Spatial distribution characteristics and enrichment factors of high-fluorine groundwater in the Kuitun River basin of Xinjiang Uygur Autonomous Region in China

The Kuitun River Basin of Xinjiang Uygur Autonomous Region in China is the area experiencing the first large-scale endemic arsenic and fluorine poisoning incident in mainland China. However, existing studies mostly focused on the enrichment factors of high-arsenic groundwater in this area. In this study, the distribution characteristics and formation factors of high-fluorine groundwater in the Kuitun River Basin were investigated with the aim of clarifying the migration and enrichment mechanism of high-fluorine groundwater in the study area. The source, distribution, and geochemical characteristics of the fluorine in groundwater in this area were studied in detail by water sample collection, hydrogeological survey, and mathematical statistics. The results show that the F- concentration in groundwater in the Kuitun River Basin varied within the range of 0.48-6.41 mg L-1, with a mean value of 1.13 mg L-1; the distribution level of fluorine in groundwater was low in the south and high in the north; the majority of fluorine originated from the rock minerals in the aquifers of southern mountainous areas and plain areas. The formation of high-fluorine groundwater is related to the hydrochemical environment, where Ca2+ inhibits the enrichment of fluorine, while the weak alkaline environment, HCO3-, and Na+ facilitate the enrichment of F-. Dissolution and sedimentation of fluorine-containing minerals, cation exchange, and evaporation-concentration process are the major factors contributing to the formation of high-fluorine groundwater.