title: Geochemical factors controlling the occurrence of high fluoride groundwater in the Nagar Parkar area, Sindh, Pakistan.
abstract: Fluoride concentrations in groundwater near Nagar Parkar in the Thar Desert of southeastern Pakistan range from 1.13 to 7.85 mg/l, and roughly 78% of the samples contain fluoride in concentrations that exceed the drinking water standard of 1.5mg/l set by WHO. The groundwater is alkaline (pH 7.1-8.4), brackish (TDS 449-15,933 mg/l), and classified as Na-Cl type water. This prevailing chemical character reflects the influence of saltwater intrusion, high evaporation rates, and ion exchange. Groundwater is also supersaturated with respect to calcite, which promotes the removal of Ca(2+) and HCO(3)(-) from solution. As a result, groundwater is generally undersaturated with respect to fluorite, the mineral that typically controls the upper limit of fluoride concentrations. This study examines a number of geochemical parameters in an effort to discover the controls on fluoride concentrations in groundwater. High fluoride concentrations are associated with high TDS, high pH, high Na concentrations, and high sodium absorption ratios (SAR). This suggests that elevated fluoride levels are the result of enhanced fluorite solubility due to Ca depletion and high ionic strength and the release of fluoride from colloid surfaces under high pH conditions. Contrary to what has been found in other studies, sample depth and water temperature do not appear to have a significant role in the distribution of fluoride within the groundwater.
authors: Applied Chemistry Research Centre, PCSIR Laboratories Complex, Off University Road, Karachi 75280, Pakistan. tahirrafique92@yahoo.com
authors: Tahir
authors: T
authors: Rafique
authors: Shahid
authors: S
authors: Naseem
authors: Tanzil Haider
authors: TH
authors: Usmani
authors: Erum
authors: E
authors: Bashir
authors: Farooque Ahmed
authors: FA
authors: Khan
authors: Muhammad Iqbal
authors: MI
authors: Bhanger
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D005459:Fluorides / Q000032:analysis* / Q000302:isolation & purification; D005618:Fresh Water; D005843:Geography; D019015:Geologic Sediments; D005844:Geology; D006863:Hydrogen-Ion Concentration; D007477:Ions; D010154:Pakistan; D012964:Sodium / Q000032:analysis; D012965:Sodium Chloride / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D014881:Water Supply
chemical_list: D007477:Ions; D014874:Water Pollutants, Chemical; D012965:Sodium Chloride; D012964:Sodium; D005459:Fluorides