Fluoride distribution and health risk assessment in groundwater of Tanzania's Singida Region: implications for drinking water quality and irrigation.

Fluoride (F⁻) pollution poses a significant public health concern in the regions located in the fluoride belt of Tanzania which includes the Singida Region. Groundwater in this belt contains F⁻ that exceed the World Health Organization's recommended limit of 1.5 mg l. The hydrochemistry, distribution of F, and the non-carcinogenic health risk associated with F⁻ pollution in the fluoride belt of Tanzania remain largely unexplored. This study evaluated the hydrochemistry, F⁻ distribution in groundwater, assessed its regulation by major ions, estimated non-carcinogenic health risks, and examined the water's suitability for drinking and irrigation using 71 samples. The parameters analyzed included pH, electrical conductivity (EC), total hardness (TH), Ca⁺, Mg⁺, Na⁺, K⁺, Cl⁻, SO, HCO⁻, and F⁻. The results indicate that F⁻ pollution is prevalent in the Singida Region, with concentrations ranging from 0.17 to 13.00 mg l. Of the water samples analyzed, 56.34% were within the safe limits, while 43.66% exceeded the threshold. The percentage of water samples with a Hazard Quotient (HQ) > 1 for F⁻ was found to be 61.97% for infants, 60.56% for children, and 39.43% for adults, indicating a potential non-carcinogenic health risk from elevated F⁻ levels in drinking water particularly among infants and children. F exhibited a negative correlation with TH, and positive correlations with Na⁺, pH, and HCO⁻. The assessment of irrigation suitability using indices such as Sodium Adsorption Ratio (SAR), Kelly's Ratio (KR), Sodium Percentage (%Na), and Magnesium Adsorption Ratio (MAR) indicates that the groundwater is generally suitable for irrigation purposes.