Sciences

FLOURIDE CONTAMINATION OF 

GROUND WATER 

FLUORIDE CONTAMINATION IN GROUNDWATER

M.Sc. 2NDYEAR (APPLIEDGEOLOGY)

ROLL NO - 

CONTENTS:-

Introduction

Properties offluorine

Fluoride ingroundwater

Sources

Adverseeffects

Fluoride contamination in groundwater in India,Odisha andWorld

Mitigation

References

INTRODUCTION:-

Groundwaterisconsideredasthemajorsourceofdrinkingwaterinmostplaceson earth.

Usuallypeopleusegroundwaterfordrinkingandotherdomestichouseholdpurposes such as cooking without any physical or chemicaltreatment.

•Thisisnotahealthypracticeandmayleadtonumberofhealthdisorders.However, this practice cannot be avoided due to lack of treated piped water supply system in several parts of developingcountries.

•When the chemical composition of groundwater is not within the prescribed standards for drinking or irrigation or industrial water, they become unsuitable. And excess amount of fluoride in groundwater is a major cause of pollution.

PROPERTIES OF FLUORINE:-

Fluorine belongs to halogen family represented as ‘F’ with atomic weight18.998 and atomic number9.

Itoccursasadiatomicgasinitselementalformandhasavalencenumber1.Itis the most electronegative and the most reactive when compared to all chemical elements in the periodic table (Greenwood and Earnshaw, 1984; Gillespie et al., 1989).

It has an oxidation state of -1 and occurs as both organic andinorganic compounds.

It is the 13th most abundant element in the earth’s crust (Weinstein andDavison, 2003). Its natural abundance in the earth’s crust is 0.06 to 0.09% (Fawell et al., 2006) and the average crustal abundance is 300 mg/kg (Tebutt,1983).

Fluoride does not exhibit any colour, taste or smell when dissolved in water. Hence, it is not easy to determine it through physical examination. Only chemical analysis of the groundwater samples can determine the concentration of thision.

FLUORIDE IN GROUNDWATER

Groundwater with fluoride concentration above the permissible limit setby WHO i.e 1.5 mg/l have been recorded in several parts of theworld.

In 1984, WHO estimated that more than 260 million people living all overthe world consume water with fluoride concentration above 1 mg/l (WHO, 1984).

The problem of high fluoride in groundwater has been reported by several researchers in India, China, Japan, Sri Lanka, Iran, Pakistan, Turkey, Southern Algeria, Mexico, Korea, Italy, Brazil, Malawi, North Jordan, Ethiopia, Canada, Norway, Ghana, Kenya, South Carolina, Wisconsin and Ohio.

Most of the people affected by high fluoride concentration in groundwater live in the tropical countries where the per capita consumption of water is more because of the prevailingclimate.

In places like Ghana, people consume 3 to 4 liters of water which is higher than the WHO estimate of 2 l/adult/day (Apambire et al.,1997).

The risk of fluorosis is higher in these places. However, incidence of fluorosis in people living in other parts of the world has also been reported. The intensity of fluorosis problem is very serious in the two heavily populated countries of the world namely India and China (Ayoob and Gupta,2006).

SOURCES OF FLUORIDE IN GROUNDWATER

Aquifer material:-

•Most of the fluoride in groundwater is naturally present due to weathering of rocks rich in fluoride.Waterwithhighconcentrationoffluorideismostlyfoundinsedimentsofmarine origin and at the foot of mountainous areas.

•Fluoride occurs as sellaite , fluorite or fluorspar , cryolite , fluorapatite , apatite , topaz , fluormica(phlogopite),biotite,epidote,amphibolesuchastremoliteandhornblende,mica, clays, villuanite andphosphorite.

Granitic rocks which are a typical source of fluoride rich rocks contain fluoride ranging between500and1400mg/kg,whichismuchhigherthananyotherrocktype.Theworld average content of fluoride in granitic rocks is 810 mg/kg . The weathering of these rocks results in increased fluoride content ingroundwater.

