Hydrochemical investigation of groundwater and probabilistic health risk assessment from fluoride and iron intake in a ferruginous Barind tract

Hydrochemical properties of groundwater (n = 32) collected from eight Gram Panchayats (GP) in Kushmandi Block of South Dinajpur District in West Bengal, India and human health risk posed by groundwater fluoride (F⁻) and iron (Fe) are reported. About 18% and 28.7% of the collected water samples exceeded the permissible limits for F⁻ and Fe, respectively, as per prescribed potable water quality standards of WHO and Bureau of Indian Standards. Total Dissolved Solid in groundwater never exceeded the acceptable limit of 500 mg l ⁻¹ (maximum value was 301.6 mg l ⁻¹) while NO₃- ranged from near zero to 17.8 mg l⁻¹, never exceeding the safe limit of 45 mg l⁻¹. Hydrogeochemical analyses revealed the dominance of Ca/Na-bicarbonate type water throughout the Block and indicated that fluorite (CaF₂) could be the most prominent source of F⁻ in groundwater. Non-carcinogenic health risk index due to exposure to F⁻ was more than unity in infants, children and adults in the order of HQ_Children>HQ_Infant>HQ_Adult. Sensitivity analysis to ascertain non-carcinogenic human health risk of F⁻ through multi-exposure pathways undertaken by Monte Carlo (MC) simulation (Oracle Crystal Ball, version 11.1.2.4.850) indicated that concentration of F⁻ and Fe (Ci), their ingestion rate (IR), and exposure duration (ED) were the most influential governing factors behind non-carcinogenic health risks posed by F⁻ and Fe consumption. Groundwater was rated as having ‘Low’ irrigation water quality (Sodium Adsorption Ratio, SAR <10 and Residual Sodium Carbonate, RSC of 0.41–2.88). Other important parameters of irrigation water quality, such as electrical conductivity (maximum 409 μS cm⁻¹) and chloride (maximum 30.8 mg l⁻¹), were also well within the recommended safe limits.