Health risk assessment in an area of dental fluorosis disease from high fluoride drinking water: a case study from southeastern Türkiye

ABSTRACT This study focuses on identifying fluoride (F‒) concentrations and its health risk assessment (HRA) in drinking water sources in south-eastern Türkiye. Groundwater quality was assessed using some graphical approaches such as Schoeller and Piper diagrams and GIS mapping. Average daily exposure dosages through oral and dermal contact exposure routes were considered to determine the potential health risk of F‒ in groundwater. Groundwater samples were taken from 53 points in spring, summer, autumn, and winter seasons. The results showed that the average annual F‒ concentrations in water resources in the study area were 0.26‒3.62 mg/L. According to the HRA results, the highest F‒ health risk in this region was observed in children, followed by teenagers and adults. This study indicated that there is a strong relationship between the high health risk (4.28 > 3.5) in children and dental fluorosis caused by high F‒ concentration in groundwater.


Introduction
Fluoride (F -) is an electronegative reactive and trace element naturally found in the environment, plants, and both surface and groundwater (Wu et al. 2015;Subba Rao et al. 2020;He et al. 2020).Poor quality drinking water is known to cause about 80% of diseases worldwide, with about 65% of this due to endemic fluorosis, according to a report from the World Health Organization (WHO 2002).A great number of studies have highlighted the relationship between increasing human health problems and environmental pollutants such as F -(Yazici- Karabulut et al. 2019;Demir Yetis et al. 2021).When considering risk factors, extreme F -levels are a major threat in many countries worldwide (Adimalla et al. 2018;Li et al. 2019;Liu et al. 2022).Long-term F -intake above the acceptable limits is known to lead dental and skeletal fluorosis.Some researchers have demonstrated an increase in the oxidative stress, DNA damage and apoptosis biomarkers levels in water users with borderline high-level F - (Kirmit et al. 2020).Studies on this subject report that long-term consumption of F -in drinking water sources with concentrations exceeding 1.5 mg/L leads to an increase in the severity of dental fluorosis (WHO 2006;Khan et al. 2020).The National Research Council (NRC) has set daily F -consumption standards of 0.1-0.5 mg per day for infants younger than six months, 0.2-1 mg per day for infants six to 12 months, 0.5-1 mg per day for children one to three years old, 1-2.5 mg per day for children four to six years old, 1.5-2.5 mg per day for children up to seven years old, and 1.5-4 mg per day for adults (National Research Council 2001).
HRA is an influential approach to determining the prevalence of health problems caused by high F -levels in groundwater.Various studies in different regions around the world have studied this method to investigate the health risk associated with oral or dermal F -intake in groundwater (Mukherjee et al. 2019).The amount of non-carcinogenic risk from F -exposure is investigated by considering the physiological and behavioural differences of people of children, teenagers, and adults.As mentioned earlier, the associated health risks such as dental and skeletal fluorosis due to high F -levels are of paramount significance, especially for children and teenagers.In a study by Li et al. (2019), the occurrence and spatial distribution of F -in groundwater of 18 sampling points in the Loess Plateau of China were defined, geochemical and anthropogenic factors affecting F - concentration were determined, and a human health risk assessment was made.It has been concluded that children are at higher risk than adults in the region, which is similar to our current study.Fida et al. (2022), determined that the surface and groundwater resources in Pakistan are highly contaminated with toxic metals and microbial contaminants and reported that most of the pollutants are unsafe for human consumption as they exceed the WHO quality standards for drinking water.Mthembu et al. (2022) conducted a comprehensive study to assess the levels of heavy metals in drinking water and their health risks to humans in the Maputaland coastal aquifer in South Africa.In this study, the health risk ratio was found to be 43% in children and 26% in adults, according to groundwater samples.In the results of the study, it is obtained that treating contaminated groundwater before consumption has been suggested.Treatment of contaminated groundwater used for drinking purposes is the only option to provide safe drinking water to the local community.Today, there are many F -removal technologies worldwide, such as membrane processes, electrodialysis, adsorption, ion exchange, coagulation, and electrocoagulation.All these methods have advantages and disadvantages.There are F -removal studies using adsorption and electrocoagulation methods specific to the study area with high efficiency (Atasoy et al. 2016(Atasoy et al. , 2018;;Yazici-Karabulut et al. 2019;Yazici-Karabulut et al. 2023).
In most arid and semi-arid regions, particularly in developing countries such as Türkiye, dependence on groundwater for agriculture, irrigation, and drinking is widespread and F -concentration in groundwater has significant effects on human health (Atasoy et al. 2016;Yazici-Karabulut andAtasoy 2019a, 2019b).Previous health studies of F -contamination and its effects in the Sarım and Karataş region have produced significant results (Yeşilnacar 2010;Yesilnacar et al. 2016;Atasoy and Yesilnacar 2017).Such studies have examined water supply sources and the effect of dental fluorosis; however, no previous study has been conducted on HRA corresponding to seasonal F -changes.HRA is very important to ensure safe drinking water access to local people and to develop and use groundwater resources rationally.In this context, the purpose of this study is (a) determination of F -concentration in water resources and distribution networks in the study area; (b) investigation of seasonal variations of F -concentration in the region, and mapping of F -levels with Geographical Information System (GIS); (c) statistical explanation of the relationship between high F -levels and health risks and dental fluorosis.

