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The systematically varying properties and generally coherent and predictable behavior of rare earth elements (REE) make them potential tracers for studying water/rock interaction and weathering processes. In this work, a compilation and analysis of REE data in mineral and thermal waters were performed, focusing on their content and distributions in different hydrogeological systems, to quantify the natural REE variability and to discuss the controlling factors of REE concentrations. Quantitative challenges presented by multiply censored data were addressed with nonparametric and multivariate statistical methods. Considering a regional character of the research the application of Q and R mode Hierarchical Cluster Analysis with spatial analysis was an important approach for meaningful interpretation of large data set. An efficient approach to analyze differences between obtained HCA groups (clusters) was using a plot of reference-normalized concentrations. The results showed that REE data along with anomalies of Ce and Eu and inter-element ratios were good indicators of the aquifer lithology (hydrogeological systems formed in granitoid and volcanic rocks of various age, two main types of hydrogeological basins, and carbonate aquifers). The important mechanisms controlling REE migration in water were hydrochemical conditions in aquifers. The significance of the applied statistical analyses was represented by defining specific hydrochemical fingerprints of identified hydrogeological systems with distinct geochemical characteristics where REE showed the necessity of understanding of complex geological and hydrogeological settings, geodynamic evolution, and hydrogeochemical processes in fluid flow systems.

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]

A new approach using hydrochemical characterization of mineral water in Serbia was applied in this paper. After field research and groundwater sampling, laboratory measurements were conducted. Trace and ultratrace elements in 174 samples of mineral water were analyzed using HR ICP–MS and methods to determine gross alpha/beta activities were applied. Hierarchical cluster analysis (HCA) was used on selected variables: major ions (Ca, Mg, Na, Cl, HCO3, SO4), Si, temperature, electrical conductivity (EC), pH and Eh. Results showed that variability of chemical characteristics, and diverse mineral and thermal water types were grouped into six clusters. Geochemical conditions of each cluster were considered in detail in terms of basic hydrochemical parameters, geological characteristics, and the contents of particular elements. There were certain regularities among the separated groups. Water differed in temperatures, dissolved mineral substances, pH, Eh values and gas content, which indicated different hydrogeological conditions. Variations among clusters in natural radioactivity, the content of essential elements and rare earth elements (REE) are also discussed.

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.