Hydrogeochemical and Geospatial Insights into Groundwater Contamination: Fluoride and Nitrate Risks in Western Odisha, India

Abstract

Fresh groundwater is essential for sustaining life and socio-economic development, particularly in regions with limited safe drinking water alternatives. However, contamination from natural and anthropogenic sources poses severe health and environmental risks. This research examines the health risks linked to groundwater quality in the agroeconomic region of Boudh district, Odisha, India, where residents depend on untreated groundwater due to limited access to alternative sources. A total of 82 groundwater samples were analyzed during pre- and post-monsoon of the year 2023 using multivariate statistical methods (PCA, correlation analysis) to determine pollutant sources and regulatory factors, while XRD was employed to characterize fluoride-bearing minerals in associated rock samples. Fluoride concentrations range from 0.14 to 4.6 mg/L, with 49% of samples exceeding the WHO limit of 1.5 mg/L, which raises significant health concerns. Nitrate levels fluctuate between 1.57 and 203.51 mg/L, primarily due to agricultural fertilizers. A health risk assessment (hazard quotient and hazard index) indicates that 63% of samples fall into the low-risk category, 21% into moderate-risk, and 16% into high-risk. Children (HI = 29.23) and infants (HI = 19.51) are at the greatest health risk, surpassing that of adult males (HI = 12.2) and females (HI = 11.2). Findings provide scientific evidence for policymakers to implement groundwater protection and remediation strategies. Immediate interventions, including water quality monitoring, defluoridation measures, and community awareness programs, are essential for ensuring long-term water security and public health.

1. Introduction

Water is increasingly threatened due to population growth, industrialization, and unsustainable exploitation [1,2]. Groundwater contributes nearly 62% to irrigation, 85% to rural water supply, and 50% to urban water supply [3]. With surface water dwindling, reliance on groundwater is rising, yet its availability varies due to geological and climatic factors [4,5]. By 2050, the global population will double, with India accounting for 87% of this increase [6]. Agriculture alone consumes over 60% of available water, intensifying competition [7]. India, with just 4% of the world’s freshwater but 16% of its population, faces a looming water crisis. Per capita water availability has plummeted from 5000 m³/year in 1947 to a projected 1000 m³/year by 2050 [8]. Overexploitation has led to groundwater depletion, declining well yields, rising extraction costs, and food security risks [9]. Contamination further exacerbates the crisis, with 80% of diseases linked to unsafe water [10]. Sustainable management is urgent. A conjunctive approach is key to balancing groundwater and surface water, artificial recharge, and conservation [11]. Advanced tools like remote sensing (RS), GIS, and geophysics enable precise aquifer mapping and recharge zone identification [12,13,14,15]. Technologies such as PC-based data storage, retrieval, analytical systems, and mathematical and solute transport modeling form the foundation of scientific groundwater management [16]. Automation of groundwater monitoring and real-time data transmission enhances decision-making, ensuring efficient and sustainable groundwater governance [17].

Groundwater contamination by fluoride and nitrate has emerged as a critical environmental and public health concern worldwide, leading to severe health conditions such as fluorosis and methemoglobinemia [18]. The natural dissolution of fluoride-containing minerals, such as fluorite, villiaumite, apatite, cryolite, micas, and hornblende, which are frequently found in igneous and sedimentary rocks, is the leading cause of fluoride’s presence in groundwater [19]. In addition to geogenic sources, human activities such as excessive fertilizer and pesticide application, improper sewage disposal, sludge deposition, and declining water tables further contribute to fluoride contamination [20,21]. Similarly, nitrate pollution in urban groundwater in urban areas is attributed mainly to agricultural runoff, particularly from chemical fertilizers and pesticides, and nitrate pollution is determined by dominantly leaking wastewater [22,23]. Health risk assessments play a crucial role in identifying the potential hazards associated with these contaminants [24]. However, limited research in India has focused on evaluating the long-term health risks associated with prolonged exposure to fluoride- and nitrate-contaminated groundwater [25,26].

Fluorosis is a widespread concern affecting several Asian countries, including Thailand, Bangladesh, China, India, Pakistan, and Sri Lanka, as well as many regions in Europe, North and South America, and Africa [27,28]. In India, fluoride-rich groundwater is prevalent across numerous states [29]. Northern India includes Jammu and Kashmir, New Delhi, Uttar Pradesh, Haryana, and Punjab, while Southern India faces contamination in Telangana, Andhra Pradesh, Karnataka, Tamil Nadu, and Kerala. In Western India, Gujarat, Rajasthan, and Maharashtra report high fluoride levels, whereas Central Indian states like Madhya Pradesh and Chhattisgarh also experience significant contamination. In Eastern India, fluoride-rich groundwater is affected by Odisha, Jharkhand, Bihar, Assam, and West Bengal [30,31,32].

Health risk assessment is essential for assessing the dangers of different contaminants in drinking water [33]. The assessment usually relies on the daily water consumption and the hazard quotient (HQ) of pollutants for various age groups, such as adults and children [34]. Studies indicate that HQ and total hazard index (HI) values reveal greater vulnerability among children and females due to their higher intake relative to body weight [35]. Furthermore, youngsters are most at risk for fluorosis, and HQ tends to decline with maturity.