Study area
The study area is located between Şanlıurfa city centre and Suruç and Bozova districts in the Southeast Anatolia region and covers an area of approximately 1350 km 2 (Demir Yetis et al. 2021).It is located between 36º 40"-38º 02" North latitudes and 37° 50"-40° 12" East longitudes.The area of Şanlıurfa's territory is 18,584 km 2 , and 98.3% of the provincial territory is covered by plateaus; 61.7% by plateaus, 22% by mountains and 16% by plains with arable land.Air masses shape the climatic conditions of the region.The region is influenced by tropical air masses of terrestrial origin, especially in summer, and humid air masses from the Mediterranean in winter.For this reason, the air temperature of the region in the summer months rises above 40°C.Due to the terrestrial conditions that are effective in winter, the air temperature drops to around 18.5°C.Considering the precipitation conditions in the study area, the precipitation is seen in the winter months with the effect of the Mediterranean precipitation regime.In summer, there is almost no precipitation in the region.The long-term average annual precipitation is 435 mm.Irregular precipitation conditions prevail in the region.While the annual average relative humidity in Türkiye is around 51%, the average relative humidity in the region, can drop to 31.5%, especially in the summer (Karabulut et al. 2022).The location map of the studied area, including the situation, location, and coordinates of the two villages in Şanlıurfa is provided in Figure 1.The drinking water of the villages within the study area was generally supplied by wells at 100-150 meters depth drilled in the last 10-15 years by the government and by boreholes drilled by private people.

Geology and hydrogeology
Geogenic and anthropogenic sources are the two main sources of F -in groundwater, respectively (Li et al. 2019).F -enrichment in shallow groundwater is mostly caused by arid and semi-arid climates, intense evaporation, ion exchange, and slow groundwater flow (Wang et al. 2018).An increase in F -concentration in groundwater can be seen as a result of increasing human activity and some anthropogenic factors like fertilizer application and wastewater discharge.Groundwater seepage from the aquifer containing poor-quality water to the aquifer holding good-quality water can also produce F -elevation, especially when groundwater cones are created as a result of heavy groundwater abstraction (Li et al. 2019).
Sedimentary rocks and volcanites are two distinct geological formations that are very significant, according to an analysis of the geology in the selected area.Pleistocene aged basalts were formed during the Karacadağ intrusion as a result of the magma coming to the surface through cracks, fractures and holes and spreading.This unit does not have aquifer characteristics in this region.For many years, spring water, drinking water, and domestic use have all been provided by basalts in the Siverek Karacadağ region.There haven't been any reports of a volcanic F -issue in the area.Pliocene aged formation does not show aquifer characteristics.Additionally, the water quality is quite low in areas where water supply is very low.The Oligocene -lower Miocene aged formation shows an aquifer feature hydrogeologically.The Eocene aged formation typically consists of crystallised limestone.Due to the region's extensive development of karstic features, it is a significant aquifer (Demir Yetis et al. 2021).
For the purpose of supplying the area with potable water, wells have been dug over the previous 10-15 years.Almost all of the 53 sampling points selected among these wells are located within the Oligocene-Lower Miocene aged unit as shown on the geological map in Figure S1 and this unit consists of clayey-limestones.The ion exchange between F -and OH -, which may accelerate fluorite dissolution in some clay minerals, may be the cause of the elevated F -concentrations found in the groundwater in the research area.Subba Rao (2011), Malago et al. (2017) and Sunkari et al. (2022) supported this situation in their studies.The main sources of F -enrichment and contamination in groundwater are water-rock interactions in an alkaline environment under dry climatic circumstances and the existence of F-bearing minerals in the bedrock.Alkaline environment and the presence of bicarbonates create a favorable condition for high F -waters (Ling et al. 2022).
In the Yesilnacar et al. (2016) investigation on the geology of the study area and the prevalence of fluoride/fluorosis cases, no F-containing minerals were discovered in the results of XRD and XRF analyzes on 200 borehole samples taken from two villages.However, the fact that no F -containing minerals were observed in the samples does not mean that this is the case.Because, in a study conducted in the study area in 2013, F -concentrations exceeding optimal values and fluorosis cases were detected (Yeşilnacar et al. 2013).Subsequently, a similar situation was observed in water samples taken in 2018 within the scope of the current study (Table 1).This is an indication of the presence of F -mineral in groundwater used as a drinking water source in the region.As a result, it is highly probable that the high F -content in the groundwater is due to the presence of F -mineral as nodules in the clayey limestone due to the geological formation of the region described in detail above and the transmission of F -ions into the aqueous environment as a result of rock-water interaction.

