Hydrogeochemical factors controlling the occurrence of chronic kidney disease of unknown etiology (CKDu)

Chronic kidney disease of unknown etiology (CKDu) has posed a serious threat to human health around the world. The link between the prevalence of CKDu and groundwater geochemistry is not well understood. To identify the potential geogenic risk factors, we collected 52 groundwater samples related to CKDu (CKDu groundwater) and 18 groundwater samples related to non-CKDu (non-CKDu groundwater) from the typical CKDu prevailing areas in Sri Lanka. Results demonstrated that CKDu groundwater had significantly higher Si (average 30.1 mg/L, p < 0.05) and F⁻ (average 0.80 mg/L, p < 0.05) concentrations than those of non-CKDu groundwater (average 21.0 and 0.45 mg/L, respectively), indicating that Si and F⁻ were the potential risk factors causing CKDu. The principal hydrogeochemical process controlling local groundwater chemistry was chemical weathering of silicates in Precambrian metamorphic rocks. Groundwater samples were mostly undersaturated with respect to amorphous silica and clay minerals such as talc and sepiolite, which was conducive to silicate weathering and elevated Si concentrations in groundwater. Decreased Ca²⁺ being facilitated by calcite precipitation and cation exchange between Ca²⁺ and Na⁺ favored fluorite dissolution and thus led to high groundwater F⁻ concentrations. Competitive adsorption between OH-/HCO3- and F⁻ also enhanced the release of F⁻ from solid surfaces. This study highlights the CKDu potential risk factors regarding groundwater geochemistry and their enrichment factors, which helps in preventing the prevalence of CKDu.