Chemical Properties of Fluorine

Transcription

1 Small doses of fluoride have beneficial effects on the teeth by hardening the enamel and reducing the increase of caries, but excessive intake of fluoride results in dental and skeletal fluorosis Amongst the various elements, fluoride is thirteenth in the order of abundance in the earth s crust. Fluorine is the most electronegative of all known elements (electronegativity 4.0; Pauling, 1960) and the most reactive. Its abundance in the continental crust is about 626 µg/g (Henderson 1982, Periakali et al., 2001).It rarely occurs free in nature, therefore in minerals, fluorine is generally found as the fluoride ion (F-). Occurrence of fluorine in groundwater has drawn worldwide attention due to its considerable impact on human physiology (Kundu et al., 2001). Fluorine occurs mainly as free fluoride ion in natural waters, though fluoride complexes of Al, Be, B and Si are also encountered under specific conditions. The assimilation of fluoride into the human body from potable water at the level of 1mg/l enhances bone development and prevents dental caries. The maximum tolerance limit of fluoride in drinking water specified by the World Health Organization (WHO, 1984) is 1.5 mg/l. The disease fluorosis is caused by an element known as fluorine, the 13th most abundant element available in the earth crust. Chemical Properties of Fluorine Element of Halogen group with molecular weight 19 and atomic number 9. Fluorine is the most electro negative of all elements This fluorine exists as a diatomic molecule with remarkably low dissociation energy (38 K cal/mole). As a result it is highly reactive and has strong affinity to combine with other elements to produce compounds known as Fluoride. The problem of fluorosis has been known in India for a long time. The disease earlier called mottled enamel was first reported by Viswanathan (1935) to be prevalent in human beings in Madras Presidency in Mahajan (1934) reported a similar disease in cattle in certain parts of old Hyderabad state. However, Shortt (1937) was the first to identify the disease as fluorosis in human beings in Nellore district of Andhra Pradesh. Impact of fluoride on human health Increasing population in developing countries and high industrialization of the advanced countries are creating environmental problems of enormous dimensions. Fluoride contamination of drinking water is one of such problems Worldwide. At present, twenty nine countries, are reported to be affected with fluorosis, the fluoride related disease. The problem in India too is known for quite a long time. More than 23 countries in the world, including India, have problems with F- in the drinking water (Susheela, 1993). The problems are most pronounced in the states of Andhra Pradesh, Bihar, Gujarat, Madhya Pradesh, Punjab,

2 Rajasthan, Tamil Nadu and Uttar Pradesh while excess F- may induce hypocalcaemia (Sherlin and Verma, 2000).In India, about 62 million people are at risk of developing fluorosis from drinking high fluoride groundwater (Andezhath et al., 1999). Fluoride is important for the development of teeth and the bones (Phipps, 1995; Czarnowski et al., 1999; ADA 2001). Small doses of fluoride have beneficial effects on the teeth by hardening the enamel and reducing the increase of caries, but excessive intake of fluoride results in dental and skeletal fluorosis (Billings et al., 2004; Chaturvedi et al., 1999) and other disorders may also occur (Connet, 2003). The maximum tolerance limit of fluoride in drinking water specified by the World Health Organization (WHO,1984) is 1.5 mg/l. Dental and skeletal fluorosis has been reported in many countries of the world, notably in African countries (Manji et al., 1989; Ghana (Apambire et al., 1997); South Africa (Ncube et al., 2005), India, (Susheela et al.,1993; Mukherjee et al., 1995; Gupta et al., 2005; Rajashree et al., 2007; China (Ren and Shugin, 1988; Yong and Hua, 1991; Japan (Hamamoto, 1957), Iran (Zohouri et al., 2000); Canada (Boyle and Chagnon, 1995). In these countries fluoride levels in the range of mg/l in groundwater have been reported. Types of Fluorosis Dental Fluorosis: Generally ingestion of water having a fluoride concentration above mg/l may lead to dental mottling, an early sign of dental fluorosis which is characterized by opaque white patches on teeth. In advanced stages of dental fluorosis, teeth display brown to black staining followed by pitting of teeth surfaces. Dental fluorosis produced considerable added dental costs (tooth deterioration) and significant physiological stress for affected population. Dental fluorosis is endemic in 14 states and 1, 50,000 villages in India. The problems are most pronounced in the states of A.P., Bihar, Gujarat, M.P., Punjab, Rajasthan, Tamil Nadu and Uttar Pradesh (Pillai and Stanley, 2002). Types of mottling are shown in Figure-1. Figure: 1 Types of Mottling

