Application of the modified ISO LSC method for uranium in water measurement: analysis of groundwater from Serbia and Bosnia and Herzegovina

Uranium, as a natural radionuclide in drinking water, may pose a potential risk to public health due to its toxicity and radioactivity. Monitoring of uranium and other radionuclides in natural water sources is of key importance for assessing the radiological safety of the environment and the influence of geological formations on the distribution of radionuclides. This paper presents the application of a previously developed modified liquid scintillation spectrometry (LSC) method, based on ISO 13169:2018, for the determination of total uranium activity concentration in natural waters. The method was applied to real groundwater samples collected from geologically diverse areas of Bosnia and Herzegovina and Serbia, including locations near former uranium mines. The modification of the reference ISO-based procedure consists in the use of a certified reference material of natural uranium instead of the 236U calibration standard recommended by ISO 13169, as well as in the application of three alternative water-immiscible two-phase scintillation cocktails (Ultima Gold F, Opti-Fluor O and Mineral Oil) in combination with extraction using bis(2-ethylhexyl) hydrogen phosphate (HDEHP). In this way, the modified approach improves the practical accessibility of calibration and increases the operational flexibility of the procedure, while enabling the assessment of the suitability of different scintillation systems for application to real natural water samples. The measurements, made with the ultra-low-background Perkin Elmer Quantulus 1220 LS detector and with the use of the bis(2-ethylhexyl)phosphate extractor, show variations in uranium concentrations depending on the geological characteristics of the area. The aim of this study was to assess the applicability of the previously validated modified protocol to real environmental samples. The results showed variations in total uranium activity, with elevated values recorded only in samples collected near former mining areas, whereas in most other samples the activity was close to the minimum detectable activity or below it. Results indicate that the presence of uranium in groundwater does not depend exclusively on the presence of uranium-bearing lithologies, but also on local geological and hydrogeological conditions that enable its mobilization. The applied modified ISO-based LSC procedure proved to be a suitable analytical tool for the screening and monitoring of total uranium in natural waters and provides a good basis for further research, wider monitoring and public health risk assessment.