Sampling and analysis
The locations and routes of the groundwater sampling points belonging to the study were determined by using 1:25000 scale topographic and digital geological maps.A total of 53 groundwater sampling points were selected to determine the F -level.The samples were taken seasonally over a period of one year.Global Positioning System (GPS) was used to specify the coordinates of the sampling points.A portable Hach-Lange HQ40d multi-meter was used (in-situ) to identify F - concentrations in groundwater.F -analyses of the groundwater samples were carried out using the procedures described in the EPA method 340.2, APHA method 4500-F, and ASTM D1179-99 (Yesilnacar et al. 2016).Fluorosis classifications and dental examinations were undertaken by local dentists practicing within the study area.Exploration drilling was performed at two villages to determine the geological structure.The preserving and transporting of drilling samples were conducted using the procedure described in ASTM D5079-08 (Demir Yetis et al. 2021).
GIS is a spatial variation method used in the mapping of water quality determination, HRA and groundwater utilization rates (Liang et al. 2019).The ArcGIS ArcMap 10.5 was used to compose F - spatial distribution maps in the study area.There were coherent spatial variations F -concentration levels, especially between the summer and spring seasons.In general, it was observed that the F - concentrations increased from south to north.Digital Elevation Model (DEM) data at 30 m intervals to be used as a baseline map was provided by the US Geological Survey for the digital elevation models of the region.Spatial distribution maps and F -hazard index were produced using the Inverse Distance Weight (IDW) interpolation method.
Hydrogeochemical evaluations were made using various diagrams.Among these, the Piper and Schoeller diagrams have been used specifically to investigate and describe the hydrogeochemical facies of the groundwater in the study area and the order of the major ion abundance.Water quality parameters of Ca 2+ , Mg 2+ , K + , Na + , HCO 3 − , SO 4 2- , Cl -and NO 3 -along with F -were analyzed at 53 groundwater sampling points.
Descriptive statistics, such as average, standard deviation, and minimum and maximum for the parameters, and statistical analysis, such as one-way analysis of variance (one-way ANOVA) test results, were estimated using the Statistical Package for the Social Sciences (SPSS) program.Dean's Dental Fluorosis Index (Dean Index -The Community Fluorosis Index) captures (Dean's 1942) classification of individuals into categories from 0.0 (normal) to 4.0 (severe).Dental fluorosis degrees usually follow Dean's classification index, with 0 = no dental fluorosis and 4 = severe dental fluorosis (Dean 1942).

