SPATIAL VARIABILITY OF FLUORIDE LEVELS AND THEIR IMPLICATIONS ON THE DRINKING WATER QUALITY IN THE LAKE VICTORIA GOLD FIELDS, NORTHWEST TANZANIA

Water scarcity and quality are the major challenges to the water supply authorities in many parts of the southern globe. The current quality challenges include mineral imbalances in drinking water caused by natural and anthropogenic factors. This study discusses the spatial variability of natural fluoride levels measured in drinking water sources in the two regions within the Lake Victoria Basin (LVB). The classical exploratory data analysis results demonstrated non-normality in the fluoride levels across the two regions. The probability of accessing a fluorotic source across the studied regions was 0.47. At the regional level, the probability was 0.36 and 0.53 in Shinyanga and Mwanza regions, respectively. At the district level in Mwanza Region, Misungwi, Magu and Kwimba Districts demonstrated the highest probabilities with values of 0.57, 0.90, and 0.92, respectively. In Shinyanga Region, the Districts demonstrating the highest probabilities were Kishapu and Shinyanga MC with probability values of 0.74 and 0.78, respectively. The positive and significant Moran’s I statistic indicated the spatial clustering process in the fluoride levels where 40% of the sources formed a cluster with high fluoride levels exceeding 1.5 mg/L (98%), dominating the eastern part of the two regions. On the other hand, 40% of the sources formed a cluster of drinking water sources with low fluoride levels below 1.5 mg/L. Most of these sources dominated the western part of the studied regions. However, 21% of sources had fluoride levels below 0.5 mg/L presenting another health hazard in terms of dental caries. The high levels of fluoride in the hotspot zone are probably mobilized in the water systems through the interaction between water and weathered rocks in the migmatite-granitoid meta-sediment complex and the fine clastic lacustrine sediments and evaporates. The eutric planosols dominate this setting which could also be explaining factors of the highly variable fluoride levels in groundwater. This study provides new insights into the geogenic contamination by fluoride in water systems used for drinking purposes in the raw form. For that matter, the findings of the study are crucial for the LVB authority in the studied regions to plan for the risk management strategy and provision of alternative sources of drinking water sources to the local community, especially in rural areas.