Evaluating Groundwater Metal and Arsenic Content in Piatra, North-West of Romania

The results for the physico-chemical content of the examined water samples (P1–P6) are presented in Table 1. As seen from Table 1, the electrical conductivity (EC) values for wells P1 to P6 exhibit a notable variation, suggesting diverse levels of ion concentration in the respective groundwater sources. Well P4 stands out with the highest conductivity at 1205 μS/cm, potentially indicating a higher concentration of dissolved ions or minerals. In contrast, wells P3 and P6 demonstrate the lowest conductivity values at 172 μS/cm and 252 μS/cm, respectively, suggesting a lower presence of dissolved ions. Wells P2, P5, and P1 fall in between, showcasing moderate electrical conductivity values of 398 μS/cm, 192 μS/cm, and 736 μS/cm, respectively. These variations could be attributed to geological factors, such as differing soil compositions or proximity to potential contamination sources, influencing the conductivity of the groundwater in each well. A previous study [46] on another well within the region registered much higher values (1575–2480 μS/cm), attributed to the interaction with aquifer rocks. EC serves as evidence of salt content in water, and the ingestion of water with elevated EC levels may contribute to a range of health issues, including but not limited to cancer, diarrhea, hepatitis, and gastroenteritis, impacting vital organs such as the heart, kidneys, and stomach [48].

Dissolved oxygen (DO) indicates water stratification and the contamination degree [49]. In this study, DO varied between 5.33 and 9.77 mg/L. Wells P3, P5, and P6 have relatively high DO concentrations, measuring 9.06 mg/L, 9.77 mg/L, and 9.55 mg/L, respectively. These elevated levels suggest favorable conditions for aerobic organisms and may indicate well-oxygenated water. Conversely, wells P2 and P4 show lower DO values at 5.65 mg/L and 5.33 mg/L, possibly indicating reduced oxygen availability in these wells. Well P1 falls in between, with a dissolved oxygen level of 6.79 mg/L. Discrepancies in these values may be ascribed to a variety of factors, including groundwater flow patterns, biological activities, and environmental conditions. The low amounts of DO (P2 and P4) lead to a lack of freshness, a fad taste, and unfriendly conditions of microorganisms that make the water not potable [50]. High amounts of DO (P3, P5, and P6) increase the organic suspended matter rich in pathogens [49,50].

pH ranged between 6.98 and 7.61, within the thresholds established for drinking water, indicating a weak acidic to weak basic character, which can indicate a low pollution level with organic and inorganic compounds [51]. Due to rock interaction and rich amounts of carbonates, pH has a basic character and changes the taste of water, possibly leading to skin and eye rashes [52]. Turbidity ranged between 1.14 and 8.75 NTU. Such variations in the turbidity levels across the six wells indicate differences in water clarity. Well P3 exhibits the highest turbidity at 8.75 NTU, suggesting a higher concentration of suspended particles or sediments in the water. P6 follows closely with a turbidity of 5.48 NTU, indicating moderately cloudy water. Wells P2 and P5 demonstrate moderate turbidity levels at 3.92 NTU and 2.56 NTU, respectively. P1 and P4 exhibit lower turbidity levels at 1.31 NTU and 1.14 NTU, suggesting relatively clear water. These variations in turbidity may be influenced by factors such as land use, soil composition, and human activities in the vicinity of each well. High turbidity levels can indicate potential contamination or natural sedimentation processes. Higher values may be caused by the presence of bacteria, plankton, iron and aluminum hydroxide, sludge, and colloidal matter. Water characterized by elevated turbidity posed an epidemiological threat because it facilitated the suspension of particles, serving as a medium for pathogens [40]. The consumption of water with high turbidity levels may result in health issues, particularly intestinal diseases, and can also induce distortion in aquatic ecosystems [53].

