Travertine increases the concentration of trace elements in groundwater in Chahar Takab, Fariman county, northeast Iran

ORIGINAL ARTICLE Environmental Earth Sciences (2025) 84:129 https://doi.org/10.1007/s12665-025-12144-0 Introduction Two billion people worldwide lack access to safe drinking water (United and Nations 2022). Furthermore, half of the global population experiences severe water scarcity for at least part of the year (IPCC 2022). This situation is projected to intensify in the future due to climate change and population growth (World Meteorological and Organization 2022). Consequently, groundwater has become a vital water source, supplying half of the world’s domestic water needs (UNESCO World Water Assessment Programme 2022). In rural areas without supply systems, it often serves as the only viable option for providing basic water access (UNESCO Daniel Rosado [email protected] 1 Department of Hydrology and Water Resources Management, Institute for Natural Resource Conservation, Kiel University, Kiel 24118, Germany 2 Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran 3 Department of Chemical and Environmental Engineering, Universidad de Sevilla, Camino de los Descubrimientos, s/n, Sevilla 41092, Spain Abstract Groundwater has emerged as a crucial water source, supplying half of the world’s domestic water needs, particularly in rural areas without supply systems. This study assesses the impact of travertine formations, on water quality in Chahar Takab village, Iran, focusing on suitability for human consumption and ecosystem sustainability where groundwater is the primary source. Thirty-four samples from various sources, including travertine springs, surface water, and groundwater, underwent ICP-OES analysis. Travertine springs exhibited higher electrical conductivity (EC), lower pH, and elevated concentrations of major cations (Na, Ca, Mg) and anions (Cl, HCO3). In them, all samples exceeded European Union limits for Cl and Na in drinking water. Hydrochemical facies were influenced by water-rock interactions, leading to Ca-HCO3 dominance in surface and groundwater samples and Ca-Mg-Cl dominance in travertine springs. Heavy metal analysis revealed high concentrations of As, B, Fe, Mn, and Pb in travertine spring and surface water samples, with As exceeding World Health Organization limits by up to 28.5 times. Additionally, the Metal Index indicated values exceeding drinking water guidelines set by the World Health Organization in 58% of the samples. Travertine springs had the highest toxicity risks, especially for As, Cd, and Pb. Results suggest a tectonic origin for heavy metal contamination (As-containing travertine springs), emphasizing the need for mitigation measures and regular monitoring. Action is necessary to address water quality issues in the region. Highlights ●Travertine reduces groundwater quality. ●Ca-HCO3 dominates surface and groundwater. ●Ca-Mg-Cl dominantes in travertine springs. ●High concentrations of As, B, Fe, Mn, and Pb. ●Toxicity risks associated with As, Cd, and Pb. Keywords Groundwater quality · Arsenic · Heavy metal pollution · Drinking water · Travertine springs · Water scarcity Received: 16 November 2024 / Accepted: 9 February 2025 / Published online: 20 February 2025 © The Author(s) 2025 Travertine increases the concentration of trace elements in groundwater in Chahar Takab, Fariman county, northeast Iran MaryamRezanezhad1,2· Mohamad HoseinMahmudy-Gharaie2· NicolaFohrer1· DanielRosado1,3 1 3 Environmental Earth Sciences (2025) 84:129 World Water Assessment Programme 2022). Remarkably, the Asia-Pacific region leads global groundwater extraction, with seven of the top ten groundwater-extracting nations (Bangladesh, China, India, Indonesia, Iran, Pakistan and Turkey) accounting for approximately 60% of the world’s total groundwater withdrawal (UNESCO World Water Assessment Programme 2022). Although groundwater resources are often abundant, their quality can be affected by industries, mining, urban effluents and other anthropogenic activities, as well as natural factors such as specific lithologies or the presence of