3 Skeletal Fluorosis: Skeletal fluorosis may occur when fluoride concentrations in drinking water exceed 4-8 mg/l, which leads to increase in bone density, calcification of ligaments rheumatic or arthritic pain in joints and muscles along with stiffness and rigidity of the joints, bending of the vertebral column and excessive bone formation or osteosclerosis, a basis symptom of skeletal fluorosis (Teotia and Teotia, 1994; Ekambaram and Vanaja, 2001). Crippling skeletal fluorosis can occur when a water supply contains more than 10 mg/l (WHO 1984) is shown in Figure-2. Figure: 2 Extent of Skeletal Fluorosis

4 Table-1 Concentration of fluoride in drinking water and its effects on human health (Source: International Drinking water Standards (1971), WHO. Geneva) International Status: Extent of Fluorosis The following countries have been identified for the problem of fluorosis: Pakistan, Bangladesh, Argentina, United States of America, Morocco, Middle East countries, Japan, South African Countries, New Zealand, and Thailand etc. National status: Endemic fluorosis related to the presence of fluoride in water is a public health problem in most of the Indian states. More than 90% of the rural population uses ground water for domestic purposes. Major problems are being faced by the country due to the presence of excess fluoride, arsenic and nitrate in ground water in certain parts of India. The problem has reached alarming proportions affecting at least 17 states of India: (I) % districts are affected - Andhra Pradesh, Tamil Nadu, Uttar Pradesh, Gujarat, Rajasthan (II) 30-50% districts are affected - Bihar, Haryana, Karnataka, Maharashtra, Madhya Pradesh, Punjab, Orissa, West Bengal (III) < 30 % districts are affected - J & K, Delhi, Kerala Sources of Fluoride Various sources of fluoride entering the body are drinking water, food, industrial exposure, drugs and cosmetics etc. However, drinking water is considered as the major contribution to fluoride entering the human body. 1. Drinking Water The major source of fluoride in the groundwater is fluoride bearing rocks from which it get weathered and/or leached out and contaminates the water. Fluorides occur in three forms, namely, fluorospar or calcium fluoride (CaF2), apatite or rock phosphate [Ca3F (PO4)3 and cryolite (Na3AlF6). Concentration of fluorides is five times higher in granite than in basalt rock areas. Similarly, shale has a higher concentration than sandstone and limestone. Alkaline rocks contain the highest percentage of fluoride (1200 to 8500 mg/kg) (Chand,

5 1998). The Geological survey of India has brought out considerable data which reveal that fluorite, topaz, apatite, rock phosphate, phosphatic nodules and phosphorites are widespread in India and contain high percentage of fluorides. 2. Food Items Besides water, food items especially agricultural crops are heavily contaminated with fluoride as they are grown in the areas where the earth s crust is loaded with fluoride bearing rocks. The fluoride content in food material mainly depends upon: 1. Fluoride level in soil 2. Fluoride level in atmosphere 3. Use of fertilizers and pesticides and other sources of contamination. The fluoride content of some food items has been given in Table-2 Table 2 Fluoride content in various food items (Source: Prevention and Control of Fluorosis in India: Vol. 1 (Health Aspects) (Ed. Susheela, A. K.) Rajiv Gandhi National Drinking Water Mission, New Delhi) 3. Industrial Exposure: Various industries involving the manufacture of phosphate fertilizers, aluminium extraction, fluorinated hydrocarbons (refrigerants, aerosol propellants etc.), fluorinated plastics (polytetrafluoroethylene etc.), petroleum refining and hydrogen fluoride