Risk characterization from fluoride exposure
In this study, the United States Environmental Protection Agency (USEPA) method was taken on to utilize potential adverse health risks associated with groundwater F -exposure through direct ingestion and dermal contact (Wang and Li 2022).To determine the F -exposure for the populations of the study area, an evaluation was carried out on three groups [children (aged 0-10); teenagers (aged 11-18); adults (aged 19-70)].The exposure to high level of F -in groundwater was regarded in terms of potential and dermal dose, figured using Equations ( 1) and (2), respectively.
Where EDI ing and EDI derm are the estimated chronic daily intake of F -(mg/kg/day) through direct ingestion and skin absorption, respectively (Tables S1 and S2).C w represents the concentration of F -in groundwater (mg/L) (Table 1), IR is the groundwater ingestion rate (L/day), EF is the exposure frequency (day/year), AF is the F -adsorption factor, ED is the exposure duration in years, BW is the mean body weight in kg, AT represents the average time for non-carcinogenic effect in days, SA is the body surface area in cm 2 exposed to the groundwater, K p is the dermal permeation constant in cm/h, F -is the fraction of surface skin contact with the groundwater (unitless), ET s is the exposure time in h/day when bathing, and CF is the groundwater conversion factor (1 L/ 1000 cm 3 ).
The F -absorption efficiency in the digestive system is close to 100%.Considering the risks that children are exposed to, AF was taken as 100% (AF = 1).The average daily water consumption rates in adults, teenagers, and children were 1.95, 1.58, and 1.25 L/day.Body weights of objective groups were averaged as 57.03, 46.25, and 16.68 kg, respectively.The non-carcinogenic effect of F -on human health can be calculated as hazard quotient (HQ ing ) following Equation (3), Where RfD represents the reference dose of F -and is used in risk assessment of daily exposure.The USEPA recommended oral reference dose for F -(RfD ing ) is 0.06 mg/kg/day.HQ ing <1 indicates fewer non-carcinogenic effects, while HQ ing >1 shows significant non-cancer health hazards and exceeds the acceptable level.In this research, the parameters used to assess health risk assessment are shown in Table 2.
As seen in Table S3, 867 people, including 451 (0-18 age range) students, were examined in 17 villages within the study area in order to evaluate F -exposure through drinking water.Fluorosis cases have also been identified in the region, including in the study area.A comprehensive statistical evaluation of these screening results is provided in the results and discussion section.

Spatial and seasonal variations of fluoride in groundwater
The spatial distribution of F -concentration levels in groundwater were measured at 53 sampling points as shown in Figure 2. According to this, F -amounts exceeding 1.20 mg/L were observed to be higher at W-39 (1.65 mg/L), W-31 (1.47 mg/L), W-10 (1.30 mg/L) and W-11 (1.33 mg/L) points.Overall, no remarkable seasonal variation was determined in F -concentration levels.Thus, the study area groundwaters are within acceptable limits (between 650 and 2500 µS/cm) for EC, as seen in Table S4.Additionally, no remarkable seasonal variation was observed in EC values.Annual average groundwater temperature and pH are 20.92°C and 7.76, respectively.
The presence of high F -in the groundwater of the study area may be the release of F -ions into the aquatic environment by dissolving as a result of the interaction of F-containing minerals locally in the Oligocene -lower Miocene aged clayey-limestones with water.The reason for the absence of F -ions in the groundwater of other sampling points in the study area can be expressed as the fact that the water in these wells is supplied from the Eocene aged limestones, which has the most important aquifer in the region (Yeşilnacar 2010).Groundwater chemistry is derived mainly from  underground rocks by natural geochemical mechanisms controlling it.This indicates that groundwater geochemistry is mainly controlled by the geogenic origin and then modified by the anthropogenic source (Li et al. 2019).

