Determination of Iodine-129 in twenty soil and sediment reference materials

Full text: ¹²⁹I in soil and sediments are paid increasing attention for the purpose of environmental radioactivity monitoring, and understanding the historic nuclear activities and their impacts. Accurate measurement of ¹²⁹I is vital, which greatly increases the requirement of various certified reference materials (CRMs). However, only few CRMs with low level of ¹²⁹I are available for accurate determination of ¹²⁹I in samples remote from nuclear sites and facilities. Here, this work investigated the concentrations of ¹²⁹I and ¹²⁷I, and ¹²⁹I /¹²⁷I atomic ratios in twenty Chinese soil and sediment CRMs commercially available, as well as one in-house soil standard material (XASTD), with high-temperature pyrolysis combustion in coupling with ICP-MS and accelerator mass spectrometry (AMS) measurements. This study presents that ¹²⁹I concentrations in the twenty CRMs and one laboratory soil standard range from 0.31×10⁶ atoms/g to 34.7×10⁶ atoms/g, which were 1-4 orders of magnitude lower than those reference materials in use. For accurate measurement of ¹²⁹I, the effect of salinity content in the samples on iodine current intensity of AMS measurement is firstly discussed. Significant salinity effect could occur when high-salinity sample is analysed, which is mainly due to the formation of abundant strong oxidant during the pyrolysis process, resulting in iodine existing as iodate instead of iodide. And finally, an analytical procedure was recommended for the low- and high-salinity soil and sediment samples. In summary, these reported data of the CRMs and the laboratory in-house control soil standard material would broaden the group of available reference materials, be useful for method development of low-level ¹²⁹I samples, interlaboratory comparison and short- and long-term quality control, as well as extend ¹²⁹I applications in geological, environmental and nuclear sciences.