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

Abstract

Increasing attention has been paid to ¹²⁹I in soils and sediments for the purpose of environmental radioactivity monitoring, and understanding 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 a few CRMs with low levels 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 coupled with ICP-MS and accelerator mass spectrometry (AMS) measurements. This study demonstrates that ¹²⁹I concentrations in the twenty CRMs and one laboratory soil standard range from 0.31 × 10⁶ atoms per g to 34.7 × 10⁶ atoms per g, which were 1–4 orders of magnitude lower than those of the reference materials in use. For accurate measurement of ¹²⁹I, the effect of salinity content in the samples on the iodine current intensity of the AMS measurement is firstly discussed. Significant salinity effect occurred when a high-salinity sample is analysed, which is likely due to the formation of abundant strong oxidants during the pyrolysis process, resulting in the existence of iodine as iodate instead of iodide. And finally, an analytical procedure is recommended for the low- and high-salinity soil and sediment samples. In summary, the reported data of the CRMs and the laboratory in-house control soil standard 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.