Studies from China [36,37,38,39], Iran [40,41], Ghana [42,43], Indonesia, and Saudi Arabia [21,44,45,46] reinforce global concerns regarding groundwater contamination, highlighting that children are at greater health risk. Several studies have documented high HQ and HI values in India, particularly among children. This trend has been reported in Coimbatore City [47], Nirmal Province, South India [48], Raebareli District [49], Aurangabad District in Bihar [50], and different regions of Maharashtra [51].

The Boudh district and the rest of Western Odisha have certain defining features that make it particularly susceptible to groundwater contamination. The region’s granite, gneiss, and charnockite bedrocks are fluoride reservoirs because of the prolonged period of groundwater’s interaction with mineralized bedrock. At the same time, shallow water tables, extensive fertilizer usage in agriculture, and poor sanitation facilities add to the problem of nitrate intrusion. These factors, along with high reliance on untreated groundwater and the region’s susceptibility to drought, create a unique combination of natural and human-introduced risks.

Despite the increasing concerns over groundwater contamination in Odisha, limited studies have been conducted in the Boudh district to assess the severity and spatial distribution of fluoride and nitrate contamination. Existing groundwater quality studies in Odisha primarily focus on broader regional assessments, lacking detailed hydrogeochemical and health risk evaluations specific to hard rock terrains like Boudh. Additionally, while some research has examined fluoride and nitrate levels, comprehensive spatial mapping using geospatial techniques (GIS and RS) and health risk assessment (HQ and HI) remains scarce [52,53]. This study bridges the research gap by integrating hydrogeochemistry, spatial analysis, and health risk modeling to the following:

• To analyze the spatial variation in fluoride and nitrate concentrations in groundwater across the Boudh district.
• To investigate the geological and anthropogenic factors influencing groundwater contamination.
• To conduct a health risk assessment using hazard quotient (HQ) and total hazard index (HI) for different age groups.
• To employ remote sensing (RS) and GIS techniques for groundwater quality mapping and contamination hotspot identification.
• To propose sustainable groundwater management and mitigation strategies for the region’s safe drinking water supply.

This research integrates hydrogeochemistry, geospatial technology, and health risk assessment to address groundwater contamination in a drought-prone region. By providing a scientifically robust, data-driven evaluation of fluoride and nitrate contamination in the Boudh district, this study advances knowledge on groundwater quality. It contributes to sustainable water resource management in fluoride-prone regions.

2. Materials and Methods

2.1. Study Area

The study area, Boudh district, is an administrative district in Odisha (Figure 1), a state of India, comprising three blocks: Harabhanga, Boudh, and Kantamal. It is geographically bounded by 20°23′–20°52′ latitude N and 83°34′–84°48′ longitude E and falls under toposheet numbers 64 P/10, 11, 13, 14, 15 and 73 D/1, 2, 5, 6, 7, 10 and 11, covering an area of 3098 km².

Hard crystalline rocks from the Eastern Ghats Group predominantly occupy the Boudh district. Minor occurrences of sandstone, shale, laterite, and alluvium are observed. The hard rock includes biotite gneiss, porphyritic granite gneiss, granite, charnockite, khondalite, and amphibolite (Figure 2). Weathering is pronounced along fissures and joints. The charnockite rocks are compact and hard, with little weathering and poor water bearing. Granite and granite gneiss form hills and hillocks; the rocks form hills with well-developed joints and have limited groundwater development (Figure 2). In addition, weathered residuum and fractures within granitic formations serve as limited groundwater reservoirs, making the aquifers highly susceptible to overexploitation [54]. The rugged terrain and fissured rock structures lead to low rainwater infiltration, resulting in discontinuous aquifers with moderate to poor yields [55]. Frequent droughts and erratic rainfall patterns further aggravate groundwater scarcity in the region. Both natural and anthropogenic factors influence groundwater quality in the district. Geogenic sources, such as fluoride leaching from granite and gneiss formations, contribute to fluoride contamination, while nitrate contamination mainly arises from the extensive use of chemical fertilizers in agricultural practices. Some groundwater samples have also recorded localized occurrences of elevated iron concentrations. The district experiences extreme climatic conditions, with very hot summers reaching 45 °C and cold winters dropping to 4 °C, reflecting significant seasonal temperature variations. The average annual rainfall is approximately 1510 mm, with the southwest monsoon contributing 76% of the precipitation. Boudh district has five classes of land use, namely forest (182,995 hect.), agricultural land (8438 hect.), wasteland (7406 hect.), settlement, and water bodies, which have been interpreted from the Landsat-8 satellite imageries (Figure 3). The district is covered with forest (182,995 hect.), which accounts for 41.22% of the total area, indicating more than the state average, i.e., 30%. As per the 2011 Census, the district had a population of approximately 441,162, which is projected to rise to around 530,800 by 2025.

The important subsurface geological features, such as fractures, faults, foliation, etc., which control the occurrence, distribution, and movement of groundwater, have been identified and mapped. This has helped in delineating the aquifer geometry. It is found that the aquifers exhibit a wide variation in nature and geometry from place to place. Unconfined aquifers restricted within the weathered zone formed in the entire area except rocky outcrops up to a depth of 25 m below ground level. A semi-confined or confined aquifer develops in a fracture region at a depth of 100 m below ground level. The cross-sectional profile diagram of different blocks shows the aquifer disposition zone (Figure 4). The analyses of the survey indicated that the entire population of the region depends on groundwater for drinking, domestic consumption, and agriculture. The water present in the semi-confined zone in the fractured rock joints goes up to a depth of 100 m below ground level. Groundwater occurs in unconfined, semi-confined, and confined states.