Hydrochemical facies of groundwater
Piper diagrams were used to assess the hydrogeochemical faces in the research region utilizing major cations (Ca, Mg, Na, and K) and anions (HCO 3 , SO 4 , and Cl).According to the hydrochemistry of the samples that were studied, the primary cations were identified in the following order of average abundance: Ca > Mg > Na > K, while the major anions were discovered in the following order: HCO 3 > SO 4 > Cl.It is well-known that bicarbonates cause groundwater to become more alkaline.Most of the study area's groundwater has an alkaline composition, which shows that the majority of the dissolved carbonates are in the form of bicarbonates.The ion exchange process, as well as the weathering of minerals like halite and dolomite are what cause Na, Cl, and HCO 3 to dominate the ionic concentration in groundwater (Ram et al. 2021).
Based on the Piper diagram, it has been determined that HCO 3 -Ca⋅Mg and Ca + HCO 3 water types are the predominant types in the study area.The groundwater of the study area has a higher concentration of alkaline earth elements (Ca + Mg) than alkaline elements (Na + K).Moreover, weak acid roots (CO 3 + HCO 3 ) are more prevalent than strong acid roots (SO 4 + Cl).Consequently, the water type in this region is indicative of waters with carbonate hardness in excess of 50%.It is believed that the length of time that groundwater interacts with anthropogenic pollutants has a role to play in the formation of different water types within the area.Furthermore, agricultural activities are known to impact water chemistry.As illustrated in Figure S2, the primary locations of groundwater sampling points in the study area were found to be located within the main hydrochemical facies of HCO 3 -Ca⋅Mg.
In the semi-logarithmic Schoeller diagram, almost all of the groundwaters in the study area are Ca + HCO 3 (Figure S3).Therefore, groundwater is dominated by high HCO 3 and Ca ions, indicating that more F -is dissolved in groundwater due to limestone precipitation, which can be well described in chemical processes.These results are consistent with the results in the Piper diagram.Mir et al. (2017) used the Schoeller diagram method to classify the facies of water resources in a study conducted on the quality of water resources in the Sistan-Baluchistan region of Iran to manage a possible water shortage during dry periods.In a similar study, Aksever et al. (2016) used the Schoeller diagram to specify the water quality for drinking and irrigation in a Turkish region.Additionally, Al-Barakah et al. ( 2017) also benefited from this method.

Risk assessment
Hazard index was calculated as oral and dermal exposure.The findings obtained show that the HQ values in the oral exposure were much higher than those in the dermal exposure.For this reason, distribution maps were created for HQ ing data only.Table 3 indicates that the HQ ing value taken from the wells for adult age groups is below the hazard index in all seasons.However, for children, the HQ ing value was higher than the indicated hazard index, especially in the summer and autumn.Furthermore, total hazard index of the sampling points calculated seasonally are included in Table S5.
The HQ ing values for each individual sampling point are shown in Table 3.According to this table, in the study area, the summer HQ ing ranged from 0.05 to 0.47, 0.21 to 1.95, and 0.46 to 4.28 for children, teenagers, and adults, respectively.The risk density of dental fluorosis is split into five ranks, including no risk (0.5 < HQ ing <1), mild risk (1 < HQ ing <1.5), moderate risk (1.5 < HQ ing <2.5), high risk (2.5 < HQ ing <3.5), and very high risk (HQ ing >3.5), according to a hazard index.
The maximum HQ ing value for children was calculated as 4.28 in the summer and 0.03 for adults in the autumn (Figure 3).This study showed that there is a strong relationship between the high health risk (4.28 > 3.5) in children and dental fluorosis because of the high F -in ground water.The HQ ing value in children was found to be higher than one.According to the results of the study, children are at the highest risk, followed by teenagers and then adults.The reason behind the high risk for children is low BW, resulting in higher exposure doses for lower age groups.Kumar et al. (2019) showed that the risk of danger is higher in children than in young people and adults.Martínez-Acuña et al. ( 2016) determined that children in the city of Zacatecas, Mexico, face higher  hazard risks in consuming high F -water.Aslani et al. (2019) reported that the highest noncarcinogenic risk of F -was in the children group.Guissouma et al. (2017) showed that the young population (infants and children) in Tunisia were more exposed to F -health risks.In a study conducted in Poldasht, Iran, the relationship between drinking water F -in two regions with low and high drinking water F -levels, and fertility, infertility and abortion in women living in these regions was examined.According to the results obtained, the F -level in 85% of the samples is higher than 1.5 mg/L, the upper limit WHO recommended for drinking water.In light of all the data, it was concluded that when all age groups were considered in a group, it was statistically significant, and it was stated that high F -values had a negative effect on women's health (Yousefi et al. 2018).Yousefi et al. (2019) on F -exposure and its health risk assessment, the noncarcinogenic risks of F -for the 4 F -exposed populations differed for children > teenagers > adults > infants, respectively, and for three age groups (children, teenagers and adults) for each season found HQ values higher than 1.Similarly, Dehghani et al. (2019) found the level of F -in groundwater samples in Larestan district of Iran exceeded the limits set by WHO, and approximately 70.6%, 48.2% and 34.4% of HQ values for children, teenagers and infants in these regions exceeded 1 safety level.This study shows that these age groups are at risk of F -through drinking water consumption.
In the study area, it should be noted, HQ ing for children is highest in summer, followed by spring, winter, and autumn.In other words, as the seasonal temperature increased throughout the region, the hazard risk increased.The study area is defined as an arid and semi-arid region, and the high concentration of F -in summer can be attached to the wane in precipitation.In addition, high water requests in both the private and agricultural sectors can result in drops in groundwater levels.In seasons of higher precipitation (spring, autumn, and winter), lower F -levels can also be seen as a result of the dilution of F -levels in groundwater.The adult age group has significantly decreased areas of very high risk in these seasons, and the risk-free areas are expanded significantly compared to the child-age group (Figure S4).
The HQ value was found to be above 1 in all target groups (children, teenagers and adults), especially in hot seasons such as summer and spring.Particularly vulnerable residents have been exposed to potentially non-carcinogenic risks.Therefore, special precautions should be taken and implemented to reduce the negative health effects on the people of the region who use high F - waters (Yazici-Karabulut et al. 2023).However, in some cases where socio-economic and environmental conditions are unsuitable, and this method is not very convenient.

