Groundwater forms an integral part of the hydrological cycle and represents one of the most important natural sources of drinking water on a global scale. Due to its geological accumulation and relative isolation from surface sources, groundwater is characterized by stable quality and availability, making it suitable for long-term use in supplying the population with water. Worldwide, it provides approximately 30 % of drinking water, while in many European regions, including the Slovak Republic, its share of supply exceeds 70 %. This fact underscores the key role of groundwater in meeting basic living needs and protecting public health (Krishnamoorthy et al., 2023). From a public health perspective, it is essential to monitor and analyze the presence of chemical and microbiological contaminants in groundwater, which may pose a serious environmental risk. In Slovakia, one of the most significant problems is the excessive occurrence of nitrates, especially in areas with intensive agricultural activity, where the application of industrial fertilizers leads to the migration of these substances into groundwater. Chronic exposure to elevated nitrate concentrations is associated with the risk of methemoglobinemia in infants and potential carcinogenic effects upon long-term exposure (Shaban et al., 2023).
In addition to nitrates, heavy metals such as arsenic, lead, and cadmium also pose an environmental threat. These may be present in groundwater due to natural geological sources or anthropogenic contamination resulting from industrial and municipal activities. These elements have demonstrated neurotoxic, nephrotoxic, and carcinogenic effects that can lead to serious health problems. Long-term exposure to lead, for example, is associated with cognitive impairment, reduced intelligence in children, and damage to the central nervous system. Arsenic is a known carcinogen that increases the risk of skin, lung, and bladder cancer, and can also cause chronic liver disease and cardiovascular problems. Cadmium adversely affects kidney function, causes osteoporosis, and increases the risk of prostate cancer. Another significant risk factor is organic contaminants, such as pesticides and their metabolites, whose persistence and ability to bioaccumulate lead to endocrine system disruption. These substances can act as endocrine disruptors, affecting hormonal balance, which can result in reproductive problems, birth defects, reduced immunity, and an increased risk of developing chronic diseases, including some types of cancer (Sankhla et al. 2019).
From a legislative and regulatory perspective, it is important to ensure the sustainable protection and management of water resources, including groundwater. This protection is provided through relevant legal frameworks and monitoring programs that set rules for water quality, pollution prevention, and the minimization of environmental risks. The implementation of these measures enables a coordinated approach to water resource protection at both national and international levels and is crucial for the long-term sustainability and safety of drinking water (Bo et al., 2022).
The aim of this paper is to provide a detailed assessment of the current state of groundwater quality in the Slovak Republic, identify the main sources of contamination, and analyze the potential impacts on public health. At the same time, the importance of an interdisciplinary approach integrating knowledge from hydrogeology, environmental toxicology, epidemiology, and public health is emphasized as a necessary prerequisite for the effective management and protection of these strategic drinking water resources.
Material and Methods
This work is based on a secondary analysis of data from reports on the state of the environment of the SR, published by the Ministry of the Environment and the Slovak Environmental Agency (SAŽP) on the Enviroportal. The main analysis concerns data for 2023, which are subsequently compared with data for the period 2020–2023. The monitored indicators include physicochemical parameters (e.g., nitrates, ammonium ions, iron, manganese), selected heavy metals (arsenic, lead, cadmium), and organic substances (particularly pesticides and their metabolites). The assessment focuses on exceedances of legislative limits for drinking water and environmental standards. The data originate from regular groundwater monitoring carried out in accordance with applicable legislation, taking into account the geographical distribution of sites, the frequency of contaminant occurrence, and their concentrations. Statistical analysis enables the identification of the most frequently exceeded parameters in 2023 and the assessment of their trends compared to previous years. The results are also compared with the scientific literature on health risks associated with long-term exposure to groundwater contaminants in order to evaluate possible impacts on public health.
