The heterogeneous nature of water well fluoride levels in Sri Lanka: An opportunity to mitigate the dental fluorosis

Objectives: The study aimed to use Geographic Information Systems (GIS) to investigate the spatial distribution of the concentration of fluoride (F) in groundwater resources of Sri Lanka, and the geographic accessibility to an alternative water source having a low or safe F limit to mitigate dental fluorosis. Methods: The study used randomly collected (6107) groundwater samples from Sri Lanka and categorized them as “dentally optimal” and “unsafe” based on their F content. The minimum distance from an identified high F source (above dentally optimal level) to a safe groundwater source was determined using geospatial analysis. Results: Dentally optimal F sources (<1 and <1.5 mg/L) were identified among the high F groundwater sources (>2 mg/L), some even within a walking distance of 500 m. Results indicated that 26% of dentally unsafe groundwater sources (2.0 mg/L+ wells) had a low F source (<1.0 mg/L) available within a distance of 500 m. It was also evident that 39% of high F wells (2.0 mg/L+ wells) had a low F well (<1.5 mg/L) within a distance of 500 m, if the WHO guideline value for optimal F levels (1.5 mg/L) was assigned as the safe F limit. Conclusion: The spatial approach demonstrated a reasonable access to alternative water sources with low or safe F limit in endemic fluorosis areas. Optimizing the use of accessible low F sources is highly recommended as the first-line option to mitigate dental fluorosis in Sri Lanka since the defluoridation methods introduced in past did not provide sustainable oral health solutions for the inhabitants in high-risk areas.