Geochemical controls of high fluoride groundwater in Umarkot Sub-District, Thar Desert, Pakistan

• Published in: The Science of the total environment Vol. 530-531; pp. 271 - 278
• Main Authors: Rafique, Tahir, Naseem, Shahid, Ozsvath, David, Hussain, Riaz, Bhanger, Muhammad Iqbal, Usmani, Tanzil Haider
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-10-2015
• Subjects: Base ion exchange; Calcite precipitation; Evaporation; Fluoride ions; Mineral weathering; Thar Desert; Umarkot; Base ion exchange; Mineral weathering; Fluoride ions; Umarkot; Thar Desert; Evaporation; Calcite precipitation
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2015.05.038

Groundwater samples (n=152) were collected in the Thar Desert of the Umarkot Sub-District, Pakistan to evaluate the geochemical controls on the occurrence of high fluoride (F−) levels within the study area. Fluoride concentrations range from 0.06 to 44.4mg/L, with mean and median values of 5.22 and 4.09mg/L, respectively; and roughly 84% of the samples contain fluoride concentrations that exceed the 1.5mg/L drinking water standard set by WHO. The overall groundwater quality reflects the influences of silicate mineral weathering and evaporation. Fluoride originates from the weathering of minerals derived from Type-A granite and possibly anion exchange (OH− for F−) on clays and weathered micas under high pH conditions. High fluoride levels are associated with Na–HCO3 type water produced by calcite precipitation and/or base ion exchange. Depleted calcium levels in groundwater allow higher fluoride concentrations to occur before the solubility limit for fluorite is reached.
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•Fluoride in groundwater ranged from 0.06 to 44.40mg/L (mean value of 5.22mg/L).•84% of samples exceeded 1.5mg/L (recommended WHO limit for fluoride).•Silicate mineral weathering and evaporation controlled overall groundwater quality.•Weathering of minerals derived from Type-A granite released fluoride.•Water influenced by calcite precipitation and base ion exchange contained high F−.