Groundwater quality monitoring in 2023 was conducted at a total of 757 sites of the state hydrological network of the Slovak Hydrometeorological Institute (SHMÚ), including boreholes and springs. The chemical status of groundwater was monitored in accordance with the framework monitoring program, which distinguishes between baseline monitoring (conducted once every six years) and operational monitoring, in which samples are collected annually. In response to specific environmental burdens, extraordinary monitoring was carried out in the Slaná River basin, covering nine sites. At these locations, samples were collected at twice the standard volume approved for 2023. The evaluation of laboratory analyses was performed in accordance with the requirements of Decree No. 91/2023 Coll. of the Ministry of Health of the Slovak Republic, which defines drinking water quality indicators, their limit values, and the rules of risk management in drinking water supply systems (Enviroportál 2023).
Results
Most Frequent Exceedances of Limit Values in 2023
The most commonly detected exceedances of limit values in 2023 included elevated concentrations of manganese (Mn) and total iron (Fe), which indicate reducing and oxidation-reduction conditions in groundwater. Exceedance of the limit value for manganese (0.05 mg/l) was recorded in approximately 35 % of samples, with a maximum measured concentration reaching 1.2 mg/l. For iron (limit 0.2 mg/l), exceedances occurred in approximately 28 % of cases, with a maximum value reaching 3.5 mg/l. Frequent exceedances were also recorded for chlorides (Cl⁻) and sulfates (SO₄²⁻), indicating anthropogenic pressure, mainly due to agricultural management, with chloride concentrations in some locations exceeding 250 mg/l, significantly exceeding the limit of 200 mg/l (Enviroportál 2023).
High levels of ammonium ions (NH₄⁺) and nitrates (NO₃⁻) – recorded in 142 cases – represent a typical consequence of excessive fertilization and improper handling of organic substances. The limit value for nitrates (50 mg/l) was exceeded at these sites, with maximum concentrations reaching up to 320 mg/l, representing a significant health risk for the population (Enviroportál 2023).
In the area of trace elements, permissible values were exceeded for arsenic (As), aluminum (Al), nickel (Ni), mercury (Hg), lead (Pb), selenium (Se), and antimony (Sb). For example, the maximum measured concentration of arsenic reached 25 µg/l, exceeding the limit of 10 µg/l set for drinking water. These elements originate from natural geochemical processes as well as from industrial activity or historical contamination of the area (Enviroportál 2023).
Extended monitoring of pesticides in 2023 revealed significant exceedances of limits, especially for substances such as prometryn, desethylatrazine, glyphosate, flufen, and lenacil. For example, glyphosate exceeded the limit of 0.1 µg/l in some locations by up to three times. Among volatile organic compounds (VOCs), the most problematic were tetrachloroethylene (PCE), trichloroethylene (TCE), vinyl chloride, and 1,2-dichloroethane (1,2 DCA), with the highest concentrations found in Moldava nad Bodvou, reaching values up to 15 µg/l for PCE, significantly exceeding the limits set for drinking water. Regular exceedances of dichlorobenzenes occurred at the site of Bratislava – Za Dynamitkou (Enviroportál 2023).
Elevated values of total organic carbon (TOC) and chemical oxygen demand (CODₘₙ) reflect significant organic pressure on water quality, with TOC exceeding the limits set by the decree, reaching values up to 5 mg/l in some samples, indicating pollution by organic substances of various origins (Enviroportál 2023).
Groundwater Quality Trends in Vulnerable Areas (2020–2023)
Between 2020 and 2023, intensive monitoring was carried out in so-called vulnerable areas, which are most at risk from an environmental perspective due to pollution by nitrogen compounds originating from agricultural activity (Enviroportál 2023).
The results showed that 65.1 % of monitored sites had low nitrate concentrations (0–24.99 mg/l NO₃⁻), while in 16.3 % of cases the statutory limits were exceeded (>50 mg/l), and in 25.3 % of cases maximum exceedances were recorded (Enviroportál 2023).
Despite these exceedances, it can be stated that the overall quality of groundwater remained stable, and a reduction in the area of vulnerable zones is being considered without significant risk of deterioration in water quality. Trend assessment showed that nitrate concentrations were:
- stable in 38.1 % of sites,
- increasing in 31.8 % of sites, and
- decreasing in 30.2 % of sites.
Special attention was given to areas with extremely high concentrations (≥ 250 mg/l), particularly in the Danubian Lowland region, where excessive concentrations of pesticides also frequently occur (Enviroportál 2023).
