0016-7622/2018-92-3-337/$ 1.00 © GEOL. SOC. INDIA | DOI: 10.1007/s12594-018-1017-4 JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.92, September 2018, pp.337-345 Salinization and Deterioration of Groundwater Quality by Nitrate and Fluoride in the Chittur Block, Palakkad, Kerala E. Shaji, a* , Gómez-Alday, J.J. b , Hussein, S. c , Deepu, T. R. a and Anilkumar, Y. a a Department of Geology, University of Kerala, Kariavattom Campus, Trivandrum - 695 581, India b Hydrogeology Group, Institute for Regional Development (IRD), University of Castilla-La Mancha (UCLM), Albacete, Spain c Department of Geology, Faculty of Science, United Arab Emirates University (UAEU), Al Ain, United Arab Emirates *E-mail: shajigeology@gmail.com ABSTRACT Chittur block represents a mid-land region of Palakkad district, Kerala and the block differs from the rest of the blocks in its climate and availability of groundwater. About 75% of the people depend on agriculture for their livelihood. Results showed that groundwater salinity levels (up to 1,963 mg/L TDS),fluoride (up to 6.3 mg/L) and nitrate (up to 141 mg/L) contents have increased significantly in tandem with the increase in groundwater abstraction. Before human intervention the chemical weathering of gneisses and granites was the main process impinging on the chemical signature of groundwater. The initial chemical equilibrium conditions change with increasing groundwater withdrawal rates and fertilizer input, in a milieu of lower natural groundwater recharge. The appearance of higher levels of bicarbonate, linked to denitrification processes, and the decrease in calcium, due to calcite precipitation, can lead to increased content of sodium and fluoride in groundwater. In this scenario the use of groundwater resources for human consumption and agriculture represents a public health risk if water management actions do not change the trend in water use in the near future. The potential loss of fertile soil by groundwater salinization must also be considered when planning sustainable policies in a region with over dependence on groundwater resources. INTRODUCTION Groundwater quality preservation is one of the major concerns worldwide. The Government of India affirms that groundwater has become one of the important sources of water for meeting the requirements of various economic sectors since the last few decades. Agricultural development, industrialization and urbanization have lead to the overexploitation and contamination of groundwater resources in some hydrogeological systems in India. These facts result in adverse environmental impacts and threaten the long-term sustainability of water resources (CGWB, 2010). Groundwater quality depends on water-rock interactions, in which geology and weathering can play an important role, as also anthropogenic activities and climate. Changes in land use are one of the most influential factors in groundwater pollution (Benson et al. 2006; De Andrade et al. 2008; Jiang et al. 2008; Jalali 2009; Martín-Queller et al. 2010). On a global scale, Flowers (1999) pointed out that salinity has already affected approximately 50% of all irrigated land. Martinez- Beltran and Manzur (2005) calculated the total global soils affected by salt at 8.31 Mkm 2 . Salinity can cause yield reduction in agriculture, by driving metabolic dysfunctions in plants due to osmotic stress and the disruption of ion homeostasis (Hasegawa et al. 2000). Increasing soil salinization is also occurring in India (Wichelns, 1999). Salinity always exists in ground water but in variable amounts. It is mostly influenced by aquifer material, solubility of minerals, duration of contact and factors such as the permeability of soil, drainage facilities, quantity of rainfall and above all, the climate of the area. Around 200 million people in 25 nations are in great risk of fluoride (F - )-induced diseases (Ayoob and Gupta 2006). In India about 60-65 million people use F - contaminated groundwater for drinking. China is one of the the worst affected countries (Jadhav et al 2015). Many states from India are afflicted with fluorosis (Panda et al. 2012 and references therein). Fluoride in small concentrations (<1.0 mg/L) has been tested to be beneficial in reducing the incidence of dental carries by formation of dental enamel (Bell and Kudwing 1970). The use of fluoride-contaminated drinking water is a well-known risk factor for public health (Mahramanhioglu et al. 2002; Jadhav et al. 2015). Due to the strong electronegativity of F - , it is attracted by Ca 2+ in bones and teeth (Susheela et al. 1993). Fluoride contents higher than 1.5 mg/L are not suitable for drinking purposes. Such concentrations in groundwater have resulted in staining of tooth enamel. Fluoride concentrations ranging between 5.0 and 10.0 mg/L may lead to bone deformation. Fluoride content in groundwater in India varies considerably (Handa 1975, Rafique et al. 2009, Reddy et al. 2010, Singh and Mukherjee 2015). Similar results were found while studying the occurrence of F – in the Palamu district (Jharkhand, India) up to 4.2 mg/L (Raju et al., 2012). High F – groundwater (up to 5.75 mg/L) has been reported from both phreatic and deeper aquifers in the eastern part of Palakkad district (Shaji et al, 2007, Deepu and Shaji 2011) and in sedimentary aquifers of Alleppey (Raj and Shaji, 2017). Groundwater deterioration by NO 3 – degrades the groundwater quality and impacts negatively on ecosystems. Elevated NO 3 – contents in drinking water is a health concern since the endogenous reduction of NO 3 – to NO 2 – , and the nitrosation of nitrites can form N-nitroso compounds which have been described as cancer precursors (Gulis et al., 2002; De Roos et al., 2003; Ward et al., 2005; Yang et al, 2007). The long-lasting impact of NO 3 – contamination is more important in rural areas of the developing world where groundwater constitutes the main source of potable water. Nitrate contamination in some agricultural regions of India are as high as 684 mg/L (Anantapur district; Suthar et al. 2009 and references therein). Recently, Brindha et al. (2012, 2013) found that the high NO 3 – concentration (up to 879.65 mg/L) in groundwater in Nalgonda district (Andhra Pradesh) is due to deficient sanitation services and leaching from animal waste. This work investigates the mechanisms and geochemistry of salinization with special emphasis on its relationship with the fate of fluoride and nitrate in order to identify plausible geochemical reactions under the current exploitation regime. In Kerala, over dependence on groundwater for domestic, irrigation and industrial purposes has led to the lowering of water table and water scarcity (CGWB, 2007).