Assessment of hydrochemistry, fluoride distribution, and non-carcinogenic health risks in groundwater of the Manyara region, Tanzania.

Fluoride (F-) contamination in groundwater is a major global public health concern. Prolonged intake of F⁻ above 1.5 mg/L and 10 mg/L may lead to skeletal fluorosis and crippling fluorosis, respectively. The Manyara region, located within Tanzania's fluoride belt in the Eastern African Rift Valley, is one of the areas most affected by elevated F- levels in groundwater. The extent of F⁻ pollution and associated health risks in this region remains poorly documented. This study assessed the hydrochemistry, spatial distribution of F-, non-carcinogenic health risks, and the suitability of groundwater for drinking and irrigation using 225 borehole water samples collected from all six districts of the region. Parameters analyzed included pH, EC, TH, Ca2+, Mg2+, Na+, K+, HCO3-, Cl-, SO42-, NO3-, and F-. Irrigation suitability of water was evaluated using EC, %Na, RSC, SAR, Kelley's Ratio, and MAR. Results show that F- levels ranged from 0.01 to 23.44 mg/L. Overall, 48.00% of samples contained F- above 1.5 mg/L, and 3.56% of samples exceeded 10.0 mg/L. The Hazard Quotient (HQ) values ranged from 1.00 to.06 (infants), 0.91-6.35 (children), and 0.35-2.42 (adults), indicating elevated health risks, particularly for infants and children. EC values ranged from 63.18 to 8,911.50 µS/cm, with 19.11% of samples exceeding the recommended limit of 2,500 µS/cm. The order of ions was found to be Ca2+  > Na+  > Mg2+  > K+ and HCO3⁻ > Cl- > SO42- > NO3- > F-. Most samples were suitable for irrigation, but high salinity poses localized challenges.