Fluoride abundance and their release mechanisms in groundwater along with associated human health risks in a geologically heterogeneous semi-arid region of east India

Abstract

The present study investigated the source, release mechanisms, mobility and controlling factors of fluoride in groundwater. It has been conducted in the semi-arid rural tract of Birbhum district, located in the eastern part of peninsular India which comprises of the granite genesis aquifers, soft to medium hard rocks with laterite and lateritic soils and alluvial aquifers. The groundwater fluoride level of the study area varied from 0.3 to 9.36 mg/L with an average value of 1.7 mg/L. In the granite region, weathering of granitic rocks, dissolution and iron-exchange processes are responsible for fluoride occurrence in groundwater and its concentration is controlled by the concentration of carbonate and bicarbonate ions. In clay, laterite soil and sedimentary aquifer regions, pH of the circulating water and clay/soil, surface charge characteristics of clay/soils, soil permeability and residence time control the groundwater fluoride through adsorption/desorption of fluoride by the clay and laterite soil. High evaporation rate of the study area also plays an important role to increase the groundwater fluoride concentration. The study also evaluated the health risks to the residents based on the dose-response characterization and USEPA human health risk assessment model through ingestion and dermal contact exposure pathways. The population of infants and children within the study area is more susceptible to the non-carcinogenic health hazards of fluoride than adults. This takes place mainly through direct ingestion route where the dominance order of the population is infants > children > men > women.