Fluoride Geochemistry and Health Hazards: A Case Study

Abstract

This chapter was aimed to identify the relationship between fluoride (F) enrichment and prevalence of endemic fluorosis in a rural area of Nuzendla mandal in Guntur District, Andhra Pradesh, India. The concentration of F varies from 0.5 to 12.4 mg/L in pre-monsoon groundwater and 0.14 to 16.0 mg/L in post-monsoon groundwater in the collected and analyzed fifty water samples. Dental survey conducted in the study area based on Dean Classification Index indicated different degrees of dental fluorosis due to the varying concentrations of F in drinking water. The significant positive correlation is identified between the F content of groundwater and urine fluorosis-affected children. The F level in urine suggests that a high level of endemic fluorosis is prevalent in the Nuzendla mandal due to the consequence of a higher concentration of F in underground aquifers. This study concludes that the high concentration of F in groundwater leads to increased dental deformities among the surveyed people and also urinary F is a good indicator of community exposure F.

1. Introduction

Fluoride (F) occurs in rocks, soil, air, water, plants, and animals as well as in human body. Fluoride content in subsurface water is controlled by temperature, pH and solubility of F-bearing minerals. The subsurface water, most of which originates from rainfall or surface water bodies, gains minerals during its transport and residency period of earth crust [1, 2]. Continuous intake of F contaminated groundwater (>1.5 mg/L) without proper treatment cause chronic endemic fluorosis. There is a close relationship between environmental F and general health. Fluoride deficiency increases incidences of dental caries among the population, while the excess F intake causes dental, skeletal fluorosis, and other forms of non-skeletal tissue fluorosis. Hydrofluorosis is a major toxicological and public health problem in water-stressed regions.

Fluorosis continues to be an endemic problem around the world. Moderate levels of F ingestion reduce incidences of dental caries and also promote healthy development of bones and teeth [3, 4]. Hydroxylapatite is main mineral phase of the human teeth enamel. Dental fluorosis, which is characterized by mottling of tooth surface, is the most adverse effect of overexposure to dietary F. Fluoride accumulates in dentin, which is the mineralized tissue underlying the enamel, and its chronic overexposure could cause dentin to crack more easily [4]. Children within the age group of 0–12 years are most prone to fluorosis as their body tissues are in formative stage.

Fluorosis, which was initially considered to be a problem of teeth only, has now turned to be a serious health hazard affecting many other body systems manifesting through joint pains, muscular pain; skeletal deformations, and malformations characterized by increased in bone mass and density, pain and stiffness in backbone, hip region, and other joints. This is because continuous intake of high F causes ligaments of spine become calcified and ossified [5]. Studies indicate that F intake could increase probability of cancer in the kidney and bladder based on tendency for hydrogen fluoride (HF) to form under the acidic conditions such as urine [6].

Fluoride occurs in natural waters mainly in the form of F, whose concentrations may range up to 2800 mg/L [7]. Fluoride levels are high in groundwater where the source minerals such as amphiboles, micas, fluorapatite, topaz, cryolite, certain clays, and villiaumite [8]. Enrichment of F in Geological substrate is from the fluorite mineral phase in the rocks along with the weathering of rocks.

Hydrochemical techniques are normally employed in the water quality management. In these techniques, the data regarding the origin and behavior of major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and anions CO₃²⁻, HCO₃⁻, Cl⁻, SO₄²⁻) in the groundwater permits the elucidation of the hydrogeochemical compositions of the water [9]. This generally varies depending upon the solubility of the chemical components from the dissolution of the mineral component of the rocks that host the aquifer.

The current work was aimed to investigate the relationship between the consumption of water from natural high F terrain and the prevalence of dental fluorosis in the study area.

2. The study area

2.1 Location and climate of the study area

Nuzendla mandal is the present study area, which is located in Narasaraopet Revenue Division of Guntur District, Andhra Pradesh, India (Figure 1). It lies in between the latitudes 79°33′28″–79°52′51″ E, and longitudes 15°49′26″ and 16°01′42″ N and extends to an area of about 350 km² and is distributed in 20 rural villages. The area experiences a semi-arid climate, with minimum and maximum temperatures of 16.8°C and 48.5°C, respectively. Rentachintala of Guntur district (nearest IMD station) records the highest temperatures (48.5°C) during summer (March to May). The daily sunshine hours range from 3.5 to 10.5, with a mean of 7.5. The relative humidity is from 30% to 80% with a mean of 52%. The mean wind velocity ranges from 4.7 to 16.3 km/h, with an average of 10.5 km/h. The wind velocity is higher during the southwest monsoon compared to the rest of the period. The average annual rainfall for a period of 12 years (1991–2013) is 718.38 mm. The semi-arid climate of the study area with average annual rainfall initiates the evaporation process which plays a crucial role in the release of F fluoride from underlying rocks into the groundwater.