6 manufacturing units are mainly responsible for airborne fluoride. Fluoride dust and fumes pollute the environment; inhaling dust and fumes is as dangerous as consuming fluoride containing food, water or drugs. Not only the industrial workers are affected but the people living in the vicinity of such industries may also get afflicted. 4. Drug and Cosmetics The sodium fluoride containing drugs for Osteoporosis, Osteosclerosis and dental caries are in use for many years. The prolonged use of these drugs may cause fluorosis. Additionally, the toothpastes and mouth-rinses (whether labelled fluoridated or otherwise) also contain higher fluoride concentration. The fluoride content arising from raw materials used for the manufacturing of tooth-paste, namely, calcium carbonate, talc and chalk can have as high as mg/kg of fluoride. In the fluoridated brands of tooth-pastes, the fluoride content has been reported up to mg/kg. Moreover, some of the mouth rinses are nothing but fluoridated water of a very high fluoride concentration. Background of fluoride occurrence in some parts of India with Special emphasis on Uravakonda, Anantapur District, Andhra Pradesh Fluoride sources and geological influence: Fluoride incidence in groundwater is mainly a natural phenomenon, influenced basically by the local and regional geological setting and hydro-geological conditions. The chief sources of fluoride in groundwater are the fluoride-bearing minerals in the rocks and sediments. The important fluorine-bearing minerals are fluorite, apatite, certain amphiboles and micas. Geology of the study area is shown on figure-3. The concentration of fluoride in groundwater is limited due to the low solubility of most fluorides. The solubility values of sodium fluoride, magnesium fluoride and calcium fluoride at 18 C are 42,200 mg/l, 87 mg/l and 15 mg/l respectively. Magnesium fluoride is more soluble than calcium fluoride. Sodium fluoride is very soluble (Karanth, 1987). Results from groundwater of study area suggest that the fluoride content of 95% of analyzed groundwater samples exceeds the permissible limit of 1.5 mg/l. The source of fluoride in the natural water can be traced to the occurrence of fluorine-rich granitic rocks and soils derived from those rocks. The semi- arid climate with high temperature and low rainfall and the generally alkaline nature of the soil are contributing factors to enhance the fluoride content of groundwater. Fluoride concentrations of groundwater of the study area are significantly correlated with ph, EC, Total; hardness, sodium and bicarbonate concentrations and negatively correlated with Ca2+ and Mg2+. ph is more favorable for fluoride dissolution activity. Conclusions The widespread incidence of fluorosis in India bearing both health and social problem has now become a great concern nowadays. As an immediate solution, to alleviate the human sufferings defluoridation of groundwater and supply of safe drinking water is the only option. The Nalgonda technique is recommended, of the defluoridation methods. Traditional irrigation practices, such as flooding, should be replaced by adopting effective irrigation

7 techniques such as drip irrigation to prevent weathering and leaching, and to reduce water and evaporation loss. Rainwater harvesting techniques can be implemented effectively to reduce fluoride content. Improving the nutritional status of population by adequate calcium intake which is directly associated with a reduced risk of dental flurosis. Vitamin C ingestion also safeguards against the risk of fluorosis. In areas of high fluoride concentration easily available local materials such as clay, serpentine and marble can be used to reduce the fluoride content if geological and geochemical investigations be carried out prior to the implementation of water supply schemes. An emphasis on people awareness about the adverse effects to human health of high F- concentrations in drinking water and education on the mechanisms necessary to improve the health status of the population are essentials. Suggested readings ADA 2001 Position of the American Dietetic Association: the impact of fluoride on health. J.Am. Diet Assoc 101: Andezhath, S.K., Susheela, A.K., Ghosh, G., Fluorosis Management in India: The impact due to networking between health and rural drinking water supply agencies, IAHS- AISH Publ-260, Apambire WM, Boyle DR, Michel FA 1997 Geochemistry, genesis and health implications of floriferous ground water in the upper regions of Ghana. Environmental Geology 359(1); Billings RJ, Berkiowitz RJ, Watson G 2004 Teeth. Pediatrics 113: Boyle DR, Chagnon M 1995 An incident of skeletal fluorosis associated with ground waters of the maritime carboniferous basin, Gaspe region, Quebec, Canada. Environmental Geochemistry and Health 17; Chand, D., Fluoride and human health- causes for concern. Indian J. Env. Prot., 19(2): Chaturvedi, A.K., Pathak, K.C and Singh, V.N., Fluoride removal from waster by adsorption on china clay. Appl.Clay Sci., 3: Connet 2003 US National Research Council Subcommittee on Fluoride in Drinking water. Fluoride 36: Czarnowski, W., Kerchniak, J., Urbanska, B., Stolarska, K., Taraszewska, M. and Muraszko, A., The impact of water borne fluoride on bone density. Fluoride 32(2): Ekambaram, P. Vanaja, P., Calcium preventing locomotor behavioral and dental toxicities of fluoride by decreasing serum fluoride levels in rats. Environ. Toxicol. Pharmacol. 9, Gupta S.K., Deshpande R.D 2005 Origin of high fluoride in groundwater in the North Gujarat-Cambay region, India. Hydrogeology Journal, Volume 13, No 4, August, Hamamoto E 1957 On bone changes observed in residents of a high fluoride zone. In; Utzino S (ed) medico-dental resources on fluorides. Japan society for the promotion of science, Tokyo, pp Henderson P(1982) Inorganic chemistry Pergamon press, Oxford Kharb, P., Susheela, A.K., 1994 Fluoride ingestion in excess and its effects on organic and certain inorganic constituents of soft tissues. Med. Sci. Res, 22, Karanth (1987) Groundwater assessment, development and management, Tata McGraw Hill, New Delhi. Kundu N., Panigrahi m.k., Tripathy S, Munshi S, Powell M.A., haul B.R 2001 Geochemcial appraisal of fluoride contamination of groundwater in the Nayagarh District of Orissa, India. Environmental Geology (2001) 41: Mahajan, Annual Report. VIO Hyderabad State, 3, Indian Council of Agricultural Research, New Delhi. Manji F, Baelum V, Fejerskov O 1986 Dental fluorosis in an area of Kenya with 2 mg/1 fluoride in the drinking water. J. Dent Res 65;

