Human health implications of metal pollution in the Betwa-Yamuna river system, India: evidence from Monte Carlo risk modelling

This study evaluates water quality and human health risks at the Betwa–Yamuna confluence in Hamirpur District, India, using monthly data collected from June 2023 to May 2024. Physicochemical parameters (pH, EC, TDS, temperature) and trace metals (As, Pb, Cd, Cu, Fe, Mn, Mo, Ni, Zn) were assessed against WHO and USEPA standards. Arsenic ranged from 0.001–0.011 mg/L and exceeded the WHO limit (0.01 mg/L) in several samples, while Pb (0.0004–0.012 mg/L) occasionally exceeded its guideline. EC exceeded 1200 µS/cm and TDS surpassed 500 mg/L during pre-monsoon months, indicating strong solute enrichment under low-flow conditions. Non-carcinogenic risk assessment showed median HQ values for arsenic of 0.98 for children and 0.42 for adults, with 95th percentiles reaching 2.28 and 0.97, respectively. Children’s HI values exceeded 1.0 in all seasons and surpassed 2.0 during pre-monsoon. Carcinogenic risk for arsenic exceeded the USEPA threshold (1 × 10⁻ 4 ) in 38% of adult and 9% of child Monte Carlo simulations. Probabilistic analysis (10,000 iterations) indicated HI > 1 in 67% of child runs and 23% of adult runs. The results demonstrate substantial health risks, particularly for children, and highlight the urgent need for arsenic and lead source control, seasonal water quality monitoring, and community-level drinking water treatment, with priority given to child-focused risk protection.