Figure 1.

Location map of Nuzendla mandal of Guntur district, Andhra Pradesh, India.

3. Geology of the study area

The study area is under laid by the rock formations ranging from Archaean to Permo-carboniferous age (Table 1). The rock formations include quartz-mica-schist, banded-biotite-hornblende-gneiss/granite, and coarse-grained sandstone (Figure 2). Major part of the study area is occupied by quartz-mica-schist. The second dominant rocks in the study area are biotite-hornblende granitic/gneisses with migmatite and pegmatite patches, which are observed from the northern part of the study area. A small portion in the eastern and southern parts is covered by coarse-grained sandstones [11]. A very small area in the eastern part is occupied by gabbro. Mineralogically, quartz-mica-schist is composed principally of quartz and mica, and generally of muscovite and biotite. The modal composition of quartz-mica schist shows 25% of muscovite, 15% biotite, 30% orthoclase, 20% quartz, and 10% plagioclase and chlorite, together with some opaque minerals [12]. The biotite-hornblende granitic/gneisses appear in their light and dark color banded texture. The light color band is composed of quartz and plagioclase feldspar, while the dark color is composed of biotite, hornblende, and opaque’s. The modal composition of biotite-hornblende granitic/gneisses have 34.25% of quartz, >3.75% k-feldspar, 20.35% of plagioclase, 35% of biotite, 5.2% hornblende, 0.5% chlorite,0.15% of sphene, 0.15% of zircon, 0.3% of epidote and 0.10% fluorite and 0.4% opaques [13]. Since the coarse-grained sandstones of Gondwana age are considered to be the weathered product of Eastern Dharwar Craton, it is essentially composed of quartz and little proportion of feldspars, together with accessories of biotite, hornblende, apatite, epidote, fluorite, sphene, zircon, etc. The volume percentage of the different minerals depends on the cementing material and environment of deposition. The muscovite and biotite micas, fluorite minerals contribute to the higher F levels in this study.

Super group	Group	Lithology	Age
	Gondwana	Coarse-grained Sandstone	Permo-carboniferous
Unconformity
—	Acid/mafic; intrusives	Gabbro/Norite; Alkali feldspar; granite	Paleo-Proterozoic to; Meso-Proterozoic
Eastern; Dharwar; Carton	Udaigiri; group	Quartz-biotite-; Muscovite-chlorite schist	Archaean to
	Peninsular; gnessic complex	Banded-biotite- hornblende-granite/gneiss-with migmatite patches	Paleo-Proterozoic

Table 1.

Geological succession of the study area [10].

Figure 2.

Geological Map of Study area.

4. Hydrogeology of the study area

Generally, groundwater occurs in all the formations of the study area. But it occurs under phreatic conditions in the weathered and fractured rocks at shallow depths and under semi-confined to confined conditions in the deeper fractured rocks. Development of the aquifer conditions in the quartz-mica schist and banded-biotite-hornblende-gneiss is generally less due to lack of primary porosity. However, the occurrence and movement of groundwater in the rocks depend on the development of extent of weathered rock portions and degree of the fractures in the rocks. The depth of weathering in the rocks is from 2 to 12 m below ground level (bgl) and the fractured rocks from 3 to 32 m bgl. Development of groundwater is through shallow wells (dug wells) and deep wells (bore wells/tube wells) in the study area. The depth of dug wells varies from 5.50 to 18.50 m bgl.

5. Materials and methods

5.1 Methodology

The methodology comprises of field procedures and analytical techniques. The field procedures include mapping techniques, well inventory and collection of groundwater samples and survey on health implications caused by F. The analytical techniques include the determination various physicochemical parameters of collected groundwater samples.

