Katalin Hegedűs-Csondor

Demand for groundwater resources as drinking water is highly increasing worldwide. Groundwater accounts to 92% of drinking water sources also in Hungary. Through rock-water interactions, different elements can be enriched in groundwater including naturally occurring radioactive elements, which may have considerable health risk. Due to the hierarchically organized movement of groundwater, the spatial distribution of dissolved solid content, and associated physical, chemical and kinetic processes are also systematized. Areas of different hydraulic regimes even within the same aquifer are characterized by different geochemical environments, which is decisive in case of the mobility of redox-sensitive elements, such as uranium and radium. The groundwater flow system approach, therefore, helps to understand the origin of the different physicochemical characteristics and components of groundwater. Moreover, the vulnerability to any changes depends also on both the type of the hydraulic regime and the order of the hierarchically nested flow system. This study aimed to identify the cause of gross alpha activity exceeding the parametric value of 0.1 Bq/L in groundwater-derived drinking water in northwestern part of Hungary using a regional groundwater flow system approach. Sampling of springs, drinking water and thermal wells was performed in 2021 and in 2024. In-situ water quality parameters were recorded on the field. The concentrations of major ions and trace elements, oxygen and hydrogen isotopic ratios and activity concentration of radioactive isotopes (uranium, radium, radon) were determined by laboratory measurements. Local groundwater flow conditions were characterized by pressure-elevation profiles. In drinking water samples total U activity concentration up to 540 mBq/L was measured that can be connected to local geogenic sources related to the metamorphic outcrop of Sopron Mountains and to the Pannonian sediments in its surroundings. The radionuclide-specific measurements explained that the elevated gross alpha activity identified in several drinking water wells is a result of dissolved uranium favored by the prevailing oxidizing environment of local flow systems and/or recharge areas. Low activity concentrations of 226Ra and 222Rn were measured in all samples except one sample, where 301 mBq/L of 226Ra and 219 Bq/L of 222Rn activity concentration was found. The presence of radium could be attributed to regional flow systems; however, the high concentration of radon activity cannot be accounted for solely by the decay of radium calling for further detailed investigation. The results highlight also that climate change induced groundwater level decline will enhance the problem with uranium. This work has been implemented by the National Multidisciplinary Laboratory for Climate Change (RRF-2.3.1-21-2022-00014) project within the framework of Hungary's National Recovery and Resilience Plan supported by the Recovery and Resilience Facility of the European Union. Furthermore, some radioactivity measurements were supported by the open-access scheme of the European Commission’s Joint Research Centre (JRC) (Research Infrastructure Access Agreement No. 36227-1).

Global changes are increasingly pushing for more sustainable resources, such as geothermal energy. The thermal waters of the karst system in Budapest (Hungary) have so far been used mainly for balneological purposes. It is thus expected that in the near future they will more intensely be used for geothermal purposes as well. To this end, a comprehensive research project has been launched by the Geological Survey of the Supervisory Authority for Regulatory Affairs to gain a better understanding of the system and to assess the impact of future projects via numerical simulations. One task of this research was to perform a geochemical water sampling campaign to gain simultaneous geochemical results and characterize a baseline. In this project, also the most abundant natural radioactive isotopes in groundwater, uranium, radium and radon were measured, which were previously successfully used in the natural discharge areas to characterize fluids of different flow paths. Now, these natural tracers were applied in the entire regional study area. Liquid scintillation technique was used to measure the activity concentration of radon. For radium and uranium, an innovative method, selectively adsorbing Nucfilm discs measured by alpha spectrometry was applied. Based on the first results, the radon content in water samples was either below the detection limit or less than 40 Bq/L. However, 284 Bq/L activity concentration was measured in one location, which is high compared to the 100 Bq/L value for drinking water. Fluid mixing was hypothesized here. Uranium activity concentrations were also low (8-17 mBq/l), which is associated with the mostly reductive conditions of the sampled groundwater. The reducing environment of higher order flow paths is confirmed by our sampling results by the measured higher radium contents. The radium content of the samples ranged from 10 to 1823 mBq/L. The highest radium content was found in sample BPGT-08, which with its high dissolved solid content suggests the presence of waters with a long groundwater residence time and a possible connection with organic matter (hydrocarbons). The other radium activities show similar values to those measured by previous studies in the region. For two water wells, we contributed to the interpretation of the total alpha measurements by measuring the activity concentrations of radium and uranium as alpha decay radionuclides. Our measurements allowed for the characterisation of groundwater flow systems, the identification of different geochemical environments and possible fluid mixing.