Dental fluorosis risk
In the 1930s, Dean et al. investigated F -levels in water and dental fluorosis.The "dose-response" relationship between naturally occurring F -concentrations in water sources and dental fluorosis was established with data from 22 cities in 10 states in the USA.McClure (1943) defined 1.0 mg F − /L as the "allowable" level for naturally occurring F -in water supplies according to US drinking water standards.Dean and colleagues focused primarily on F -dosage in water and dental caries in their dental fluorosis studies.They conducted their studies on dental fluorosis and caries simultaneously (Whelton et al. 2019).The Dean index is an evaluation based on the aesthetic appearance of dental fluorosis (Figure S5).
A total of 10,777 teeth of 451 students in 53 villages were examined, including 5396 permanent teeth and 5381 primary teeth.As a result of the dental examination, severe dental fluorosis was detected in the children in the study area.Examples of dental fluorosis degrees of the children's teeth examined at all points in the study area are seen in Figure S6.Accordingly, the highest degree of fluorosis was found in Sarım and Karataş villages (Derin et al. 2023).
A geomedical map of the study area was produced, taking into account the measured F - concentration and the geological structure of the region, as well as the degrees of dental fluorosis obtained as a result of dental examinations (Figure S6).It can be clearly seen that the level of fluorosis strongly coincides with regions where groundwater F -amounts are high.It is also possible to establish a relationship between the fluorosis events of the geological unit and the groundwater with high F -content.Demir Yetis et al. ( 2021) noted the efficiency of X-ray fluorescence (CaO, SiO 2 , MgO, Fe 2 O 3 , P 2 O 5 , and K 2 O) and X-ray diffraction (Quartz and Zr) analysis results from rock data in regions with high levels of dental fluorosis and F -. Definitively, the F -contained in the rock structure affects the F -content in the groundwater.In children who consume this water, the degrees of dental fluorosis vary depending on the F -level in the water.A small point should be clarified: even though the F -level in the groundwater of Kızılburç village was 0.65 mg/L, fluorosis was specified to be at degree 4, potentially because the number of subjects was low, and the students are transported from small villages to the schools in larger villages by way of intervillage migration and transportation systems.Consequently, the prepared thematic map may be one of the most significant results of this study (Figure S7).
According to the results of this study and the study conducted by Atasoy and Yesilnacar (2017), the amount of F -in groundwater varies between 1 and 4 mg/L.In these two villages in particular, samples obtained were higher than the values deemed acceptable by the WHO (0.5-1.5 mg/L).High F -concentrations in groundwater caused dental fluorosis in region.Derin et al. (2018), groundwater samples were taken from the same points in 2018 to investigate whether the current problem persists.According to the groundwater analysis results, the average F -concentration was obtained as 2.35 mg/L.It has been found that these measured values are still above the allowable limit.In addition, a female student who had a dental examination 10 years earlier was examined again.Dental fluorosis is still a problem for her and others (Figure S8).