travertine springs (Kumar et al. 2019; Vardhan et al. 2019). The chemical interactions between groundwater and minerals, known as hydrogeochemical processes, that involve mineral dissolution and precipitation, ion exchange, oxidation-reduction reactions, and adsorption-desorption mechanisms, together with the geological characteristics of an area, such as rock type, mineral composition, and structural features, largely influence the physicochemical characteristics of groundwater (Aju et al. 2022; Islam 2023). The so-called heavy metal (i.e. trace elements) are frequent pollutants of groundwater and their presence has become a global issue with potential adverse impacts on human health (Amaral et al. 2018; He and Wu 2019a, b; Masoudinejad et al. 2018). Groundwater is particularly affected by non-anthropogenic elements such as As, F, Cr, B, and others, which originate from geological formations, water-rock ion exchange, and degassing of magma intrusion (Delkhahi et al. 2020). Among the mentioned heavy metals, especially inorganic As pollution in groundwater resources became a global challenge (Roh et al. 2017). Inorganic As constitutes the main form of As found in groundwater, surface water, and soil (Pazhoor et al. 2021). It can be present in water as Arsenite, As (III), the most toxic form of As, and as Arsenate, As (V), less toxic (Biswas et al. 2019; Chakraborti et al. 2016). The primary source of inorganic As in groundwater is geological weathering, but also anthropogenic sources can be involved (Biswas and Sarkar 2019). As has been categorized as a Group A carcinogen, denoting it as a ‘known’ human carcinogen, by both the United States Environmental Protection Agency (USEPA 2004) and the International Agency for Research on Cancer (American Cancer Society 2020). This classification is based on the chronic toxicity effects of As in drinking water. To mitigate this risk, the World Health Organization (WHO) lowered the permissible limit for As in drinking water to 10 µg/l (Foster et al. 2019). Usually, As concentrations in uncontaminated surface water ranges from 1 to 10 µg/l. However, in mining and mineralization areas, these levels can significantly escalate (Kumar et al. 2019). Travertine rock is a unique type of limestone formed by the deposition of CaCO3 from hydrothermal vents along fractures and faults in the Earth’s crust (Grootjans et al. 2015; Henchiri et al. 2017; Kano et al. 2019; Pola et al. 2014; Shiraishi et al. 2020). Travertine is a sedimentary freshwater carbonate rock that forms from hydrothermal water springs rich in Ca²⁺ and with high partial pressure of CO₂ (Kano et al. 2019). When this water emerges at the surface, rapid CO₂ degassing occurs, increasing pH and triggering the precipitation of CaCO₃ according to the reaction: Ca²⁺ + 2HCO₃⁻ ⟷ CaCO₃ + CO₂ + H₂O (Kano et al. 2019). Typically, travertine formation involves CO₂ and fluids of deep origin (Janssens et al. 2020). In contrast, tufa, another freshwater carbonate, forms in cool, ambient temperature freshwater environments through biologically induced processes and often contains remnants of microand macrophytes, invertebrates, and bacteria (Kele and Bódai 2022). Additionally, tufa forms from shallow CO₂ sources, such as soil biodegradation or plants (Janssens et al. 2020). Travertine springs waters are frequently rich in various elements, including potentially high levels of trace elements, due to the travertine rock-water interaction in deep aquifers (Durowoju et al. 2015). This process can directly reduce the quality of surface and groundwater or cause alterations through infiltration, discharge–recharge pattern of groundwater, inter-aquifer exchange, etc. Consequently, it can hinder the suitability of these waters for drinking and agricultural purposes (Kampouroglou and Economou-Eliopoulos 2016; Rezaei et al. 2018). The effects of travertine spring waters on trace elements, especially As, have attracted attention of researchers worldwide (Kano et al. 2019; Rezaei et al. 2018). Geothermal areas in Japan and locations with thermal activity in New Zealand have reported exceptionally high As