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What is “Fluoride”: Chemical Structure, Uses, Health Effects

fluoride in water explanationFluorine is a natural trace element that does not occur in its elemental form because it is highly reactive, thus, it is a flammable, irritating, and toxic halogen gas. Fluorine is one of the most powerful oxidizing agents. Fluorine therefore only exists in a reduced form in nature as fluoride in a number of minerals like fluorspar, cryolite, or fluorapatite. The chemical formula for fluoride is F with a -1 electrical charge.  Fluoride is classified as the simplest inorganic monatomic anion of fluorine. Fluoride is considered a trace element.

Fluoride is mainly used as an additive to public drinking water in a process called municipal water fluoridation to reduce tooth decay. Fluoride compounds are widely used in industrial applications including the aluminum and fiberglass industries. Fluoride compounds are also used in the manufacturing of fertilizers, bricks, and ceramics.

The main health issues due to fluoride are in the bone and dental skeletal systems. One of the health effects of elevated fluoride levels includes skeletal fluorosis which is a bone disease caused by an excessive accumulation of fluoride in the human bones that is characterized by extreme density and hardness, resulting in weakened or fragile bones. As the bones become hardened and less elastic, this increases the risk of fractures. Overall, as a result of bones thickening and an increase in bone density, this can lead to impaired joint mobility.

Excessive exposure to high levels of fluoride in drinking water especially in children can cause dental fluorosis, although this can also be experienced in adults. Dental fluorosis is a dental condition that is characterized by whitish, yellowish to brownish discoloration of teeth, tooth surface irregularities, and pits on teeth that are very noticeable. On the other hand, low concentrations of fluoride of up to 0.7 mg/l are beneficial from a dental perspective because they provide protection against dental caries or cavities, especially in children.

Excess fluoride has also been linked with damage to the thyroid gland resulting in an uncontrolled secretion of the parathyroid hormones. The net result is a depletion of calcium in bone structures and excess calcium levels in the blood system. Depletion of calcium in bones increases their vulnerability towards fracturing.

Recent medical studies have linked excessive exposure to fluoride in pregnant women to poorer cognitive outcomes and lower Intelligent Quotient (IQ) scores of the children after birth. Furthermore, fluoride was identified as one of the 10 industrial chemicals that could be hazardous to child development. This tallies with the Recommended Dietary Allowances (RDAs) and Estimated Average Requirements (EARs) as set by the United States Food and Nutrition Board of the National Institutes of Health. The RDAs and EARs recommend lower fluoride intake in infants and children as well as restrictive levels in pregnant and lactating ladies.

Why does fluoride get into tap water?

Fluoride can get into tap water through a process called municipal water fluoridation. Municipal water fluoridation is when fluoride salt is added to public drinking water to a level recommended for reducing tooth decay, normally at a dosage not exceeding 1 mg/liter. This is achieved at a municipal treatment level by injecting or introducing hydrofluosilicic acid, sodium silicofluoride, or sodium fluoride into the municipally treated water before delivery to water users. According to the United States Department of Health and Human Services, an optimum level of 0.7 mg/l is needed to balance the supply of fluoride on one hand to reduce tooth decay, and on the other hand to prevent dental fluorosis.

After scientific research in the 20th century that unearthed less tooth decay in children that consumed water with naturally occurring fluoride, water fluoridation started becoming popular. Although it is not universally practiced or mandatory, water fluoridation is popular in municipal water treatment. In 2016, about 73% of United States community water schemes practiced municipal water fluoridation.

The practice of municipal water fluoridation has a number of benefits. Although there are other ways of supplying fluoride like toothpaste and dietary supplements, municipal water fluoridation has been found to be the most cost-effective way of supplying fluoride to all people supplied by that community water supply system thus reducing tooth decay by about 25% in children and adults.

The supply of fluoride via water fluoridation also reduces tooth cavities or the severity of cavities, reduces the need for tooth fillings and extractions, and minimizes the pain of tooth decay.  Overall, municipal water fluoridation can save millions of dollars to families and the health systems of any given country.

