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Introduction

Fluorine, the 13th most abundant element of the earth’s crust, represents

about 0.3g / kg of earth’s crust. Its molecular weight is 19 and atomic number is

9. It occurs mainly in the form of chemical compounds such as sodium fluoride or

hydrogen fluoride, which are present in minerals fluorspar fluorapatite, topaz and

cryolite. The physicochemical properties of fluorides available in the form of

sodium fluoride and hydrogen fluoride are given in Table. 1.1. In India, fluorite

and topaz are widespread and contain a high percentage of fluoride. Fluoride

pollution in the environment occurs through two channels, namely natural and

anthropogenic sources (Cengeloglu et al. 2002).

Fluoride is frequently encountered in minerals and in geochemical

deposits and is generally released into subsoil water sources by slow natural

degradation of fluorine contained in rocks. Fluorine is an important element for

human beings, as it helps in growth and prevents the enamel of the teeth from

dissolving under acidic conditions. Various dietary components influence the

absorption of fluorides from gastrointestinal tract and the absorbed fluorides are

distributed throughout the body. Drinking water and sea food are good sources of

fluoride. Fluoride is beneficial to health if the concentration (CF) of the fluoride

ion (F-) in drinking water is less than 1.5 mg/L (WHO 1994).A higher

concentration causes serious health hazards. The disease caused manifests itself in

three forms, namely, dental, skeletal, and non-skeletal fluorosis. Dental fluorosis

produces widespread brown stains on teeth and may cause pitting (Bulusu and

Nawlakhe, 1992). Skeletal fluorosis causes crippling and severe pain and stiffness

of the backbone and joints (Bulusu and Nawlakhe, 1992). Even though extensive

studies have been conducted, there seems to be no effective cure for these

diseases. Therefore, it is desirable to drink water having a fluoride concentration

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less than certain value. Hence, drinking water with CF > 1.5 mg/L (1 mg /L in

India) needs treatment (WHO1994).

Table1:1 Physiochemical properties of common forms of fluoride

Property Sodium Fluoride

(NaF)

Hydrogen Fluoride

(HF)

Physical state White, crystalline powder

Colour less liquid or gas with biting smell

Density (g/cm3) 2.56 _

Water solubility 42g/L at100 C Readily soluble below 200C

Acidity _ Strong acid in liquid form; weak acid when

dissolved in water

Source: (Pranab Kumar Rakshit, 2004)

1.1 Fluoride in water: An overview

Throughout many parts of the world, high concentrations of fluoride

occurring naturally in groundwater and coal have caused widespread fluorosis - a

serious bone disease - among local populations. A range of everyday products,

notably toothpaste and drinking water, the fluoride in small doses has no adverse

effects on health to offset its proven benefits in preventing dental decay. But more

and more scientists are now seriously questioning the benefits of fluoride, even in

small amounts (UNICEF Report, 1980). Since some fluoride compounds in the

earth's upper crust are soluble in water, fluoride is found in both surface waters

and groundwater. In surface freshwater, however, fluoride concentrations are

usually low - 0.01 ppm to 0.3 ppm.

In groundwater, the natural concentration of fluoride depends on the

geological, chemical and physical characteristics of the aquifer, the porosity and

acidity of the soil and rocks, the temperature, the action of other chemical

elements, and the depth of wells. Because of the large number of variables, the

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fluoride concentrations in groundwater can range from well under 1 ppm to more

than 35 ppm. In Kenya and South Africa, the levels can exceed 25 ppm. In India,

concentration up to 38.5 ppm has been reported in drinking water (UNICEF).

Table1:2 Permissible limit of fluoride in drinking water prescribed by

various organizations

Name of the organization Desirable limit (mg/L)

Bureau of Indian Standards (BIS) 0.6-1.2

Indian Council of Medical Research (ICMR) 1.0

The Committee on Public Health Engineering

Manual and Code of Practice, Government of India

1.0

World Health Organization (International

Standards for Drinking Water)

1.5

1.2 Basic facts about fluoride:

Fluoride exists fairly abundantly in the earth's crust and can enter

groundwater by natural processes; the soil at the foot of mountains is particularly

likely to be high in fluoride from the weathering and leaching of bedrock with

high fluoride content.

According to 1984 guidelines published by the World Health Organization

(WHO) fluoride is an effective agent for preventing dental caries if taken in

'optimal' amounts. But a single 'optimal' level for daily intake cannot be agreed

because the nutritional status of individuals, which varies greatly, influences the

rate at which fluoride is absorbed by the body. A diet poor in calcium, for

example, increases the body's retention of fluoride.

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Water is a major source of fluoride intake. WHO (1984, guidelines)

suggested that, areas with a warm climate, the optimal fluoride concentration in

drinking water should remain below 1 mg/liter (1ppm or part per million), while

in cooler climates it could go up to 1.2 mg/liter. The differentiation derives from

the fact that we perspire more in hot weather and consequently drink more water.

