Characterization of fluorine pollution and evaluation of multi-media environmental health risk in Daihai watershed: Based on coupled uncertainty-sensitivity modeling

Excessive fluoride levels have become a critical concern in contemporary society, with China ranking among the nations most severely affected by fluoride pollution. To investigate the health and ecological risks associated with excessive fluoride, 80 surface water samples, 80 sediment samples, 152 groundwater samples from rural drinking wells surrounding the lake, and 64 tributary samples flowing into Lake Daihai were consecutively collected between 2023 and 2024. A comprehensive spatiotemporal analysis of fluoride concentrations in Lake Daihai's water body, sediments, and surrounding groundwater was conducted using ArcGIS and Origin software. The potential ecological risks of Lake Daihai's surface water and sediments were evaluated using the integrated pollution index method, the entropy method, and the modified Nemero index method. A human health risk model was applied to evaluate the health risks of groundwater around Lake Daihai. Monte Carlo uncertainty analysis and the Crystal Ball sensitivity analysis system were combined to estimate the probability of exceeding non-carcinogenic risk thresholds and to identify sensitivity levels for fluoride-related ecological risks across different population groups. The results indicate that the average fluoride concentration in Lake Daihai's water bodies is 6.22 mg/L, while groundwater in surrounding rural drinking wells ranges from 0.11 to 3.78 mg/L, exceeding the national average of 0.66 mg/L. Surface water fluoride concentrations exhibited an overall seasonal pattern of spring increase, summer decrease, and autumn rebound. Sediment fluoride concentrations showed a gradient pattern of higher in the northwest, lower on the east/southwest shores. Groundwater fluoride concentrations generally followed a pattern of higher on the east/west shores, lower on the north shore. The surface water bodies of Lake Daihai face potential ecological risks, with over 99 % of samples exhibiting a hazard quotient (HQ) greater than 1 and an average HQ of 3.12. This finding indicates a state of moderate risk and high instability, characterized by potential mobility and bioavailability. The ecological risk of fluoride in sediments is generally classified as mild to moderate contamination. For groundwater samples, the non-carcinogenic risk threshold exceeded standards in 85 % of infants (THQ > 1.0), 60 % of adults, and 30 % of children and adolescents. Uncertainty model analysis indicates non-carcinogenic health risk exceedance probabilities of 74.25 % for infants, 28.18 % for children, 24.82 % for adolescents, and 42.47 % for adults, with infants facing the highest non-carcinogenic fluoride risk. Sensitivity analysis reveals F^- contribution as the primary factor for non-carcinogenic risks in infants (73.9 %) and children (30.6 %).