5.2 Field procedures

The mapping techniques covered geological mapping, demarcation of geomorphological features and preparation of slope, soil, drainage and land use/land cover maps. This work was carried out, using the Survey of India toposheets of 56P/12, 56P/16, 57M/9, and 57M/13 on a scale of check 1: 50,000. Indian Remote Sensing Satellite (IRS) ID Linear Imaging Self Scanner (LISS) III of geocoded false color composite of December 9, 2012 on 1:50,000 scales are used to get information on soils, geomorphological features, lithology, lineaments, and land use/land cover with a limited ground truth. Geological mapping was carried out by marking the contacts between the geological formations as well as the structural features. Geomorphological features were demarcated based on the field observations and the available literature.

Fifty groundwater samples were collected in pre-monsoon (month of May) and post-monsoon (November) seasons during the year 2012 in the study area. Prior to water sampling, sampling bottles soaked in 1:1 HCl for 24 h were rinsed with distilled water, followed by deionized water. They were washed again prior to each sampling of the filtrates. The bottles were tightly capped to protect the samples from atmospheric CO₂, adequately labeled, and preserved in the refrigerator till they were taken to laboratory for measurement. Data on location of wells, geographic coordinates, type of well, depth to groundwater level, and water taste was collected. The variations in the groundwater levels in the wells were recorded, using a water level recorder.

The people living in the study area suffering from different stages of fluorosis by consuming fluoridated water were identified. The dental fluorosis stages were identified by adopting Dean’s classification [10]. The fluoride levels are examined in the human body through the analysis of urine samples of the effected persons.

5.3 Analytical techniques

The collected groundwater samples from the field were analyzed for chemical variables, using the standard water quality methodology of the American Public Health Association [10]. The chemical variables include pH, electric conductivity (EC), total dissolved solids (TDS), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), bicarbonate (HCO₃⁻), chloride (Cl⁻), sulphate (SO₄²⁻), nitrate (NO₃⁻) and fluoride (F⁻). The pH and EC of the groundwater samples were measured in the field, using a portable pH meter (60510-ISE, YSI Pro plus) and EC meters (60530-ISE, YSI Pro plus). The TDS was calculated from EC adhering to the procedure of conversion factor adopted by Hem [14]. The rest of the chemical variables were determined in the laboratory immediately after the groundwater sampling. A summary of the analytical procedures is listed in Table 2. All concentrations of chemical parameters are expressed in milligrams per liter (mg/L), except pH (units) and EC (μS/cm at 25°C).

Chemical parameters	Methods
Bicarbonate (HCO3^−)	Titration with HCl
Calcium (Ca^2+)	Titration with EDTA
Carbonate (CO3^2−)	Titration with HCl
Chloride (Cl^−)	Titration with AgNO3
Fluoride (F^−)	Spectrophotometer
Hydrogen ion concentration (pH)	pH meter (60510-ISE, YSI Pro plus)
Magnesium (Mg^2+)	Calculation (TH- Ca^2+)
Nitrate (NO3^−)	Colorimeter
Potassium (K^+)	Flame photometer
Silica (Si)	Spectrophotometer
Sodium (Na^+)	Flame photometer
Specific Electrical Conductivity (SEC)*	SEC meter (60530-ISE, YSI Pro plus)
Sulphate (SO4^2−)	Spectrophotometer
Total dissolved solids (TDS)	SEC X Conversion factor (0.64)

Table 2.

Methods used for chemical analysis of groundwater.

5.4 Hydrogeochemical facies

The concept of hydrogeochemical facies has been used here to provide a model for explaining the distribution and genesis of principal types of groundwater, as it reflects the response of chemical processes in a lithological framework and the pattern of water flow in it [15, 16].

5.5 Piper’s trilinear diagram

A Piper trilinear diagram was used in understanding the hydrogeochemical characteristics of groundwater in the area [17]. It consists of two triangles, one for plotting cations and the other for plotting anions, and one diamond-shaped field from which hydrochemical facies were identified.

