Probabilistic human health risk assessment and Sobol sensitivity reveal the major health risk parameters of aluminum in drinking water in Shiraz, Iran.

Overuse of aluminum salts (a.k.a., alum) in coagulation and flocculation processes in water treatment raises concerns about increased levels of aluminum (Al) in drinking water. In this study, we present a probabilistic human health risk assessment (HRA) for non-cancerogenic risks, with Sobol sensitivity analysis, to vet the concern of increased health risk from Al in drinking water in Shiraz, Iran, for children, adolescents, and adults. The results show that the concentration of Al in the drinking water in Shiraz varies significantly between winter and summer seasons and varies considerably spatially across the city irrespective of the season. However, all concentrations are below the guideline concentration. The HRA results show that the highest health risk is for children in summer, and the lowest is for adolescents and adults during winter, with generally higher health risks for younger age groups. However, Monte Carlo results for all age groups suggest no adverse health effects due to Al exposure. The sensitivity analysis shows that the sensitive parameters vary across age groups. For example, the Al concentration and ingestion rate pose the most risk for adolescent and adult groups, and children group, respectively. More importantly, the interaction of Al concentration with ingestion rate and body weight is the controlling parameters for evaluating HRA rather than Al concentration alone. We conclude that while the HRA of Al in Shiraz drinking water did not indicate significant health risk, regular monitoring and optimal operation of the coagulation and flocculation processes are essential.

Global water quality changes posing threat of increasing infectious diseases, a case study on malaria vector Anopheles stephensi coping with the water pollutants using age-stage, two-sex life table method.

BACKGROUND: Water pollution due to uncontrolled release of chemical pollutants is an important global problem. Its effect on medically important insects, especially mosquitoes, is a critical issue in the epidemiology of mosquito-borne diseases. METHODS: In order to understand the effect of water pollutants on the demography of Anopheles stephensi, colonies were reared in clean, moderately and highly polluted water for three consecutive generations at 27 °C, 75% RH, and a photoperiod of 12:12 h (L:D). The demographic data of the 4th generation of An. stephensi were collected and analysed using the age-stage, two-sex life table. RESULTS: The intrinsic rate of increase (r), finite rate of increase (λ), mean fecundity (F) and net reproductive rate (R0) of An. stephensi in clean water were 0.2568 d-1, 1.2927 d-1, 251.72 eggs, and 109.08 offspring, respectively. These values were significantly higher than those obtained in moderately polluted water (r = 0.2302 d-1, λ = 1.2589 d-1, 196.04 eggs, and R0 = 65.35 offspring) and highly polluted water (r = 0.2282 d-1, λ = 1.2564 d-1, 182.45 eggs, and R0 = 62.03 offspring). Female adult longevity in moderately polluted (9.38 days) and highly polluted water (9.88 days) were significantly shorter than those reared in clean water (12.43 days), while no significant difference in the male adult longevity was observed among treatments. CONCLUSIONS: The results of this study showed that An. stephensi can partially adapt to water pollution and this may be sufficient to extend the range of mosquito-borne diseases.

Contamination, probabilistic health risk assessment and quantitative source apportionment of potentially toxic metals (PTMs) in street dust of a highly developed city in north of Iran.

Street dust (SD) are the particulates that primarily originated from Earth's crust and secondary alteration and erosion of natural and anthropogenic materials. The multi-dimensional pollution and health risk assessment of potentially toxic metals (PTMs) in these particles remain unknown in the majority of world urban areas. The elemental concentration, mineralogy, and micro-morphology of street dust were determined by inductively coupled plasma mass spectrometry (ICP-MS), SEM-EDX, XRD, and petrographical observation. Multivariate statistical analysis combined with positive matrix factorization (PMF) and Monte-Carlo simulations were applied to source identification and health risk assessment of PTMs. A severe enrichment of Sb, Cu and Zn and moderate contamination of Sn, Pb, and Cr were observed in the samples particularly in the areas with higher loads of traffic. The results of geochemical indices showed that K, Al, Mn, and V have natural/geogenic origins. While Sb, Pb, Cr, Cu, and Zn showed an enrichment relative to the background values with dominant anthropogenic sources. The results were confirmed by source appointment techniques. The results of deterministic and probabilistic health risk assessment by Monte-Carlo simulations revealed the non-carcinogenic nature of As, Mn, and Pb for children mainly through skin and ingestion routes. It can be concluded that the chemical compound of street dust in Gorgan city is affected by both natural (loess deposits) and anthropogenic sources. Also, children are in the risk of exposure to PTMs in street dust more than adults.