2.2. Methodology

Groundwater samples were collected from 82 borewells and dug wells within the village area of Boudh district during the pre-monsoon and post-monsoon periods of 2023 (Figure 1). All groundwater samples were collected from rural settlement areas across Boudh district, as other parts of the region were inaccessible due to logistical and terrain constraints. The samples were drawn from dug wells and deep borewells, with the borewells typically reaching depths of approximately 300 feet (91 m). These wells are primarily used for domestic and agricultural water supply. Sampling locations were selected to ensure spatial coverage across all accessible rural settlements in the district, with attention to areas of reported groundwater use and suspected contamination risk. This research focuses on hydrogeological investigations and groundwater management in the Boudh district, Odisha, where limited studies have been conducted. A comprehensive geological, geochemical, and hydrological dataset was generated using advanced tools such as remote sensing (RS), GIS, and multivariate statistical techniques [56,57]. These tools helped analyze groundwater conditions and formulate strategies for its sustainable management in this drought-prone region.

Rock analysis is a crucial tool for geological research. When examining geological materials, researchers typically conduct two types of studies: chemical analysis and mineralogical or physical analysis. In this study, mineralogical research was conducted using X-ray diffraction (XRD) and optical microscopes (transmitted light) to investigate mineral phases and textures. Optical microscopy was used to study the mineralogy of rocks. The LEICA DM 2500 P microscope (Leica Microsystems, Wetzlar, Germany), which features both transmitted and reflected light systems, facilitated the identification of the rock samples. The results of optical microscopy were validated by X-ray diffraction (XRD) examination. In this procedure, a crystal with lattice planes spaced apart by a distance “d” was exposed to X-rays of a specified wavelength. At particular angles (θ), the X-rays are diffracted according to Bragg’s equation,

nλ = 2d sin θ

(1)

where

λ is the wavelength of the X-rays;

θ is the diffraction angle;

d is the interplanar spacing.

Using the measured 2θ diffraction angles, the corresponding values were calculated. These values were then compared with the JCPDS data book (1980) for mineral identification [58].

The purpose of conducting XRD and microscopic analysis was to identify fluoride-bearing minerals such as fluorapatite, biotite, and hornblende in the local geology (

Table 1. XRD operating parameters used for mineralogical analysis.

Name of Unit	Rigaku Created Ultima IV with a Graphite Monochromator, Automated Slit, and Receiving Slit.
Target used	Cu Kα
Scanning rate	1°/min
Tube voltage	30 Kv
Current	40 Ma
Range	2 × 103 cps

). This supports the hydrogeochemical investigation by establishing mineralogical evidence for fluoride release into groundwater via water–rock interaction in granitic and gneissic aquifers.

To assess the dataset’s distribution and central tendency, the physicochemical properties of groundwater were examined using several statistical measures, including mean, median, mode, and standard deviation. Higher SD values indicate more variability within the dataset. The standard deviation (SD) quantifies the degree to which the data deviates from the mean. Excel Software 3.8.3 was used to calculate the SD.

The coefficient of correlation (R²) represents the squared value of the coefficient of multiple correlations, ranging from 0 to 1, and helps in understanding the strength of relationships among variables.

To investigate geochemical processes influencing groundwater composition, multivariate factor analysis was conducted using Principal Component Analysis (PCA) and correlation matrix analysis for both pre-monsoon and post-monsoon periods, employing IBM SPSS 25 [59,60]. The correlation coefficient matrix was generated to assess interrelationships among different measured parameters. The PCA was performed using hydrogeochemical parameters including fluoride (F⁻), nitrate (NO₃⁻), iron (Fe), pH, EC, Ca²⁺, Mg²⁺, and TDS, based on 82 groundwater samples collected during the pre- and post-monsoon seasons of 2023. PCA was used to transform original variables into uncorrelated new variables (principal components), with varimax rotation applied to obtain a rotated component matrix. In this study, eigenvalues above one were considered significant for interpretation.

An assessment was also conducted to evaluate the non-cancer health risks linked to groundwater fluoride (F⁻) and nitrate (NO₃⁻) contamination [61,62]. This health risk evaluation focused on four demographic groups based on age: female adults, male adults, children, and infants. The chronic daily intake (CDI) for both fluoride and nitrate was determined using the following equations:

$${{\mathrm{CDI}}_{\mathrm{F}}}^{-}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{F}-}\times \mathrm{I}\mathrm{r}\times \mathrm{E}\mathrm{d}\times \mathrm{E}\mathrm{f}}{\mathrm{B}\mathrm{w}\times \mathrm{E}\mathrm{t}}}$$

(2)

$${\mathrm{CDI}}_{{{\mathrm{NO}}_3}^{-}}={\displaystyle \frac{{\mathrm{C}}_{{{\mathrm{N}\mathrm{O}}_3}^{-}}\times \mathrm{I}\mathrm{r}\times \mathrm{E}\mathrm{d}\times \mathrm{E}\mathrm{f}}{\mathrm{B}\mathrm{w}\times \mathrm{E}\mathrm{t}}}.$$

(3)

The Health Hazard Quotient (HHQ) for fluoride and nitrate was determined as follows:

$${\mathrm{H}\mathrm{H}\mathrm{Q}}_{{\mathrm{F}}^{-}}={\displaystyle \frac{{\mathrm{C}\mathrm{D}\mathrm{I}}_{{\mathrm{F}}^{-}}}{{\mathrm{R}\mathrm{f}\mathrm{D}}_{{\mathrm{F}}^{-}}}},$$