The guideline value (permissible upper limit) for fluoride in drinking water was

set at 1.5 mg/liter, considered a threshold where the benefit of resistance to tooth

decay did not yet shade into a significant risk of dental fluorosis.

In many countries, fluoride is purposely added to the water supply,

toothpaste and sometimes other products to promote dental health. It should be

noted that fluoride is also found in some foodstuffs and in the air (mostly from

production of phosphate fertilizers or burning of fluoride-containing fuels), so the

amount of fluoride people actually ingest may be higher than assumed.

It has long been known that excessive fluoride intake carries serious toxic

effects. But scientists are now debating whether fluoride confers any benefit at all.

1.3 Fluoride: good or bad for health?

Fluoride was first used to fight dental cavities in the 1940s, its

effectiveness defended on two grounds:

• Fluoride inhibits enzymes that breed acid-producing oral bacteria whose

acid eats away tooth enamel. This observation is valid, but some scientists

now believe that the harmful impact of fluoride on other useful enzymes

far outweighs the beneficial effect on caries prevention.

• Fluoride ions bind with calcium ions, strengthening tooth enamel as it

forms in children. Many researchers now consider this more of an

assumption than fact, because of conflicting evidence from studies in India

and several other countries over the past 10 to 15 years. Nevertheless,

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agreement is universal that excessive fluoride intake leads to loss of

calcium from the tooth matrix, aggravating cavity formation throughout

life rather than remedying it, and so causing dental fluorosis. Severe,

chronic and cumulative overexposure can cause the incurable crippling of

skeletal fluorosis (A.Tiwari et.al. 2009).

1.4 Symptoms of Fluorosis:

Dental fluorosis, which is characterized by discolored, blackened, mottled

or chalky-white teeth, is a clear indication of overexposure to fluoride during

childhood when the teeth were developing. These effects are not apparent if the

teeth were already fully grown prior to the fluoride overexposure; therefore, the

fact that an adult may show no signs of dental fluorosis does not necessarily mean

that his or her fluoride intake is within the safety limit.

Chronic intake of excessive fluoride can lead to the severe and permanent

bone and joint deformations of skeletal fluorosis. Early symptoms include

sporadic pain and stiffness of joints: headache, stomach-ache and muscle

weakness can also be warning signs. The next stage is osteosclerosis (hardening

and calcifying of the bones), and finally the spine, major joints, muscles and

nervous system are damaged.

Whether dental or skeletal, fluorosis is irreversible and no treatment exists.

The only remedy is prevention, by keeping fluoride intake within safe limits.

1.5 Fluorosis worldwide:

The latest information shows that fluorosis is endemic in at least 25

countries across the globe (Figure1.1). The total number of people affected is not

known, but a conservative estimate would number in the tens of millions. In 1993,

15 of India's 32 states were identified as endemic for fluorosis. In Mexico, 5

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million people (about 6% of the population) are affected by fluoride in

groundwater. Fluorosis is prevalent in some parts of central and western China

and caused not only by drinking fluoride in groundwater but also by breathing

airborne fluoride released from the burning of fluoride-laden coal. Worldwide,

such instances of industrial fluorosis are on the rise (UNICEF).

Some governments are not yet fully aware of the fluoride problem or

convinced of its adverse impact on their populations. Efforts are therefore needed

to support more research on the subject and promote systematic policy responses

by governments.

Endemic Fluorosis in different countries of the world (UNICEF)

Figure 1.1

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1.6 Fluoride in India:

India is among the many countries in the world, where fluoride

contaminated ground water is creating health problems. Safe drinking water in

rural areas of India is predominantly dependent on groundwater sources, which

are highly contaminated with fluoride. The concentrations in 17 States out of 32

are endemic for fluorosis being 1 to 48 mg/L. About 62 million people including

6 million children are affected with dental, skeletal and non-skeletal fluorosis.

This involves about 9000 villages affecting 30 million people (Nawlakhe

and Paramasivam, 1993). It must be noted that the problem of excess fluoride in

drinking water is of recent origin in most parts. Digging up of shallow aquifers for

irrigation has resulted in declining levels of ground water. As a result, deeper

aquifers are used, and the water in these aquifers contains a higher level of

fluoride (Gupta and Sharma, 1995).

In India, the states of Andhra Pradesh, Bihar, Chhattisgarh, Haryana,

Karnataka, Madhya Pradesh, Maharashtra, Orissa, Punjab, Rajasthan, Tamil

Nadu, Uttar Pradesh and West Bengal are affected by fluoride contamination in

water.

Worst affected: - Rajasthan and Gujarat in North India and Andhra in South

India.

Moderately affected: - Punjab, Haryana, M.P. and Maharashtra.

Mildly affected: - T.N., W.B., U.P., Bihar and Assam.

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Fluoride affected states in India (UNICEF, New Delhi, 2001)

Figure 1.2

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1.7 Fluoride in Rajasthan:

In Rajasthan the existence of fluorides was first detected in 1964 when a

survey was under taken by state PHED in collaboration with NEERI on the basis

of reports of some peculiar diseases. The concentration in ground water varied

from as low as zero to 18.00ppm as maximum.