concentrations in water, reaching 6400 µg/l and 8500 µg/l, respectively (Shakeri et al. 2020). Therefore, studies investigating As contamination have been conducted worldwide, including the United States, China, Argentina, Chile, Bolivia, Peru, Mexico, Bangladesh, Japan, India, Nepal, among others (Ayotte et al. 2015; Bhowmick et al. 2018; He et al. 2020; Hossain et al. 2016; Huq et al. 2020; Mueller 2017; OrtegaGuerrero 2017; Tapia et al. 2019) and has recently been reported in Iran (Mohammadzadeh and Mansouri Daneshvar, 2020). In the Fariman area, northeast Iran, numerous travertine springs align with fault and fracture trends, often corresponding to inner faults. Over time, travertine springs have led to the leaching of toxic elements from alteration zones into local water sources. Given the extensive distribution of travertine springs in Chahar Takab village, their alignment with faults, and the significant human population relying on these waters for drinking, agriculture, and other purposes, we aim to assess the impact of travertine formations and the regional geology on major and minor components in water 1 3 129 Page 2 of 14 Environmental Earth Sciences (2025) 84:129 and, therefore, their suitability for both human consumption and sustaining aquatic ecosystems within the catchment area. This objective aligns with the concerns highlighted in the United Nations World Water Development Report 2022 regarding the lack of reliable data for area-specific groundwater assessments to enable informed policies and groundwater resources management. Materials and methods Study area The study area lies between latitude 35°20’ to 35°34’ N and longitude 59°53’ to 60°04’ E. It includes Chahar Takab (35°29’56.8"N 59°53’15.6"E), a rural village located in Fariman county, Razavi Khorasan province (northeast Iran), 25 km south of Fariman city and 115 km southeast of Mashhad city (Fig. 1). The study area has a BSk climate according to the Köppen climate classification (World Bank 2021). Fariman city experiences cold and long winters. In the coldest months (December and January) temperature can drop to -17 °C while in the hottest (July and August) can reach 36 °C (Iran Data Portal 2022). Annual rainfall is in the range of 150 to 200 mm (Iran Data Portal 2022). The study area lacks Paleocene and Oligocene facies. The oldest geological unit dates back to the Precambrian period and consists of a sequence of metamorphic rocks (Iran Oil and Company 1957). Near Chahar Takab village, a Miocene rock formation is present, characterized by layers of clay or siltstone interbedded with conglomerate, along with limestone layers to the southeast (Iran Oil and Company 1957). A geological map with data of the United Stated Geological Survey is in the supplementary material (Figure S1). In-situ parameters and water sampling In-situ parameters were measured, and water samples were collected from 34 sampling points in July 2019. In situ parameters included pH, electrical conductivity (EC) and temperature. Two bottles of water (500 ml) were collected at each point. Each bottle was washed three times with local water prior to water collection and no air bubbles were allowed in the bottles after collection. Due to the limited Fig. 1 Location of the water sampling points 1 3 Page 3 of 14 129 Environmental Earth Sciences (2025) 84:129 oxygen, carbonate (CO3 2−), bicarbonate (HCO3 −) and total alkalinity (T) were measured immediately after sampling using the titration method with phenolphthalein and methyl orange, following ISO 9963-1:1996. Sulfate (SO4 2−) was measured with a spectrophotometer (DU-6 Spectrophotometer, 420 nm; BECKMAN) at 420 nm following Standard Methods 4500-SO4 2− E with barium chloride (BaCl2) and other reagents. Chloride (Cl−) was determined by titration with silver nitrate (AgNO3) and potassium chromate (K2CrO4 − 5%) following Standard Methods 4500-ClB. Ca and Mg, were analyzed by titration with EDTA according to Standard Methods 3500-Ca B and Standard Methods 3500Mg B. To analyze As and the rest of the metals, 100 ml of collected water samples were filtered (0.25 μm) and acidified to