5.6 Dental survey

A questionnaire pre-format prescribed by Rajiv Gandhi Drinking Water Mission [18] and earlier described by Dahyia et al. [19] was used to score the incidence and degree of manifestation of dental fluorosis. Clinical dental examination was executed rendering to the requirements defined by the World Health Organization Formational Oral Health Surveys [20] by taking 10 minutes as an orientation period spell for the basic examination of a child. The test area was prepared with the required hygiene and safety measures, using previously sterilized instruments and having easy access to sterilization procedures, and using a plane mirror and a periodontal probe. Community fluorosis index (CFI) was calculated based on equation [1] as

$$CFI=\frac{\mathrm{Number}\mathrm{of}\mathrm{people}\times \mathrm{Deans}\mathrm{numerical}\mathrm{weight}}{\mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{people}}$$E1

The symptoms of dental fluorosis among the communities were recorded using, randomized sampling method. The results were classified into seven categories based on the Dean’s classification viz., normal, questionable, very mild, mild, moderate, moderately severe, and severe. The classifications were given a numerical weights of 0.0, 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0, respectively, in order of increasing severity [21, 22, 23, 24].

5.7 Urine sample collection and analysis

A total of 50 urine samples (one sample from each location where the groundwater samples were collected) were collected from the children of same age group (10–12 years age group). The samples were further classified into high (>1.5 mg/L), intermediate (0.6–1.5 mg/L), and low F (<0.6 mg/L) based on groundwater F content. Pre-labeled 500-ml plastic-capped disposable bottles (prewashed and dried containing 0.2 g of ethylene diamine tetra-acetic acid, EDTA) were distributed to the selected persons in the villages of the study area and brought to the laboratory in an ice box and stored at 4°C in a refrigerator. EDTA (0.2 g) was added to check and minimize the interference from complexation of F by cations such as calcium. The samples were analyzed for F content using the 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate SPADNS method. The individuals were also explained the importance of the program and were motivated to cooperate in this study. An informed consent was obtained from the participants. Information on the drinking water sources, dietary practice, period of living in a particular location, and other related data were collected through an open-ended questionnaire.

6. Results and discussion

6.1 Hydrogeochemical evolution

A trilinear diagram is widely used in understanding the hydrogeochemical evolution of groundwater [17]. The diagram consists of two triangles and one diamond-shaped field. The left side triangle is for plotting of cations (Ca²⁺, Mg²⁺ and Na⁺ + K⁺) and the right side triangle for plotting of anions (HCO₃⁻ + CO₃²⁻, Cl⁻, and SO₄²⁻) expressed in percentage. The diamond-shaped field (consisting of the total cations and anions), which is the upper side of these two triangles is used for representing the overall chemical quality of groundwater. The Zone-5 represents carbonate hardness (Ca²⁺: HCO₃⁻ type), zone 6 non-carbonate hardness (Ca²⁺: Cl⁻ type), the zone-7 non-carbonate alkali (Na⁺: Cl⁻ type), the zone-8 carbonate alkali (Na⁺: HCO₃⁻ type), and the zone 9 mixed types. The chemical data of the groundwater samples are plotted in the Piper’s diagram (Figure 3). Most groundwater samples fall in the center as well as in the right lower corner of the cation triangle in both the seasons. It indicates the high concentration of Na⁺ in the groundwater.

Figure 3.

Hydrogeochemical facies during pre-and post-monsoon periods.

Most of the anions in pre-and post-monsoon groundwater samples fell in center of the triangle representing HCO₃⁻ type. Therefore, the groundwater is dominated by Na⁺-HCO₃⁻ facies in general, which is further supported by hydrogechemical facies (Table 3). In the centrally located diamond-shaped field, the groundwater samples fall in zones 5–9. It suggests that the fresh water (zone 5) moves towards saline water (zone 7) through the zones of 6–8, following the flow path. That means the initial water quality is controlled by water-rock interaction and is subsequently modified by anthropogenic sources. Because of this, the concentrations of Na⁺ and Cl⁻ increase, which enhance the TDS content, are including the F content in the groundwater.

F− Range (mg/L)	Pre-monsoon	MeanCa^2+ (mg/L)	MeanNa^+ (mg/L)	Mean HCO3^2− (mg/L)	Mean TDS (mg/L)	% of samples	Post-monsoon	Mean Ca^2+ (mg/L)	Mean Na^+ (mg/L)	Mean HCO3^2− (mg/L)	Mean TDS (mg/L)	% of samples
< 0.6	Ca > Mg > Na > K: HCO3 > NO3 > Cl > SO4	156	87	308	981	2	Ca > Mg > Na > K: HCO3 > NO3 > Cl > SO4	168	132	337	1192	6
0.6 – 1.5	Na > Ca > Mg > K: HCO3 > Cl > NO3 > SO4	117	216	346	1,207	38	Ca > Na > Mg > K: HCO3 > Cl > NO3 > SO4	156	182	375	1265	28
>1.5	Na > Ca > Mg > K: HCO3 > Cl > NO3 > SO4	83	338	427	1,445	60	Na > Ca > Mg > K: HCO3 > Cl > NO3 > SO4	66	456	461	1655	66

Table 3.

Hydrogeochemical facies of groundwater during the pre-and post-monsoon periods of study area.

6.2 Mechanisms controlling groundwater chemistry

To understand the groundwater interaction with precipitation (rainfall), rock, and evaporation as mechanisms controlling the water chemistry [25], the ratios for major cations (Na⁺ + K⁺: Na⁺ + K⁺ + Ca²⁺) and for major anions (Cl⁻: Cl⁻ + HCO₃⁻) computed from the ionic concentration of groundwater of the study area are plotted against TDS (Figure 4).

Figure 4.

Mechanisms controlling groundwater chemistry (after Gibbs [25]).

Most groundwater samples fall in the rock domain in both the seasons, where the TDS is between 100 and 1000 mg/L (Figure 4). The remaining groundwater samples are observed from the evaporation domain, where the TDS is more than 1000 mg/L. Falling off the groundwater samples in the rock domain indicates the water-rock interaction. The average values of TDS, Na⁺, HCO₃⁻, and Cl⁻ vary from 844 to 981, 107.8 to 94.5, 271 to 284.75, and 95.4 to 88.5 mg/L from pre- to post-monsoon, where the TDS is less than 1000 mg/L, while they are from 1402 to 1583, 306.68 to 380.54, 408.2 to 430.17, and 239.2 to 278.85 mg/L in the respective seasons, where the TDS is more than 1000 mg/L (Table 4). The increase of Na⁺ and Cl⁻ from TDS less than 1000 mg/L to TDS more than 1000 mg/L concentrations are mainly caused by anthropogenic pollution. Because of this reason, the groundwater samples move towards the evaporation domain from the rock domain, as also reported by Wang et al. [26], Mamatha and Rao [27], Li et al. [28], and Narasimha and Sudarshan [29] in other regions (Figure 4).

TDS range (mg/L)	Na^+ (mg/L)		Cl^− (mg/L)		HCO3^− + CO3^2− (mg/L)
	Pre-monsoon	Post-monsoon	Pre-monsoon	Post-monsoon	Pre-monsoon	Post-monsoon
<1000	107.80	101.00	95.4	87.00	328.40	353.00
>1000	306.73	365.30	239.20	269.85	479.46	500.91

Table 4.

Classification of Na⁺, Cl⁻ and HCO₃²⁻ + CO₃²⁻ based on TDS range.

Since the groundwater quality is dominated by Na⁺ and HCO₃⁻ ions due to rock-water interaction, this factor appears as governing process for the release of F from the country rocks. As a result, the groundwater shows the higher F content. Similar conditions have been reported by Li et al. [30] in China. On the other hand, the evaporation and/or anthropogenic activity increases the Na⁺ and Cl⁻ contents, which make the higher TDS.

6.3 Human health survey

Human health survey has been conducted in the present study area to analyze the fluorosis hazards with respect to F⁻ content in the selected endemic villages of T. Annavaram, Talrapalli, Datlavaripalem, Marellavaripalem, and Upplapadu. Dental health survey collected 659 data samples on people, including the males (213), females (214), and children (232) to understand the severity of fluorosis hazard in this area. The results of dental survey carried out in the selected villages of study area are presented in Table 5.

Name of the village	Population surveyed	Adults						Children
		Male			Female			Children
		People surveyed	Effected people		People surveyed	Effected people		Surveyed	Effected	%
			People	%		People	%	Children	Children
T.Annavaram	76	30	26	86.67	30	18	60	16	10	62.5
Talrapalli	180	54	22	40.74	54	11	20.37	72	41	56.94
Datlavaripalem	155	43	37	86.05	44	33	75	68	58	85.29
Marellavaripalem	113	41	28	68.29	41	32	78.05	31	24	77.42
Upplapadu	135	45	14	35	45	10	25	45	19	42.22
Total	659	213	127	—	214	104	—	232	152	—
Average				63.35			51.68			64.87

Table 5.

Results of dental survey in the selected villages of study area.

The results of dental survey population are compared with the Dean’s Classification Index (1942) of tooth surface (15; Table 6). The results of Dental Fluorosis Index (DCI) and Community Fluorosis Index (CFI) are presented in Table 7. Out of the 76 members surveyed in T. Annavaram, the people who come under questionable, very mild, mild, moderate, moderately severe, and severe categories are 2, 7, 12, 16, 11, and 6 respectively. These contribute 71.05% of the fluorosis (Figure 5a). In Talrapalli, 180 people are surveyed. The mentioned categories are 20, 18, 14, 14, 4, and 4 respectively, which contribute 41.11% of the fluorosis (Figure 5b). Datlavaripalem records the highest dental hazard in the people in the respective categories are 17, 32, 19, 22, 17, and 21 (Figure 5c). These are contributes 88.27% of the fluorosis. In the Marellavaripalem, the total surveyed people are 155. Out of which, the questionable, very mild, mild, moderate, moderately severe, and severe categories are 15, 18, 14, 12, 11, and 14 respectively, contributing 74.33% of the dental fluorosis (Figure 5d). The lowest dental fluorosis (34.29%) is recorded in the Upplapadu village (Figure 5e) where the questionable, very mild, mild, moderate, moderately severe, and severe categories are 5, 8, 10, 6, 3, and 11 respectively. The above data indicate the different degrees of fluorosis according to varying concentrations of F in drinking water. In the present study area, the concentration of F varies from 0.5 to 12.4 mg/L in pre-monsoon groundwater and 0.14 to 16.0 mg/L in post-monsoon groundwater.

Deans number	Category	Indication of tooth surface
0	Normal	Translucent, smooth enamel with a glossy appearance
0.5	Questionable	Seen in endemic areas, borderline between normal and very mild
1	Very mild	Small opaque, paper-white areas scattered irregularly over the labial and buccal surface of teeth
1.5	mild	White opaque areas are more extensive but do involve many surfaces
2	Moderate	Entire tooth surface involved, minute pitting often present on labial and buccal surfaces, brown surface, brown stains, frequently disfiguring
3	Moderately severe	Entire tooth surface involved marked pitting with intense brown stain
4	Severe	Widespread, deep brown or black areas, corrosion type of mottled enamel

Table 6.

Dean’s classification [14].

Village	AverageF^− Value	Normal	Questionable	Very Mild	Mild	Moderate	Moderately severe	Severe	Total	CFI	% of DF
1	3.38	26	2 (1)*	7 (7)*	12 (18)*	16 (32)*	11 (33)*	6 (24)*	76	1.51	71.05
2	1.56	106	20 (10)	18 (18)	14 (21)	14 (28)	4 (12)	4 (16)	180	0.58	41.11
3	6.08	27	17 (8.5)	32 (32)	19 (28.5)	22 (44)	17 (51)	21 (84)	155	1.60	88.27
4	3.7	29	15 (7.5)	18 (18)	14 (21)	12 (24)	11 (33)	14 (48)	113	1.41	74.33
5	1.93	92	5 (2.5)	8 (8)	10 (15)	6 (12)	3 (9)	11 (44)	135	0.86	31.85

Table 7.

Results of dental fluorosis and community fluorosis index.

^*

Figures shown in the brackets indicates the Calculated DCI values for each individual category.

Village names: 1; T. Annavaram; 2. Talrapalli; 3. Datlavaripalem; 4. Marellavaripalem; 5. Uppalapadu.

Figure 5.

Pie plot showing the different degrees of dental hazard in the study area.

Figure 6 indicates that the dental fluorosis in the surveyed villages is high in children (64.87%) compared to men (63.35%) and women (58.38%). This could be due to effect of the drinking water on children, in particular as their body tissues are in their growth stage [31, 32]. The effect of fluorosis is higher in males compared to female. Generally, the males take more drinking water and diets than the females due to their greater physical activity. This is also supported by the significant positive correlation between average F content in groundwater and the percentage of dental fluorosis.

Figure 6.

Histogram showing the dental hazards in the study area.

6.4 Community fluorosis index

Community Fluorosis Index (CFI) was calculated based on the symptoms of dental fluorosis with respect to DCI [14, 23]. Criteria for people with symptoms of dental fluorosis are identified and classified in each category based on CFI. CFI is the ratio of the number of people affected in each category and Dean’s numerical weight to total number of affected people (Eq. (1)). If CFI is greater than 0.6; fluorosis is considered to be a public health problem in that area [14, 23, 24, 25].

Higher prevalence rates of endemic fluorosis are observed in four out of five screened villages. The CFI values of T. Annavaram, Datlavaripalem, Marellavaripalem, and Uppalapadu are 1.51, 1.60, 1.41, and 0.86 respectively which may cause public health problems. Tarlapalli village is the only one showing CFI value (0.58) is less than 0.6, where there is no fluorosis hazard was observed (Table 7).

The above dental survey in the study area indicates that there is different degree of fluorosis hazard due to varying concentration of F in drinking water, quantity of water consumption, intake of nutrients at risk, dietary substance, hot climate condition and long period exposure after digestion of in human body [33].

6.5 Urine sample analysis survey

The urine sample analysis survey is carried out alongside, the dental survey. F is excreted primarily through urine [34], which is an early indicator of fluoride poisoning. The F content in urine depends on the concentration of F in the drinking water. The acceptable concentration of urine F is 1.0 mg/L [35]. The results of the urine samples of current study area showed that minimum and maximum urinary F concentrations are 1.2 and 16.2 mg/l, while the groundwater samples (mean of both seasons) show 0.42–14.2 mg/l, respectively (Table 8). The urine samples were further classified as low (<0.6 mg/L), intermediate (0.6–1.5 mg/L) and high (>1.5 mg/L) based on mean F− content in the groundwater.

F^− range in groundwater	Range and mean F^− content in groundwater (mg/L)	Range and mean F^− content in urine (mg/L)	% of samples
<0.6 mg/L	0.45	1.2	4
	(0.14–0.50)	(1.2)
0.6–1.5 mg/L	1.14	2.52	32
	(0.76–1.14)	(1.4–4.2)
>1.5 mg/L	2.75	4.93	64
	(1.55–14.20)	(2.1–16.2)

Table 8.

Data* on different F⁻ concentrations in groundwater and urine (mg/L).

^*

Mean F^– concentration of groundwater for pre- and post- monsoon seasons.

The minimum and maximum of urine F concentrations among the low (<0.6 mg/L), intermediate (0.6–1.5 mg/L) and high (>1.5 mg/L) F areas ranged from 0.45 to 1.2 mg/l, 1.4 to 4.2 mg/L and 2.1 to 16.2 mg/L respectively. The corresponding mean values were 1.2 mg/L, 2.52 mg/L, and 4.93 mg/L respectively (Figure 7). The lowest urine concentration (1.2 mg/L) is observed in low F areas (with F < 0.6 mg/L in water) and the highest urine concentration (16.2 mg/L) was observed among areas of high F concentration (>1.5 mg/L) in water. This was also supported by excellent positive correlation between the urinary and groundwater F (Figure 8). The mean F concentration in urine has enhanced from low to high F groups (Table 8). The urine F content even in the low F areas exceeded the acceptable concentrations of 1.0 mg/L. This shows that the groundwater consumed by the individuals was the main causative factor for fluorosis hazard.

Figure 7.

Results of F− content in urine and groundwater* samples of study area.

Figure 8.

Mean F− content in groundwater vs urine fluoride.

7. Conclusion

The present study reveals that the underground drinking water of the investigated area was contaminated with F. The population of the study area was therefore chronically exposed to higher levels of F from drinking water. There was a significantly positive correlation between the F content of groundwater and urine of the fluorosis-affected children in the study area. This suggested that a high level of endemic fluorosis is prevalent in the study area due to the consequence of a higher concentration of F in underground aquifers. The highest number of fluorosis-affected children (85.29%) was recorded from Datlavaripalem village. It can be concluded that the high F in groundwater leads to increased incidences of dental fluorosis among the surveyed people. Also this study indicates that urinary F is a good indicator of community exposure F. The study revealed that the F level in urine was higher than the accepted levels. It is also evident that other sources of dietary F intake other than drinking water contributed significantly to community overexposure to fluoride in the studied areas. This calls for urgent interventions to mitigate effects of excessive environmental fluoride in these areas

Acknowledgments

The author wants to thank Dr.P.V. Nageswara Rao, Assistant Professor, Department of Geology, Acharya Nagarjuna University for his constant encouragement throughout this work.