Hydrogeochemistry, water quality, and potential human health risk assessment of groundwater in a drought-prone area, Bangladesh

The intensifying issue of water contamination poses a growing threat in developing, industrialized, and agricultural regions, endangering the environment, human health, and economic development. Therefore, understanding the recharge mechanisms, hydrogeochemistry, water quality, and groundwater risk assessment is crucial for effective water resource management. Forty-five water samples were analyzed for their isotopic and chemical compositions to evaluate the sources of recharge and suitability. The study area is divided into the Younger Ganges Floodplain (YGF), Older Mahananda Floodplain (OMF), and Pleistocene Barind Tract (BT), which exhibit heterogeneous aquifer thicknesses, subsurface geology, and varying recharge dynamics. Cation concentrations followed the order of Ca²⁺>Na⁺>Mg²⁺>K⁺, while the dominant anions were HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ > NO₂⁻. Most parameters were within standard limits, where elevated concentrations were attributed to natural processes (e.g., silicate weathering, cation exchange, and carbonate dissolution) and anthropogenic sources (e.g., fertilizer use and sewage leakage). Isotopic analysis revealed active rainfall recharge in the YGF aquifer, while the BT demonstrated no recent recharge, likely due to the presence of a thick, impermeable clay layer. The OMF, on the other hand, exhibited both recently recharged and stagnant water, reflecting spatial heterogeneity in aquifer characteristics. Piper and Chadha diagrams classified the groundwater as Ca²⁺–Mg²⁺–HCO₃^- type, indicating temporary hardness. Hydrogeochemistry was predominantly influenced by ion exchange, rock-water interactions, and the dissolution of calcite and dolomite. The Entropy Water Quality Index (EWQI) values revealed good water quality in BT, unsuitability in YGF, and good to poor quality in OMF. Non-carcinogenic health risk assessments revealed arsenic as the highest risk, followed by NO₂⁻, NO₃⁻, Mn, and Fe, with children facing greater exposure than other groups. Non-carcinogenic risk limits were exceeded in 53.33 % of samples for both children and females and in 33.33 % for males. To mitigate these risks, strategies should focus on improved agricultural practices, reduced fertilizer application, modified irrigation methods, and public awareness campaigns. This study provides valuable insights into groundwater conditions in Chapai Nawabganj, contributing to sustainable water resource management and the protection of public health.