With the exception of P1, P4, and P6, all other samples are highly rich in NH₄⁺, almost two times the MAC established for the drinking water. The high amount is related to anthropogenic activities, for example, the intense use of fertilizers or fecal deposits. If consumed, water with NH₄⁺ in high amounts might cause convulsion, hepatic encephalopathy, coma, and death. Such water contaminated with NH₄⁺ can be treated through energetic chlorination and filtration process [63]. The NO₃⁻ concentrations are below the MAC (50 mg/L), between 1.28 and 4.21 mg/L (Table 1). The sources of NO₃⁻ include intensive agricultural practices, sewage and septic tank leakage, manure and contaminated sludge deposits, as well as microbial decomposition. Groundwater contamination with NO₃⁻ is influenced by the geological and hydrogeological structure. Consuming water rich in NO₃⁻ is linked to the onset of illnesses like cancer and methemoglobinemia [62]. As for chlorides, all wells are within the allowable limit, except for well P4, which has more than double the maximum allowable limit of 250 mg/L. The anomalous presence of heightened chlorine levels in a singular well, as opposed to others within the same town, underscores the complexity of localized water quality dynamics. Chlorides (salts of metals with hydrochloric acid), indicative of water salinity, are essential for the body’s electrolyte balance, but excessive salinity renders water unsuitable for drinking due to potential chemical aggressiveness [35]. PO₄³⁻ are lower than 0.4 mg/L, with potential sources represented by the intense use of fertilizers and detergents, but also with geogenic origin. An elevated phosphate concentration can change both the flavor and color of water [64]. Variations in the levels of ammonium, chlorides, nitrates, and phosphates among wells in the same close region or town can be attributed to diverse factors, including differences in geological formations, land use practices, and proximity to pollution sources. Additionally, variations in well construction, depth, and maintenance practices may influence the vulnerability of wells to contamination. These local factors influence the interaction of water with surrounding soils, rocks, and contaminants, contributing to the unique composition of each well and the resulting differences in water quality parameters. For example, one study [65] focuses on 10 wells from Remeti locality in very close proximity to Piatra town (the locale housing the six wells analyzed in the present paper). The ammonium levels reported in Remeti wells were up to more than four times higher than the MAC, presenting a maximum of 2.38 mg/L compared to the maximum in Piatra, which is P4 = 1.09 mg/L; also, in Remeti, phosphates were within admissible limits except for one well (0.78 mg/L) comparable to the ones in this study. Nitrate amounts were also excessively higher in wells from Remeti than in the P1–P6 samples in this study. This could be explained by more intense agricultural practices in the former compared to the latter, coupled also with the heavy practice in Romanian countryside involving the application of animal manure. Teceu locality is also in close proximity to Piatra town, and water analysis on a well in Teceu [46] revealed values for ammonium, chlorides, nitrates, and phosphates within the legal limits for potable water. However, it should be stated that [46] only analyzed one well in that specific town, which would be a limitation for stating the pollution levels for wells in the area.

The concentrations of major metals (Ca, Mg, Na, and K), of metals found at lower concentrations (Li, Al, Ba, and Sr), of heavy metals (Fe, Mn, Sn, Ti, Cr, Cu, Ni, Pb, and Zn), and As are shown in Table 2.

Calcium and magnesium are essential elements for the human body; thus, their presence in water is not typically a cause for concern, unless there are underlining medical conditions (i.e., kidneys). While their presence in high amounts leads to hard water, which is organoleptically changed, the World Health Organization (WHO) acknowledges that hard water has no known adverse health effects and may even contribute to the intake of essential minerals. However, the WHO does report that the taste sensitivity threshold for Ca²⁺ within the range of 100–300 mg/L, contingent on the accompanying anion, and it is likely that the taste threshold for magnesium is lower than that for calcium. In certain cases, consumers are known to tolerate water hardness exceeding 500 mg/L [66]. Here, the highest magnesium value is found in fountain P4, while the lowest value is found in well P3. All values fall within the maximum allowable limit of 50,000 μg/L. The presence of such ions, the presence of calcium- and magnesium-rich minerals in rocks and soils, and the characteristics of aquifers through which water flows. Also derived from geological source is potassium, with the highest level being observed in the water from fountain P4, while the lowest value is in the water from fountain P2. However, all values fall within the maximum allowable limit of 10,000 μg/L.

