Mechanism of Fluoride and Nitrate Enrichment in Hard-Rock Aquifers in Gooty Mandal, South India

Abstract

The aim of this study is to understand the mechanism of Fluoride (F −) and Nitrate ( $$ {NO}_3^{-}\Big) $$ enrichment of groundwater in the semi-arid region of Gooty Mandal, Anantapur district, Andhra Pradesh, India. A total of 72 groundwater samples were collected from representative bore wells during pre- and post-monsoon seasons 2014 and physico-chemical parameters were analyzed. Chemometric analysis, i.e., basic statistics, Pearson’s correlation coefficient (r) and geochemical modeling, were employed for estimating the saturation index of fluorite (CaF 2) and calcite (CaCO 3). Based on the Piper classification, most of the groundwater samples were identified as of sodium-bicarbonate $$ \left({Na}^{+}-{HCO}_3^{-}\right) $$ type. The order of abundance of major anions and cations in groundwater was found as $$ {HCO}_3^{-}>{Cl}^{-} $$ > $$ {NO}_3^{-} $$ > $$ {\ SO}_4^{2-} $$ > $$ {\ {CO}_3^{2-}> F}^{-} $$ and Na + > Ca 2+ > Mg 2+ > K +. Most of the major ions exceeded acceptable limits of drinking water standards in the collected groundwater samples. Excessive F − and $$ {NO}_3^{-} $$ concentrations in drinking water may have negative effects on human health. The F −concentration ranged from 0.8 to 3.8 mg/L and 0.9 to 4.1 mg/L with a mean of 2.1 and 2.3 mg/L during pre- and post-monsoon seasons, respectively. The $$ {NO}_3^{-} $$ concentration during pre- and post-monsoon varied from 3.08 to 1114 mg/L and from 3 to 1242 mg/L with a mean of 238 and 201 mg/L, respectively. 78% and 83% of samples for F − and 67% and 61% of samples for $$ {NO}_3^{-} $$ exceeded the maximum acceptable limits of drinking water standards in both seasons. The study reveals that the groundwater is extremely dangerous for drinking purpose in normal condition and the groundwater chemistry in the study period was mostly influenced by ion exchange and anthropogenic activities.