Hydrochemistry, quality, and potential health risk appraisal of arsenic-enriched groundwater in central-west Bangladesh using the integrated water quality index and Monte Carlo simulation

Groundwater contamination is a critical global environmental and public health concern, with ongoing degradation of subsurface water threatening access to safe drinking water. In this study, groundwater was analyzed operating atomic absorption spectroscopy (AAS) to assess hydrochemistry, water quality, and health risks. The hydrochemical facies indicate a Ca-Mg-HCO₃ water type, mainly influenced by carbonate weathering together with silicate weathering, and calcite dissolution. The average concentrations of As, Fe, and Mn exceed World Health Organization (WHO) guidelines by 19, 19, and 9.8 times, respectively. A strong correlation among these elements suggests that the reductive dissolution of Fe/Mn (- oxy) hydroxides is the key mechanism driving arsenic mobilization. Although irrigation water quality indices indicate suitability for agriculture, the integrated water quality index (IWQI) classifies the groundwater as highly improper for drinking due to elevated trace elements. The hazard index (HI) for arsenic is 43 for children and 15.5 for adults, significantly surpassing the United Nation Environmental Protection Agency (USEPA) safety threshold (HI ≤ 1), whereas Fe and Mn present no non-carcinogenic risk (NcHR). Carcinogenic risk (CR) from arsenic ranges from 1.59 × 10^-4 to 1.04 × 10^-2, averaging 40 times above the acceptable limit (CR > 10^-4). Monte Carlo simulations further estimate that approximately 9 individuals per 100,000 may develop cancer from heavy metal exposure, representing an unacceptably high level of risk.