural , pre-nuclear levels. Since such AMS measurements require chemical separati on of iodine from the matrix, a wide variety of separation schemes are nece ssary for environmental analyses. We report here on such schemes for the an alysis of soils, plants and soft tissue. They are applied exemplarily to an alyses of soils from the vicinity of Chernobyl. For chemical separations pr ior to analysis, contamination control and blank analyses are essential. He re, we discuss quality control procedures in detail, both for RNAA and AMS. In the case of AMS we use ion-chromatography (IC) for the determination of stable iodine. The IC analysis is included in the separation schemes for e nvironmental materials. First AMS-analyses of terrestrial biospheric materi als demonstrate that natural environmental levels of 129I are lower than pr eviously deduced from investigations using RNAA,but higher than expected fr om model calculations. AMS is capable of providing the missing knowledge ab out the radioecology of I-129. (C) 1998 Elsevier Science B.V. All rights re served.