Riverbank-filtered systems are cost-effective and sustainable drinking water supply systems along major rivers. However, they are strongly dependent on the river stage. Climate change-induced extremely low or high river stages may cause water quantity and quality problems. In this study, a riverbank-filtered drinking water supply system along the Danube River in Hungary was investigated from a geochemical aspect at lower and higher river stages. We also aimed to understand the origin of elevated (>100 mBq L–1) gross alpha activity measured in some wells. 10 producing, 2 monitoring wells, and the Danube were sampled at lower and higher river stages. Physico-chemical parameters were recorded on-site and the samples were analysed for major ions, trace components and hydrogen (δ2H) and oxygen (δ18O) stable isotopic compositions as well. 234U, 238U and 226Ra activity concentrations were determined by alpha spectrometry using selectively adsorbing Nucfilm discs. 222Rn activity was measured by liquid scintillation counting. Uranium activity was measured in the highest concentration (up to 222 mBq L–1) among the examined radionuclides. 226Ra and 222Rn activities were barely above the detection limit. Based on these results, the previous non-compliant elevated gross alpha activity is caused by dissolved uranium in the groundwater. A spatial pattern was recognized in the geochemical characteristics of the produced water. Total dissolved solid, iron and manganese content and also uranium activity concentrations show increasing values from N to S, which corresponds well to the occurrence of organic matter-rich, clayey floodplain deposits underlying the aquifer and to their higher position to the S. Stable isotope ratios point to the increased influence of surface waters in the N due to the position of an irrigation channel. Besides spatial variation, a temporal change was observed, too: higher uranium activity was measured at a lower river stage (up to 222 mBq L–1) compared to concentrations at a higher river stage (up to 126 mBq L–1). This phenomenon could be explained by the dynamic relationship between the groundwater and the river. The hydraulic gradient between the river and the wells decreases with decreasing river stage, which resulted in longer residence time of the water. The longer the residence time, the more the oxygen-rich water interacts with the clayey basement layers facilitating uranium remobilization. This process will become increasingly dominant in extremely low river stages during long-lasting drought periods in the future and might lead to water quality problems. Our study highlights the vulnerability of riverbank-filtered drinking water supply systems, which can jeopardize their long-term use in the future. The research is part of a project which was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014.

In Hungary, the drinking water supply almost exclusively uses groundwater resources. Recent investigations revealed that waterworks have difficulties in maintaining the proper quantity and quality (e.g. because of elevated gross alpha activity concentration) of drinking water in certain settlements in NE Hungary. To understand and to solve these groundwater-related issues, there is a need for a thorough understanding of groundwater flow dynamics and the associated geochemical characteristics in the broader area. The aims of the present study in the research area are 1) to evaluate the groundwater flow systems based on measured hydraulic data on regional and local scale, 2) to characterize the geochemical composition of the waters based on archive geochemical data to support the hydraulic studies 3) to use natural radioanuclides (234U/238U ratio, 226Ra and 222Rn) as natural tracers to evaluate local water quality issues. Firstly, regional groundwater flow mapping was carried out in the study area. Based on data collected from archive well documentation, a database was built containing the main properties (e.g. coordinates, water level, well depth, screening) of 722 wells. Pore pressure and hydraulic head values were calculated. To examine the horizontal groundwater flow directions, six potential maps were constructed between -200 m asl and 600 m asl elevation intervals. On the other hand, 34 pressure-elevation profiles were compiled to understand the vertical flow dynamics and identify the different flow regime areas (i.e. recharge, midline, discharge). The results showed that in the examined depth, topography-driven groundwater flow systems exist. Recharge areas are characteristic of the hilly and mountainous areas along the Hungarian-Austrian border, while discharge regime is dominant in the surroundings of Lake Fertő/Neusiedl and along water courses. The dominant horizontal flow direction is from W- SW to E-NE. The geochemical results were evaluated in the groundwater flow system context. Uranium was identified as the main cause of elevated gross alpha activity. The results contribute to the sustainable production of healthy drinking water and planning of new drinking water abstraction sites. The research is part of a project which was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014. The study is also supported by the ÚNKP-23-5 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.