pH < 2 with nitric acid to prevent metal oxidation (Ghosh et al. 2019). Potassium (K) and Sodium (Na) as well as As, Cd, Cr, Co, Pb, Mn, Ni, Zn were determined with an ICP-OES (76004555 SPECTRO ARCOS System). water resources in travertine springs, samples were collected there with a syringe. The points were categorized into three groups, as detailed in Table 1. Group 1 comprised samples from travertine springs located at high altitudes (average: 1776 m.a.s.l.). Group 2 consisted of surface water collected at the highest locations (1827 and 1957 m.a.s.l.). Group 3 involved various types of groundwater samples: springs, well water, and groundwater transported in aqueducts. Group 3 samples were collected at lower altitudes (average: 1578 m.a.s.l.), except for CRW1, CRW27, CRW30 and CRW32, which were collected at higher altitudes (1754 to 2097 m.a.s.l.). Laboratory analysis Samples were transported to the Central Laboratory of Ferdowsi University in Mashhad, Iran, where all laboratory analysis were conducted. To prevent any reaction with Table 1 Coordinates and altitude of the sampling points Group Point Latitude (North) Longitude (East) Altitude (masl) Source of water 1 - Travertine springs CRW2 35° 29’ 50.4” 59° 53’ 53.7” 1761 Travertine spring (1) CRW3 35° 29’ 48.6” 59° 53’ 54.6” 1779 Travertine spring (2) CRW4 35° 29’ 48.3” 59° 53’ 55.0” 1783 Travertine spring (3) CRW5 35° 29’ 48.2” 59° 53’ 56.0” 1772 Travertine spring (4) CRW6 35° 29’ 48” 59° 53’ 55.9” 1794 Travertine spring (5) CRW7 35° 29’ 47.9” 59° 53’ 55.8” 1785 Travertine spring (6) CRW28 35° 29’ 41” 59° 53’ 57.0” 1761 Travertine spring (7) 2 - Surface water CRW8 35° 29’ 8.8” 59° 54’ 25.7” 1827 River water CRW9 35° 29’ 10.7” 59° 54’ 30.1” 1911 Waterfall 3 - Ground water CRW1 35° 29’ 57.7” 59° 54’ 7.7” 1754 Chahar Takab spring CRW10 35° 30’ 6.2” 59° 53’ 12.6” 1686 Drinking water CRW11 35° 33’ 58.2” 59° 55’ 22.5” 1502 Golesheikh village aqueduct CRW12 35° 33’ 54.4” 59° 56’ 9.9” 1488 Golesheikh village well CRW13 35° 33’ 26.1” 59° 55’ 2.1” 1502 Kalate Rostam aqueduct CRW14 35° 32’ 46.5” 59° 57’ 25.4” 1620 Mazare Bi Abe aqueduct CRW15 35° 32’ 0” 59° 57’ 25.4” 1460 Taraz Khaki village spring CRW16 35° 32’ 2.7” 59° 59’ 42.7” 1444 Taraz Khaki village aqueduct CRW17 35° 30’ 58.6” 59° 58’ 29.5” 1553 Golestan village aqueduct CRW18 35° 30’ 36.3” 59° 59’ 12.3” 1549 Kariz Balagh village aqueduct CRW19 35° 30’ 45.2” 60° 0’ 12.2” 1461 Kariz Balagh village spring CRW20 35° 30’ 29.3” 60° 1’ 20.9” 1460 Galayem aqueduct CRW21 35° 30’ 49.1” 60° 1’ 6.5” 1439 Heidar spring of Galayem village CRW22 35° 29’ 14.2” 60° 1’ 3.1” 1569 Chaharbid aqueduct CRW23 35° 29’ 27.6” 60° 2’ 40.4” 1461 Kariz Sokhte aqueduct (1) CRW24 35° 28’ 42” 60° 3’ 36.6” 1429 Chenarbo aqueduct CRW25 35° 29’ 36” 60° 2’ 8.7” 1451 Kariz Sokhte aqueduct (2) CRW26 35° 31’ 37.5” 60° 0’ 5.2” 1448 Kariz Balagh aqueduct CRW27 35° 29’ 32.9” 59° 54’ 11.4” 1815 Spring surrounding the travertine springs CRW29 35° 29’ 45” 59° 54’ 2.0” 1737 Spring surrounding the travertine CRW30 35° 29’ 33” 59° 56’ 31.0” 2097 Aqueduct infront of Golesheikh village CRW31 35° 32’ 7” 59° 53’ 44.0” 1575 aqueduct in front of Mazare Bi Abe CRW32 35° 29’ 28.3” 59° 57’ 54.8” 1955 Spring surrounding Golestan village CRW33 35° 32’ 17” 59° 57’ 14.0” 1468 Spring before Mazare Bi Abe village CRW34 35° 31’ 39” 59° 56’ 10.0” 1530 Estakhr village aqueduct 1 3 129 Page 4 of 14 Environmental Earth Sciences (2025) 84:129 Results and discussion In situ parameters Temperature, pH and conductivity values are presented in Fig. 2 and all the values are compiled in the supplementary material (Table S1). Results have been categorized into three groups based on water type, as shown in Table 1. Temperature in group 1 displayed the highest mean (average 22.4oC, range 17.5-28.5oC) compared to group 2 (average 15oC, range 14.5-15.5oC) and group 3 (average 18.5oC, range 14.5-25.5oC). pH exhibited a lower average within travertine springs of group 1 (average 6.94, range 6.17– 7.66) compared to groups 2 (average 8.31, range 8.28–8.33) and 3 (average 7.93, range 7.26–8.92). Regarding conductivity, higher values were observed in