Spatial pattern, hydrogeochemical controlling processes and non-carcinogenic risks of fluoride-enriched groundwater in the North Henan Plain, Northern China

High fluoride (F-) groundwater (F->1.5 mg/L) widely occurred in the North Henan Plain, located in the arid and semi-arid region of the lower reaches of the Yellow River, which poses a threat to the health of local residents. Seventy-six groundwater samples were collected from the quaternary aquifers in 2022 to explore the spatial pattern of F-, hydrogeochemical evolution processes, and driving factors of F- release using hydrochemical and isotopic analysis, and hydrogeochemical simulation. The health risk was evaluated to determine the hazards of excessive intake of F- for people with different ages using Monte Carlo simulation. Results showed that 54 % of groundwater and 57 % of surface water samples exceeded the WHO recommended limit (1.5 mg/L). The hydrogeological settings have a significant impact on the spatial variability of groundwater F-. In the low-lying area in the front of alluvial fan, groundwater with elevated F- concentration prevail duo to shallow burial depth of groundwater table and strong evaporation. Dissolution of fluorite and removal of Ca2+ resulted from calcite precipitation are the dominant controlling factors responsible for elevated F- content in groundwater from the Yellow River crevasse fan, where the groundwater is characterized by low TDS and high F- due to the lateral recharge from Yellow River. In the Yellow River floodplain, groundwater F- increases with groundwater flow direction. Prolonged water-rock interaction and evaporation promote the formation of sodic groundwater, facilitating the enrichment of F- in groundwater in the northeast part of study area. Compared to adults, the intake of high F- groundwater was more harmful to infants and children. These findings have important implications for F- mobilization driven by climate, sedimentary setting and anthropogenic factors, and health risk prevention.