Comprehensive assessment of water quality and associated health risks in an arid region in south Iran.

This study aims at investigating the quality of drinking water and evaluating the non-carcinogenic risk of fluoride and nitrate ions in drinking water, and fluoride in tea in Zarrin Dasht, Iran. We focus on tea since it is the most popular drink among Iranian people and in the study region. We collected and analyzed 23 drinking water samples and 23 tea samples from different locations in the study region. Based on the water quality index, the consumed drinking water does not have a good quality in most Zarrin Dasht areas. Accordingly, the water quality index (WQI) is poor and very poor in 70% and 13% of the water samples, respectively. The average fluoride concentration of the tea samples is 2.71 mg/L. The mean values of Fluoride Hazard Index (HIfluoride) are 3.77, 2.77, and 2.33 for children, teenagers, and adults, respectively, which are higher than the safe limit of 1. The Nitrate Hazard Index (HInitrate) is higher than the safe limit of 1 in 8.7% of the samples. The results of the Monte Carlo simulation demonstrate that HIfluoride and HInitrate are higher than 1 in all the groups, except for adults. According to the results of the sensitivity analysis, ingestion rate and body weight have a large effect on HIfluoride and HInitrate, but body weight is inversely associated with sensitivity. According to the Piper diagram, saline water is the predominant type in Zarrin Dasht. Besides, the results of the principal component analysis (PCA) show a high correlation between fluoride and pH, which could be related to the effect of pH on fluoride dissolution and ion exchange. Therefore, appropriate measures are recommended to be taken in order to reduce the amount of fluoride in the drinking water resources of this region. Reduction of tea consumption can also be considered an important factor in decreasing the amount of fluoride intake.

Two distinct mechanisms of fluoride enrichment and associated health risk in springs' water near an inactive volcano, southeast Iran.

Groundwater fluoride contamination is a major issue of water pollution in the world with health hazards such as dental and skeletal fluorosis. This research focused on exposure to the high concentration of fluoride in the springs water in the Bazman volcanic area, southeast Iran. The combination of chemical/isotopic analysis, geochemical modeling, health risk assessment and multivariate statistical methods were applied to investigate the contamination and sources of fluoride in the samples. Groundwater samples were collected from cold and thermal springs. Major ions, fluoride, trace elements and stable isotopes δ18O and δD were measured in the samples using standard methods, ICP-MS and OA-ICOS, respectively. Fluoride content in springs varied from 0.5 to 3.75 mg/L with an average value of 1.66 mg/L. The highest fluoride concentrations were observed in the eastern cold springs while thermal springs showed the minimum fluoride contents. The majority of samples showed F contents higher than the calculated optimal concentration of fluoride (0.75 mg/L). Reaction of fluorite mineral with HCO3 and replacement of F in clay minerals and metal oxy-hydroxides with OH- in water were likely cause fluoride enrichment in the eastern springs. Whereas, in the western springs and thermal springs, origin of fluoride was related to weathering of muscovite, cryolite, apatite and fluoroapatite minerals. The δ18O and δ2H of the water samples displayed the impact on evaporation on fluoride enrichment in all spring water samples. The average value of contamination index (Cd) in the water samples was 1.94 categorizing medium risk level while springs S7, S8, S9 and S4 were above the threshold value of Cd index. The fluoride hazard quotient (HQ) showed that 25%, 44%, 56% and 0% of springs' water resources had high risk level for age group of adults, teenager, children and infants, respectively. Therefore, health risk of fluoride in drinking water resources were in the following order: children > teenager > adults > infants.

Distribution of microplastics in upstream and downstream surface waters of the Iranian rivers discharging to the southern Caspian Sea.

Microplastic pollution in the riverine ecosystems has caught many attentions in the scientific literatures. However, little information is available about the abundance and distribution of microplastics of the rivers discharging to the Caspian Sea. The aim of this study was to assess the spatial and seasonal distribution of microplastics in the surface waters of thirteen rivers discharging to the southern Caspian Sea. Microplastics were found in all stations with uneven distributions. The average concentrations of microplastics in the stations during snowmelt and dry seasons were 1.406 ± 0.1380 microplastics/m3 and 0.4070 ± 0.01500 microplastics/m3, respectively. Positive gradients of the rivers microplastics concentration from upstream to downstream were found. White/transparent polyethylene (PE) particles with the shape of fragment/film and the length (L) of ≤ 1 mm were the most common microplastics in the surface waters of the rivers discharging to the southern Caspian Sea. Also, the mean concentration of microplastics in spring snowmelt and runoff period was 3.45 times higher than in dry period. Factors such as sewage and household wastes; landfills; and recreational-tourism, fishing and agricultural activities along the rivers may contribute to microplastic contamination in downstream stations. Our data provide baseline information of microplastics in surface waters of rivers discharging to the southern Caspian Sea.

