Defluoridation

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Defluoridation is the downward adjustment of the level of fluoride in drinking water. Worldwide, fluoride is one of the most abundant anions present in groundwater. Fluoride is more present in groundwater than surface water mainly due to the leaching of minerals. Groundwater accounts for 98 percent of the earth's potable water. [1] An excess of fluoride in drinking water causes dental fluorosis and skeletal fluorosis. The World Health Organization has recommended a guideline value of 1.5 mg/L as the concentration above which dental fluorosis is likely. [2] Fluorosis is endemic in more than 20 developed and developing nations. [3]

Contents

History

Fluorosis was not identified as a problem until relatively recently. Few attempts to defluoridate water came before the 20th century. [4] In the 1930s, several nations began to investigate fluoride's negative effects and how best to remove it. An aluminum and sand filter that removes fluorine from water was devised by Dr. S. P. Kramer in 1933; in 1945, M. Kenneth received a French patent for a water defluoridation technique; and in 1952, a functioning activated alumina community defluoridation plant was commissioned in Bartlett, Texas, USA. [5]

Techniques

While various defluoridation techniques have been explored, each has its limitations. Existing techniques are often too costly (because the geographic areas prone to fluorosis are among the poorest regions on the planet), ineffective or even dangerous (some of the remediation processes add other contaminants to the water). The main techniques that have been, and continue to be, investigated with varying degrees of success include: adsorption, precipitation, ion exchange and membrane processes. [6]

Adsorption can be achieved with locally available adsorbent materials with high efficiency and cost-effectiveness. Cost-effective and locally-available herbal and indigenous products offer promising options. The process is dependent on pH and the presence of sulfate, phosphate, and bicarbonate which results in ionic competition. Disposal of fluoride-laden sludge is problematic.

Precipitation is the most well-established and most widely used method, particularly at the community level. However, it has only moderate efficiency and a high chemical dose is required. Excessive use of aluminum salts produces sludge and adverse health effects through aluminum solubility.

The so-called Nalgonda technique for reduction of fluoride involves stirring in of alum and lime, whereupon some of the fluoride precipitates together with aluminum hydroxide, and the water can be decanted and filtered. [7]

Ion Exchange removes fluoride up to 90-95% and retains the taste and colour of the water. Sulphates, phosphates, and bicarbonates also result in ionic competition in this method. Relatively high cost is a disadvantage and treated water sometimes has a low pH value and high levels of chloride.

Membrane processes are effective technique and do not require chemicals. It works at wide pH range and interference by other ions is negligible. Negatives include higher costs and it skilled labour. This process is not suitable for water with high salinity. [2]

Calcium amended-hydroxyapatite is the most recent defluoridation technique in which aqueous calcium is amended to the fluoride contaminated water prior to contact with uncalcined synthetic hydroxyapatite adsorbent. [8] In this novel defluoridation technique, amending aqueous calcium successfully prevents the dissolution of hydroxyapatite during the defluoridation and also enhances the defluoridation capacity of hydroxyapatite. In addition to these features, this ″calcium amended-hydroxyapatite″ defluoridation technique provides calcium-enriched alkaline drinking water and drinking of this defluoridated water may also help in fluorosis reversal. Thus, it is expected that utilization of this defluoridation technique to provide safe drinking water helps in the mitigation of fluorosis. [8]

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<span class="mw-page-title-main">Phosphate</span> Chemical compound

In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid, a.k.a. phosphoric acid H3PO4.

<span class="mw-page-title-main">Apatite</span> Mineral group, calcium phosphate

Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ion, respectively, in the crystal. The formula of the admixture of the three most common endmembers is written as Ca10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6F2 and Ca10(PO4)6Cl2.

Fluoride is an inorganic, monatomic anion of fluorine, with the chemical formula F−
, whose salts are typically white or colorless. Fluoride salts typically have distinctive bitter tastes, and are odorless. Its salts and minerals are important chemical reagents and industrial chemicals, mainly used in the production of hydrogen fluoride for fluorocarbons. Fluoride is classified as a weak base since it only partially associates in solution, but concentrated fluoride is corrosive and can attack the skin.

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.

<span class="mw-page-title-main">Tooth enamel</span> Major tissue that makes up part of the tooth in humans and many animals

Tooth enamel is one of the four major tissues that make up the tooth in humans and many animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp. It is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink. In rare circumstances enamel fails to form, leaving the underlying dentin exposed on the surface.