the travertine springs of group 1 (average 8733 µS/cm, range 4780–12360 µS/ cm) compared to surface water of group 2 (average 419 µS/cm, range 408–430 µS/cm) and groundwater of group 3 (average 1273 µS/cm, range 560–4850 µS/cm). Sample 28 displayed some differences with other samples of group 1, including the lowest conductivity in this group, probably because was distant from the rest. Results indicated that pH is lower and dissolved salts are higher in travertine springs, a characteristic attributed to their geothermal origins (Kano et al. 2019). These springs originate from groundwater that permeates limestone-rich geological formations, becoming enriched in Ca²⁺ and HCO₃⁻ through the dissolution of CaCO₃ by CO₂ present in the water (Hiett et al. 2022; Luo et al. 2022). As water emerges from the springs, changes in pressure and temperature lead to CO2 degassing, reducing the solubility of calcium carbonate and precipitating dissolved ions in the surrounding areas (Brilli and Giustini 2023; Gao et al. 2023; Ranjbaran and Zamanzadeh 2021; Wang et al. 2015). Travertine springs interestingly examplify groundwater geochemistry influenced by the interaction between alkalinity and dissolved CO2 (Brilli and Giustini 2023; Ranjbaran and Zamanzadeh 2021). The process of CO2 uptake by water at depth and its release at the surface not only regulates pH and alkalinity but also drives the continuous formation and growth of travertine deposits around the spring. None of the samples of group 1 meet the drinkability criteria set by the European Union (European Parliament 2020). Specifically, all the samples within this group surpass the established conductivity limit of 2500 µS/cm, and additionally, CRW2, CRW3, and CRW4 samples fall below the lower pH threshold within the prescribed range of 6.5–9.5. Conversely, the conductivities of samples in groups 2 and 3 remained below this limit. Hydrochemical facies and Piper diagrams The concentrations of the major cations (Na+, K+, Ca2+, Mg2+) and major anions (HCO3 −, CO3 2−, SO4 2−, Cl−) were used to determine the hydrochemical characteristics of water samples. These data were represented in a Piper diagram using D-Piper software (Moreno Merino et al. 2021). Piper diagrams classify water into 6 ranges or types: first type (calcium bicarbonate water, Ca-HCO3), second type (sodium chloride, Na-Cl), third type (calcium magnesium chloride, Ca-Mg-Cl), fourth type (calcium bicarbonate sodium, Ca-Na-HCO3), fifth type (calcium chloride, Ca-Cl) and sixth type (sodium bicarbonate, Na-HCO3). The Piper diagram shows water type, ion exchange, element dissolution or deposition, as well as mixing with other waters (Hounslow 2018; Shakoor et al. 2018). Pearson correlation coefficient Pearson correlation coefficients for major cations and anions, pH and EC in groundwater were calculated using SPSS software. Correlation analysis provides valuable insights into ions with common origins, as well as those contributing significantly to pH and EC levels in the water (Yousefi et al. 2018). Metal Index (MI) Metal Index (MI) introduced by Tamasi and Cini (2004) was calculated using trace elements data using the following formula. MI = ∑ n i=1 Cf (MAC) i where Cf is the concentration of each element in water, MAC is the maximum allowable concentration for a metal element based on drinking water guidelines from various sources, including the World Health Organization (WHO 2022): As (10 µg/l), B (2400 µg/l), Cd (3 µg/l), Cr (50 µg/l), Cu (2000 µg/l), Mn (80 µg/l), Ni (70 µg/l), Pb (10 µg/l), Se (40 µg/l); the European Union (European Parliament 2020): Fe (200 µg/l); and the USEPA (USEPA 2022): Zn (5000 µg/l). Finally, i represents the ith sample. A higher metal index value indicates a higher concentration of metals relative to the allowable limit and, therefore, lower water quality. If the concentration of a particular element is higher than the allowable limit (MI > 1), the water is considered contaminated for that element. Conversely, if the concentration of an element is lower than the allowable limit (MI < 1), the water is considered free of contamination by that element. 