Sources and hotspots of microplastics of the rivers ending to the southern Caspian Sea.

The occurrence of microplastics (MPs) in beach sediments of the southern Caspian Sea was well documented, however, there are still many unknowns about the abundances and distributions of MPs in the rivers ending to the Caspian Sea. Here, bank sediments of 26 sites in the thirteen rivers were surveyed in two seasons. However, there was not any significant difference (p > 0.05) between the concentrations of MPs during the two seasons. MPs were detected in all samples with mean concentrations of 214.08 ± 14.35 MPs/kg. The most common size, shape, color, and polymer types of MPs were L < 300 µm, fragment/film, white/transparent, and polystyrene (PS), respectively. In all rivers, positive MP gradients from upstream to downstream were observed. Maximum concentrations of MPs were found in the downstream parts of Chalus, Haraz, and Safarud rivers. Recreational-tourism and fishing activities had significant positive relationships (p < 0.05) with concentration of MPs in the rivers.

Environmental magnetic signatures in mangrove ecosystems in northern Persian Gulf: Implication for pollution assessment in marine environment.

Magnetic properties of root, bark, and leaf of mangrove (Avicenna marina) and sediment were determined for pollution assessment at three locations in the northern coast of the Persian Gulf. The study revealed that the sources of the particles deposited on leaf surfaces can be discriminated via saturation isothermal remanent magnetization (SIRM) values and heavy metal. However, different factors including wind direction, size of the magnetic particles and crown density, play a role using SIRM for biomonitoring of atmospheric particulate matter. For leaves, the significant correlations between SIRM and leaf elemental contents indicated that the deposited particles on their surface mainly have geogenic sources. The magnetic analyses revealed that leaves are more suitable than bark for monitoring atmospheric pollution using mangrove trees due to the effect of different factors including dense crown of trees, washing of tree trunk by sea waves, and elements translocation from roots and sediments. Instead, the positive and significant correlation between the SIRM values for sediments and mangrove roots, and no or negative correlation between sediments and roots with barks and leaves indicates that the magnetic properties of the sediments and mangrove roots are suitable indicators of pollution in aquatic environment.

Occurrence of microplastics (MPs) in the gastrointestinal tract of fishes: A global systematic review and meta-analysis and meta-regression.

The presence of Microplastics (MPs) in food has become a global health concern in the last two decades. In this study, an attempt was made to obtain articles about the occurrence of MPs in the gastrointestinal tract (gt) of fishes using searching the Scopus and PubMed databases from 1 January 1990 to 10 August 2021. The occurrence of MPs was meta-analyzed using the random effect model (REM). The results indicate that pooled occurrence of MPs in gastrointestinal of fishes was 2.76 P/gt: 95%CI:2.65-2.86 P/gt. Occurrence MPs in gastrointestinal of fishes in closed water sources (5.86 P/gt) was higher than free water sources (2.46 P/gt). In addition, the rank order of water sources based on occurrence MPs in gastrointestinal of fish was Lake (5.50 P/gt) > Estuary (5.46 P/gt) > River (2.91 P/gt) > Bay (2.85 P/gt) > Sea (2.58 P/gt) > Ocean (1.29 P/gt). The lowest and highest occurrence MPs in gastrointestinal of fishes were observed in high-income economies (1.45 P/gt) and low-income economies (8.08 P/gt), respectively. The higher frequency of color in MPS was related to blue with polyethylene-type polymers. Therefore, control plans to reduce the occurrence of MPs in fishes is recommended.

Microplastics captured by snowfall: A study in Northern Iran.

