Controlling factors of fluoride in groundwater in a part of South India
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ORIGINAL PAPER
Controlling factors of fluoride in groundwater in a part of South India N. Subba Rao 1
Received: 25 April 2017 / Accepted: 5 November 2017 # Saudi Society for Geosciences 2017
Abstract Fluoride (F−) is the most important element for human health. Hydrogeochemical survey was conducted to probe into the controlling factors of F− in the groundwater of a semi-arid part of South India. The study area comprises of F−-bearing minerals (hornblende, biotite, and apatite) in the Precambrian rocks, sandstones in the Upper Gondwana rocks, and clays in the Quaternary formations. Forty-seven percent of the total groundwater samples have the higher F− content than its permissible limit of 1.50 mg/L prescribed for drinking purpose. The chemical data of the groundwater is analyzed to assess the geochemical processes dominating the F−-bearing groundwater, using Piper and Gibbs diagrams, correlations, saturation indices, ionic ratios, and multivariate analysis. Piper diagram shows that the groundwater quality is characterized by Na+-HCO−3 and Na+-Cl−types, while the Gibbs diagrams suggest that the groundwater chemistry is mainly controlled by water-rock interactions and is subsequently modified by human activities. The F− groundwater is positively correlated with pH, total dissolved solids, Mg2+, Na+, K+, 2+ − HCO −3 , Cl− , SO 2− 4 , and NO 3 and negatively with Ca , representing the influences of geogenic and anthropogenic origins on the groundwater system. Geochemical ratios and saturation indices indicate that the processes of mineral dissolution, ion exchange, and evaporation mainly govern the high F− groundwater, while the chemical fertilizers cause for the enrichment of F−in the groundwater. Cluster and principal component analyses further support the above findings.
* N. Subba Rao [email protected] 1
Department of Geology, Andhra University, Visakhapatnam 530 003, India
Keywords Fluoride . Groundwater . Geogenic origin . Anthropogenic source . Semi-arid region
Introduction Normally, the small amount of fluoride (F−) is essential for development of bones and formation of dental enamel (Handa 1975). However, low concentration of F− (< 0.60 mg/L) in drinking water results in dental decay, while an excess of it (> 1.50 mg/L) causes dental fluorosis (WHO 2011; BIS 2012). Drinking water with F− content in between 0.60 and 1.50 mg/L is, thus, stipulated as safe limit for human health. In the world, more than 260 million people suffer from fluorosis (Amini et al. 2008) due to drinking of water with higher F−content (> 1.50 mg/L). Contamination of groundwater with F−is widespread especially in Africa, China, India, Iran, Kenya, Nigeria, Pakistan, South America, and Srilanka (Ayoob and Gupta 2006), posing high health risk to people (Wu and Sun 2016; Li et al. 2016a). In India, the first case of endemic fluorosis was reported due to higher concentration of F− in groundwater as long as 1937 in the Prakasam district (erstwhile Guntur District), Andhra Pradesh (Short et al. 1937). About 61 million people suffer fr
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