1 3 Page 5 of 14 129 Environmental Earth Sciences (2025) 84:129 that minimum levels of approximately 20 to 30 mg/l Ca and 10 mg/l Mg in drinking water could yield health benefits, including reduced cardiovascular mortality (WHO 2005). The World Health Organization also indicate that the taste threshold for Ca ions falls within the range of 100– 300 mg/l, depending on the associated anion, and suggests that the taste threshold for Mg is probably lower than that for Ca (WHO 2022). In the case of Ca, all the samples in group 1 and some in group 3 are above these limits indicating suboptimal characteristics for drinking water. In the case of Mg, samples in group 1 well exceed the threshold, as well as most of the samples of groups 2 and 3. Elevated Na in groundwater and springs is often attributed to the weathering of plagioclases, which have a high Na content, such as albite in igneous rocks. Also, to other Nacontaining silicate minerals, such as nepheline, part of the feldspathoid group and present in igneous rocks. Furthermore, the presence of minerals such as halite and mirabilite in evaporitic rocks has also been associated with increased Na concentrations (Nugraheni and Sunjaya 2019). In the study area, high Na concentrations exhibit a strong correlation with Cl (R2 = 0.8) in group 1 samples, with a slope of 1.1. This slope is close to the 1:1 ratio typically associated Concentrations of the major cations (Na+, K+, Ca2+, Mg2+) and major anions (HCO3-, CO32-, SO42-, Cl-) As detailed in the supplementary material (Table S1), the predominant anion in group 1 samples was Cl− (average 1462 mg/l, range 504–2190 mg/l), followed by HCO3 − (average 1002 mg/l, range 622–1391 mg/l) while in groups 2 and 3, HCO3 − was the predominant anion (averages 198 and 309 mg/l, ranges 195–201 and 238–421 mg/l, respectively). Among cations, Na showed the highest concentrations (average 1200 mg/l, range 435–1808 mg/l) in group 1. Group 2 presented similar levels of Ca (average 70 mg/l) and Mg (average 100 mg/l), while in group 3, Mg exhibited the highest concentration (average 254 mg/l, range 90–790 mg/l). The European Union and the USEPA set a limit of 250 mg/l Cl− and 200 mg/l Na in drinking water (European Parliament 2020; USEPA 2023, 2022). All group 1 samples and some in group 3 exceeded these limits and therefore, are unsuitable for drinking, while all groups 2 samples remained within the permissible range. Defining thresholds for Ca and Mg in drinking water remains a challenge. Several researchers have proposed Fig. 2 Elevation, temperature, pH and electrical conductivity in three groups of water samples (group 1, travertine springs, red; group 2, surface water, green; group 3, groundwater, blue) collected in Chahar Takab, Fariman county, northeast Iran along with drinking water thresholds for pH (6.5) and conductivity (2500 µS/cm) set by the European Union (European Parliament 2020) 1 3 129 Page 6 of 14 Environmental Earth Sciences (2025) 84:129 The lithology and mineralogy of the aquifer determines the hydrochemical facies type found in the groundwater. The predominance of calcium bicarbonate (Ca-HCO3) in group 2 and 3 indicates the dissolution of calcite and carbonate rocks. In the travertine springs of group 1, the abundance of Ca and Mg ions indicates a large ion exchange process. Pearson correlation coefficient Pearson correlation coefficients are presented in Table 2. The significant relationships among pH, EC and HCO3 − can be attributed to the close contact between travertine spring water and CaCO3. Consequently, these waters exhibit higher level of EC and HCO3 −, and also a lower pH due to the contact with CO2 (Luo et al. 2022). EC displays a positive and very strong correlation with all the main anions and cations, except CO3 2−, which is explained by the dependence of EC on dissolved ions. A strong positive correlation is observed between HCO₃⁻ and Na, particularly in group 1. This aligns with the findings of Guettaf et al. (2017), who noted that elevated HCO3 − in water increases the deposition of CaCO3 and MgCO3, and therefore proportionally increases