Fluoride in groundwater: a case study in Precambrian terranes of Ambaji region, North Gujarat, India

摘要

Fluoride is one of the critical ions that influence the groundwater quality. World Health Organization (WHO, 1970) and Bureau of Indian Standards (BIS, 1991) set an upper limit of 1.5 mg L sup?1/sup in F sup?/sup concentration for drinking water purpose and above affects teeth and bones of humans. The presence of fluoride in groundwater is due to an interaction of groundwater and fluoride bearing rocks. Fluoride rich groundwater is well known in granitic aquifers in India and elsewhere. Generally, the concentration of F sup?/sup in groundwater is controlled by local geological setting; leaching and weathering of bedrock and climatic condition of an area. The main objective of the present study is to assess the hydrogeochemistry of groundwater and to understand the abundance of F sup?/sup in groundwater in hard rock terranes of Ambaji region, North Gujarat. A total of forty-three representative groundwater samples were collected and analyzed for major cations and anions using ICP-AES, Ion Chromatograph (Metrohm 883 Basic IC Plus) and titration methods. The F sup?/sup concentration in groundwater of this study area ranges from 0.17 to 2.7 mg L sup?1/sup . Among, twenty groundwater samples have fluoride exceeding the maximum permissible limit as per the BIS (1.5 mg L sup?1/sup ). It is also noticed that residents of this region are affected by dental fluorosis. The general order of the dominance of major cations and anions are Ca sup2+/sup Mg sup2+/sup Na sup+/sup K sup+/sup and HCO 3 - Cl sup?/sup F sup?/sup respectively. Geochemical classification of groundwater shows most of the samples are the alkaline earth-bicarbonate type. The semi-arid climatic conditions of the region, the dominance of granitoid-granulite suite rocks and the fracture network in the disturbed and brittle zone has facilitated the development of potential aquifers and enrichment in F sup?/sup concentration in this area. The concentration of fluoride is due to high evaporation rate, longer residence time in the aquifer zone, intensive and long term pumping for irrigation.