Samples of fresh snow (n = 34) have been collected from 29 locations in various urban and remote regions of northern Iran following a period of sustained snowfall and the thawed contents examined for microplastics (MPs) according to established techniques. MP concentrations ranged from undetected to 86 MP L-1 (mean and median concentrations ~20 MP and 12 MP L-1, respectively) and there was no significant difference in MP concentration between sample location type or between different depths of snow (or time of deposition) sampled at selected sites. Fibres were the dominant shape of MP and µ-Raman spectroscopy of selected samples revealed a variety of polymer types, with nylon most abundant. Scanning electron microscopy coupled with energy-dispersive X-ray analysis showed that some MPs were smooth and unweathered while others were more irregular and exhibited significant photo-oxidative and mechanical weathering as well as contamination by extraneous geogenic particles. These characteristics reflect the importance of both local and distal sources to the heterogeneous pool of MPs in precipitated snow. The mean and median concentrations of MPs in the snow samples were not dissimilar to the published mean and median concentrations for MPs in rainfall collected from an elevated location in southwest Iran. However, compared with rainfall, MPs in snow appear to be larger and more diverse in their shape and composition (and include rubber particulates), possibly because of the greater size but lower terminal velocities of snowflakes relative to raindrops. Snowfall represents a significant means by which MPs are scavenged from the atmosphere and transferred to soil and surface waters that warrants further attention.

Microplastic pollution in inshore and offshore surface waters of the southern Caspian Sea.

In this study, as the first comprehensive monitoring, the occurrence of microplastics (MPs) in inshore and offshore surface waters of the southern Caspian Sea was investigated. Our data indicated that MPs, which were detected in all the samples, were widely distributed in the thirteen studied stations. Non-normally distribution of the MPs was observed among the studied stations (p<0.05). The average concentration of microplastics in the selected stations was 0.246 ± 0.020 MP/m3. In most of the transects, negative gradients of MPs from coastal waters to deeper waters were observed. The dominant size and color of MPs in the inshore and offshore water samples was 1000-5000 µm and white-transparent, respectively. Films and fibers constituted about 50% and 40% of the total number of MPs of the water samples, respectively. Also, polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were the three main polymer types of microplastics in the inshore and offshore surface waters. Our data provide valuable evidence for the comparative assessing of future data regarding decreases or increases of MPs in the southern Caspian Sea.

Spatial distribution of microplastics in sandy beach and inshore-offshore sediments of the southern Caspian Sea.

The occurrence of microplastics (MPs) in nearshore zones of the southern Caspian coasts is well documented; however, no data are available on MP occurrence in offshore sediments. In this study, six sandy beach stations and 18 inshore-offshore stations (six transects) were surveyed. MPs were detected in all sediment samples. The mean abundances of MPs in the beach and inshore-offshore stations were 196.67 ± 11.58 and 103.15 ± 7.21 MPs/kg, respectively. Fibers constituted the most common shape of MPs. Polystyrene (PS) and polyethylene terephthalate (PET) were the major polymer types found in the beach and inshore-offshore sediments, respectively. In most transects, negative MP gradients were observed from nearshore to offshore, which showed that coastal fishing, tourism, and rivers were the main sources of MPs in this area. These results will improve our understanding on MPs pollution in the marine ecosystem. We recommend further MP studies in different parts of the Caspian Sea to develop appropriate management programs.

The concentration of potentially hazardous elements (PHEs) in the muscle of blue crabs (Callinectes sapidus) and associated health risk.

In this study, the concentration of potentially hazardous elements (PHEs) in the muscle of Blue crabs (Callinectes sapidus) from the Strait of Hormuz was analyzed and following the health risk in the consumers by uncertainty and sensitivity analysis in the Monte Carlo simulation (MCS) technique was estimated. Fifty-eight blue card samples (male blue crabs = 33 samples; female blue crabs = 25 samples) were collected in the Strait of Hormuz from May to September 2020 for analysis of Nickel (Ni), Lead (Pb), Cadmium (Cd), and Iron (Fe) using Flame Absorption Spectrometer (FAAS). The order of PHEs in the in muscle male blue crabs was Fe (414.37 ± 288.07 µg/kg.ww) > Pb (238.78 ± 87.83 µg/kg.ww) > Ni (92.57 ± 39.72 µg/kg.ww) > Cd (52.73 ± 18.39 µg/kg.ww) and in female blue crabs Fe (461.16 ± 320.56 µg/kg.ww) > Pb (230.79 ± 125.59 µg/kg.ww) > Ni (84.13 ± 46.07 µg/kg.ww) > Cd (67.412 ± 43.93 µg/kg.ww). The concentration of PHEs muscle of male blue crabs and female blue crabs was not significantly different (P-value > 0.05). Uncertainty of non-carcinogenic risk revealed that P95% of total target hazard quotient (TTHQ) in the adult and children consumers due to ingestion male blue crabs was 5.30E-3 and 1.08E-3, respectively, and P95% of TTHQ in the adult and children due to ingestion female blue crabs was 7.05E-3 and 1.20E-3, respectively. P95% of TTHQ in both adult and children consumers was lower than one value. Therefore, consumers are at the acceptable range of the non-carcinogenic risk due to ingestion muscle of male and female blue crabs in Bandar Abbas. Although the non-carcinogenic risk of blue crab was in the safe range, due to the increase in its consumption and the increase of pollution sources in the Persian Gulf, it is recommended to monitor PHEs in Blue's muscle crabs.