8 Mukherjee S., Case studies on sporadic fluoride contamination in ground water, UNNAO, district, Uttar Pradesh, India. Ncube CF Schutte EJ 2005 The Occurrence of fluoride in South Africa groundwater; A water Quality and Health problem. Waster South Africa, Vol. 31, No: 1 January Pauling, L The nature of the chemical Bond, 3rd edition. Cornell University Press, New York. Periakali P, Subramnian S, Eswaramoorthi S, Arul B, Rajeswara Rao N, Sridhar SGD (2001) Distribution of fluoride in the groundwater of Salem and Namakkal districts, Tamil Nadu. J.Appl. Geochem 3(2) ; Phipps K 1995 Fluoride and bone health J. Public Health Dent 55: Pillai,K.S., Stanley,V.A,2002.Implication of fluoride an endless uncertainty. J.Environ.Biol.23,81-87 Rajashree A A Workshop on Integrated Fluorosis Mitigation Challenges and Avenues was jointly organized by NEERI and UNICEF at NEERI, Nagpur on 31st January and 1st February Ren FR, Shugin J 1988 Distribution and formation of high fluoride ground water in China. Environ Geol Water Sci Shortt, W.E., 1937, Endemic Fluorosis in Nellore District, South India. Indian Medical Gazette, 72: 396. Sherlin, D.M.G., Verma RJ Amelioration of fluoride induced hypocalcaemia by vitamins. Human EXP. Toxicology. 19, Susheela AK, Bhatnagar M, Bahadur R 1993 Prevalence of endemic fluorosis with gastorintestinal manifestations of people living in some North Indian villages. Fluoride 20; Teotia, M., Teotia S.P., Singh, K.P., 1994 Endemic fluoride toxicity and dietary bone disease and deformities in India: year Ind. J. Pediatr 65, Viswanathan, G.R., 1935, Annual Report Madras. Indian Council of Agricultural Research, New Delhi. (Quoted from Indian Institute of Science, 33A, 1, 1951). WHO 1984 Guidelines for drinking water quality, vol 12, Health criteria and other supporting information. World Health Organization, Geneva. Yong L, Hua ZW 1991 Environmental characteristics of regional groundwater relation to fluoride poisons in north China. Environ geol. Water Sci 18; Zohouri FV, Rugg-Gunn AJ 2000 Sources of dietary fluoride intake in 4-year old children residing in low, medium and high fluoride areas in Iran. Int J Food Sci Nutr 51; About the Authors V.Sunitha and M. Ramakrishna Reddy are at present with the Department of Geoinformatics, Yogi Vemana University, Kadapa, A.P. E mail: vangala_sunitha@yahoo.com