Enrichment mechanism and probabilistic health risk assessment of high-fluoride groundwater in Gaomi City, China

Fluoride (F) is the most important inorganic pollutant in groundwater that affects human health, and analyzing the causes of high-fluoride groundwater is a prerequisite for protecting the health of residents. To comprehensively understand the enrichment characteristics of groundwater in the high-fluoride areas, this study systematically investigated the concentrations of fluoride in Gaomi City, a typical study area in the Jiaolai Plain and explored the spatiotemporal distribution patterns, enrichment mechanisms, and the probabilistic health risk associated with F-. The results indicate that there is serious fluorine pollution in groundwater, which is mainly concentrated in the alluvial plain in the north and affected by topographical and aquifer characteristics. Favorable runoff conditions effectively improve the fluoride status of shallow groundwater on both sides of rivers and in hilly areas. Hydrogeochemical methods reveal the mechanism of fluoride enrichment. The relative contributions rates of different hydrogeochemical processes to the fluoride enrichment are as follows: dissolution and precipitation (39.02%) > cation exchange (25.25%) > competitive adsorption (19.48%) > seawater intrusion (3.14%) > evaporative and concentration (1.99%). Health risk assessment based on Monte Carlo simulation shows that health risk susceptibilities of different populations are infants (76.07%), children (66.59%), teenagers (44.54%), and adults (5.68%), respectively. In addition, targeted management suggestions are put forward regarding the enrichment mechanisms of fluoride in groundwater and its impact on health. These findings have significant implications for controlling regional diffuse F- contamination in groundwater, protecting public health, and promoting social development in regions with a high risk of groundwater fluoride contamination.