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The objective of this paper was to determine background values (BV) and anomalous values (AV) of U and Th in groundwater and to establish hydrogeochemical conditions which lead to the elevated concentrations of these elements in groundwater. The methodology included planning and collecting of water samples, laboratory work, and assessment of BV and AV concentrations in accordance with the dataset distribution, based on consideration of hydrogeochemical conditions in the hydrogeological system. Groundwater sampling included 144 occurrences of mineral and thermal water from Serbian territory, belonging to different hydrogeological systems. Field parameters were measured for temperature (T), pH, electrical conductivity (EC), oxidation–reduction potential (ORP), dissolved oxygen (DO), and carbon dioxide (CO2). Standard laboratory measurements were applied for the determination of major chemical components (Ca, Mg, Na, K, Cl, HCO3, and SO4) and U and Th concentrations were measured by ICP-MS. The first step for obtaining U and Th threshold values was based on non-parametric statistical analysis on the data sets. Further analysis of threshold values enabled establishing hydrogeochemical conditions influencing elevated concentrations of U and Th and setting up the logistic regression (LR) model. Differences in the hydrochemical properties of U and Th can be observed based on predictor variables from LR models. Physico-chemical parameters Eh and pH, groundwater type, and geochemical environment (cretaceous igneous rocks) were significant predictors for elevated uranium concentrations, while significant predictors in the thorium LR model were the pH value, the concentration of SO4 in the solution, and the water-bearing rocks (tertiary igneous rocks).

Magnesium is chemical element commonly found in the environment and the main constituent of many types of minerals and rocks. This element is also essential to man. Owing to its abundance in nature, magnesium is present in all water resources and generally occur as the dominant cation, with calcium, in those that feature low TDS levels, whose origin is associated with large formations of sedimentary rocks (limestones, dolomites), and to a lesser extent with the degradation of silicate minerals that contain Mg. Magnesium concentrations in groundwater of Serbia vary over a wide range and their distribution is not uniform, but certain laws of nature do apply. The variation in the concentrations of this ion depends on the considered hydrogeological province, while within a single province it is a consequence of Serbia’s highly complex geology. The best examples are the Carpatho-Balkanides, with predominant karstified rock formations, and the Vardar Zone where ophiolites prevail but the makeup is much more complex than that of the Carpatho-Balkanides. [Projekat Ministarstva nauke Republike Srbije, br. 43004]

Multivariate statistical analyses are used for reducing large datasets to a smaller number of variables, which explain main hydrogeochemical processes that control water geochemistry. Factor analysis (FA) allows discovering intercorrelations inside the data matrix and grouping of similar variables, i.e. chemical parameters. In this way new variables are extracted, which are called factors, and each factor is explained by some hydrogeochemical process. Applying FA to a dataset that consists of 15 chemical parameters measured on 40 groundwater samples from Serbia, four factors were extracted, which explain 73.9% of total variance in the analyzed dataset. Interpretation of obtained factors indicated several hydrogeochemical processes: the impact of sea water intrusions and volatiles in previous geological periods, solutes diffusion from the marine clay, cation exchange and dissolution of carbonate and silicate minerals. [Projekat Ministarstva nauke Republike Srbije, br. 43004]

Twenty-one bottled mineral and spring waters from Serbia were analyzed for 16 inorganic chemical parameters, including lanthanides and yttrium which belong to the group of so-called rare earth elements (REE). REE concentrations in the bottled water samples varied over a broad range, from 5.39 to 1585.82 ng/L. Total concentrations in the bottled water samples were calculated taking into account the classification of lanthanides into heavy (HREE) and light (LREE), with yttrium added to the HREE group. The LREE concentrations ranged from 3.62 to 1449.63 ng/L, while those of the HREE were from 0 to 136.19 ng/L. Distinct REE signatures were observed in waters that drained specific rocks. The REE patterns in groundwater from granitic and related rocks showed LREE and HREE enrichment, while groundwater with mafic rock influence exhibited slightly LREE enrichment. Several bottled water samples featured naturally-occurring carbon dioxide, whose solutional capacity contributed to the highest REE concentrations in the analyzed samples. High REE concentrations are also a result of sudden changes in oxidation-reduction conditions, which particularly affect La, Ce and Eu. Aquifers developed in granitic and related rocks (methamorphic and sedimentary rocks) constitute favorable environments for HREE in groundwater, corroborated by the occurrence of HREE in bottled water samples. The bottled water samples largely exhibited a negative cerium anomaly and nearly all the samples showed a positive europium anomaly.

2/11 M20 М23

For the present study, 172 groundwater samples (collected from wells and natural springs in Serbia) were analyzed for different chemical parameters including uranium. For each groundwater sample, information was compiled about the basic parameters of its chemical composition. Most of the samples were found to be of the Na – HCO3 and Ca, Mg − HCO3 water types, while only a few were classified as the Ca, Mg – SO4 or Na − Cl type. HR–ICP–MS is an analytical technique used for uranium determinations. The measured concentrations of uranium were in the range from 0.0005 μg/L to 25.34 μg/L.