One of the largest natural thermal lakes in the world, Lake Hévíz is located in the southwestern part of the Transdanubian Range’s karst system (Hungary). It is fed by springs with different temperatures, which are located in a cave beneath the lake. The mixing of cold and hot waters generates the lake’s sulphuric therapeutic water, and it is responsible for the cave formation at the bottom, resulting in the lake's unique ecosystem. The presented research aimed at the comprehensive geochemical characterization of waters in the wider surroundings of the lake (lake water, springs, observation, drinking water, and thermal water wells). Investigating the geochemical characteristics of water took on a novel perspective through the innovative application of radionuclides as natural tracers. Within the framework of this investigation, we utilized uranium, radium, and radon isotopes to identify the mixing of fluids and infer the mixing end members in the Hévíz karst system. Alpha spectrometry was applied on selectively adsorbing Nucfilm discs as an inventive approach to measure uranium and radium isotopes. Moreover, stable isotopic ratios of hydrogen and oxygen (δ2H and δ18O) were determined to supplement the information on waters with different origins. Hydrochemical water analysis for measuring the concentration of major ions and trace elements was carried out using ICP-MS, ion chromatography, and UV-Vis spectrophotometry. The inferred fluid end members and their compositions are anticipated to provide insightful information on the hydrogeological functioning of the Lake Hévíz karst system, which is indispensable in sustainable water resource management and understanding climate change's impact. Keywords: Thermal lake; Hydrogeochemical characteristics; Mixing fluids; Radionuclides; Stable isotopes; ICP-MS, Nucfilm, Alpha spectroscopy

In Hungary, the drinking water supply relies upon groundwater resources of up to 98%. As a drinking water resource, groundwater must meet strict quality requirements in order to minimise any health effects arising from daily water consumption. Water-rock interactions enrich groundwater not only with essential elements (e.g. Ca, Mg) but also with undesired substances such as heavy metals or radioactive elements. In the last few years, a thorough drinking water quality monitoring campaign was carried out in Hungary, revealing that some parts of the country are characterised by relatively high uranium concentrations. The causes of these elevated activities have not been properly investigated, yet. However, understanding the controls of the release and mobility of uranium is critical in proper groundwater management.Baják et al (2022) developed a one-dimensional (1-D) geochemical model using the code PHREEQC (Parkhurst and Appelo, 2013) to examine the processes that determine the fate of uranium in the siliciclastic Miocene-Quaternary aquifer system near Velence Hills, some 50 km off Budapest. Here, the geological build-up (granitic rocks on the surface) favours the high uranium content in groundwater, which is characterised by oxidising conditions. The 1-D model included redox-controlled kinetic reactions as well as other potential uranium-controlling processes (e.g., surface complexation). The results suggested that uranium distribution is sensitive to redox changes in the aquifer and its mobility in groundwater especially depends on the residence time of water compared to the reaction times controlling the consumption of oxidising species.This study introduces a two-dimensional multicomponent reactive transport model developed using the PHT3D code (Prommer et al., 2003), which is a coupling between MODFLOW and PHREEQC. The model builds on and extends the capability of the 1-D model to simulate uranium mobility across the multiple flow paths of the aquifer systems. The model calibration accounts for 30 groundwater samples collected from drinking water wells in the study area. Physico-chemical parameters (temperature, pH, specific electric conductivity, redox potential) were measured on-site, and the samples were analysed for natural tracers (δ16O, δ2H, 234U, 238U, 226Ra) to gain further insight into the geochemical processes of the aquifer system.This research was supported by the ÚNKP-23-4 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund and was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. The research is part of a project which was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014.References:Baják, P., Csondor, K., Pedretti, D., Muniruzzaman, M., Surbeck, H., Izsák, B., Vargha, M., Horváth, Á., Pándics, T., Erőss, A., 2022. Refining the conceptual model for radionuclide mobility in groundwater in the vicinity of a Hungarian granitic complex using geochemical modeling. Applied Geochemistry 137, 105201.Parkhurst, D.L., Appelo, C.A.J., 2013. Description of Input and Examples for PHREEQC Version 3—A Computer Program for Speciation, Batch-Reaction, One-Dimensional Transport, and Inverse Geochemical Calculations. (USGS Technical No. 6(A)43). U.S. Geological Survey, Denver, CO, USA.Prommer H, Barry, D.A., Zheng, C. (2003). MODFLOW/MT3DMS based reactive multi-component transport modeling. Ground Water, 41(2).

