Entropy water quality index and probabilistic health risk assessment from geochemistry of groundwaters in hard rock terrain of Nanganur County, South India

Sixty-one groundwater samples collected from the hard rock terrain of Nanganur region in South India, were evaluated for hydrogeochemistry as well as groundwater quality for drinking and irrigation purposes. Additionally, the probabilistic non-carcinogenic human health risks associated with fluoride and nitrate concentrations were assessed using the US Environmental Protection Agency (USEPA) mathematical model. The hydrogeochemical facies, i.e. Ca2+-Mg2+-SO42- and Na+-Cl-SO42-, are result of weathering and dissolution of rocks, ion exchange between Ca2+ and Na+, and precipitation of CaCO3, and influences of anthropogenic sources. Molar ratio Na+/Cl-, and distributions of Ca2++Mg2+ versus HCO3-+SO42-, Ca2++Mg2+ versus total cations (TC), and Na++K+ versus TC indicate that silicate weathering is the prime source for the ions. Gibbs diagram also suggests that rock-water interaction is the primary process of ionic concentrations in this groundwater system. About 18% groundwater samples show medium salinity and low sodium hazards and 73% of them, however, have high salinity and low sodium hazards. Wilcox diagram indicates that most groundwater samples (92%) are suitable for irrigation. However, 66% of them exceeded the prescribed limits of nitrate (45 mg/L) and 62% these groundwater samples exceeded limit of fluoride (1.5 mg/L) for drinking purpose. Hazard quotient of nitrate (HQ(Nitrate)) and HQ(Fluoride) as well as total non-carcinogenic health risk of fluoride and nitrate (HITotal) indicates that infants and children are more vulnerable to non-carcinogenic risk than adults. Based on these results, we recommend regulation of fertilizer application and appropriate remediation for defluoridation of drinking water to prevent the further health risk.