Discussion
The results of groundwater quality monitoring in Slovakia for 2023 confirm persistent environmental challenges associated with oxidation-reduction processes and significant anthropogenic pressure. The most serious problem is exceeded concentrations of Mn and Fe, which signal unbalanced oxidation-reduction conditions in the groundwater environment. This condition is likely the result of insufficient oxygen supply to aquifers and the presence of reducing substances in the geological substrate, leading to increased mobilization of these elements into groundwater. Such a chemical environment significantly limits the usability of water for drinking purposes and causes technical problems, such as corrosion of water supply networks, and aesthetic deterioration of water quality, including color and turbidity (Bagordo et al., 2024).
Similar processes were documented in detail in the study by Molnárová et al. (2025), which monitored the impact of Slaná River contamination following the siderite mine accident in 2022. The discharge of water with a high content of Fe, Mn, As, and Ni caused a significant deterioration in groundwater quality in the surrounding area, particularly at the Betliar site. Elevated concentrations of Mn and Fe underscore the importance of continuous monitoring of oxidation-reduction processes and their effect on the mobilization of these elements (Molnárová et al., 2025). An important and current example is also the earthquake that struck eastern Slovakia in October 2023. In some affected villages (e.g., Ďapalovce, Rafajovce), residents reported changes in well water quality, including turbidity and altered taste, accompanied by elevated concentrations of iron and manganese. This phenomenon points to the sensitivity of groundwater redox conditions to seismic disruption of the rock environment and highlights the need for extraordinary water quality monitoring even in the event of natural disasters. Similar mechanisms of the Fe and Mn redox cycle were also examined in detail by Bábek et al. (2023), who confirmed the fundamental role of these processes in influencing groundwater quality in the Morava River basin (Bábek et al., 2023).
In addition to metals, elevated concentrations of nitrogen compounds, especially NH₄⁺ and NO₃⁻, represent a significant environmental problem, frequently exceeding established limits. This condition is closely linked to intensive agricultural land use, where excessive fertilizer application, inappropriate agrotechnical practices, and insufficient protective measures lead to the migration of nitrogen substances into groundwater. Elevated nitrate concentrations are not only an ecological risk, as they contribute to the eutrophication of surface waters, but also represent a serious health threat to humans. In the human body, nitrates can be reduced to nitrites, which then react with amines to form N-nitroso compounds – chemical substances with known carcinogenic effects. These compounds are associated with an increased risk of developing cancer of the stomach, esophagus, and bladder. In infants, additionally, methemoglobinemia may develop, a condition in which hemoglobin loses its ability to effectively transport oxygen, which can be life-threatening (Abascal et al., 2022). Research by Ortmeyer et al. (2022) in Germany, Denmark, and Ireland points to similar causes of excessive nitrate concentrations resulting from unsustainable agro-environmental pressure across Europe. Despite the existence of regulatory frameworks such as the European Nitrates Directive (91/676/EEC), many areas remain vulnerable, requiring more comprehensive measures including improved monitoring and environmentally oriented fertilizer management. These conclusions are also relevant for the Slovak Republic, where, despite the overall stabilization of average nitrate concentrations in the period 2020–2023, sites with exceedances of limit values are still identified, highlighting the need for targeted and effective measures in the area of water protection (Ortmeyer et al., 2022).
Another important group of contaminants is trace elements (e.g., As, Al, Ni, Hg, Pb, Se, Sb) and specific organic substances such as pesticides, polycyclic aromatic hydrocarbons (PAHs), or VOCs. Elevated concentrations of these substances are typical for locations with industrial activity or near municipalities without sewerage systems, underscoring the necessity of detailed investigation of contamination sources and the introduction of targeted measures to reduce emissions. The most critical are exceedances of toxic substances such as PCE, TCE, and vinyl chloride, which are known for their carcinogenicity and chronic toxicity. Long-term exposure to these contaminants can lead to damage to the liver, kidneys, central nervous system, and an increased risk of developing tumor diseases, particularly of the liver, kidneys, and lungs. Some of these substances also have mutagenic, teratogenic, and neurotoxic effects, posing a particular risk to sensitive population groups such as children, pregnant women, and persons with reduced detoxification capacity (Pierri et al., 2021). Research by Hong et al. (2024) further notes that PCE contamination can cause long-term disruption of groundwater microbial communities, thereby negatively affecting their ecological stability even decades after initial exposure. These findings support the need for modernization of monitoring protocols, including the expansion of surveillance to include bioindicators that enable early identification and prevention of the negative impacts of environmental contaminants not only on human health but also on the functional balance of groundwater ecosystems (Hong et al., 2024).
