Groundwater nitrate and fluoride profiles, sources and health risk assessment in the coal mining areas of Salt Range, Punjab Pakistan

Abstract

To assess the loading profiles of groundwater nitrate (NO₃^-) and fluoride (F^-), their spatial distributions, geochemistry and associated health risks were determined for 131 groundwater samples from eastern (ESR), central (CSR) and Trans-Indus Salt Ranges (TSR) in Pakistan. Groundwater NO₃^- concentrations were 0.2-308 mg/L (mean 59 mg/L) in ESR, 2.7-203 mg/L (mean 73 mg/L) in CSR and 1.1-259 mg/L (mean 69 mg/L) in the TSR. Forty-one %, 57% and 36% of the ESR, CSR and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 50 mg/L NO₃^-. Likewise, groundwater F^- concentrations ranged from 0.1-1.8 mg/L (mean 0.6 mg/L), 0.1-2.7 mg/L (mean 0.9 mg/L) and 0.3-2.5 mg/L (mean 1.6 mg/L) mg/L in the ESR, CSR and TSR sites, respectively. In this case, 3%, 17% and 27% of the ESR, CSR and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 1.5 mg/L F. Oxidation of coal and coal waste resulted in the release of NO₃^- to groundwater. By contrast, enrichment of F^- in groundwater was due to dissolution and cation exchange processes. Elevated values of the Higher Pollution Index (PI) and Health Risk Index (HRI) reflect a non-acceptable carcinogenic risk for drinking water NO₃^- and F^- which should be addressed on a priority basis to protect human health.

Keywords: Fluoride; Geochemistry; Groundwater; Health risk assessment; Nitrate; Pollution index.