Aluminum (Al) stands out as the most prevalent metallic element found in the Earth’s crust. While poorly absorbed in the gastrointestinal tract, its bioavailability increases in drinking water, potentially impacting human health. According to Law 311/2004, the legal limit for aluminum content is 200 µg/L. One potential origin of aluminum is the application of Al₂(SO₄)₃ during the water treatment procedure [29]. Recognized as a neurotoxin on a broad scale, exposure to aluminum has been associated with neurodegenerative conditions, including Parkinson’s, Alzheimer’s, and multiple sclerosis. Studies indicate cognitive decline at Al intake ≥0.1 mg/day from water, with elevated levels posing an increased risk of cognitive impairment in the elderly, leading to heightened vulnerability to hip fractures and adverse health effects [67].

Manganese is also naturally abundant, and water rich in Mn is characterized by an unpleasant metallic taste and a muddy odor. The presence of manganese in the water distribution system forms deposits that can settle as a black precipitate [29]. According to Water Law 311/2004, the permitted limit for manganese content should not exceed 50 µg/L. The values obtained in the studied wells are low, ranging from 1.4 to 8.5 µg/L. Manganese originates from diverse sources, encompassing industrial practices like alkaline battery and cleaning product manufacturing, agricultural activities involving the application of fungicides, fertilizers, and pesticides, as well as mining operations.

Barium is a naturally occurring element that can be found in groundwater, including well water. While low levels of barium are generally considered to be naturally present and not harmful, elevated concentrations can pose health risks. Barium can enter groundwater through the weathering of certain rocks and minerals. Barium can deposit in muscles, lungs, and bones because it resembles calcium but is absorbed more quickly [41]. The highest barium value was observed in the water from fountain P4, while the lowest value was observed in the water from fountain P3. All values fell within the permissible limit, which is 7000 µg/L.

Arsenic is a toxic contaminant that is colorless, odorless, and tasteless and is commonly found in high concentrations in groundwater. Arsenic found in groundwater is susceptible to abrupt variations [29]. For this study, the measured values in groundwater vary between 0.22 and 9.8 µg/L. Wells P1, P3, and P6 exhibit arsenic concentrations well below the permissible limit at 5.4 µg/L, 0.22 µg/L, and 0.55 µg/L, respectively. Wells P2 and P5 approach the threshold with values of 8.5 µg/L and 6.3 µg/L, suggesting a moderate risk of arsenic exposure. P4 records the highest arsenic level at 9.8 µg/L, nearing the maximum limit and indicating a potential health concern. Communities relying on well water for drinking, particularly in rural areas, face heightened vulnerability to arsenic contamination. Geological conditions, often prevalent in rural regions, may lead to naturally occurring arsenic in aquifers. Limited resources for water monitoring and regulatory oversight contribute to the unknowing consumption of arsenic-contaminated water. Rural populations, dependent on wells and lacking alternative water sources, are at direct risk of health issues associated with arsenic exposure. Challenges in accessing clean water alternatives, agricultural practices, and a lack of awareness further compound the issue. Ingesting water containing a substantial amount of arsenic can result in significant immediate and/or prolonged health issues, including but not limited to vomiting, diabetes, heart diseases, cancer, spontaneous abortion, childhood cancer, and potential fatality [68]. Following ingestion, arsenic is swiftly absorbed by the gastrointestinal tract and undergoes metabolism. As for chromium, according to Water Law 311/2004, the legal limit is 50 µg/L. In this study, the obtained values varied between 1.7 and 55.8 µg/L. Sample P3 exceeds the legal limit of 50 µg/L, highlighting the need for immediate attention and remediation to ensure compliance with established water quality standards. The other samples, while below the legal limit, may still warrant monitoring and preventive measures to maintain water quality within acceptable levels. The variation in chromium levels, with higher concentrations in sample P3 compared to others in the same village, may stem from localized geological, anthropogenic, or hydrogeological factors. Chromium, a highly toxic heavy metal, is linked to health risks such as cancer, DNA damage, and oxidative stress. It is present in water in hexavalent (Cr(VI)) and trivalent (Cr(III)) forms, and Cr(VI) is especially toxic for individuals with respiratory issues [69].

