Ionic flux and geological release of fluoride in groundwater sources of a semi-arid tropical region in south India

Abstract

ABSTRACT Groundwater with excess fluoride content is a major issue in most of the states in India. Mineral ions and its seasonal fluctuations are influencing fluoride contamination in groundwater sources to a greater extent. Reports on health issues from several regions of south India have instigated detailed studies on groundwater fluoride contamination and the geo-environmental reasons underlying it. Fluoride contamination in the groundwater sources of Palakkad district, a semi-arid tropical region in South India, was assessed along with major anions and cations. The study revealed that 89% of Po, 88% of Pr, and 52% of Mo samples exceeded the BIS limit of fluoride concentration of 1.0 mg/L. The piper plot and correlation studies affirm that fluoride contamination is accelerated by a higher concentration of magnesium, sodium ions and a lower concentration of calcium and dissolved iron. The negative correlation of fluoride with nitrates supports its geological origin. Fluoride contamination is highly linked with the hornblende biotite gneiss (~ 42%) distributed in the central-eastern part of the district. IDW interpolation defines a maximum of 3.4 mg/L of fluoride in the groundwater sources. The overdose of fluoride in drinking water, which exceeded the OFC level, is noted to be the reason for the prevalence of fluorosis in the study area. The study recommends 0.61 mg/L of fluoride as an OFC limit for drinking purposes.