(4)

$${\mathrm{H}\mathrm{H}\mathrm{Q}}_{{{\mathrm{N}\mathrm{O}}_3}^{-}}={\displaystyle \frac{{\mathrm{C}\mathrm{D}\mathrm{I}}_{{{\mathrm{N}\mathrm{O}}_3}^{-}}}{{\mathrm{R}\mathrm{f}\mathrm{D}}_{{{\mathrm{N}\mathrm{O}}_3}^{-}}}}.$$

(5)

The overall Health Index (HI) was calculated as follows:

$${\mathrm{H}\mathrm{I}=\mathrm{H}\mathrm{H}\mathrm{Q}}_{{\mathrm{F}}^{-}}+{\mathrm{H}\mathrm{H}\mathrm{Q}}_{{{\mathrm{N}\mathrm{O}}_3}^{-}}.$$

(6)

All the equations are derived from the previous studies on the topic analyzed in this study [63,64].

3. Results

The drinking water quality was assessed by comparing the physicochemical characteristics of groundwater samples with the guidelines established by WHO (2017) and ISI (1983) [65,66]. Whereas some water samples had higher than allowed levels of fluoride (F⁻), nitrate (NO₃⁻), iron (Fe), turbidity, and total hardness (TH), all samples had concentrations of calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), sulfate (SO₄), chloride (Cl), and total alkalinity.

3.1. Physicochemical Characteristics of Groundwater

Table 2. Physicochemical characteristics of groundwater samples [65].

Parameter	Desirable	Permissible	Range	Inference
pH	6.5	8.5	7.28–8.5	Slightly alkaline, it affects solubility.
Turbidity	1	5	0.27–11.00 NTU	High values indicate suspended particles.
Sodium (Na)	50	200	39–207.5 mg/L	Higher levels may impact taste and BP.
Potassium (K)	10	12	1.3–13.15 mg/L	Possible agricultural/industrial contamination.
Calcium (Ca)	30	200	16.5–285.6 mg/L	Contributes to hardness and causes scaling.
Magnesium (Mg)	30	120	2.2–140.34 mg/L	This leads to hardness and affects taste.
Chloride (Cl)	250	1000	15–915 mg/L	High values may indicate saline intrusion.
Sulfate (SO4)	200	300	1.04–152.03 mg/L	Excess may cause laxative effects.
Iron (Fe)	-	1	0.18–2.25 mg/L	A total of 11.2% of samples exceed the permissible limit, affecting taste and staining.
Total Dissolved Solids (TDS)	500	1000	240–2143 mg/L	A total of 20% of samples are brackish, affecting potability.
Total Hardness (TH)	200	600	50–1291 mg/L	A total of 50% of samples are very hard, requiring treatment.
Total Alkalinity	200	600	285–607 mg/L	Indicates the buffering capacity of water.
Bicarbonate (HCO3−)	100	250	115.5–608.5 mg/L	High levels in 50% of samples, affecting hardness.
Carbonate (CO32−)	100	250	0–171.5 mg/L	Influences alkalinity and water hardness.
NO3 (mg/L)	45	45	1.57–203.51 mg/L	A total of 16% of samples in the high-risk category are linked to agricultural fertilizers and waste oxidation.
F (mg/L)	1	1.5	0.14–4.6 mg/L	Exceeds WHO limit (1.5 mg/L) in some samples; causes fluorosis at high levels.

summarizes key physicochemical parameters of groundwater in the study area. Each parameter and its significance in water quality is as follows:

pH (7.28–8.5): Indicates the acidity or alkalinity of water. The slightly alkaline nature suggests good buffering capacity and minimal risk of corrosiveness but may affect the solubility of minerals.

Turbidity (0.27–11.00 NTU): Measures water clarity. Higher turbidity may indicate the presence of suspended particles, organic matter, or microbial contamination, which can impact water quality and treatment processes.

Sodium (Na) (39–207.5 mg/L): An essential electrolyte, but excessive levels may contribute to salinity and affect the taste of water. Prolonged high sodium intake can be a concern for individuals with hypertension.

Potassium (K) (1.3–13.15 mg/L): A vital nutrient for human health. Found in natural waters at low concentrations, but elevated levels may indicate contamination from fertilizers or industrial activities.

Calcium (Ca) (16.5–285.6 mg/L): A key component in water hardness. Higher concentrations contribute to scaling in pipes and appliances but are not harmful to human health.

Magnesium (Mg) (2.2–140.34 mg/L): Another major contributor to water hardness. It is essential for human metabolism, but excessive amounts can lead to a bitter taste and scaling in plumbing systems.

Chloride (Cl) (15–915 mg/L): Affects the taste of water. Elevated levels can indicate saline water intrusion, industrial pollution, or agricultural runoff, though all samples remain within permissible limits.

Sulfate (SO₄) (1.04–152.03 mg/L): Important for biological functions, but high concentrations can cause a laxative effect and an unpleasant taste. The values found are within safe limits.

The groundwater of Boudh district has noteworthy differences in physicochemical properties, as summarized in Table 2. pH values from 7.28 to 8.5 indicate slight alkalinity, which tends to help dissolve minerals, especially fluoride. There is wide variation in turbidity, where some locations surpass the esthetic level, which indicates the possible presence of suspended solids or organic matter. Sodium and potassium concentrations are moderate to high, which may result from agricultural or domestic drainage. Hardness-related ions such as calcium and magnesium are present in considerable quantities, making the water very hard in some parts, though not directly harmful to health. Some elevated chloride levels in a few samples might suggest a minor saline influence on sulfate, which is acceptable throughout the study area. The data suggest spatial variability, with some sites exhibiting parameters that raise concerns about palatability and health.

