Hydrochemical characterization, heavy metal contamination, and human health risk assessment of borehole water in Mbeya Urban, Tanzania

Background Borehole water is a major domestic water source in many urban and peri-urban areas with inadequate centralized piped supply infrastructure. Purpose and Methodology This study evaluated the hydrochemical characteristics, heavy metal concentrations, and human health risks of borehole water in Mbeya Urban, Tanzania. A total of 15 water samples were analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), major anions (Cl⁻, SO 4 2 ⁻, HCO 3 − , F⁻, NO 3 ⁻), major cations (K⁺, Na⁺, Mg 2 ⁺, Ca 2 ⁺), and heavy metals (Cr, Pb, Cd, Cu, As). Results Piper and Chadha plots showed Na–HCO 3 dominance at Ituha and Ca–Mg–HCO 3 dominance at Isyesye and Itezi, with hydrogeochemical evolution controlled by silicate weathering, base ion exchange and recharge. Heavy metal concentrations ranged from 0.08–0.10 µg/ml (As), 1.27–2.59 (Cu), 1.43–2.66 (Pb), 4.64–8.63 (Cr), to 3.17–5.74 (Cd). Non-carcinogenic risk was acceptable for adults (HI < 1) but exceeded unity for children's oral exposure at several sites, peaking at M2 (HI = 1.21). Monte Carlo simulations showed adult oral Cd cancer risk of 4.70 × 10⁻ 4 to 1.13 × 10⁻ 3 and children's risk of 1.80 × 10⁻ 3 to 4.30 × 10⁻ 3 , both exceeding the 1 × 10⁻ 4 threshold. For Cr, oral cancer risk ranged from 6.35 × 10⁻ 5 to 1.50 × 10⁻ 4 in adults and 2.40 × 10⁻ 4 to 5.70 × 10⁻ 4 in children; dermal cancer risk ranged from 5.90 × 10⁻ 4 to 1.44 × 10⁻ 4 in adults and 1.70 × 10⁻ 3 to 4.20 × 10⁻ 3 in children, exceeding the threshold, suggesting potential cancer risk. Conclusions These elevated Cd and Cr cancer risks call for continuous monitoring and targeted mitigation to safeguard public health.