concentrations of Na. Moreover, As and sulfate have a positive and significant correlation, suggesting their concurrent release into the water. Thus, As and B can be linked to the oxidation of sulfide minerals in regenerative mineralization, in addition to travertine sources. Heavy metals analysis and Metal Index (MI) The results of the heavy metal analysis are depicted in Fig. 4 and detailed in the supplementary material (Table S2). Group 1 samples showed the highest metal concentration averages in the cases of As, B, Cd, Cu, Fe, Mn, Zn and Se. The average concentrations of several elements in groups 1, 2 and 3 surpassed the drinking water standards established by the World Health Organization (WHO 2022). Specifically, the average concentrations of As in groups 1 and 2 (285 µg/l; 15.4 µg/l), B in group 1 (21660 µg/l), Fe in groups 1 and 3 (680 µg/l; 176 µg/l), Mn in group 1 (215 µg/l) and Pb in group 1 (12.1 µg/l). Furthermore, several individual samples exhibited metal concentrations that exceeded the mentioned standards, as indicated in Fig. 4. On the contrary, the average values of Cd, Cr, Cu, Mn, Ni, Zn, and Se, were lower. Notably, As concentrations in group 1 samples were exceptionally high, exceeding the 10 parts per billion (ppb) limit set by World Health Organization (WHO 2022), the United States Environmental Protection Agency (USEPA 2022) and the European Union (European Parliament 2020). These results suggest that most of the heavy metals in the with halite weathering, suggesting that halite dissolution is likely the primary source of these elevated ion concentrations (Zhang et al. 2020). Sulfates concentrations were higher in group 1 (average 33.1 mg/l, range 14.4–55.3 mg/l) and lower in group 3 (average 13.3 mg/l, range 0.02–48.5 mg/l) and group 2 (average 0.12 mg/l, range 0.08–0.16 mg/l). All measured samples fell below the World Health Organization limit of 250 mg/l for sulfates in drinking water. Similar to Ca and Mg, this limit serves as a guideline for public acceptability and taste detection rather than as a health-based guideline (WHO 2022). The predominant source of SO4 2− has been associated with reactions of water and travertine rock (Hamidian et al. 2019). These results show an increase on sulfate concentrations in group 1 samples, where travertine is present, while the baseline sulfate concentration in group 3 samples remain relatively low. This difference is likely attributed to the reduced presence of sulfate-bearing minerals in the geological formations of group 3 areas. Concerning bicarbonates, travertine spring waters of group 1 exhibited elevated levels of HCO3 − (average 1002 mg/l, range 622–1391 mg/l) due to limestones decomposition (Kano et al. 2019) compared to group 2 (average 198 mg/l, range 195–201 mg/l) and group 3 (average 309 mg/l, range 238–421 mg/l). This concentration in group 1 was likely different when the water was still underground. When groundwater rises to the surface, CO2 dissolved in water evaporates because of the new equilibrium with the very low CO2 content of the air, therefore, the pH increases, bicarbonate decreases and carbonate increases (Ulloa-Cedamanos et al. 2020). If calcium ions were present in water, both would precipitate as CaCO3 (Ulloa-Cedamanos et al. 2020). Based on the geological units displayed in the map in Figure S1, i.e. Q: Quaternary; Pg: Paleogene; Pz: Paleozoic; K: Cretaceous, unit K shows higher concentrations of all ions, lower pH, and higher EC. These values are attributed to the presence of travertine springs within this unit. In contrast, no significant differences are observed between units Pg and Pz, except for Na and Cl, which are higher in Pg compared to Pz. Hydrochemical facies and Piper diagrams The piper diagram (Piper 1944) is depicted in Fig. 3. In the present study, group 1 samples belong to third type (calcium magnesium chloride, Ca-Mg-Cl). Group 2 samples are classified as the first type (calcium bicarbonate water, CaHCO3). Within group 3, most samples align with the first type, although one sample aligns with the third type (calcium magnesium chloride, Ca-Mg-Cl), and another with the fourth type (calcium bicarbonate sodium, Ca-Na-HCO3). 