275-8 Geostatistical Insights into Fluoride Risk Zones in Rwanda’s Drinking Water Sources

Session: Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part II

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Geogenic groundwater contamination and its health effects are the current global concerns, particularly in regions where the population relies on groundwater as a primary source of drinking water. Fluoride (F-) is one of the geogenic groundwater contaminants occurring in varying amounts in more than 30 countries across the continents. This study conducted a spatial analysis of F⁻ occurrence in Rwanda's drinking water sources using the univariate Local Moran’s I statistical method at 0.05, 0.01, and 0.001 significance levels to identify spatial clusters and outliers. The results revealed that approximately 31% of potential High-High spatial patterns were significant clusters of elevated F⁻ concentrations ranging between 0.62 mg/L and 5.07 mg/L, with 47% of sources exceeding the World Health Organization (WHO) permissible limit of 1.5 mg/L. Conversely, 28% of potential Low-Low spatial patterns represented clusters with low F⁻ concentrations (0.02 mg/L to 0.60 mg/L), 79% of which were below 0.5 mg/L, posing a potential dental caries risk. Spatial outliers were also detected, including nine Low-High outliers (F⁻: 0.05–0.54 mg/L), where eight sources had levels below 0.5 mg/L, and 20 High-Low outliers (F⁻: 0.63–2.11 mg/L), of which only one exceeded the WHO limit, while others remained within the safe range (0.5–1.5 mg/L). Spatial mapping revealed three distinct High-High clusters: (1) northeast of Lake Kivu, spanning parts of the Western, Northern, and Eastern Provinces; and (2) and (3) in the north and southwest of the Eastern Province. These clusters occurred in areas dominated by Cenozoic Volcanic and undifferentiated Precambrian basement rocks, suggesting geological influence on F⁻ enrichment through prolonged water-rock interaction. Two significant Low-Low clusters were identified: one in central Northern Province and another extending into the Southern Province, characterized by fold mountain topography, possibly affecting F⁻ distribution. The observed spatial variability underscores the role of hydrogeological settings in controlling fluoride concentration in water sources, highlighting areas of concern for both excess fluoride exposure and deficiency-related dental health risks.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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