Fluoride ion contamination in the groundwater of Mithi sub-district, the Thar Desert, Pakistan |
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| Authors: | Tahir Rafique Shahid Naseem Muhammad I Bhanger Tanzil H Usmani |
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| Institution: | (1) Applied Chemistry Research Centre, PCSIR Laboratories Complex, Off University Road, Karachi, 75280, Pakistan;(2) Department of Geology, University of Karachi, Karachi, 75270, Pakistan;(3) National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan |
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| Abstract: | Groundwater samples were collected from various localities of Mithi sub-district of the Thar Desert of Pakistan and analysed
for fluoride ion along with other chemical parameters. The area is mainly covered by sand dunes and kaolin/granite at variable
depths. Results showed that collected water samples were severely contaminated by the presence of fluoride ion and most of
the samples have higher concentration than prescribed WHO standards (1.5 mg/l) for drinking water. Fluoride ion concentrations
ranged between 0.09 and 11.63 mg/l with mean and median values of 3.64 and 3.44 mg/l, respectively, in this area whereas,
distribution pattern showed high concentrations in the vicinity of Islamkot and Mithi towns. The content of F− has also been correlated with other major ions found in the groundwater of the study area. The positive correlation of F− with Na+ and HCO3
− showed that the water with high Na+ and HCO3
− stabilizes F− ions in the groundwater of the Thar Desert. The pH versus F− plots signifies high fluoride concentration at higher pH values, implying that alkaline environment favours the replacement
of exchangeable OH− with F− in the groundwater of Mithi area. The saturation indices (SI) of fluorite (CaF2) and calcite (CaCO3) in the groundwater samples showed that most of the samples are oversaturated with respect to calcite whereas majority of
samples have been found under saturated with respect to fluorite. The log TDS and Na/Na+Ca ratio reflected supremacy of weathering
of rocks, which promotes the availability of fluoride ions in the groundwater. Piper diagram has been used to classify the
hydrofacies. In the cation triangle, all samples are Na-type, while the anion triangle reflects major dominance of Cl-type
with a minor influence of HCO3
− and SO4
−. |
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| Keywords: | Groundwater Fluorosis Fluoride ion The Thar Desert Mithi Pakistan |
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