In compliance with Water Law 311/2004, the permissible limit for nickel content stands at 20 µg/L. Recorded nickel values, ranging from 2.2 to 12.4 µg/L, are influenced by factors like pH, soil composition, and depth [29]. Acknowledged as a significant contributor to groundwater pollution by the U.S. Environmental Protection Agency, nickel’s potential toxic and health risks necessitate a comprehensive understanding of public safety [70]. Despite being a crucial element for the good functioning of enzymes, blood, the endocrine system, and gene synthesis, various studies highlight nickel’s disruptive impact on glucose metabolism and insulin secretion through biological mechanisms [70]. The presence of nickel in drinking water from wells can exert various influences on the surrounding environment. Nickel concentrations, when used for irrigation, may result in soil contamination, impacting plant health and altering the overall ecosystem in the well area. Interactions with the aquifer and subsurface geology can lead to the leaching of nickel into the well water from surrounding rock formations or anthropogenic sources. The overall groundwater quality in the well area is affected, posing concerns for both human consumption and agricultural use. Persistent contact with heightened nickel concentrations in drinking water poses health concerns, while the potential for corrosion or deterioration of well infrastructure adds another layer of concern.

According to Water Law 311/2004, the legal limit for lead content is 10 µg/L. The obtained lead content values ranged between 3.7 and 9.3 µg/L. Lead is one of the 275 priority-controlled pollutants by the U.S. and Chinese Environmental Protection Agencies [68]. Lead and its compounds can enter groundwater through mining activities. Lead is challenging to eliminate after its accumulation in the human or animal body because it can cause a diverse array of physical and mental issues [71,72]. The accumulation of lead in the human body causes damage to all organs, including the central nervous system, affects the liver, thyroid, and bones, and causes brain injuries and infertility [29,72]. Due to the physiology of the body, children, being more vulnerable than adults to lead contamination, suffer from constant brain damage, with approximately 18 million affected by lead poisoning [72]. Controlling lead pollution in drinking water is of vital importance [71].

As for copper, according to Water Law 311/2004, the legal limit is 100 µg/L. The highest value was found in well P6 (6.4 µg/L). Increased copper levels can arise from natural processes, like the breakdown of rocks, and human activities, including mining, industry, and agriculture. Drinking water containing elevated copper levels may result in stomach and headache discomfort, along with irritation of the eyes and nose [73]. Hence, monitoring the copper content is essential.

According to Water Law 311/2004, the legal limit for zinc content is 5000 µg/L. The zinc content at the sampling points is low. Sampling point P3 recorded double the zinc content (21.3 µg/L) compared to other points, probably due to a higher interaction of groundwater with rocks. Zinc, a naturally occurring element, undergoes slow enrichment in groundwater through interactions with rocks, influenced by inorganic carbon content and pH, and it is recognized for its significant mobility within water systems. Zinc exhibits opalescence and an astringent taste [29]. The mobility of Zn in water is predominantly affected by pH, with other factors like clay content, phosphorus availability, concentration of organic matter, and redox conditions also contributing to its behavior [74].

The strontium content in well water samples falls within the admissible limits of 200 µg/L for four of the six samples, namely P1, P2, P3, and P5. Wells P4 and P6 notably surpass the permissible limit, with sample P4 reading almost twice the legal amount, raising concerns about potential health risks associated with elevated strontium levels. The variations in strontium concentrations among wells in the same village could be attributed to geological factors, such as the composition of the subsurface rocks, which may contain higher concentrations of strontium. As this element is essential for general human health, it may be neglected in the overall water assessment. However, Sr has the potential to substitute for calcium and magnesium in bone, potentially impacting bone growth and strength. One study [75] emphasizes the noteworthy inverse correlation between the incidence of rickets in children and the Ca/Sr ratio in the potable water available for public consumption in China. A lower Ca/Sr ratio is associated with a higher incidence of rickets, suggesting a potential link between the calcium-to-strontium ratio and bone health in children. This finding underscores the importance of considering the Ca/Sr ratio in assessing the overall effect of strontium in the water supply for public consumption, particularly in regions with high strontium concentrations, to ensure adequate management and supervision of water quality.