3.2. Water Quality Concerns

The analysis of water samples for iron (Fe) indicates concentrations from 0.18 to 2.25 mg/L, with 11.2% of the samples exceeding the maximum permissible limit. The Total Dissolved Solids (TDS) concentration ranges from 240 to 2143 mg/L, resulting in 80% of groundwater samples being classified as fresh and 20% as brackish. Villages with TDS levels over 1000 mg/L include Charichhaka, Puruna Katak, Lunibahal, Bohira, Sampoch, Biranarsinghpur, Bamanda, Sarasara, Kantamal, Kultajore, Murusundhi, and Jogindrapur.

Total hardness (TH) values vary between 50 and 1291 mg/L. According to the TH classification, 1.2% of the samples are categorized as soft, 7.3% as moderately hard, 23.17% as hard, and 50% as very hard. The total alkalinity in groundwater ranges from 285 to 607 mg/L. Bicarbonate (HCO₃⁻) concentrations range from 115.5 to 608.5 mg/L, while carbonate (CO₃²⁻) levels range from 0 to 171.5 mg/L, with nearly half of the samples exhibiting elevated HCO₃⁻ concentrations. In the northeastern villages, the groundwater is primarily classified as hard to very hard (Table 2).

3.3. Spatial Distribution of Nitrate and Fluoride

Nitrate contamination in groundwater primarily originates from anthropogenic activities such as the oxidation of nitrogenous waste in human and animal excreta, wastewater irrigation, and the excessive use of inorganic fertilizers and manure [67,68]. In the study area, nitrate concentrations range from 1.57 to 203.51 mg/L (

Table 3. Nitrate and fluoride contamination in groundwater.

Parameter	Range	Inference
Nitrate (NO3−)	1.57–203.51 mg/L	A total of 16% of samples in the high-risk category are linked to agricultural fertilizers and waste oxidation.
Fluoride (F−)	0.14–4.6 mg/L	Exceeds WHO limit (1.5 mg/L) in some samples; causes fluorosis at high levels.

). A significant proportion of the samples (63%) fall within the low-risk zone, while 21% are categorized as moderate risk and 16% as high risk. The high nitrate levels, particularly in villages such as Adenigarh, Charichhaka, Lunibahal, Sarasara, and Kantamal, are closely associated with agricultural practices and shallow groundwater tables, making them more susceptible to contamination.

Groundwater fluoride concentrations can be found between 0.14 and 4.6 mg/L, while levels exceeding 50 ppm are pretty unusual. The WHO (2017) [65] indicates that the safe limit for fluoride in drinking water is 1.5 mg/L. Some samples surpass this limit in the area studied, which may lead to health risks like fluorosis, affecting both teeth and bones. The primary contributors to fluoride in groundwater are the dissolution of fluoride-rich minerals, including fluorite, apatite, biotite, hornblende, and muscovite. The chemical weathering of these minerals releases fluoride into the groundwater, further exacerbated by local hydrogeological conditions.

The percentage of samples along with fluoride (F⁻) concentration in the Boudh area is given below, and the iso-concentration map is shown in Figure 5. The dissolution of fluoride-bearing minerals in groundwater contributes to fluoride contamination, as represented by the following geochemical reactions:

Fluorite: CaF₂ + 2NaHCO₃ → CaCO₃ + 2Na⁺ + 2F⁻ + H₂O + CO₂.

(7)

Apatite: Ca₅(PO₄)₃₂ (F, OH) → Ca₅(PO₄)₃ (OH)₂ + 2F⁻.

(8)

Biotite: K(Mg, Fe)₃ (AlSi₃O₁₀)O₁₀F₂ + 2OH⁻ → K(Mg, Fe)₃ (AlSi₃O₁₀) (O₁₀) (OH)₂ + 2F⁻.

(9)

Hornblende: Ca₅Mg₅(Si₆Al₂O₂₂)F₂ + 2OH⁻ → Ca₅Mg₅(Si₆Al₂O₂₂) (OH)₂ + 2F⁻.

(10)

Muscovite: K(Mg, AlSi₃O₁₀)F₂ + 2OH⁻ → K(Mg₃(AlSi₃O₁₀) (OH)₂) + 2F⁻.

(11)

The fluoride (F⁻) concentration in groundwater samples from the Boudh area varies significantly.

Table 4. Fluoride concentration in samples.

Fluoride (F−) Concentration (mg/L)	Percentage of Samples (%)
<0.5 ppm (not desirable)	35.36
0.5–1.5 ppm (permissible)	36.58
>1.5 ppm (above permissible)	28.04

shows the percentage distribution of samples based on fluoride levels.

Figure 6 depicts several villages, including Karanjkata, Chhatranga, Harabhanga, Trilochanapur, Sampoch, Bilaspur, Ambagaon, Ailachula, Jogindrapur, Damodarpur, Charichhaka, Tambasena, Bagchipara, Nedisahi, Jharkamal, and Barajhuli, with fluoride concentrations over the allowable limit of 1.5 mg/L.