1 3 Page 7 of 14 129 Environmental Earth Sciences (2025) 84:129 surpassing the averages of group 2 (2.38) and group 3 (2.74). Within group 1, CRW3 and CRW4 stands out with exceptionally high MI values of 86.13 and 61.95, respectively. In Group 3, CRW29 is notable for its elevated MI value of 12.41. The contribution of individual metals to the MI calculation in group 1 reveals values exceeding one for waters are related to travertine springs in the region. However, the occurrence of As in natural waters is related to the water-rock interaction process (Kalender et al. 2015). Figure 5 illustrates the Metal Index (MI). Results show that 58% of all sampling points have values exceeding one. Group 1 exhibits the highest average MI value (44.99), Table 2 Pearson correlation coefficients between hydrochemical parameters in waters from Chahar Takab, Fariman county, northeast Iran pH EC CO3 2HCO3 -Cl-SO4 2Ca2+ Mg2+ Na+K+ pH 1 EC -0.61** 1 CO3 20.38 0.25 1 HCO3 --0.81** 0.88** -0.02 1 Cl--0.59** 0.98** 0.26 0.84** 1 SO4 2- -0.23 0.63** 0.37*0.50** 0.62** 1 Ca2+ -0.70** 0.67** 0.42 0.84** 0.65** 0.38*1 Mg2+ -0.62** 0.96** 0.10 0.85** 0.95** 0.58** 0.58** 1 Na+-0.57** 0.96** 0.24 0.83** 0.95** 0.61** 0.69** 0.90** 1 K+-0.50** 0.95** 0.37*0.78** 0.94** 0.66** 0.61** 0.87** 0.94** 1 * Significance at the significance level of 0.05 ** Significance at the significance level of 0.01 Fig. 3 Piper diagram of water samples collected in three groups of waters (group 1, travertine springs; group 2, surface water; group 3, groundwater) located in Chahar Takab, Fariman county, northeast Iran 1 3 129 Page 8 of 14 Environmental Earth Sciences (2025) 84:129 Beyond the immediate toxicity risks posed by heavy metal-contaminated drinking water, bioaccumulation can increase the risks to humans and other living beings. Some trace elements such As, Cd, Pb, and Hg can cause health problems even at low concentrations (Avigliano et al. 2019; Gupta et al. 2019). Conclusion This study highlights the importance of assessing the quality of groundwater, particularly in regions where it serves as a primary water source for human consumption and agricultural purposes. Chahar Takab village in Fariman county, northeast Iran, relies significantly on groundwater, with travertine springs playing a prominent role in the local water supply. This research reveals the water quality variability of different water sources (travertine springs, surface water, and groundwater) within the study area and key role of As (28.53), B (9.03), Fe (3.40), and Pb (1.21). A summary of non-potable samples and their parameters failing to meet the drinking water standards set by the World Health Organization (2022) and the European Union (2020) is provided in Table 3. Figure 6 illustrates the proportions of trace-elementsassociated risk classes within the 3 groups of water samples according to the guidelines proposed by the United Nations Economic Commission for Europe for the maintenance of aquatic life (UNECE, 1993), as described in Table 4. In summary, samples of group 1 have the highest toxicity risk, with three metals (As, Cd, Pb) having samples classified in class 2 or higher. In contrast, group 3 displays toxic risks for only two elements (Pb and Cd), and group 2 only for one element (Pb). Therefore, Pb shows toxicity in all groups, reaching class 4 in group 1. Cd exhibits toxic associated risks in group 1 and 3, reaching class 4 in group 1. Finally, As shows toxicity risk of class 2 in most of the samples of group 1. Cr, Cu, Ni and Zn fall completely in class 1 in all the groups and therefore, toxicity is not expected. Fig. 4 Concentrations of trace elements in three groups of waters (group 1: travertine springs, red; group 2: surface water, green; group 3: groundwater, blue) located in Chahar Takab, Fariman county, northeast Iran, and comparison with the World Health Organization’s drinking water limits (WHO 2022) indicated by black horizontal lines. If a horizontal line is not present, the limit exceeds the range of the graph or is not defined 1 3 Page 9 of 14 129