Comprehensive evaluation of surface water quality: heavy metals, speciation, and human health risks in an industrial region of West Bengal, India

Abstract This study evaluates the hydrogeochemical characteristics, heavy metal (HM) contamination, irrigation suitability, and associated human health risks of surface water in an industrial area affected by dye-manufacturing activities in West Bengal, India. A total of 30 surface water collected in triplicate were analysed. Major ions were determined using standard American Public Health Association (APHA) methods, HMs were quantified using atomic absorption spectrometry (AAS), and aqueous speciation was modelled using Visual MINTEQ. The water was slightly alkaline, with pH values ranging from 7.18 to 8.92 (mean 7.79±0.41). Extremely high salinity was observed, as electrical conductivity ranged from 2500 to 21,000 μS cm⁻¹ (mean 11,300±4272 μS/cm), while total dissolved solids varied between 1500 and 12,600 mg/L (mean 6780 ± 2563 mg/L), exceeding World Health Organization (WHO) guideline values. Major cations followed the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺, whereas dominant anions were HCO 3 ⁻ > Cl⁻ > SO 4 2 ⁻, reflecting combined geogenic and anthropogenic influences. Mean concentrations of heavy metals were elevated, with values of Cr (0.97 mg/L), Pb (0.23 mg/L), Ni (0.19 mg/L), Cu (0.06 mg/L), and Cd (0.004 mg/L). Except for Cu, all metals exceeded WHO permissible limits, indicating substantial contamination. Pollution indices (Pi) confirmed severe degradation, with Pi > 1 for Pb, Ni, Cr, and Cd. High average values of C d (48.89), Heavy Metal Evaluation Index (HEI), 53.65, and Heavy Metal Pollution Index (HPI), 338.73, indicated high to extreme pollution, while Water Pollution Index (WPI) values (1.51–5.27) classified all samples as severely polluted. Speciation modelling showed Cd predominantly occurred as Cd 2+ (52.35%) and CdCl + (32.10%), suggesting high mobility. Lead (Pb) was predominantly present as PbCO 3 (aq) (39.47%) and PbHCO 3 + (31.31%), Ni largely as Ni 2+ (63.15%), and Cr(VI) mainly as CrO 4 2 ⁻. Copper was largely present as CuCO 3 (aq) (67.94%). Irrigation indices indicated suitability, although overall water quality remained poor. Human health risk assessment identified Pb and Cr as posing non-carcinogenic risks, while Cr presenting the highest carcinogenic risk, particularly for children (CR > 1 × 10⁻ 4 ). Overall, the findings highlight severe surface water degradation and underscore the urgent need for remediation measures and stricter regulatory intervention.