Uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes Milena-Pérez, A. Piñero García, Francisco Benavente Herrera, José Exposito-Suárez, V. W. Vacas-Arquero, P. Ferro García, María Ángeles Uranium natural isotopes 234U/238U Groundwater The authors wish to thank the Spanish Nuclear Safety Council (CSN), given its support to the Radiochemistry and Environmental Radiology Laboratory of the University of Granada since 1993 as a member of the laboratories of the Spanish Sparse Network for Environmental Surveillance. This paper studies the uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes from 52 groundwater samples in the province of Granada (Betic Cordillera, southeastern Spain). According to the geological complexity of the zone, three groups of samples have been considered. In Group 1 (thermal waters; longest residence time), the average uranium content was 2.63 ± 0.16 μg/L, and 234U/238U activity ratios (AR) were the highest of all samples, averaging 1.92 ± 0.30. In Group 2 (mainly springs from carbonate aquifers; intermediate residence time), dissolved uranium presented an average value of 1.34 ± 0.13 μg/L, while AR average value was 1.38 ± 0.25. Group 3 comes from pumping wells in a highly anthropized alluvial aquifer. In this group, where the residence time of the groundwater is the shortest of the three, average uranium content was 5.28 ± 0.26 μg/L, and average AR is the lowest (1.17 ± 0.12). In addition, the high dissolved uranium value and the low AR brought to light the contribution of fertilizers (Group 3). In the three groups, 235U/238U activity ratios were similar to the natural value of 0.046. Therefore, 235U detected in the samples comes from natural sources. This study is completed with the determination of major ions and physicochemical parameters in the groundwater samples and the statistical analysis of the data by using the Principal Component Analysis. This calculation indicates the correlation between uranium isotopes and bicarbonate and nitrate anions. 2026-01-19T12:03:42Z 2026-01-19T12:03:42Z 2020-11-06 journal article A. Milena-Pérez et al. Journal of Environmental Radioactivity 227, 106503. https://doi.org/10.1016/j.jenvrad.2020.106503 https://hdl.handle.net/10481/109889 10.1016/j.jenvrad.2020.106503 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier