HIGH FLUORIDE CONCENTRATION IN THE GROUNDWATER OF UTTANGARAI TALUK, KRISHNAGIRI DISTRICT, SOUTH INDIA Sridhar.N1, Chandrasekar.N2, Subbarayan.M.R3 1,2,3Department of Civil Engineering &Earth sciences, Jayam College of Engineering and Technology, (India) ABSTRACT The present study has been made to evaluate the Fluoride concentration of Groundwater collected from Uttangarai Taluk in Krishnagiri District of South India. Geochemical studies were carried out on 34 samples from 24 villages and they were analyzed for fluoride and other water quality parameters (EC, TDS, pH, TH, Na, K, Ca, Mg, Cl, CO3, HCO3 and SO4). Groundwater is the only source of drinking water in this area, as due to depletion of surface waters, more and more people are using groundwater for drinking purpose and these are exposed to health vulnerability. This study reveals that fluoride concentration varies between 0.37ppm and 3.47ppm with an average of 1.79ppm. The dominance of cations and anions are as follows: Ca2+ > Na+> Mg2+> K+ and SO4 2-.- > HCO3 - > Cl - > CO3-.The source for high fluoride is found to be due to leaching of the ion from biotite rich segregations in the country rock particularly shear zones. The results indicate that the groundwater quality in the vicinity of shear zone needs to study in detail. Key Words: Fluoride concentration, Electrical conductivity (EC), Total dissolved solids (TDS), pH. I. INTRODUCTION Groundwater forms a major source of drinking water in urban as well as in rural areas. More than 90% of the rural Population uses groundwater for domestic purposes. The most widespread contamination in India is that of elevated levels of fluoride. It is widely prevalent in different parts of India, particularly in the state of Andhra Pradesh, Tamil Nadu, Uttar Pradesh, Gujarat, and Rajasthan, where 50-100% of the districts have drinking water sources containing excess level of fluoride (CGWB 2014). The occurrence of fluoride in groundwater is mainly due to natural or geogenic contamination and the source of contamination of often complex and site specific (Saxena and Ahmad 2003). Fluorspar is commonly known as an ore of mineral fluorite. Fluorite/Fluorspar occurs in many rocks in varied forms. The fluoride content of the rocks, due to repeated weathering, gets slowly dissolved in water, when the water acquires acidic nature. In this procedure, water gets contaminated by fluoride (Acharya & Mathi, 2010). A permissible limit of fluoride concentration in drinking water as per WHO (2011) guideline is up to 1.5 mg/L. (WHO, 2011 and BIS, Revised 2003). The excessive amount of fluoride in water and environment is poisonous. Excessive fluoride concentrations in ground water have been reported in India, where 17 states are facing fluoride problem (Yadav and Khan 2010). Endemic 433 | P a g e fluorosis remains a challenging and extensively studied national health problem in India. The high concentrations of fluoride in groundwater in India have resulted due to the dissolution of fluorite, apatite, micas, amphiboles with the OH, F group and topaz from the local bedrock (Chidambaram 2000). The occurrence of the fluoride in groundwater is predominantly geogenic. Fluoride enrichment in groundwater takes place mainly through leaching and weathering of the Fluoride bearing minerals present in the rocks and sediments which depends on several factors such as the origin of water, composition of water bearing medium, the length of time the water has been in contact with the medium, the temperature and pressure conditions, ion- exchange, rate of recharge and discharge. In groundwater, the natural concentration of fluoride depends on the geological, chemical and physical characteristics of the aquifer, the porosity and acidity of the soil and rocks, the temperature and the action of other chemical elements (Tahaikt et al. 2008). The important fluoride-bearing minerals are; fluorite (fluorspar), fluorapatite, cryolite, biotite, muscovite, lepidolite, tourmaline, hornblende series minerals, glucophane-riebeckite. Besides these, there are anthropogenic source of fluoride also, like phosphatic fertilizer, cowdung and urban waste. Fluoride is essential for the development of tooth enamel, dentin, and the bones. It is harmful when it exceeds the permissible limit of 1.5 mg l–1(WHO 2011) in water. The problems are most pronounced in the states of Andhra Pradesh, Bihar, Gujarat, Madhya Pradesh, Punjab, Rajasthan, Tamil Nadu and Uttar Pradesh (Pillai and Stanley, 2002). Low concentration of fluoride below 0.5 ppm causes dental caries (Acharya et. al.2008). Manikandan et al. (2012) higher concentration of fluoride was noted in hard rock terrain of this district. It is found that nearly 58 % of the samples have more fluoride corresponding to magnesium water types. This is due to the release of fluoride from the magnesium-bearing minerals like biotite, hornblende or reasons of weathering of apatite/hydroxyapatites that is observed in charnockites. Various studies have been reported about fluoride content in water bodies in different part of India. The increase of F− concentration with SI of dolomite also shows a closer affinity of this ion to Mg2+ (Manivannan et. al. 2010). Environmental hydrogeochemistry and genesis of fluoride in groundwater of Dindigul district, Tamilnadu in India (Chidambaram et al. 2012). The Krishnagiri district contains minerals with higher amounts of fluoride (CGWB 2009), (Manikanda et. al., 2011). The favorable factor which contributes to rise of fluoride in ground water is presence of fluoride rich rock salt system (G S Tailor et. al., 2010). F– ions released into the groundwater are considered to be controlled by the degree of saturation of fluorite and calcite, and the concentration of Ca2+, HCO3 –, and Na+ ions in groundwater, among other natural geochemical processes (Mamatha and Rao, 2010). Chemical weathering under arid to semiarid conditions may seem to have favoured high concentration of fluoride in ground water (Kausik Kumar Das et. al. 2012). Drinking water in the Krishnagiri district of Tamilnadu containing high level of fluoride as conformed by the prevalence of dental and skeletal flurosis among the people of the village in this region. It is of course well known that fluorosis is caused by the consumption of drinking water containing high fluoride. The prevalence of dental fluorosis in the village of the Uttangarai block of Krishnagiri district prompted us to determine the fluoride levels of all available drinking water sources in order to identify the fluoride endemic areas that require immediate adoption of remedial measure to prevent the problem of fluoride toxicity. 434 | P a g e II. STUDY AREA The study area is bounded by latitudes 12° 18’ N to 12° 25’ N and longitudes 78° 35’ E to 78° 32’ E and situated at an average height of 1000 m above mean sea level. Uthangarai is bounded by Vellore district in the North and Thiruvannamalai district in the East, Pochampalli taluk in the West and Dharmapuri District in the South (Fig.1). Groundwater generally occurs under phreatic conditions in the weathered mantle and under semi- confined conditions in the fractured zones at deeper levels. The thickness of weathered zones in the district ranges from less than a meter to more than 15 m (CGWB 2009). A major portion of the Krishnagiri district consists of quartzofelspathic gneiss and followed by charnockites in the south western part of the district. The eastern part of the district is mainly composed of syenites, granite felsite and epidote hornblende gneiss. There are also patches of basic, ultrabasic and mafic rocks. Amphibolite patches are noted in the northern part of the district. Quartz reef is hosted by both hornblende schist of the region and the champion gneiss (quartzofelspathic gneiss) (GSI 2009). Ponnaiyar is the major river draining the district and is ephemeral in nature. The normal annual rainfall over the district varies from about 750 to about 900 mm. Fig. 1. Study area map 435 | P a g e III. METHODOLOGY Thirty four groundwater samples were collected in one liter polyethylene bottles with airtight lids. pH was measured using portable pH meter and EC were measured by EC meter in the field itself. With respect to cations, Calcium and Magnesium were analyzed following volumetric method; Sodium and Potassium were analyzed using Flame photometer; and with respect to anions, Chloride and Bicarbonate were estimated by volumetric method; Nitrate, and Sulfate were estimated by turbidity method. All chemical analyses were carried out following APHA method (APHA, 1999). Fluoride content was determined using an ion analyzer (Orion modal 720 – pH-ise-FLURIMETRE, USA) equipped with a fluorine selective electrode. Chemical analyses of groundwater in this study were classified by a graphical technique described by piper (1944). IV. RESULT AND DISCUSSION Water is an indispensable natural resource on earth. Two-third of the earth surface is covered by water. It is an essential and vital component for survival of all the living beings. It constitutes about 70% of the body weight of almost all living organisms. Potable water is the water that is free from disease producing micro-organisms and chemical substances. The scarcity of clean and potable drinking water has emerged as most serious environment issue of the twenty first century (Das N.C 2013). The sources of fluoride have been divided in two sections dealing with water and soil. Fluoride concentration in drinking water in various places of India is illustrated in Table 1. Table