Hydrogeochemical appraisal of fluoride in groundwater of Langtang area, Plateau State, Nigeria

Abstract

Consumption ofhigh fluoride in groundwater ofLangtang area, manifest in the inhabitants of the area in form of dentalfluorosisand skeletal fluorosis inolder group.The aim of this study wasto appraise thehydrogeochemistry of fluoridein the groundwaters of Langtang area. Thirty seven surfaceand groundwater samplesandnine rocksamples werecollectedinLangtang area for geochemical analysis.The Inductively Coupled Plasma Emission Spectrometry(ICPOES) was used to detect cations. The anions (Cl-, SO4=and Br-) were determine by Ion Chromatography method.Fluoride wasdeterminedby the Specific Ion Electrode and bicarbonate was determined by titration. Major oxides,trace elements and rare earth elements for the rock samples were determined by the XRF method and fluorine by theFusion method.Polishedthin sections for rocks were preparedand studied.Geochemicalresults from analysis ofthesamples (rock and water)show that four major rock units make up the geology of the area; coarse porphyritic biotitegranite, migmatite, rhyolite and riebeckite granites, the minor ones are pegmatite, trachyte, aplite and fine to mediumgrained biotite granites. The rhyolite, the riebeckite granitesand trachytehave the highest level of fluorine content inthe area (1,470, 1000, 900and 800ppm)respectively. The fluorine mineral (Fluorite) crystallized in the late stage ofthe magma asreplacement of Fe/Mg mineral probably hornblendeor biotite.Fluorine is leachedinto the groundwaterfrom the rhyolite under the slightly alkaline (Ca-Mg-HCO3evolving Na-HCO3) water in the area. The two majorgroundwater types (Ca-Mg-HCO3and Na-HCO3) in the area have good relationship with content of fluoride in water.Although, the riebeckite granites have high fluorine content, contribution of fluoride fromthem is towards the southernportion of the map,owing to the groundwater flow direction. The different water sources in the area do not showvariation in content of fluoride in water. However, groundwater barriers (dykes) may be responsible for some areahaving low fluoride (<1.5 mg/l) content. The consumption of high content of fluoride in the area has resulted in severedental fluorosis in both children and youths and bowing of legs (Genu Valgum) in children with no discriminationbetween the sexes