Potentially Toxic Elements (PTEs) in the Fillet of Narrow-Barred Spanish Mackerel (Scomberomorus commerson): a Global Systematic Review, Meta-analysis and Risk Assessment.

The contamination of seafood like narrow-barred Spanish mackerel (Scomberomorus commerson) fillets by potentially toxic elements (PTEs) has converted to worldwide health concerns. In this regard, the related citations regarding the concentration of PTEs in fillets of narrow-barred Spanish mackerel were collected through some of the international databases such as Scopus, Cochrane, PubMed, and Scientific Information Database (SID) up to 10 March 2020. The concentration of PTEs in fillets of narrow-barred Spanish mackerel fish was meta-analyzed and the health risk (non-carcinogenic risk) was estimated by the total target hazard quotient (TTHQ). The meta-analysis of data indicated that the rank order of PTEs in fillet of narrow-barred Spanish mackerel was Fe (10,853.29 µg/kg-ww) > Zn (4007.00 µg/kg-ww) > Cu (1005.66 µg/kg-ww) > total Cr (544.14 µg/kg-ww) > Mn (515.93 µg/kg-ww) > Ni (409.90 µg/kg-ww) > Pb (180.99 µg/kg-ww) > As (93.11 µg/kg-ww) > methyl Hg (66.60 µg/kg-ww) > Cd (66.03 µg/kg-ww). The rank order of health risk assessment based on the country by the aid of TTHQ for adult consumers was Malaysia (0.22251) > Philippines (0.21912) > Egypt (0.08684) > Taiwan (0.07430) > Bahrain (0.04893) > Iran (0.03528) > China (0.00620) > Pakistan (0.00316) > Yemen (0.00157) > India (0.00073). In addition, the rank order of health risk assessment based on the country by the aid of TTHQ for child consumers was Malaysia (1.03838) > Philippines (1.02257) > Egypt (0.40523) > Taiwan (0.34674) > Bahrain (0.22832) > Iran (0.16466) > China (0.02892) > Pakistan (0.01474) > Yemen (0.00731) > India (0.00340). Therefore, the children in Malaysia and the Philippines were at considerable non-carcinogenic risk. Hence, approaching the recommended control plans in order to decrease the non-carcinogenic risk associated with the ingestion of PTEs via the consumption of narrow-barred Spanish mackerel fish fillets is crucial.

Physico-chemical properties and reactive oxygen species generation by respirable coal dust: Implication for human health risk assessment.

This study investigates the mineralogy, micro-morphology, chemical characteristics and oxidation toxicity of respirable dusts generated in underground coal mines. The active sampling was applied to collect airborne particulates with aerodynamic diameter <4 µm (PM4) at depth greater than 500 m from earth surface. The average mass concentration of PM4 was extremely higher than recommended values. QXRD and FESEM-EDS analyses were applied to study the micro-mineralogy and micro-morphology of respirable dusts. The chemical analysis by ICP-MS revealed an enrichment of V, Cr, Cu, Zn, As, Ag, Cd and Sb in respirable dust compared with the background environment and world coals. The EPA's health risk model showed that the health risk posed by Cr and Co in all workplaces exceeded the acceptable risk value for human health. The synthetic respiratory tract lining fluid (RTLF) model was utilized to achieve a novel insight into the toxicity of respirable coal dust. The result showed an overall depletion of lung surface antioxidants with the decreasing trend of ascorbic acid > reduced glutathione >> urate, implying low- to medium level of oxidative stress. The result of this study can be applied globally by decision-makers to decrease hazardous exposure of mine workers to respirable dust.

Identification of microplastics in the sediments of southern coasts of the Caspian Sea, north of Iran.