Statistical evaluation
All descriptive statistical analysis for the presented parameters were forecasted using Excel 2016 software.Statistical analysis such as one-way ANOVA test analysis was done by SPSS.P values less than 0.05 were regarded statistically remarkable.In this study, descriptive statistical methods in the evaluation of data, one-way ANOVA tests for comparisons between groups, LSD multiple comparison tests for subgroup comparisons, T-tests for comparison of paired groups, and Pearson correlation tests were used.DMF(T) and df (t) are indices in this group (D: decay; M: missing; F: filled).DMF(T) shows the ratio of the total number of caries, filled, and missing teeth in the individuals examined to the total number of individuals examined; it is not expressed as a percentage.And df (t) is the calculated form of the DMF(T) index for deciduous teeth.
In general, the df (t) and DMF(T) values of these patients were 1.5898 and 0.303769, respectively.The average age of the children examined was 9.09 ± 1.60, with a minimum age of seven and a maximum of 13.P values less than 0.05 were regarded statistically remarkable.According to the ANOVA test results shown in Table 4, the df (t) value varied according to age groups (p = 0.013).A statistically significant negative correlation was observed between df (t) values and age values (r = −0.117,p = 0.013).As the age values increased, the df (t) values decreased.
The results of the LSD test, a post-hoc analysis undertaken to determine the age group of the difference, show the df (t) index is lower in the 11-13 age groups than in the other age groups (Table S6).There was no statistically significant relationship between DMF(T) values and age values (r = −0.003,p = 0.944).One-way analysis of variance determined that the DMF(T) values did not differ according to age groups (p = 0.964) (Table S7).In dental fluorosis screenings performed in 53 villages, nine students with fifth-degree fluorosis, most of them in Sarım and Karataş locations, were identified, and the rate in all screenings was 2%.Another 14 students with fourth-degree fluorosis were identified, and 22 students with a rate of 3.1% and third-degree fluorosis were identified.Its rate in all scans corresponds to 4.9% (Table S8).The average number of decayed teeth detected was 1.82.The average number of decays in milk and permanent teeth is 1.52 and 0.30, respectively.While the average number of losses in milk teeth was 0.06, no loss of permanent teeth was observed.High pH values favor the enrichment of F -in groundwater.Since Hydroxyl (OH -) replaces the F -ion in minerals containing F -and causes an increase in the F - concentration in groundwater.In addition, high pH values can trigger the dissolution of CO 2 in groundwater, causing an increase in HCO 3 -and CO 3 2- (Li et al. 2019).

Conclusion
After analyzing the geochemical processes responsible for the high F -concentration in the groundwater of the study area, the associated health risks and the effects of dental fluorosis, the following conclusions were reached.A total of 53 groundwater samples were assessed for F -.The results showed that; • The average annual concentration levels in water resources of 0.26-3.62mg/L.In all, 451 (222 were female (49.2%) and 229 males (50.8%)) four-years-old school children from the public network of the study area were evaluated.The highest F -health risk in this region was observed in children, followed by teenagers and adults.This study revealed that groundwater F -through ingestion exposure contributes to a greater non-carcinogenic risk than the dermal contact route.It has been observed that the groundwater quality is mainly characterized by Ca + HCO 3 facies.
• HQ ing values were found to be high, especially in summer months.In the study area, summer HQing values ranged from 0.05 to 0.47, 0.21 to 1.95, and 0.46 to 4.28 for children, teenagers, and adults, respectively.Serious defects and staining have been detected in the teeth of schoolage children and fourth-and fifth-degree fluorosis was found in the study area.• To reduce the F -concentration in drinking water and control fluorosis, it is necessary to take measures such as locating a different drinking water source, using bottled water for drinking, and treating the existing water with a method such as electrocoagulation or adsorption.• Farmers should be trained to reduce the impact of agricultural practices on water pollution and groundwater is used for drinking purposes in the study area.In addition, public awareness should be raised about the risk posed to human health by high F -in groundwater.

Figure 1 .
Figure 1.Location map of the study area with sampling points.

Table 1 .
The F -concentration in groundwater.

Table 2 .
The used parameters for health exposure assessment in drinking water.

Table 3 .
Seasonal hazard index values for different age groups based on oral exposure in study area.

Table 4 .
Df (t)value and its relationship with age groups.