Analysis of ¹²⁹I and its Application as Environmental Tracer

Iodine-129, the long-lived radioisotope of iodine, occurs naturally, but anthropogenic generated 129 I has dominated the environment in the past 60 years. Due to active chemical and environmental properties of iodine and the enhanced analytical capacity for 129 I measurement, the application of 129 I as an environmental tracer has highly increased in the past 10 years. Neutron activation analysis and accelerator mass spectrometry are the only techniques for measurement of 129 I at environmental level. This article mainly compares these two analytical techniques for the determination of 129 I at environmental level, and highlights the progress of these analytical methods for chemical separation and sensitive measurement of 129 I. The naturally occurred 129 I has been used for age dating of samples/events in a range of 2-80 Ma. For the purpose of this study, an initial value of 129 I has to be measured. Some progress on the establishment of an initial 129 I level in the terrestrial system are presented in this paper. A large amount of anthropogenic 129 I has been released to the environment, mainly by reprocessing nuclear fuel. Anthropogenic 129 I provides a good oceanographic tracer for studying the circulation and exchange of water mass. The speciation analysis of 129 I can also be used to investigate the geochemical cycle of stable iodine. Some representative works on the environmental tracer application of 129 I are summarized.