<span class="mw-page-title-main">Skeletal fluorosis</span> Medical condition

Skeletal fluorosis is a bone disease caused by excessive accumulation of fluoride leading to weakened bones. In advanced cases, skeletal fluorosis causes painful damage to bones and joints.

<span class="mw-page-title-main">Water fluoridation</span> Addition of fluoride to a water supply to reduce tooth decay

Water fluoridation is the controlled adjustment of fluoride to a public water supply solely to reduce tooth decay. Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride. Fluoridated water operates on tooth surfaces: in the mouth, it creates low levels of fluoride in saliva, which reduces the rate at which tooth enamel demineralizes and increases the rate at which it remineralizes in the early stages of cavities. Typically a fluoridated compound is added to drinking water, a process that in the U.S. costs an average of about $1.32 per person-year. Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. In 2011, the World Health Organization suggested a level of fluoride from 0.5 to 1.5 mg/L, depending on climate, local environment, and other sources of fluoride. Bottled water typically has unknown fluoride levels.

Fluoride toxicity is a condition in which there are elevated levels of the fluoride ion in the body. Although fluoride is safe for dental health at low concentrations, sustained consumption of large amounts of soluble fluoride salts is dangerous. Referring to a common salt of fluoride, sodium fluoride (NaF), the lethal dose for most adult humans is estimated at 5 to 10 g. Ingestion of fluoride can produce gastrointestinal discomfort at doses at least 15 to 20 times lower than lethal doses. Although it is helpful topically for dental health in low dosage, chronic ingestion of fluoride in large amounts interferes with bone formation. In this way, the most widespread examples of fluoride poisoning arise from consumption of ground water that is abnormally fluoride-rich.

<span class="mw-page-title-main">Bone char</span> Chemical compound

Bone char is a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made; however, it consists mainly of tricalcium phosphate 57–80%, calcium carbonate 6–10% and carbon 7–10%. It is primarily used for filtration and decolorisation.

<span class="mw-page-title-main">Sodium fluoride</span> Ionic compound (NaF)

Sodium fluoride (NaF) is an inorganic compound with the formula NaF. It is a colorless or white solid that is readily soluble in water. It is used in trace amounts in the fluoridation of drinking water to prevent tooth decay, and in toothpastes and topical pharmaceuticals for the same purpose. In 2021, it was the 291st most commonly prescribed medication in the United States, with more than 600,000 prescriptions. It is also used in metallurgy and in medical imaging.

<span class="mw-page-title-main">Hydroxyapatite</span> Naturally occurring mineral form of calcium apatite

Hydroxyapatite is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), often written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. It is the hydroxyl endmember of the complex apatite group. The OH− ion can be replaced by fluoride or chloride, producing fluorapatite or chlorapatite. It crystallizes in the hexagonal crystal system. Pure hydroxyapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, comparable to the discolorations of dental fluorosis.

<span class="mw-page-title-main">Activated alumina</span>

Activated alumina is manufactured from aluminium hydroxide by dehydroxylating it in a way that produces a highly porous material; this material can have a surface area significantly over 200 m2/g. The compound is used as a desiccant (to keep things dry by adsorbing water from the air) and as a filter of fluoride, arsenic and selenium in drinking water. It is made of aluminium oxide (alumina; Al2O3). It has a very high surface-area-to-weight ratio, due to the many "tunnel like" pores that it has. Activated alumina in its phase composition can be represented only by metastable forms (gamma-Al2O3 etc.). Corundum (alpha-Al2O3), the only stable form of aluminum oxide, does not have such a chemically active surface and is not used as a sorbent.

<span class="mw-page-title-main">Fluoride therapy</span> Medical use of fluoride

Fluoride therapy is the use of fluoride for medical purposes. Fluoride supplements are recommended to prevent tooth decay in children older than six months in areas where the drinking water is low in fluoride. It is typically used as a liquid, pill, or paste by mouth. Fluoride has also been used to treat a number of bone diseases.

<span class="mw-page-title-main">Dental fluorosis</span> Medical condition

Dental fluorosis is a common disorder, characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation.

<span class="mw-page-title-main">Tricalcium phosphate</span> Chemical compound

Tricalcium phosphate (sometimes abbreviated TCP), more commonly known as Calcium phosphate, is a calcium salt of phosphoric acid with the chemical formula Ca3(PO4)2. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid of low solubility. Most commercial samples of "tricalcium phosphate" are in fact hydroxyapatite.

Iron oxide adsorption is a water treatment process that is used to remove arsenic from drinking water. Arsenic is a common natural contaminant of well water and is highly carcinogenic. Iron oxide adsorption treatment for arsenic in groundwater is a commonly practiced removal process which involves the chemical treatment of arsenic species such that they adsorb onto iron oxides and create larger particles that may be filtered out of the water stream.