Fluorides make an entry in drinking water from indigenous rocks and

ground water around the mica mines (Rajasthan has rich sources of mica). In the

absence of perennial rivers, surface and canal system, groundwater remains the

main source of drinking water. It contains 2 to 20 mg/L of fluoride .Fluoride is

more common in ground water than in surface water. The main sources of

fluoride in ground water are different fluoride bearing rocks .Fluoride ions are

important in water supplies because of their peculiar characteristics. They cannot

be tolerated in too low or too high concentration. A Fluoride concentration of

approximately 0.5mg/l to 1mg/l in drinking water effectively reduces dental caries

or tooth decay without any harmful effects on health. Excess concentration of

fluoride (more than 2mg/l) causes dental fluorosis (disfigurement of the teeth) and

harm to bony structures.

All the 32 districts of Rajasthan affected are from fluorosis. Nagour,

Jaipur, Sikar, Jodhpur, Barmer, Ajmer, Sirohi, Jhunjhnu, Churu, Bikaner,

Ganganagar districts have been declared as fluorosis prone areas. People in

several districts in Rajasthan are consuming water with fluoride concentrations up

to 24 mg/l. Rajasthan has more than 51 per cent of the affected villages in the

country. The number of villages affected by fluoride has increased over time. In

1973, there were 1,871 villages with fluoride levels over 3mg/l. By 2001, this

number had risen to 10,342 villages, an increase of more than five times. This

makes Rajasthan the most severely affected state in India, with millions crippled

as the result of consuming excessive amounts of fluoride (State Institute of Health

and Family Welfare, Jaipur)

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Fluoride affected Districts in Rajasthan (2003)

Figure 1.3

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1.8 Various Health Impacts of Fluoride:

Fluoride being an electronegative element and having a negative charge is

attracted by positively charged ions like calcium (Ca++). Bone and tooth having

highest amount of calcium in the body attracts the maximum amount of fluoride

and is deposited as Calcium Fluorapatite crystals. Intake of fluoride above 1.5

mg/L may lead to serious manifestations, which are described below:-

1.8.1 Dental fluorosis:

Incidences of mottled teeth have been observed even with range of 0.7 –

1.5 mg F / l in drinking water. The minimal daily intake of fluoride that can cause

very mild or mild fluorosis is estimated to be about 0.1 mg/kg body weight (P.

Singh et.al.2011).Dental fluorosis is the loss of luster and shine of the dental

enamel. The discoloration starts from white yellow, brown to black.

(Discoloration is either as spots or horizontal streaks). Enamel matrix is laid down

on incremental lines before and after birth. Hence dental fluorosis is invariably

seen on horizontal lines or on bands on the surface of the teeth .Fluorosis is seen

as mild, moderate and severe depending on the amount of fluoride ingested during

the stages of formation of the teeth.

Teeth commonly affected by fluorosis are central incisors, lateral incisors

and the molars of the permanent dentition. It affects both the inner and the outer

surfaces of teeth.

The symptoms of dental fluorosis are as given below:

1. Loss of teeth at early age.

2. Dullness of the teeth and loss of shine with developed white and yellow

spots.

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3. Discoloration of teeth, turning into brown and black streaks or spots on the

enamel surface.

4. The teeth, once affected by dental fluorosis, cannot be reversed to normal.

Only discolored teeth can be masked by the methods as prescribed below:

Bleaching of teeth, Filling with high cure material and laminated

veneering. Capping or crowning of teeth with metals like chrome, cobalt,

gold, porcelain and acrylic.

1.8.2 Skeletal fluorosis:

Excessive quantity of fluoride deposited in the skeleton , which is more in

cancellous bone than cortical bone .Fluoride poisoning leads to severe pain

associated with rigidity and restricted movements of cervical and lumber spine,

knee and pelvic joints as well as shoulder joints . In severe cases of fluorosis,

there is complete rigidity of the joints resulting in stiff spine described as

“bamboo spine”, and immobile knee, pelvic and shoulder joints. Crippling

deformity is associated with rigidity of joints and includes kyphosis, scoliosis, and

flexion deformity of knee joints, paraplegia and quadriplegia. Skeletal fluorosis is

an irreversible process as the dental fluorosis.

The symptoms of skeletal fluorosis are as given below:

1. Severe Pain in neck, back bone or joints.

2. Stiffness in the neck.

3. Rigidity in the hip region (pelvic girdle).

4. Construction of vertebral canal and inter vertebral forearm exerts pressure

on nerves and blood vessels leading to paralysis and pain. The symptoms

of dental and skeletal Fluorosis can easily view by following photographs:

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Dental Fluorosis

Figure 1.4

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Dental Fluorosis

Dental Fluorosis

Figure 1.5

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Skeletal Fluorosis

Figure 1.6

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Skeletal Fluorosis

Figure 1.7

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Skeletal Fluorosis

Figure 1.8

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Skeletal Fluorosis

Figure 1.9

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1.8.3 Non – skeletal fluorosis:

This kind of fluorosis is often overlooked due to misconception that

fluoride affects only bone and teeth. Fluoride when consumed in excess can cause

several other kinds of manifestations;

Neurological: Nervousness, depression, tingling sensation of fingers and toes,

excessive thirst and tendency to urinate more frequently.