3.4. Geological Investigation

Microscopic analysis of rock samples reveals the mineral composition and characteristics of different rock types, including granite, charnockite, and granite gneiss, which exhibit significant mineralogical variations. These rocks mainly consist of quartz, plagioclase, feldspar, biotite, hypersthene, hornblende, pyroxene, and apatite. Quartz, feldspar, hypersthene, and plagioclase are essential minerals, whereas hornblende, biotite, and apatite serve as accessory minerals.

A thin-section analysis of granite gneiss shows that it contains quartz, microcline, biotite, and apatite. In charnockitic rocks, pyroxene appears as anhedral to subhedral porphyroblasts, filling the spaces between quartz, plagioclase, and alkali feldspar. Apatite, hornblende, and biotite serve as fluoride-bearing minerals, actively participating in rock–water interactions that release fluoride ions into the groundwater system.

A comprehensive geological investigation was conducted, including petrographic studies (megascopic and microscopic analysis) and X-ray diffraction (XRD) analysis of rock samples collected during fieldwork. These geological studies provided insights into rock types, bed orientations, fractures, faults, shear zones, intrusions, and topography, which are critical for assessing the groundwater potential of the study area.

3.5. XRD Analysis

The XRD patterns of different rock types exhibit minor variations. XRD analysis confirms the presence of fluoride-bearing minerals, including apatite [Ca₅(PO₄)₃(F, Cl, OH)], fluorapatite [Ca₅(PO₄)₅F], biotite, and hornblende, in granite and gneiss (

Table 5. Hazard quotient (HQ) and total hazard index (HI) for different age groups.

Age Group	HQ (Fluoride)	HQ (Nitrate)	Total HI
Infants	0.01–2.56	0.04–5.71	0.14–8.27
Children	0.12–2.96	0.05–6.61	0.17–9.57
Male Adults	0.08–2.19	0.03–2.89	0.12–7.08
Female Adults	0.08–2.07	0.03–4.62	0.11–6.69

). Rock powder samples were indexed using major peak profiles (Figure 7), which closely match the lattice parameters reported for fluorapatite.

Although biotite and hornblende contain lower fluoride concentrations than fluorapatite and apatite, prolonged rock-water interactions facilitate the leaching of fluoride into groundwater, contributing to its enrichment in granite and granite gneiss regions.

Fluoride-bearing minerals, including fluorapatite, apatite, biotite, and hornblende within granite and gneissic lithologies, strongly correlate with increased fluoride concentrations in groundwater samples collected from these geological regions. This corroborates the assumption that the release of fluoride is primarily controlled by the dissolution of minerals on rocks over time, particularly in the case of rock-water interactions in enduring rock aquifers with extended water residence times.

3.6. Hydrogeochemistry

3.6.1. Genesis of Groundwater Chemistry

According to [69] Gibbs’ (1970) diagram, all groundwater samples fall within the rock-dominance field, indicating that the lithology of the area primarily controls the groundwater chemistry. The high concentrations of sodium (Na) and calcium (Ca) in groundwater result from the abundance of plagioclase compared to mafic minerals. At the same time, potassium (K) and magnesium (Mg) primarily originate from mafic minerals. The dominant anion in the groundwater is bicarbonate (HCO₃⁻). Nitrate (NO₃⁻) in groundwater is attributed mainly to agricultural activities, especially the leaching of nitrogen-based fertilizers used in crop cultivation. In addition, minor contributions may be derived from the aerobic decomposition of organic matter within the soil zone (Figure 8).

The groundwater’s fluoride (F⁻) content is attributed to the weathering of fluoride-bearing minerals, such as apatite, fluorapatite, hornblende, and biotite, present in granites and gneisses. Additionally, fluoride ions (F⁻) can substitute hydroxide (OH⁻) ions in clay minerals, leading to fluoride enrichment in groundwater circulating through these minerals. Furthermore, weathering parent rocks at shallow depths may trigger ion exchange adsorption reactions in clay minerals, contributing to elevated fluoride concentrations in groundwater.

3.6.2. Principal Component Analysis (PCA)

The PCA was conducted to assess the interdependence among groundwater samples and identify the significant processes influencing water chemistry [66]. Factor scores were utilized to determine the regional distribution of dominant hydrogeochemical processes or sources of key components (Figure 9).

The PCA model identified four dominant factors, collectively explaining 80.23% of the total variance, with Factor 1 contributing the highest variance at 41.64% (Figure 10).

Factor 1: Strongly correlated with EC, TDS, TH, Cl⁻, Mg²⁺, Ca²⁺, Na⁺, SO₄²⁻, and NO₃⁻, indicating the dissolution of carbonate, sodic pyroxene, biotite, gypsum, and garnets, which are primarily found in granite gneiss. The presence of NO₃⁻ (extraction value: 0.492) suggests an additional agricultural influence as a possible source.

Factor 2: Dominated by pH, TA, HCO₃⁻, and F⁻, indicating leaching from fluoride-rich minerals under varying pH conditions. Fluoride is associated with granite, granite gneiss, pegmatite, and amphibolite rocks, particularly in the eastern part of the study area, where granite gneiss is predominant.

Factor 3: Shows a positive correlation with pH, K, and CO₃²⁻, representing potassium (K) release from feldspars due to increasing pH conditions, leading to the formation of carbonate ions (CO₃²⁻) in groundwater.

Factor 4: Associated with Fe and turbidity, representing the dissolution of lithogenic materials and the formation of iron oxides, contributing to increased turbidity in groundwater.

