Geochemical characterization of groundwater and source apportionment of potential pollutants in a tribal stretch infected with chronic kidney disease of unknown etiology

This paper draws world attention toward a tribal stretch in central India exposed to chronic kidney disease of unknown etiology (CKDu). To date, about 100 people have died and more than 300 hospitalized from a single village, Supebeda, of 1200 inhabitants. The occurrence of CKDu in this part of the world is a recent discovery and its potential pollutants are still eluding human understanding. Since groundwater is being accused as the culprit, this contribution attempts to characterize the area geochemically, study major rock-water interactions, identify potential pollutants, and apportion their sources. Analytical results of 27 groundwater samples reveal that the area suffers from NO₃⁻ (0–128.3 mg/L) and F⁻ (0–1.9 mg/L) contamination with total hardness, Ca²⁺, Mg²⁺, and Cl⁻ as other violator parameters. Comprehensive Water Quality Index classifies ∼52% of the samples as potable; ∼37% could be suitable for drinking pending certain treatment. While elevated F⁻ concentrations are due to the weathering of fluoride-bearing minerals (fluorite, amphiboles, biotite, hornblende, granite gneiss, etc.), the excess Ca²⁺ and Mg²⁺ ions are attributed to 63% of the samples exhibiting cation exchange processes (Ca²⁺, Mg²⁺, Cl⁻ < Na⁺ + K⁺) resulting from the weathering of carbonate (calcite, dolomite), anhydrite, gypsum, calc-silicate (anorthite, plagioclase, amphiboles) and ferromagnesian (hornblende, biotite) minerals in the metamorphic rocks. About 22% of the samples depict reverse ion exchange processes (Ca²⁺, Mg²⁺, Cl⁻ > Na⁺ + K⁺) due to silicate weathering including dissolution of Cl⁻ salts (albite and halite minerals) and anthropogenic inputs that also contribute to elevated concentrations of NO₃⁻.