Reliable Analysis of Uranium in Natural Waters Using Laser-induced Fluorimetry/LED-fluorimetry in the Presence of Fluoride and Diverse Humic Substances in Hot Arid Regions: Challenges and Future Perspectives

The present study highlights the challenges for reliable analysis of uranium in natural waters using laser-induced fluorimetry/LED-fluorimetry in the presence of fluoride and diverse humic substances in hot arid regions. Uranium is present in the environment as a result of leaching from natural deposits, release in mill tailings, and emissions from the nuclear industry, the combustion of coal and other fuels and the use of phosphate fertilizers that contain uranium. Complete preservation of samples, whether domestic wastewater or natural water, is a practical impossibility. After sample collection, changes in dynamic equilibrium cause the physico-chemical and biological changes to continue unavoidably. This justifies the requirement for the application of a mobile geochemistry laboratory for rapid on-site water sample analysis, ideally completed the same day. Laser-induced fluorimetry/pulsed LED-fluorimetry is a well-documented, highly sensitive, and versatile technique for the determination of uranium in water samples at µg L-1 levels, and in fact, it is more challenging due to a wide variety of water samples differing in total dissolved salts including saline water, diverse humic substances and fluoride content especially in hot arid regions as well as due to the practical impossibility of preserving natural water samples. As a result, in hot, dry climates, the most important criterion for an accurate uranium assay is the amount of time that passes between sample collection and analysis. Greater variance in major cations and anions, as well as uranium concentration, is observed in water samples with high TDS in relation to the time interval between sample collection and analysis. Furthermore, approved reference material for these matrices is unavailable, making it difficult to double-check or guarantee the accuracy of the results. Beyond doubt, LED-fluorimetry is a portable device more suitable for field conditions as well as in control laboratory, easy equipment calibration/standardization, high sensitivity, better reproducibility, cost-effective, eco-friendly, traceability, comparability.