3.6.3. Non-Carcinogenic Human Health Risks

The health risks linked to drinking groundwater contaminated with fluoride (F⁻) and nitrate (NO₃⁻) are a significant concern in arid and semi-arid regions of India. Residents in the area under study rely on groundwater for drinking and cooking. Some villages have fluoride levels exceeding 1.5 mg/L and nitrate levels surpassing 45 mg/L.

The HQ values indicate that infants and children are at the highest risk due to fluoride and nitrate exposure from groundwater. Infants and children are more vulnerable to health hazards than adults due to their lower body weight. Among the lower age groups, children are more susceptible than infants due to their higher intake of groundwater and higher exposure duration. The HI values are also significantly high in these groups, exceeding the safe limit of HI = 1, which suggests potential health risks. Children exhibit the highest HQ and HI values, making them the most vulnerable due to their higher groundwater intake and longer exposure duration. Infants also face a substantial risk, though slightly lower than children. Adults (male and female) have comparatively lower HQ and HI values. Still, the HI values exceed 6 in some instances, indicating serious non-carcinogenic health concerns under worst-case exposure scenarios.

The spatial distribution of HQ and HI closely aligns with the areas of high fluoride and nitrate concentrations (Figure 11, Figure 12 and Figure 13), suggesting that geogenic and anthropogenic sources contribute to groundwater contamination. The findings emphasize the urgent need for mitigation strategies to reduce health risks, particularly for the younger population.

4. Discussion

The analytical results indicate significantly elevated levels of nitrate (NO₃⁻) and fluoride (F⁻) in groundwater at multiple locations within the study area, posing serious non-carcinogenic health risks. The HQ values for fluoride and nitrate exposure reveal that infants and children face the highest risk, with HI values exceeding 1 in several cases, indicating potential adverse health effects. The risk decreases with age due to differences in body weight, exposure duration, and intake rates. However, adults are still vulnerable under worst-case exposure conditions, highlighting the long-term health implications of groundwater contamination.

Health risk assessment using deterministic methods identified the highest hazard quotients (HQ) in infants and children, with values exceeding the safe limit of 1 in multiple cases.

HHQ < 1: Indicate a low risk of adverse effects.

HHQ = 1: Indicates potential or significant health risks that need further evaluation.

HHQ > 1: Suggests potential or significant health risks requiring further evaluation and management interventions.

High nitrate contamination in drinking water poses risks of certain cancers, diabetes, reproductive disorders, and other health issues. Similarly, 5–10 mg/L fluoride levels can cause non-skeletal fluorosis, affecting soft tissues and organ systems. Long-term exposure to 10 mg/L from birth to adolescence has been linked to infertility, hypertension, arthritis, neurological disorders, cancer, and thyroid dysfunction. The spatial distribution of health risks closely follows the fluoride and nitrate concentration patterns, emphasizing the role of geogenic and anthropogenic contamination sources. The reverse spatial distribution of fluoride and nitrate across the Boudh district is caused by land use and lithology variations. Higher fluoride concentrations in the eastern part are mainly due to the presence of Khondalite and Charnockite formations, which are known to liberate fluoride during water–rock interaction. These hard rock areas are characterized by low permeable porosity and subsequently increase the dissolution of fluoride due to longer residence time. In addition, higher nitrate concentrations in the western part correspond with the agricultural land use-dominated region. Intensive application of nitrogenous fertilizers, accompanied by shallow groundwater levels, increases susceptibility to nitrate pollution. This regional difference demonstrates the multifaceted interplay between geological factors and human activities concerning the degradation of groundwater quality. The distinction clearly illustrates the difference in the origins of the two contaminants. Fluoride contamination in groundwater has a geogenic origin, resulting from the weathering of fluorapatite and biotite in hard rock gneiss, granite, and charnockite formations. On the other hand, nitrate pollution emanates from anthropogenic sources, primarily from over-application of nitrogen fertilizers in agriculture, poor waste management practices, and open sanitation systems. Understanding this distinction is critical for developing appropriate mitigation strategies for specific sources.

The high fluoride concentrations in shallow aquifers necessitate drilling borewells to depths of 100–120 m to access deeper, safer groundwater sources. Since groundwater is the primary drinking water source in the region, regular quality monitoring at the village level is crucial for ensuring safe consumption. Establishing water quality testing facilities will help identify contaminated sources and facilitate necessary mitigation measures to protect public health.

Along with source origins, the hydrogeochemical system significantly governs the mobility of contaminants. Fluoride is usually found in elevated concentrations in association with groundwater having a pH of 7.5–8.5, as it is more alkaline. This increase enhances desorption from mineral surfaces, increases solubility, and weakens the stranglehold of certain minerals on calcium. Furthermore, low calcium concentration in groundwater also weakens fluorite precipitation, increasing the fluoride in its dissolved form. On the other hand, the hydrological and land use conditions exert some control over the nitrate concentration. Shallow groundwater and permeable soils in cultivated areas allow for more downward leaching of nitrogen fertilizer and organic matter, worsening nitrate contamination. These hydrogeochemical conditions explain other spatial and seasonal patterns in the region.

To combat fluoride contamination, defluoridation technologies must be implemented in affected areas. Advanced methods such as reverse osmosis (RO) systems and adsorption-based technologies are highly effective, while activated alumina filters offer a cost-effective household solution. Alternatively, for long-term sustainability, defluorination methods, such as selective ion-trapping matrices and bioremediation using fluoride-absorbing plants, should be explored. Groundwater recharge measures, including rainwater harvesting and artificial recharge structures, can help dilute fluoride concentrations while ensuring sustainable water availability. These eco-friendly solutions are crucial in reducing contamination and promoting safe drinking water.

