Abstract
Abstract. 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−1 in F− 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− 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− 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− concentration in groundwater of this study area ranges from 0.17 to 2.7 mg L−1. Among, twenty groundwater samples have fluoride exceeding the maximum permissible limit as per the BIS (1.5 mg L−1). 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 Ca2+ > Mg2+ > Na+ > K+ and HCO3- > Cl− > F− 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− 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.
Highlights
The usefulness of groundwater to human is great extent
Groundwater in crystalline rocks, mainly granites/granite gneisses are vulnerable to fluoride because they often contain abundant fluoride bearing minerals
Several studies have mentioned an increase in dissolved F− concentrations with increasing groundwater residence time in the aquifer systems (Nordstrom and Jenne, 1977; Apambire et al, 1997; Edmunds and Smedley, 2013)
Summary
The usefulness of groundwater to human is great extent. Groundwater is considered to be the major source of drinking water in India. Groundwater chemistry is largely a function of the mineral composition of the aquifer through which it flows (Brindha and Elango, 2011). It depends upon physical and geological factors such as evaporation rate, residence time, aquifer media, rock–water interaction, recharge capacity, and anthropogenic activities. Fluoride in groundwater may be of geogenic (natural) or anthropogenic (Human induced). Several studies have mentioned an increase in dissolved F− concentrations with increasing groundwater residence time in the aquifer systems (Nordstrom and Jenne, 1977; Apambire et al, 1997; Edmunds and Smedley, 2013). Prolonged rock-water interactions through weathering of fluoride-rich rocks enrich fluoride concentration in the groundwater systems.
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