Muscular: Muscle weakness, stiffness, pain in muscles and loss of muscle power.

Allergic: Very painful skin rashes, which are perivascular inflammation prevalent

in women and children, pinkish red or non- persistent oval shaped bluish - red

spots on the skin.

Gastro-intestinal: Acute abdominal pain, diarrhea, constipation, blood in stool

tenderness in stomach.

Urinary tract: Urine may be less in volume, red in colour and passed with

itching and sensation.

Higher concentration of Fluoride can also damage a fetus, and adversely affect the

IQ of children.

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Table -1:3 Effects of fluoride concentration on human health

Concentration of

fluoride

Medium Effects

1 ppm Water Dental caries reduction

2ppm or < 2ppm

8ppm

Water

Water

Mottled enamel

(dental fluorosis)

10% osteosclerosis

20-80mg/day Water or food Crippling skeletal fluorosis

50ppm Water or food Thyroid changes

100ppm Water or food Growth retardation

125ppm Water or food Kidney changes

2.5-5.0ppm Acute dose Death

1.8.4 Drug induced fluorosis:

The prolonged use of drugs containing sodium fluoride is known to cause

skeletal fluorosis. During 1982, two cases of drug induced skeletal fluorosis were

reported from Switzerland. Patients of rheumatoid arthritis received uninterrupted

and prolonged treatment with niflumic acid. The daily dose of drug administered

was 3 capsules of 250 mg niflumic acid (Nifluril, UPSA Laboratories, France).

Fluoridated toothpastes and mouth rinses recommended for mouth hygiene

may cause drug induced fluorosis, particularly if the user is exposed to high

fluoride water consumption. The blood vessels in the oral mucosa and the

sublingual blood vessel absorb fluoride from these preparations. The commercial

mouth rinses are generally fluoridated preparations with very high fluoride

content.

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1.8.5 Industrial fluorosis:

Industrial fluorosis is a serious problem in the developed western and

other industrialized countries. However, due to rapid industrialization in India, the

problem of industrial fluorosis is reaching an alarming state and is compounding

the problem of endemic, water and food borne fluorosis (Anurag Tewari and

Ashutosh Dubey, 2009).

A number of industries use hydrofluoric acid and fluoride containing salts,

in the different sections of an industry for one reason or other. The industries that

use fluoride are-

1) Aluminum 2) Steel 3) Enamel 4) Pottery 5) Glass 6) Bricks 7)

Phosphate Fertilizer 8) Welding 9) Refrigeration 10) Rust Removal 11) Oil

Refinery 12) Plastic 13) Pharmaceutical 14) Tooth paste 15) Chemical Industries

16) Automobile Industry etc. Fluoride dust and fumes pollute the environment;

inhaling the dust and fumes is as dangerous as consuming fluoride containing

food, water or drugs.

1.9 Preventing fluoride poisoning

Fluoride poisoning can be prevented or minimized by using alternative

water sources, by removing excessive fluoride from drinking water, and by

improving the nutritional status of populations at risk.

Alternative water sources

Alternative water sources include surface water, rainwater, and low-

fluoride groundwater.

Surface water: Particular caution is required when opting for surface water, since

it is often heavily contaminated with biological and chemical pollutants. Surface

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water should not be used for drinking without treatment and disinfection. Many

water treatment technologies are available, but the most effective are usually too

expensive and complex for application in poor communities. Simple and low-cost

technologies, such as sand filtration, ultraviolet water disinfection or chlorine

water disinfection, are adequate in some but not all cases. Community capacity is

an essential factor in ensuring successful utilization of these technologies. Water

chlorination at household level is widely used only in emergencies.

Rainwater: Rainwater is usually a much cleaner water source and may provide a

low-cost simple solution. The problem, however, is limited storage capacity in

communities or households. Large storage reservoirs are needed because annual

rainfall is extremely uneven in tropical and subtropical regions. Such reservoirs

are expensive to build and require large amounts of space.

Low-fluoride groundwater: Fluoride content can vary greatly in wells in the

same area, depending on the geological structure of the aquifer and the depth at

which water is drawn. Deepening tube wells or sinking new wells in another site

may solve the problem. The fact that fluoride is unevenly distributed in

groundwater, both vertically and horizontally, means that every well has to be

tested individually for fluoride in areas endemic for fluorosis: extrapolating

sample tubewell tests to a larger area does not provide an accurate picture.

Changing the Dietary Habits: People living in high fluoride zone can make

certain changes in their diet, it may help them to keep away the problem of

fluorosis. Vitamin C inhibits the progress of fluorosis (P. Singh et.al. 2011).Thus

people should be directed to add items like amla, lemon, oranges, tomato,

sprouted cereals/pulses and dhainya leaves in their food. Clinical data indicate

that adequate calcium intake is clearly associated with a reduced risk of dental

fluorosis. So it is recommended to consume calcium rich food in endemic zones.