Similarly, high nitrate levels in groundwater, particularly dug wells, pose a serious health risk, mainly due to excessive fertilizer use, improper sewage disposal, and poorly managed latrine pits in rural areas. Reducing non-point source pollution through sustainable agricultural practices, organic farming, and improved sanitation infrastructure is essential. Additionally, abandoned dug wells should not be used for waste disposal, and hygiene around active borewells must be maintained to prevent contamination.

Beyond technological interventions, nutritional strategies can help mitigate fluorosis effects. A calcium-, vitamin C-, and antioxidant-rich diet can counteract fluoride toxicity, while the cultivation and consumption of fluoride-combating crops such as maize and drumstick (Moringa) provide additional benefits. Furthermore, reducing phosphate-based fertilizers, which contribute to fluoride contamination, should be encouraged. Regular water testing should be mandatory for newly drilled borewells to ensure safe drinking water. Public health authorities must raise awareness about the risks of contaminated water and promote groundwater management. Village-level awareness campaigns, school-based education programs, low-cost household water treatment solutions, and health screening camps can reduce exposure to contamination. Collaboration among government agencies, NGOs, and self-help groups is essential for long-term water safety initiatives.

The results of this research coincide with local studies conducted in the hard rock regions of Jharkhand and Chhattisgarh. One study noted high fluorine concentrations in the Palamu district of Jharkhand, attributing it to the weathering of granitic and gneissic rocks during alkaline processes [70]. In the same way, another study documented fluoride contamination in the Dongargaon block of Chhattisgarh primarily due to prolonged water–rock interaction in crystalline aquifers [71]. In Odisha, specifically in Bolangir and Nuapada districts, shallow nitrate aquifers are blighted due to fertilizer application, poor sanitation, and overstressed sanitation [72]. These observations strengthen the fact that two processes are acting simultaneously in the Boudh district, one of them being geogenic lithology and the other human-induced activities in the region.

The study results were aligned with known international patterns within areas with similar socioeconomic and hydrogeological difficulties. For instance, one study discussed the vulnerability of rural populations within Southeast Asia and the Pacific region due to their reliance on untreated groundwater and insufficient surveillance of fluoride and nitrate contaminants [5]. Further studies identified fluoride leachate sinks in the crystalline aquifers of Ghana, where mobilization was linked to pH, lithology, and extended rock–water interaction conditions observed in Boudh [19]. A global study documented co-occurring fluoride and nitrate contamination, where more than 25% of groundwater samples showed elevated nitrate concentrations. The health impact of such contamination, mostly on children and infants, was underscored in our HQ and HI assessments [23]. Another study remarked on the overwhelming burden of global nitrate contamination resulting from agricultural practices and insufficient sanitation infrastructure, widely observed in our study area [10]. These analogies augment the rationale behind our findings and highlight the need for tailored, integrated regional approaches to groundwater management.

This study supports SDG 6 (Clean Water and Sanitation), SDG 3 (Good Health and Well-Being), and SDG 13 (Climate Action) by assessing groundwater contamination, highlighting health risks, and advocating for climate-resilient water management. Aligned with India’s National Water Policy (2012) [73,74], it provides scientific evidence for groundwater protection, emphasizing strict monitoring, remediation, and safe water practices in affected regions.

Further research is needed on long-term monitoring, cost-effective defluoridation, and the impact of climate change on groundwater quality. Multi-seasonal sampling, probabilistic health risk models, and machine learning-based contamination prediction can enhance mitigation strategies. Additionally, exploring bioremediation techniques and assessing climate change effects on groundwater dynamics are crucial for sustainable management.

5. Conclusions

Groundwater is the primary source of drinking and agricultural water in the Boudh district. This study assessed fluoride and nitrate contamination, analyzed hydrogeochemical processes, and evaluated health risks using geostatistical and GIS methods. The results indicate that groundwater is slightly alkaline, with TDS and TH values classifying it as hard, fresh, or brackish. While groundwater is generally suitable for drinking, some locations exceed the WHO-recommended limits for fluoride and nitrate. Key hydrogeochemical processes influencing groundwater chemistry include rock-water interactions, silicate weathering, reverse ion exchange, and anthropogenic activities. The northern and eastern parts of the study region show higher fluoride concentrations, with 49% of samples exceeding 1.5 mg/L, mainly due to the dissolution of fluorite, apatite, biotite, and hornblende minerals. Nitrate contamination, present in 30% of samples, is primarily linked to agricultural fertilizers, latrine pits, and sewage disposal, posing significant health risks. A health risk assessment based on HQ and HI suggests that infants and children are most vulnerable. More than 63% of groundwater samples indicate potential health risks to infants, 64% to children, and over 56% to adults. These findings highlight the urgent need for safe drinking water interventions. Adequate fluoride and nitrate contamination mitigation requires a multi-pronged approach, including technological interventions (reverse osmosis, adsorption), groundwater conservation, pollution control, and public awareness programs. Additionally, nutritional supplementation with calcium- and vitamin C-rich diets can help reduce fluoride-related health risks.

The findings of this study provide valuable scientific data for policymakers, environmental agencies, and water management authorities to develop targeted groundwater protection strategies. These measures will improve public health, water security, and sustainable groundwater management in the Boudh district and other fluoride- and nitrate-affected regions.