Lake Velence is a shallow soda lake, the third largest natural lake in Hungary. The lake’s water level has been decreasing and the water quality has been declining in recent years. The shallow depth of the lake makes it more susceptible to droughts and evaporation. Climate change in Hungary will likely cause these phenomena to be more common in the future. In the lake’s water budget, only the surface water components and precipitation are considered. Revisiting the water management in the area is necessary for the local ecosystem and tourism industry. We intend to aid the efforts of the authorities and locals to stop the deterioration of the lake with exploring the surface water-groundwater interactions in the area using natural tracers. Groundwater may buffer the effects of climate change, which highlights the importance of the study. Groundwater mapping in the area proved that the lake is at the discharge point of local groundwater flow systems. In this previous study, similar uranium activity concentrations were also measured in the lake water and in groundwater samples collected by the lake indicating a close interaction between the lake and the groundwater. To further investigate this question, water samples were collected from different water sources in the catchment area of Lake Velence: from the lake, inflow streams, an artificial reservoir, and groundwater wells. The samples were analysed for stable isotopes δ2H and δ18O. Furthermore, 234U, 238U, 226Ra ,228Ra and 222Rn activity were measured by an innovative technique: alpha spectrometry applied on selectively adsorbing Nucfilm discs. Both the stable and the radioisotopes function as environmental tracers in this study to collect thorough evidence about the contribution of groundwater in the water budget of Lake Velence and in the inflowing streams. This will contribute to the sustainable water management of the whole catchment area of the Lake Velence by highlighting the role of groundwater. The research was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences and the research was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014 project.

We present an analytical method that allows for the rapid measurement of uranium in water samples. For a 50 ml sample concentrations down to about 2 micro-g/l can be measured within an hour. There are no toxic chemicals used and the whole equipment is portable and can be powered by a 12 V battery. The preparation consists of adding 200 mg silica gel to the 50 ml sample, stirring for 1 hour, filtering out the silica gel and transferring it to a semi-micro cuvette for the measurement. Several samples can be prepared in parallel, depening on the number of magnetic stirrers available. The measurement takes only 1 minute and uses the uranyl fluorescence, enhanced by the adsorption on silica gel. Excitation is done by a pulsed UV-LED at 285 nm. The delayed fluorescence signal around 520 nm is detected by a 6 mm x 6 mm Silicon Photomultiplie (SiPM) behind a 520 nm bandpass filter. Pulsing the LED, converting the SiPM output and displaying the result is controlled by an Arduino microprocessor. All details of the experimental setup as well the software code are presented. It's open source, open to be copied and the whole material costs are only around 500 Euro.

Source water quality is a key determinant of drinking water quality. The recast European Union 2020/2184 Drinking Water Directive (DWD) introduced the obligation for comprehensive risk assessment in drinking water supplies, including hazard assessment of the water source. The DWD also requires further elements of natural origin to be monitored, including U, Ca, Mg and K. The current study is the first comprehensive assessment of 15 natural elements (B, Ba, Be, Ca, Co, K, Li, Mg, Mo, Na, Se, Sr, Ti, U and V) in 1155 (82%) Hungarian drinking water sources, including surface water, bank filtered and groundwater sources. Parameters posing a risk to health (Se, V and U) were typically below the limit of quantification (LOQ), but higher concentrations (max. 7.0, 17 and 41 µg/L, respectively) may occur in confined locations. U exceeded the DWD parametric value in one water supply. Mg and Ca in the majority of the water supplies and Li in a small geographic area reached the concentration range assumed to be protective to health. Water sources were grouped in six clusters based on their elemental distribution, some of them also showing clear geographical patterns. Surface and groundwater sources were not differentiated by composition, with the exception of karstic waters (dominated by Ca and Mg). None of the investigated parameters are expected to be a source of public health concern on a national level, but local occurrences of U and Se should be investigated and managed on a case-by-case basis.

Source water quality is a key determinant of drinking water quality. The recast European Union 2020/2184 drinking water directive (DWD) introduced the obligation for comprehensive risk assessment in drinking water supplies, including the water source and incorporated new elements of natural origin in the list of parameters to be monitored. The current study is the first comprehensive assessment of 15 natural elements (B, Ba, Be, Ca, Co, K, Li, Mg, Mo, Na, Se, Sr, Ti, U and V) in 1155 (82%) Hungarian drinking water sources, including surface water, bank filtered and groundwater sources. Parameters posing a risk to health (Se, V and U) were typically below the lower limit of quantification (LOQ), but higher concentrations (max. 7.0, 17 and 41 µg/L, respectively) may occur in confined locations, the latter exceeding the DWD parametric value in one water supply. Li in a small geographical area, Mg and Ca in the majority of the water supplies reached the concentration range assumed to be protective to health. Water sources were grouped in 6 clusters based on their element distribution, some of them also showing clear geographical patterns. Water types were not differentiated, with the exception of karstic waters (dominated by Ca and Mg). None of the investigated parameters are expected to be a source of public health concern.