Volcanic ash:-

Volcanic rocks are often enriched in fluoride. Hydrogen fluorine isone of the most soluble gases in magmas and comes out partially during eruptive activity.

The aerial emission of fluoride in the form of volcanic ash during volcanic eruption reaches the surface by fall out of particulate fluorides and during rainfall. This fluoride from the soil surface will easily reach the groundwater zone along with percolatingrainwater.

Volcanic ash is readily soluble and thus the risk offluoride contamination in groundwater is veryhigh.

Fly ash:-

Like volcanic ash, fly ash from the combustion of fossil fuels also account for high fluoride. More than 100 to 150 million tons of fly ash is produced worldwide annually due to the combustion of coal especially from power plants . Inappropriate disposal of this fly ash will result in the  leaching of fluoride togroundwater.

Fertilisers:-

Phosphate containing fertilisers add up to the fluoride content in soil and groundwater . It is evident that superphosphate (2750 mg of F/kg), potash (10 mg of F /kg) and NPK (Nitrogen Phosphorous Potassium) (1675 mg of F /kg) which are phosphatic fertilisers contain remarkable amount of fluoride. In agricultural areas successive irrigation had lead to the increase in fluoride concentration ingroundwater

Adverse effects:-

Intake of fluoride higher than the optimum level is the main reason for dental and skeletal fluorosis. Depending upon the dosage and the period of exposure fluorosis may be acute tochronic.

In India 62 million people including 6 million children are estimated to have serious health problemsduetoconsumptionoffluoridecontaminatedwater(AndezhathandGosh,2000).

The health outcome by consuming fluoride at different concentration was given by Dissanayake (1991) i.e. when fluoride concentration in drinking water is below 0.5 mg/l it causes dental carries; fluoride between 0.5 to 1.5 mg/l results in optimum dental health; 1.5 to 4 mg/l causes dental fluorosis; 4 to 10 mg/l induces dental and skeletal fluorosis while fluoride above 10 mg/l results in cripplingfluorosis.

Dental fluorosis

Tooth enamel is principally made up of hydroxyapatite (87%) which is crystalline calcium phosphate . Fluoride which is more stable than hydroxyapatite displaces the hydroxide ions from hydroxyapatite to form fluoroapatite. On prolonged continuation of this process the teeth become hard and brittle. This is called dentalfluorosis.

Dental fluorosis in the initial stages results in the tooth becoming coloured from yellow to brown to black. Depending upon the severity, it may be only discolouration of the teeth or formation of pits in theteeth.

The colouration on the teeth may be in the form of spots or as streaks. Usually these streaks on the teeth arehorizontal.

Skeletal fluorosis:-

Exposure to very high fluoride over a prolonged period of time results in acute to chronic skeletalfluorosis.

Early stages of skeletal fluorosis start with pain in bones and joints, muscle weakness, sporadic pain, stiffness of joints and chronicfatigue.

During later stages, calcification of the bones takes place, osteoporosis in long bones, and symptoms of osteosclerosis where the bones become denser and develop abnormal crystallinestructure.

Inthe advanced stage the bones and joints become completely weak and moving them is difficult. The vertebrae in the spine fusetogether and the patient is left crippled which is the final stage. Skeletal fluorosis is usually not recognized until the disease reaches an advancedstage.

Skeletal fluorosis does not only affect humans but also animals fed with fluoride rich water andfodder.

Other effects:-

Other health disorders that occur due to consumption of high fluoride in drinking water to be muscle fibre degeneration, low haemoglobin levels, deformities in RBCs, excessive thirst, headache, skin rashes, nervousness, neurological manifestations, depression, gastrointestinal problems, urinary tract malfunctioning, nausea, abdominal pain, tingling sensation in fingers and toes,reducedimmunity,repeatedabortionsorstillbirths,malesterility,etc.