Microplastic (MPs) pollution in the aquatic and terrestrial environments has caught many attentions in the scientific literatures. Currently, no information is available about MPs pollution in Caspian Sea, the largest lake in the world. This study indicates the first report on the MPs pollution in the sediments of the southern Caspian coastal zones, northern Iran. Density separation method was conducted on 17 surficial sediments. The combination of observation techniques including SEM-EDS analysis, polarized light microscopy and Raman micro-spectroscopy were used to identify MPs. The abundance and size of microplastics in the samples ranged between 25 and 330 items/kg and 250-500 µm, respectively. Fibers constituted the most common MPs shape and polystyrene (PS) and polyethylene (PE) were major polymer types in the samples. The distribution of MPs in the study area reflected a patchy and irregular spatial pattern implying that the higher MPs concentration are near mouth of permanent rivers and in the regions with higher level of the fishing and tourism activities. The results showed the wide occurrence of MPs in the sediments of the world's largest lake which extend the knowledge on MPs pollution in the marine system. We also recommend further research on microplastics in different compartments of Caspian Sea to inform policy discussions and the development of appropriate management responses.

Hydrogeochemical controls on arsenic mobility in an arid inland basin, Southeast of Iran: The role of alkaline conditions and salt water intrusion.

Elevated inorganic arsenic concentrations in groundwater has become a major public and environmental health concern in different parts of the world. Currently, As-contaminated groundwater issue in many countries and regions is a major topic for publications at global level. However, there are many regions worldwide where the problem has still not been resolved or fully understood due to inadequate hydrogeochemical investigations. Hence, this study evaluates for the first time the hydrogeochemical behavior of the arid and previously unexplored inland basin of Sirjan Plain, south east (SE) Iran, in order to assess the controlling factors which influence arsenic (As) mobility and its distribution through groundwater resources. Total inorganic arsenic concentration was measured using inductive-coupled plasma optical emission spectrometry (ICP-OES). Arsenic content in groundwater of this region ranged between 2.4 and 545.8 µg/L (mean value: 86.6 µg/L) and 50% of the samples exceeded the World Health Organization (WHO) guideline value of 10 µg/L in drinking water. Groundwater was mainly of Na-Cl type and alkaline due to silicate weathering, ion exchange and evaporation in arid conditions. Elevated As concentrations were generally observed under weakly alkaline to alkaline conditions (pH > 7.4). Multivariate statistical analysis including cluster analysis and bi-plot grouped As with pH and HCO3 and demonstrated that the secondary minerals including oxyhydroxides of Fe are the main source of As in groundwater in this region. The desorption of As from these mineral phases occurs under alkaline conditions in oxidizing arid environments thereby leading to high levels of As in groundwater. Moreover, evaporation, ion exchange and saltwater intrusion were the secondary processes accelerating As release and its mobility in groundwater. Based on the results of this study, desorption of As from metal oxy-hydroxides surfaces under alkaline conditions, evaporation and intrusion of As-rich saline water are considered to be the major factors causing As enrichment in arid inland basins such as those in southeast Iran. This study proposes the regular monitoring and proper groundwater management practices to mitigate high levels of arsenic in groundwater and related drinking water wells of Sirjan Plain.

Geochemical sources, hydrogeochemical behavior, and health risk assessment of fluoride in an endemic fluorosis area, central Iran.

The present study is the first attempt to put forward the possible source(s) and health risk assessment of fluoride in Bahabad, central Iran. Fluoride concentrations ranged from 0.22 to 2.35 mg/L and 292-355 mg/kg in the groundwater and soil samples, respectively. Geochemical provenance techniques using major and rare earth elements in soils revealed that local shale is the most probable source rock of fluoride in the area. A two-step chemical fractionation method applied on soil samples demonstrated that residual and water-soluble fractions were the most probable modes of fluoride in soil, whereas exchangeable fraction had a minor role. The coefficient of aqueous migration showed that fluoride in the studied soils behaved as a mobile element. Moreover, the relative mobility indicated that soils played a more important role than rocks in releasing fluoride into groundwater. In groundwater medium, chemical weathering, evaporation, and ion exchange acted as the main geochemical controlling factors of fluoride enrichment. Findings of this study signify that the role of NaCl and NaSO4-type waters should be considered more to recognize susceptible areas to fluoride contamination in groundwater. People in the study area are exposed to high levels of fluoride intake through drinking water, thus making dental fluorosis a major public health concern in the area. Scanning electron microscopy of the dentin's enamel showed morphological modifications (e.g., cracks and fissures) in residents' enamel structures. The results of this study may lead to suitable management strategies to mitigate the endemic fluorosis problem.