Hydrochemical and contamination dynamics of groundwater in relocated tannery area, Dhaka, Bangladesh: Impacts of tannery relocation and preliminary health risks

• Groundwater quality impacted by tannery relocation in Dhaka, Bangladesh • EC and Hg exceeded safety limits at 90 % of sites; Ca and Mg at 20 % • Water-rock interaction and mineral dissolution drive groundwater chemistry • Geogenic (54.6 %), anthropogenic (20.5 %), and mixed (24.9 %) sources of contamination • Health risk assessment shows elevated carcinogenic risk for As in children This study has investigated potential changes in geochemical processes and groundwater chemistry resulting from the impact of the tannery relocation in the studied area. Ion chromatography and Energy Dispersive X-ray Fluorescence (EDXRF) were used to analyze 23 parameters viz., pH, TDS, EC, temperature, salinity, F - , Cl - , SO₄ ²- , NO₃ - , Na⁺, Mg²⁺, K⁺, Ca²⁺, Ni, Mn, Pb, Cu, Cr, Fe, Zn, Sr, As, and Hg from the collected groundwater samples in and around the BSCIC tannery industrial estate, Savar, Dhaka. Among these parameters, EC and Hg at 90 % of sites, whereas Ca and Mg at 20 % exceed the threshold limit of DoE and WHO. Hydro-chemical evaluation of groundwater indicated that water-rock interaction was the principal natural force, and dissolution of Ca and Mg-bearing minerals (silicates or carbonates) is the predominant hydro-chemical action of groundwater chemistry. WPI (0.33), along with HEI (3.31), HPI (3.01), and C d (-4.69) indices, indicated that the groundwater samples were of good quality for drinking. Multivariate statistical techniques and the PMF model predicted that geogenic, anthropogenic, and mixed sources accounted for 54.6 %, 20.5 %, and 24.9 % of groundwater contamination sources, respectively. For irrigation purposes, the groundwater demonstrated excellent quality based on SAR (4.60), SSP (3.39), KR (0.36), and MHR (30.31) values. According to the health risk assessment, the carcinogenic risk (CR) of As was higher than the maximum threshold value for both adults (5.28 × 10⁻⁴) and children (1.23 × 10⁻³), while the non-carcinogenic risk (HI) values were found within the acceptable limit (<1), except for Hg (1.67) for children.