From the perspective of organic pollution, elevated values of TOC and chemical oxygen demand (CODₘₙ) are significant indicators of the presence of organic substances that can adversely affect groundwater quality. In addition to physicochemical changes, these substances can disrupt microbial balance, thereby increasing the risk of microbiological contamination and the formation of undesirable disinfection by-products, which can be toxic to the human body. This important aspect, however, often remains insufficiently considered, although its inclusion in water quality assessment is essential for a comprehensive evaluation of groundwater status (Torrejón et al., 2023). Zhao et al. (2022) emphasize that beyond the quantitative content of TOC, its molecular composition is also important – for example, the content of bioenergetically favorable molecules such as amino sugars, which influence microbial processes including redox reactions. The transformation of these substances occurs primarily through adsorption onto minerals and biodegradation, underscoring the need to also evaluate the qualitative characteristics of organic carbon when assessing contamination risks. For humans, the presence of these organic substances and the formation of by-products pose a risk of acute and chronic health problems, including gastrointestinal irritation, allergic reactions, and long-term effects on the immune and nervous systems (Zhao et al., 2022).
From an international perspective, groundwater quality in Slovakia corresponds to trends recorded across the European Union and globally. Exceedances of Fe and Mn concentrations are common also in neighboring Central European countries such as Poland, the Czech Republic, and Hungary, where these problems affect approximately 25–30 % of groundwater samples and significantly impact the usability of resources (EEA 2022). The problem of nitrogen compounds, particularly nitrates, is a pan-European phenomenon, especially pronounced in agriculturally intensive areas. Slovakia ranks among the countries with significant environmental and health risks in this regard, with approximately 16.5 % of sites exceeding the 50 mg/l limit according to European Commission data, slightly above the EU average (EEA 2023). Contamination by trace elements and organic contaminants is typical for industrially developed regions of the EU and the world, with approximately 24.2 % of groundwater in the EU not meeting requirements, with nitrates, pesticides, and VOCs among the main causes. In Western countries such as Austria, Germany, and the Netherlands, protective zones and modern digital monitoring tools are therefore used for early detection of contamination and protection of water resources (European Commission Report 2024).
Conclusion
Groundwater quality in the Slovak Republic remains a key factor in ensuring long-term accessible and safe drinking water. The 2023 monitoring results confirm a stable yet concerning state, with regular exceedances of limit values for several contaminants. The persistent presence of pollutants in groundwater poses serious environmental and health risks that require a rigorous and interdisciplinary approach to their monitoring, assessment, and management. It is crucial to ensure effective protection of these strategic resources through the implementation of legislative measures, sustainable agricultural practices, and modernization of monitoring methods. Despite some stable trends in groundwater quality, challenges remain in the form of localized exceedances that require specific solutions and increased attention. Sustainable groundwater management is therefore essential not only for the protection of public health but also for ensuring environmental balance and quality of life for present and future generations.
Authors: Mgr. Simona Miškárová prof. MUDr. Mgr. Erik Dorko, PhD., MPH, MBA prof. MUDr. Kvetoslava Rimárová, CSc. Mgr. Anastasiia Ostafiichuk MVDr. Martina Hrubovčák Tejová The work is supported by grants KEGA 003UPJŠ-4/2024 Update and Innovation of the Public Health Study Program in the Field of Chronic Non-Communicable Disease Prevention and grant KEGA 0010UPJŠ-4/2024 Implementation of Multimedia Technologies in the Teaching of Preventive Interventions in Medical and Non-Medical Fields.
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