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It includes milk, yoghurt, leafy vegetables, drumstick leaves and sesame seed.

Foods containing anti-oxidants help in preventing fluorosis. These foods include

garlic, ginger, carrot, papaya, pumpkin white onion and green leafy vegetables.

Vitamin E also has a prophylactic role. Its sources include whole grain cereals,

vegetable oils, green vegetables and dried beans. Avoid the use of Tobacco and

beetle nut.

These do not remove Fluoride:

Boiling Water: This will concentrate the fluoride rather than reduce it.

Freezing Water: Freezing water does not affect the concentration of fluoride.

Steps to reduce Fluoride:

� Avoid fluoride supplements

Fluoride Rich Food Substances:

� Black tea and Lemon tea (tea with milk is safe)

� Black rock salt (kala namak)

� Black rock salt lased pickles

� Garam masala, salty snacks

� Chaat and Chaat masala

� Canned fruit juices

� Cannel fish

� Fluoride contaminated drinking water

� Chewing of tobacco

� Supari (arccanut) and

� Hajmola and other Churan containing rock salt

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Fluoride Rich Dental Products:

� Fluoridated toothpaste

� Mouth rinse

� Varnish and

� Sodium fluoride tablets(for treatment of Osteoporosis) (UNICEF)

1.10 Common defluoridation methods of drinking water:

Defluoridation means the removal of excess fluoride from water.

Defluoridation of drinking water has to been practiced by two options:-

(i) The central treatment of water at the source and

(ii) The treatment of water at the point of use that is, at the household

level.

In developed countries treatment at the source is the method adopted.

Defluoridation is carried out on a large scale under the supervision of skilled

personnel, usually at a treatment works alongside other treatment processes. Cost

is not then a limiting factor. The same approach may not be feasible in less

developed countries, especially in rural areas, where settlements are scattered.

Treatment may only be possible at a decentralized level, i.e. at the community,

village or household level. Treatment at the point of use has several advantages

over treatment at community level. Costs are lower, as defluoridation can be

restricted to the demand for cooking and drinking – usually less than 25% of the

total water demand. Chemical treatment of the entire water demand would lead to

production of large volumes of sludge, which requires a safe disposal.

It has been found that the removal of fluoride from potable water is not

adequate when initial concentration of fluoride in the water is very high and the

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pH of the untreated water is alkaline. Moreover, different degrees of hardness of

water require different concentrations of alum.

Limitations of point of use treatment are that reliability of the treatment

units has to be assured, and that all users should be motivated to use only the

treated water for drinking and cooking when untreated water is also available in

the house

The National Environment Engineering Research Institute in Nagpur,

India (NEERI) has evolved an economical and simple method of defluoridation,

which is referred to as the Nalgonda technique. The Nalgonda technique has been

repeatedly proven to be an economical and effective household defluoridation

technique. In this commonly used technique, fluoride is precipitated using 500

mg/L of alum and 30 mg/L of lime.

UNICEF has worked closely with the Government and other partners in

defluoridation programmes in India, where excessive fluoride has been known for

many years to exist in groundwater. In the 1980s, UNICEF supported the

Government's Technology Mission in the effort to identify and address the

fluoride problem: the Government subsequently launched a massive programme,

still under way, to provide fluoride-safe water in all the areas affected.

Defluoridation methods can be broadly divided into three categories

according to the main removal mechanism:

• Chemical additive methods

• Contact precipitation

• Adsorption/ion exchange methods

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Chemical additive methods

These methods involve the addition of soluble chemicals to the water.

Fluoride is removed either by precipitation, co-precipitation, or adsorption onto

the formed precipitate. Chemicals include lime used alone or with magnesium or

aluminum salts along with coagulant aids. Treatment with lime and magnesium

makes the water unsuitable for drinking because of the high pH after treatment.

The use of alum and a small amount of lime has been extensively studied for

defluoridation of drinking water.

The method popularly known as the Nalgonda technique (RENDWM,

1993), is one of example named after the town in India where it was first used at

water works level. It involves adding lime (5% of alum), bleaching powder

(optional) and alum (Al2(SO4)3.18H2O) in sequence to the water, followed by

coagulation, sedimentation and filtration (L.Iyenger,2005). A much larger dose of

alum is required for fluoride removal (150 mg/mg F-), compared with the doses

used in routine water treatment. As hydrolysis of alum to aluminum hydroxide

releases H+ ions, lime is added to maintain the neutral pH in the treated water.

Excess lime is used to hasten sludge settling. The dose of alum and lime to be

added in raw water with different fluoride concentrations and alkalinity levels

(G.Karthikeyan and A. Shunmuga Sundarraj, 1999).

