Assessment of processes controlling the regional distribution of fluoride and arsenic in groundwater of the Western Jilin Province, Northeast China

Groundwater is a critical resource for a locality, and high F and As contents in groundwater can substantially impact regional ecological stability. The Western Plain of Jilin has groundwater > 128 m, and F and As levels exceed the World Health Organization’s (WHO) safe drinking levels. To assess the primary processes controlling the regional distribution of F and As in the aquifer, 225 wells at varying depths were selected and analyzed for groundwater sampling in the plain. Concentration ranges of F and As in the groundwater were 0.16–7.99 and 1–310 µg/L, respectively. Approximately 33% and 20% of the samples exceeded the WHO limit for F (1.5 mg/L) and As (10 µg/L), respectively. F and As were not significantly correlated. In the central part of the plain, the groundwater upstream of the Huolin River Basin had higher As concentrations, whereas the groundwater downstream had higher F concentrations. The sources and enrichment of F and As predominantly resulted from widespread natural processes with little signs of anthropogenic influence. Regional of F and As distributions are controlled by two processes: hydrogeological controls primarily in the upstream region of the Huolin River and hydrogeochemical controls mainly occurring in the middle and downstream areas of the river. The primary hydrogeochemical processes controlling F and As distribution and migration in the study area are the dissolution of carbonate rock (where HCO₃⁻ may act as a sorption competitor), an increase in pH, and cation exchange (release of Na⁺ and adsorption of Ca²⁺). Evapotranspiration only influences the enrichment process of F and As concentrations in localized shallow groundwater. Human–induced groundwater extraction is the primary cause of F and As migration in medium and deep groundwater. The mixing of highly concentrated F- and As-containing groundwater with uncontaminated groundwater presents a potential problem for future research.