Fluoride-bearing groundwater in Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India

The functional factors responsible for fluoride (F-)-bearing groundwater used for drinking as well as for cooking in the area of Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India are discussed. The study area is a part of an Archean Gneissic Complex, consisting of banded-biotite-hornblende-gneisses, over which the Proterozoic Cumbhum quartzites, shales, phyllites, and dolomitic limestones occur. The chemistry of groundwater is dominated by carbonates (HCO3 (-) and CO3 (2-)) at a higher pH. This results in a higher total alkalinity over total hardness, causing an excess alkalinity. Sodium ion is dominated among the cations (Ca2+, Mg2+, and K+). The concentration of F- (2.1-3.7 mg/L) is higher than that of desirable national limit (1.2 mg/L) prescribed for drinking purpose. A significant positive correlation exists between F- and pH as well as that between F- and HCO3 (-) + CO3 (2-). This indicates that the alkaline condition is the prime conducive factor for dissolving F--bearing minerals more effectively leading to a higher concentration of F- in the groundwater. Furthermore, a positive chloro-alkaline index reflects the ion exchange, and an oversaturation with respect to CaCO3 indicates the evaporation. In addition, a negative relation between the well depth and F- shows the effect of solubility and/or leaching of salts in different depth levels. These factors regulate the concentration of F- in the groundwater. On the other hand, a positive correlation of F- with SO4 (2-) as well as with K+ shows the human land use activities (namely, use of chemical fertilizers, disposal of domestic wastes, etc.), which add F- to the groundwater. A significant number of the residents of the study area suffer from the health disorders related to fluorosis, which is a consequence of higher concentration of F- in the drinking water. Thus, this study emphasizes the need for supply of safe drinking water, nutritional diet, rainwater-harvesting structures, and public education to realize health for all motto of World Health Organization.