The reaction occurs through the following equations:

2 Al2 (SO4)3.18H2O + NaF + 9Na2CO3 → [5Al (OH) 3 Al (OH) 2F] +

9Na2SO4+NaHCO3 + 8 CO2 + 45 H2O

3 Al2 (SO4)3.18H2O + NaF +17NaHCO3 → [5Al (OH) 3 Al (OH) 2F] + 9Na2SO4+

17 CO2 + 18 H2O

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The Nalgonda technique has been successfully used at both individual and

community levels in India and other developing countries like China and

Tanzania. Domestic defluoridation units are designed for the treatment of 40 liters

of water. Whereas the fill-and-draw defluoridation plant can be used for small

communities. Alum treatment is seldom used for defluoridation of drinking water

in developed countries.

Contact Precipitation

Contact precipitation is a technique in which fluoride is removed from

water through the addition of calcium and phosphate compounds. The presence of

a saturated bone charcoal medium acts as a catalyst for the precipitation of

fluoride either as CaF2, and/or fluorapatite. Tests at community level in Tanzania

have shown promising results of high efficiency. Reliability, good water quality

and low cost are reported advantages of this method (Chilton, et al., 1999).

Adsorption/ion-exchange method

In the adsorption method, raw water is passed through a bed containing

defluoridating material. The material retains fluoride either by physical, chemical

or ion exchange mechanisms. The adsorbent gets saturated after a period of

operation and requires regeneration.

A wide range of materials has been tried for fluoride uptake. Bauxite,

magnetite, kaolinite, serpentine, various types of clays and red mud are some of

the naturally occurring materials studied. The general mechanism of fluoride

uptake by these materials is the exchange of metal lattice hydroxyl or other

anionic groups with fluoride.

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Fluoride uptake capacity can be increased by certain pre-treatments like

acid washing, calcinations, etc. None of the mentioned materials generally

exhibits high fluoride uptake capacities.

Processed materials like activated alumina, activated carbon, bone char,

defluoron-2(sulphonated coal) used for defluoridation of drinking water .And

synthetic materials like ion exchange resins also have been extensively evaluated

for defluoridation. Among these materials, bone char, activated alumina and

calcined clays have been successfully used in the field; (Cummins, 1985,

Susannae Rajchagool and Chaiyan Rajchagool, 1997, and Priyanta and

Padamasiri, 1996).

Application of these materials is described below:

Bone Char Method: Bone char consists of ground animal bones that have been

charred to remove all organic matter. Major components of bone charcoal are

calcium phosphate, calcium carbonate and activated carbon. The fluoride removal

mechanism involves the replacement of carbonate of bone char by fluoride ion.

The method of preparation of bone charcoal is crucial for its fluoride uptake

capacity and the treated water quality. Poor quality bone char can impart bad taste

and odour to water. Exhausted bone char is regenerated using caustic soda. Since

acid dissolves bone char, extreme care has to be taken for neutralizing caustic

soda. Presence of arsenic in water interferes with fluoride removal.

In the USA in the past, a few defluoridation plants were using bone char.

Now they have been largely replaced by activated alumina. Bone char is

considered as an appropriate defluoridating material in some developing

countries. The ICOH domestic defluoridator was developed in Thailand and uses

crushed charcoal and bone char. Its defluoridation efficiency depends on the

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fluoride concentration in raw water as well as the fluoride uptake capacity and the

amount of bone char used in the filter. Field trials in Thailand, Sri Lanka and

some African countries have shown very encouraging results (Priyanta and

Padamasiri, 1996; Mjengera et al., 1997; and Susannae Rajchagool and Chaiyan

Rajchagool, 1997). Reports from Sri Lanka have shown that with 300 gm

charcoal (mainly to remove colour and odour) and 1 kg bone char an ICOH filter

can defluoridate on an average 450 liters of water containing 5 mg/l F- at a flow

rate of 4 liters per hour. Regeneration of spent bone char is not recommended for

these household units. Instead it should be replaced with fresh material

commercially available in local shops.

Activated Alumina Method: Aluminium oxide (Al2O3) is called Activated

alumina (or calcined alumina) .It is prepared by low temperature dehydration

(300-600°C) of aluminium hydroxides. Activated alumina has been used for

defluoridation of drinking water since 1934, just after excess fluoride in water

was identified as the cause of fluorosis.

The fluoride uptake capacity of activated alumina depends on the specific

grade of activated alumina, the particle size and the water chemistry (pH,

alkalinity and fluoride concentrations). In large community plants the pH of the

raw water is brought down to 5.5before defluoridation, as this pH has been found

to be optimum and it eliminates bicarbonate interference. The mechanism of

fluoride removal is most probably the legend exchange reaction at the surface of

activated alumina. Exhausted activated alumina has to be regenerated using

caustic soda. To restore the fluoride removal capacity, basic alumina is acidified

by bringing it into contact with an excess of dilute acid (Clifford, 1990).

Activated alumina has been the method of choice for defluoridation of

drinking water in developed countries. Generally it is implemented on a large

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scale in point of source community plants. A few points of use defluoridation

units have been developed which can be directly attached to the tap. During recent

years this technology is gaining wide attention even in developing countries.