Amorphous calcium phosphate (ACP) is a glassy solid that is formed from the chemical decomposition of a mixture of dissolved phosphate and calcium salts (e.g. (NH4)2HPO4 + Ca(NO3)2). The resulting amorphous mixture consists mostly of calcium and phosphate, but also contains varying amounts of water and hydrogen and hydroxide ions, depending on the synthesis conditions. Such mixtures are also known as calcium phosphate cement.

<span class="mw-page-title-main">Remineralisation of teeth</span>

Tooth remineralization is the natural repair process for non-cavitated tooth lesions, in which calcium, phosphate and sometimes fluoride ions are deposited into crystal voids in demineralised enamel. Remineralization can contribute towards restoring strength and function within tooth structure.

<span class="mw-page-title-main">Groundwater pollution</span> Ground released seep into groundwater

Groundwater pollution occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution. Groundwater pollution can occur from on-site sanitation systems, landfill leachate, effluent from wastewater treatment plants, leaking sewers, petrol filling stations, hydraulic fracturing (fracking) or from over application of fertilizers in agriculture. Pollution can also occur from naturally occurring contaminants, such as arsenic or fluoride. Using polluted groundwater causes hazards to public health through poisoning or the spread of disease.

Topical fluorides are fluoride-containing drugs indicated in prevention and treatment of dental caries, particularly in children's primary dentitions. The dental-protecting property of topical fluoride can be attributed to multiple mechanisms of action, including the promotion of remineralization of decalcified enamel, the inhibition of the cariogenic microbial metabolism in dental plaque and the increase of tooth resistance to acid dissolution. Topical fluoride is available in a variety of dose forms, for example, toothpaste, mouth rinses, varnish and silver diamine solution. These dosage forms possess different absorption mechanisms and consist of different active ingredients. Common active ingredients include sodium fluoride, stannous fluoride, silver diamine fluoride. These ingredients account for different pharmacokinetic profiles, thereby having varied dosing regimes and therapeutic effects. A minority of individuals may experience certain adverse effects, including dermatological irritation, hypersensitivity reactions, neurotoxicity and dental fluorosis. In severe cases, fluoride overdose may lead to acute toxicity. While topical fluoride is effective in preventing dental caries, it should be used with caution in specific situations to avoid undesired side effects.

References

  1. ↑ Mullen, Kimberly. "Information on Earth's Water". ngwa.org. National Ground Water Association. Retrieved 2020-02-26.
  2. 1 2 Bose, Dr. Sreekanth; R, Dr. Yashoda; Puranik, Dr. Manjunath P (2018-07-01). "A review on defluoridation in India". International Journal of Applied Dental Sciences. 4 (3).
  3. ↑ Meenakshi; Maheshwari, R.C. (September 2006). "Fluoride in drinking water and its removal". Journal of Hazardous Materials. 137 (1): 456–463. doi:10.1016/j.jhazmat.2006.02.024. ISSN   0304-3894. PMID   16600479.
  4. ↑ Littleton, J. (August 1999). "Paleopathology of skeletal fluorosis". American Journal of Physical Anthropology. 109 (4): 465–483. doi:10.1002/(SICI)1096-8644(199908)109:4<465::AID-AJPA4>3.0.CO;2-T. ISSN   0002-9483. PMID   10423263.
  5. ↑ Rajchagool, S; Rajchagool, C. (1997). "Solving the fluorosis problem in a developing country.". In Dahi, E.; Nielsen, JM (eds.). Proceedings of the 2nd international workshop on fluorosis and defluoridation of water (PDF). Addis Ababa, Ethiopia. Archived from the original (PDF) on 2020-05-18. Retrieved 2018-11-07.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ↑ Krishnan, S; Indu, R. "How can we think ahead on Fluorosis Mitigation?". Archived from the original (PDF) on 2020-05-18. Retrieved 2018-08-21.
  7. ↑ Dahi, Eli, et al. "Defluoridation using the Nalgonda technique in Tanzania." (1996).
  8. 1 2 Sankannavar, Ravi; Chaudhari, Sanjeev (2019). "An imperative approach for fluorosis mitigation: Amending aqueous calcium to suppress hydroxyapatite dissolution in defluoridation". Journal of Environmental Management. 245: 230–237. doi:10.1016/j.jenvman.2019.05.088. PMID   31154169. S2CID   173993086.
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