Iron is the most problematic element in water. The water samples from 5 of the 6 wells analyzed fall below the legal limit of 200 µg/L, with values ranging from 132 (P5) to 195 (P2) µg/L. Sample P3, however, registers iron values of 225 µg/L, thus surpassing the allowed amount. These values indicate a potential issue with iron contamination in the well water. Elevated iron levels in drinking water can lead to several problems, including unpleasant taste, discoloration, and staining of plumbing fixtures. Additionally, high iron concentrations may indicate the presence of other contaminants or geological conditions that contribute to the contamination. The presence of higher iron levels could likely be attributed to the historical mining activities in Maramures County (different metalliferous resources including iron, copper, and manganese [76]), home to Piatra town and the six analyzed wells.

The HEI values depicted in Figure 4 varied in the range of 2.59 and 4.77 and can be classified as having a low pollution degree. The highest HEI value was calculated for P4 with 4.77, followed by P2 with 4.09, and the well with the lowest value of HEI was P1 (2.59). In the case of P4, Sr contributed the most to the HEI value (2.23), followed by As (0.98), Fe (0.88), and Pb (0.41).

An investigation into the extent of heavy metal contamination of dug and drilled wells in Seini town, NW Romania, reported higher HEI values than in the present study, ranging values between 1.5 and 14, still below 40, showing a low degree of pollution due to anthropic influences [40].

The computation of HEI provides a quick evaluation of the comprehensive quality of drinking water [79].

Table 3 displays the physico-chemical parameters employed in WQI computation, along with the corresponding parametric values, weights, relative weights, and the Q_i range.

Figure 5 illustrates the assessment of groundwater quality for wells P1–P6 using the WQI method. WQI scores ranged from 31.75 to 63.43, with a mean value of 43.68 ± 12.50. P1, P3, P5, and P6 were classified as having excellent water quality. P4, having a 50.97 score, was very close to being classified as excellent quality, and P2 water was in the good quality class.

The main contributors to the WQI scores were As with a score of WQI_As in the range of 0.64–24.88 with the highest value found for the P2 sample, Ni (1.6–9.08) with the highest value for P3, and Pb (10.83–27.23) with the highest value for P2. The high value of WQI for Cr was calculated for P3 (6.53) while P4 registered a high value for WQI_Sr (3.26). One study [46] stated that WQI indices, utilizing physico-chemical parameters of water, were employed to evaluate the water quality evolution of Teceu Lake. This lake is situated in the Upper Tisa protected area in the northwest of Romania, along with a groundwater source in close proximity. The assessment was conducted using WQI indices for the period spanning January to December 2022, presenting WQI in the range of 17.71–37.94 for groundwater source (excellent quality) while the WQI score of Teceu Lake water was between 22.95 and 146.31 and indicated excellent-quality, good-quality, and poor-quality water depending on the month in which the water samples were collected [46]. The WQI values showed an increasing trend during the month of the year, with maximum values in October and November, especially due to nutrient content, ammonium, and phosphates. In another investigation [40], focusing on Seini town in the northwest of Romania, WQI indices were derived from sixteen chemical indicators, encompassing key physico-chemical parameters, Al, and heavy metals. The findings revealed that 65% of the groundwater samples exhibited excellent quality, while the remaining samples demonstrated poor and very poor quality. This was attributed to elevated concentrations of NH₄⁺, NO₃⁻, Fe, Cu, and Pb surpassing the maximum allowable concentrations (MAC). Globally, WQI values ranging from 51.84 to 159.41 indicate that the water quality of four lakes situated in the Bangalore Urban district, the most densely populated district in the Indian state of Karnataka, falls within poor, very poor, and unsuitable categories. This assessment is based on the consideration of 10 parameters: pH, turbidity, total alkalinity, total acidity, total phosphorus, chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved oxygen (DO), nitrates, and total nitrogen [81]. Moreover, in Cameroon, the WQI scores of groundwater in the Ngoua watershed, the primary water supply source for Douala city, located at the shore of the Atlantic Ocean, vary between 2.12 and 187.21. In the computation of the WQI, the main physico-chemical indicators of water were considered: pH, turbidity, EC, total dissolved solids, salinity, and the concentrations of major cations and anions. The main contaminants in groundwater in the area were sulfates and nitrates [82].