Domestic defluoridation units have been developed in India using indigenously

manufactured activated alumina, which is commercially available in bulk

quantities. Choosing the proper grade of activated alumina is important for its

effective reuse in multiple defluoridation cycles. Around 500-1500 liters of safe

water could be produced with 3 kg of activated alumina when the raw water

fluoride is 11 and 4 mg/l respectively at natural water pH of 7.8-8.2. The

frequency of regeneration is once in 1.5-3 months. The cost of activated alumina

is around US$ 2 per kg and the total cost of the domestic filter depends upon

material used for filter assembly. Regeneration of exhausted activated alumina

costs around US$ 0.5 (Venkobachar et al., 1997).

Major requirements are the creation of demand for treatment and the

setting up of good supply and financing systems and arrangements for

regeneration. Sale of the ingredients and the provision of education and

monitoring through visits to user households has in some places become a source

of income for trained women promoters. The units are being evaluated in several

villages in India. Daily operational care for using these units is normally

negligible. However, the exhausted activated alumina has to be regenerated once

every few months. This is carried out at the village level.

Calcined clay Method: Freshly fired brick pieces are used in Sri Lanka for the

removal of fluoride in domestic defluoridation units. The brick bed in the unit is

layered on the top with charred coconut shells and pebbles. Water is passed

through the unit in an up flow mode. The performance of domestic units has been

evaluated in rural areas of Sri Lanka (Priyanta & Padamasiri 1997). It is reported

that efficiency depends on the quality of the freshly burnt bricks. The unit could

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be used for 25-40 days, when withdrawal of Defluoridated water per day was

around 8 liters and raw water fluoride concentration was 5 mg/l. As PVC pipes

are costly, a defluoridator made out of cement and bricks have also been

recommended. Apart from the methods discussed above, specific synthetic ion

exchangers and separation technologies such as reverse osmosis and

electrodialysis have also been developed for fluoride removal from potable water.

To select a suitable defluoridation method for application in developing countries,

some of the following criteria need to be considered:

• Fluoride removal capacity

• Simple design

• Easy availability of required materials and chemicals

• Acceptability of the method by users with respect to taste and cost

Both precipitation and adsorption methods have advantages and

limitations. In the Nalgonda technique easily available chemicals are used and the

method is economically attractive. Limitations of the method are varying alum

doses depending on fluoride levels in water, daily addition of chemicals and

stirring for 10-15 min, which many users may find difficult. In adsorption-based

methods like activated alumina and bone char, daily operation is negligible.

Activated alumina is costly. Hence exhausted alumina has to be regenerated using

caustic soda and acid and repeatedly reused, at least for a few cycles. Improperly

prepared bone char imparts taste and odour to the treated water. Since bone char

from point of use units is not generally regenerated, a ready supply of properly

prepared material needs to be available. Furthermore, bone char may not be

culturally acceptable to certain communities as defluoridating material.

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Brick powder: Defluoridation of groundwater using brick powder as an

adsorbent was studied in batch process. Different parameters of adsorption, viz.

effect of pH, effect of dose and contact time were selected and optimized for the

study. Feasible optimum conditions were applied to two groundwater samples of

high fluoride concentration to study the suitability of adsorbent in field

conditions. Comparison of adsorption by brick powder was made with adsorption

by commercially available activated charcoal. In the optimum condition of pH

and dose of adsorbents, the percentage defluoridation from synthetic sample,

increased from 29.8 to 54.4% for brick powder and from 47.6 to 80.4% for

commercially available activated charcoal with increasing the contact time

starting from 15 to 120 min. Fluoride removal was found to be 48.73 and 56.4%

from groundwater samples having 3.14 and 1.21 mg l−1 fluoride, respectively,

under the optimized conditions. Presence of other ions in samples did not

significantly affect the defluoridation efficiency of brick powder. The optimum

pH range for brick powder was found to be 6.0–8.0 and adsorption equilibrium

was found to be 60 min. These conditions make it very suitable for use in drinking

water treatment. Defluoridation capacity of brick powder can be explained on the

basis of the chemical interaction of fluoride with the metal oxides under suitable

pH conditions. The adsorption process was found to follow first order rate

mechanism as well as Freundlich isotherm.

Fired clay chips have a tendency to bind fluorides and are easily available in

village communities, thereby making it a proper choice for fluoride adsorption.

Fired clay chips are reported to have good fluoride removal capacity (Moges et

al.1996). The maximum capacity of the adsorbent was found to be 0.2 mg F- / g

of the adsorbent. 5 – 20 mg/L of fluoride solution can be reduced to less than 1.5

mg/L by using fired clay chips. One of the disadvantages of this process is that the

contact time required for the completion of the process is very high (150 hours).In

Introduction

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conclusion, members were not very sanguine about the efficacy of groundwater

recharge on mitigating fluoride; they emphasized collection and storage of

rainwater as a safe alternative for drinking water. Fired clay chips are reported to

have good fluoride removal capacity (Moges et al.1996). The maximum capacity

of the adsorbent was found to be 0.2 mg F- / g of the adsorbent. Studies show that

5 – 20 mg/L of fluoride solution can be reduced to less than 1.5 mg/L using fired

clay chips.

