Hydrogeochemical forecasting in a tribal stretch infected with chronic kidney disease of unknown etiology

A tribal stretch in central India has been silently suffering from the enigmatic chronic kidney disease of unknown etiology (CKDu) for the past many years. It drew national attention in 2018 when over a quarter of the population from a single village of 1200 people got hospitalized with at least 100 deaths in a few years' span. This contribution tries to understand the geochemical genesis of the problem and its evolution process through a study of major rock-water interactions. The future hydrogeochemical environment of the area has been forecasted based on saturation indices of several key minerals. Finally, a probabilistic estimation of the population's exposure to the Hofmeister ion series has been made to understand the role of the specific ion effect on the onset of CKDu. Three distinct chemical facies have been identified based on the analytical results of 27 groundwater samples: Ca²⁺-Mg²⁺-HCO₃^- (55.56 %), Ca²⁺-Mg²⁺-Cl^--SO₄^2- (29.63 %), and Na⁺-K⁺-HCO₃^- (14.81 %). The positive loadings (r) of EC and TDS with Ca²⁺ (0.89; 0.98), Mg²⁺ (0.79; 0.89), Na⁺ (0.78; 0.48), Cl^- (0.99; 0.93), and NO₃^- (0.72; 0.85) have led to groundwater hardness and salinity. Ion exchange processes and saturation indices of the geogenic minerals, such as anhydrite, gypsum, fluorite, halite, and sylvite, play crucial roles in the mineralization process. As these minerals progress toward full saturation, their dissolution with the host aquifers releases more of Ca²⁺, Na⁺, K⁺, SO₄^2-, Cl^- and F^- ions continually. This exacerbates the fluorosis problem besides increasing salinity and water hardness in the study area. The combined effects of Ca²⁺+Mg²⁺ ions with a control on the total hardness, increased Na⁺/Ca²⁺ ratio, and excess F^- ions in groundwater are suspected to be the inducing factors for CKDu. This hypothesis is strongly supported by the occurrence of Hofmeister phenomena in the tubular areas of human kidneys through ingested groundwater.