Fluorine, a Dreaded Element: A Review on Occurrence of Fluorine in Environment and its Standard Methods of Analysis

The purpose of this review is to describe various geological and chemical factors that are controlling the fluoride concentration in soil, rocks, water, air, plants, animals and food stuffs. Further to discuss well established method that is used as the standard methods of analysis. Rock, Soil, Water, air, plants, animals, foodstuffs all contain fluoride in widely varied concentration. Industries are the main source of polluting atmosphere with fluorine. In an earth crust because of precipitate of CaF2, calcium rich sedimentary rocks have high concentration of fluorine. A list of 150 fluorine bearing minerals was given by Strunz of which 63 are silicates, 34 are halides and 24 are phosphates. Even in similar rocks, the fluorine contents of mineral increases as the alkali or silica content of host rock increases. Fluorine content in soil entirely depends upon their composition and fluorine content of rock from which they have been derived. The fluoride content in ground water varies greatly depending upon the type of rock from which it originates. Pressure, temperature and chemical composition of reservoir also controls the concentration of fluorine. Three factors are controlling the fluoride distribution in ground water. (a) Size and distribution of fluorite and other fluoride bearing minerals (b) Availability of ground water in contact with those minerals (c) The duration of contact of ground water with fluoride bearing minerals and rocks. Weathering of alkaline silicic igneous rock contributes a major portion of fluoride in natural water. Fluorine content of hot springs increases with 8 Anamika Srivastava and Dr. Minaxi Lohani increasing temperature. Fluoride is widely used in various branches of industry and some fluoride compounds are formed as by products in certain process. Excessive amounts of fluoride in the form of different compounds can enter the human body by means of polluted air, water and food chain. Fluoride prevents tooth decay at 1-mg/lit concentration but causes mottled teeth (dental fluorosis), bone damages (Skeletal fluorosis) at about 5mg /lit. For adults the lethal dose is 0.2-0.35 gm F per kg body weight. Fluoride in foodstuffs depends on the nutrient uptake from the soil. Tea plant leaves are containing maximum concentration of fluoride. Concentration of fluoride in black and green tea leaves was determined by Zerabruck et al. Measurement of fluorine in various matrices involves three steps (a) Dissolution of fluoride (b) Separation of fluoride (c) Measurement of fluoride. Concentration of fluoride can be measured by (1) Ion selective electrode method (2) Photometric method (3) Ion Chromatography method (4) Ion selective Electrode flow injection analysis method. The above discussion reveals that fluorine is an essential element in human diet based upon its important role in bone and teeth mineralisation, stimulatory and inhibitory effects on many soft tissues enzymes and dental caries resistance. The increased fluoride intake with water and food as well as on occupational exposure on fluoride dust could be reason for skeletal and dental fluorosis in humans.