Fly ash Method:

Fly ash is a major solid waste by–product of coal fired power plants. It is

produced as a fine residue carried off with the flue gases and deposited in the

electrostatic precipitator. The particle size of fly ash ranges from 10 microns to a

few mm (Agarwal et al. 2003). The main components of fly ash are silica,

alumina, iron oxides, calcium oxide and residual carbon (Yadawa et al. 1989).

The presence of unburnt carbon and surface area of 1 m2 g -1, make it a good

candidate for utilization as an inexpensive adsorbent. Sieve analysis of the fly ash

showed that the size range of the particles was between 10 – 80 µm. Adsorption

studies were conducted at room temperature in a batch process with 25 g of fly

ash and 1 L of sample solution containing known concentration of fluoride (CF).

The fly ash in a beaker is mixed with 1L of sample solution and then kept idle.

Samples were withdrawn periodically from the beaker for estimating the value of

CF.

The variation of CF found with time the fluoride adsorption ability of fly

ash is higher at higher concentration levels. This remarkable property can be

explained by the fact that at higher concentrations the less accessible sites of the

adsorbents are more likely to adsorb fluoride. The adsorption capacity of fly ash is

much higher (3.5 mg F/ g fly ash) than the other adsorbents. This may be because

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of the presence of unburnt carbon particles in the fly ash which are known to be

very efficient adsorbing materials (Pranab Kumar Rakshit, 2004).

Red Mud Method:

Red Mud is a very fine material (particle size of which is generally below

75µ) and high specific surface area (around 10 m2/gm) which is produced during

the Bayer process for alumina production (Hind et al., 1999). It is the insoluble

product after bauxite digestion with sodium hydroxide at elevated temperature

and pressure. It is mainly composed of iron oxides and has a variety of elements

and mineralogical phases. The removal of fluoride from aqueous solution by

using the original and activated red mud forms has been studied by many

researchers (Lopez et al., 1998). The fluoride adsorption capacity of activated

form has been found to be higher than that of the original form. The adsorption is

highly dependant on pH. Researches have revealed that the maximum adsorption

of fluoride is at pH 5.5.For pH greater than 5.5 fluoride removal decreases

sharply. It was found that the sufficient time for adsorption equilibrium of

fluoride ions is 2 h. The possibility of removal of fluoride ion by using red mud is

explained on the basis of the chemical nature and specific interaction with metal

oxide surfaces (Yunus et a1. 2002).

Red and cleaned mud was used for batch experiments. In this experiments

mud (100 g) was washed with water and taken in a plastic beaker. One liter of a

solution containing a known concentration of fluoride (CF) was added to it. The

mixture is kept undisturbed during the course of experiment. A sample was

periodically taken out of the beaker and analyzed using the fluoride – ion

selective electrode.

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The variation of the fluoride concentration in the water (CF) adsorbed

with time. It was observed that the amount of fluoride adsorbed increases with

time up to 140 hours after which equilibrium is attained. The capacity of mud in

contact with 1 mg/L solution of fluoride in water is 0.01 mg F / g mud. The extent

of adsorption of anions by mud is a function of the pH of the system. The

adsorption is highly dependent on PH. It reveals that the maximum adsorption of

fluoride is for PH = 4.5 to 5.For PH greater than 5.5 fluoride removal decreases

sharply (B.K. Shrivastava 2009).

1.11 Area of work: Sitapura Industrial area, Tehsil Sanganer, District Jaipur

(Rajasthan).

Sitapura Industrial Area is located 6.0 Km from Jaipur Air port along NH-

12. This area is known as EPIP (Export Promotion Industrial Park). Jaipur city is

18 km from EPIP. The area is around 365.00 acres. EPIP is located in a rural-

urban setting where greenery is profuse and fresh air in plenty. The water quality

is potable in this area. Water availability by tube wells. The Depth of tube wells

are approximate 30m. Average discharge of water is 2,000 gallons per hour. The

prominent industries of in this area are chemical and automobile industries.

Thousands of residential flats are available in and around area. ITI, Polytechnics,

Engineering Institutes, Medical Institutes and Hospitals, Management, IT and

Architectural colleges, Fashion Designing Institutes .shopping complex etc. are

located in this area.

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Map of Sitapura Industrial area

Figure 1.10

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1.12 Aim of work: Due to proved health hazards, complicated procedure and

expenditure, many popular defluoridation process like - Nalgonda, Activated

alumina etc. methods are in the phase out process therefore the aim of the present

research work is to find out a best defluoridation method which is easy to use by

illiterate villagers, requires minimal expenditure, involvement of less technical

personal and effective methods for fluoride removal from drinking water so that

these methods can be apply easily every where.

1.13 Importance of defluoridation: Due to various health impacts of fluoride on

human beings the treatment of fluoride is necessary.