As fluoride is excreted in urine through the kidneys, they affect the effective functioningofthekidneys.Theyfacilitateintheformationofkidneystones.

Consumption of drinking water with high fluoride by childrenmay affect theirintelligence.

The presence of excessive fluoride in groundwater has its impact not only on humans but also on soil fertility and plant and animalgrowth.

Fluoridecontaminationin groundwaterin India:-

Of the 85 million tons of fluoride deposits on the earth’s crust, 12 million are found in India (Teotia and Teotia, 1994). Hence it is natural that fluoride contamination is widespread, intensive and alarming inIndia.

Some regions in north western and southern India are heavily affected with fluorosis (Agarwal et al., 1997; Yadav et al., 1999). About 50% of the groundwater in Delhi exceeds the maximum permissible limit for fluoride in drinking water (Datta et al.,1996).

Jacks et al. (2005) observed that high fluoride in groundwater in many parts of India was due to evapotranspiration of groundwater with residualalkalinity.

Fluoride content was higher in deeper aquifers of Maharashtra (Madhnure et al., 2007) which was due to long residence time than shallowgroundwater.

The rocks in southern India are rich with fluoride which forms the major reason for fluoride contamination ingroundwater.

It is a well established fact that groundwater in Nalgonda district, Andhra Pradesh, has high fluoride due to the inherent fluoride rich graniticrocks

The granitic rocks in Nalgonda district contain fluoride from 325 to 3200 mg/kg with a mean of 1440mg/kg.

The Nalgonda Granties contain much higher fluoride than theworld average fluoride concentration of 810 mg/kg (Wedepohl,1969).

Thus treatment of groundwater especially for fluoride before using it for drinking purpose is very essential inIndia.

Fluorideconcentration in groundwaterin Odisha:-

Mitigation measures:-

Insitu-treatment methods :-

Insitu method aims at directly diluting the concentration of fluoride (in groundwater) in the aquifer. This can be achieved by artificialrecharge.

Construction of check dams in Anantapur district, India has helped widely to reduce fluoride concentration in groundwater (Bhagavan and Raghu,2005).

Rainfall recharge also called as rainwater harvesting can be adopted using percolation tanks and recharge pits which may prove helpful. Recharge of rainwater after filtration through the existing wells can also be planned to improve the groundwaterquality.

Exsitu-treatment methods:-

Adsorption method involves the passage of water through a contact bed where fluoride is adsorbedonthematrix.Activatedcharcoalandactivatedaluminaarethewidelyusedadsorbents.

Brick, bone char, fly ash, serpentine, red mud, waste mud, rice husk, kaolinite, bentonite, charfines, ceramic etc. are some of the other absorbents capable of effectively removing fluoride fromgroundwater.

In ion exchange process, when water passes through a column containing ion exchange resin, the fluoride ions replace calcium ions in theresin.

Once the resin is saturated with fluoride ions, it is backwashed with solution containing chloride such as sodiumchloride.

The chloride ions thus again replaces the fluoride ions in the resin and is ready for reuse. But the backwash is rich in fluoride and hence care should be taken in disposing this solution.

Similarly in precipitation methods, the disposal of sludge with concentrated fluoride is a great problem. Precipitation involves addition of chemicals such as calcium which results in the precipitation of fluoride as fluorite. Aluminium salts are also used for thisprocess.

Membrane processes is also an ex-situ technique which includes methods called reverse osmosis and electrodialysis. These are advanced techniques which require high costinput.

Apart from all these it is essential to create environmental awareness among public regarding the ill effects of high fluoride. Reduction in the use of fertilisers, especially phosphatic fertilisers is important. It is better to adopt organic farming in places of fluoridethreat.

Usage of coal for combustion indoors should be avoided and the resultant fly ash obtained from combustion of fossil fuel in industries has to be disposedcautiously.

In countries with high temperature, it is advisable to reduce evapotranspiration by increasing vegetation cover. This will prevent the deposition of fluoride salts on the unsaturated zone which will subse