The human health risk associated with P1–P6 groundwater consumption was assessed for adults (men and women) and children. The average CDI results of nitrogen compounds (NO₃⁻ and NH₄⁺), metals, and As were obtained in the following order: NO₃⁻ > NH₄⁺ > Sr > Fe > Cr > Pb > Ni > As > Cu. The highest values of CDI were found for NO₃⁻ in P6, with 0.12 mg/kg∙day for adults (men and women) and 0.51 mg/ kg∙day for children. High CDI values were calculated for NH₄⁺ in P4: 0.0245 mg/kg∙day for men and women and in P1 (0.0198 mg/kg∙day) in the case of men and women, while for children the CDI was 0.105 mg/kg∙day. Between metals and As, the highest CDI was obtained for Sr in P4, with 0.01 mg/kg∙day for adults and 0.042 mg/kg∙day for children. CDI for Cr in P3 was 0.0013 mg/kg∙day for men and women and 0.005 mg/kg∙day for children. A high value of CDI was obtained for As in P4: 0.00022 and 0.00094 mg/kg∙day for adults and children, and in P2: 0.00019 and 0.00081 mg/kg∙day for adults and children. The hazard quotients and hazard index due to groundwater intake are shown in Table 4.

The risk indices were applied for NH₄⁺, NO₃⁻, Sr, Fe, As, Cr, Cu, Ni, and Pb, for which the studied groundwater sources indicated high concentrations of these constituents around the MACs. Hazard quotient (HQ) values exceeded one for chromium in well P3 for both adults and children, as well as for children in groundwater sources P1–P4. High HQ Pb values for children showed that they are exposed to health risks due to water ingestion from all the groundwater sources investigated. The lowest HI values were assessed in the case of P6 (1.02 for adults and 4.74 for children), while the highest values were calculated for P3 groundwater. In the case of children, HQ values higher than one were computed for Cr in P1–P4, for Pb in all the groundwater sources, and for As in P1, P2, P4, and P5, and for Cu in P6. Other research indicated significantly higher HQ values for children compared to those calculated for adults [56,83,84].

Conversely, the health risk assessment of the groundwater sample in Seini town, NW of Romania, indicated HQ > 1 for NO₃⁻ in some of the samples but low values of HQ for Cu, Pb, and Mn [40]. Napo et al., 2021 [56], assessed the health risk associated with oral exposure to groundwater in Togo’s coastal sedimentary basin for males, women, and children, with a mean value of HQ of 0.963, 1.226, and 2.098, especially due to manganese, nitrate, arsenic, fluoride, and cadmium. The groundwater sources were affected by seawater intrusion, evaporite dissolution, and anthropogenic contamination. Moreover, groundwater in the Xinzhou Basin, situated in the semiarid region of central-eastern Shanxi Province in North China [83], was evaluated by computing the health risk posed by the contaminants NO₃⁻, NO₂⁻, and F⁻, which exceeded the standard limits in some of the samples and found HQ oral values of 0.02 to 2.14 for men, 0.02 to 2.72 for women, and 0.04 to 4.66 for children. Health indices provide a precise evaluation of water quality risks for human consumption. Examining multiple parameters enhances the accuracy of identifying contaminants and health concerns. Utilizing these indices guides effective mitigation strategies, facilitates informed decision-making, and ultimately safeguards the well-being of communities relying on well water sources for multiple purposes.