Geochemical partitioning and leaching behaviour of geogenic contaminants from the partially weathered rocks in chronic kidney disease of unknown etiology (CKDu) endemic regions in Sri Lanka

Studies regarding geochemical partitioning and leaching behavior of Hofmeister ions, which is considered as a risk/causative factor for chronic kidney disease of unknown etiology (CKDu), are scarce. Therefore, Hofmeister ions’ leaching behavior of partially weathered rocks from CKDu endemic (Girandurukotte) and non-endemic (Sewanagala) areas, Sri Lanka were compared. Rock mineralogy was analyzed using X-ray Diffraction, and total ion contents were determined using alkaline and acid digestions. Leaching experiments were conducted for powdered rocks using HCO₃⁻ rich water and deionized water (DI) to determine the kinetics of Hofmeister ion release into groundwater. Fluoride fractionation in rocks was determined through a sequential extraction. The most abundant ions in both rocks from CKDu endemic and non-endemic areas were Cl⁻; possibly due to carbonate and silicate minerals and Mg²⁺; possibly due to biotite minerals. Maximum leaching capacities of Hofmeister ions; F⁻, Cl⁻, SO₄²⁻, K⁺, Mg²⁺, Ca²⁺ were higher with HCO₃⁻ rich water compared to deionized water in both rocks from Girandurukotte (F⁻_HCO3: 5.51 mg/kg > F⁻_DI: 2.62 mg/kg) and Sewanagala (F⁻_HCO3: 6.24 mg/kg > F⁻_DI: 3.78 mg/kg). This F⁻ variation might be due to the higher exchangeable fraction in the rock from Sewanagala (2.027 mg/kg) compared to Girandurukotte (0.963 mg/kg). Although, the organic matter bound F⁻ fraction in the rock from Girandurukotte (47.62 mg/kg) was higher than that of Sewanagala (31.66 mg/kg). However, the cumulative effect of exchangeable, carbonate bound, Fe–Mn oxide bound, and organic matter bound F⁻ fraction in the rock from Girandurukotte was higher (52.6%) compared to Sewanagala, making F⁻ a possible risk factor for CKDu.