What are the sources of fluoride?

There are a number of sources of fluoride that end up in the water system or in the human body. The sources of fluoride are listed below:

  • Dissolved fluoride in water resources: Fluoride is found naturally in many resources like groundwater and rivers. However, fluoride tends to be generally higher in groundwater than in surface water.
  • Rocks/soils/geology: The composition of rocks or soils can have a bearing on the concentrations of fluoride. Areas that have rocks or soils rich in fluoride will have higher concentrations of fluoride in water like some African countries including Tanzania and South Africa.
  • Food: Essentially all foodstuffs contain fluoride. All vegetables contain fluoride as they absorb it from soil and water.
  • Air: Natural air contains fluoride whose concentrations can be around 0.5ng/m3.
  • Anthropogenic activities: Human activities contribute to fluoride in water resources or soil. These include industrial discharges, landfill sites, and mining activities that disturb rocks and soils among others.

Is tap water fluoride different?

The concentration of fluoride in tap water is normally regulated at the point of public water treatment before distribution and can be different from the ambient fluoride levels in untreated groundwater or surface water. The upper limit for the Guidelines for Drinking Water Quality (GDWQ) according to the World Health Organisation (WHO) is 1.5 mg/l.  If the background fluoride concentration in untreated water is lower than the GDWQ, the water authority can consider practicing water fluoridation to boost the fluoride level in the drinking water so as to prevent or minimize tooth decay. If the background water quality for fluoride is higher than the GDWQ, the public water authority can consider reducing the concentration of fluoride through any of the water treatment processes to prevent dental or skeletal fluorosis.

What is the chemical structure of fluoride?

fluoride and water fluoridationFluoride is a compound or ion of the element Fluorine that has an atomic number of 10. Fluoride, therefore, exists in a reduced state. The chemical formula of fluoride is F with a -1 electrical charge.  Fluoride is classified as the simplest inorganic monatomic anion of fluorine. Fluoride is considered a trace element.

Does fluoride dissolve in water?

Yes, fluoride is soluble in water. Fluoride exists in reduced states in different compounds that are all soluble to different extents in water. Hydrogen fluoride is a pungent liquid or gas that is highly soluble in water after which it forms hydrofluoric acid. Sodium fluoride is a colorless to white solid that is moderately soluble in water. Fluorosilicic acid that is also known as hexafluorosilicic acid is a solid that is highly soluble in water. The fact that most of the compounds are moderate to highly soluble in water explains why fluoride is naturally available in all water resources whether contaminated or uncontaminated.

What are the anions of fluoride?

An anion is a negatively charged ion or atom with more electrons than protons such that they have gained one or more electrons. Anions are the ions that get attracted to the anode (negative electrode) during electrolysis.

Fluoride is an anion (F) with an electrical charge of -1. The fluoride ion comes into being when a fluoride atom that is neutral and has an atomic number of 9 gains an electron resulting in an ion with a net negative charge. Fluoride is important as an anion because it is very stable and relatively unreactive compared to before reduction when it is fluorine.

What is the standard molar entropy of fluoride?

The standard molar entropy is a measure of the amount of energy not available for doing useful work from one mole of a pure substance at a standard state of pressure and temperature. The standard molar entropy is measured in joules per mole Kelvin (J mol−1 K−1). The standard molar entropy is used in the evaluation of entropies of different substances under the same conditions of temperature and pressure. The standard molar entropy values increase with the increasing complexity of molecules. The standard molar entropy of fluoride is 145.58 J mol−1 K−1.

What is the Gmelin reference to fluoride?

The Gmelin reference contains every compound or reaction that was discovered between 1772 and 1995. The Gmelin reference is important because it contains over 800 different data fields on subjects such as the compounds’ electric, magnetic, thermal, crystal, and physiological characteristics so it is an important reference in the field of chemistry. The Gmelin reference has a database with 1.5 million compounds and 1.3 million different reactions, with over 85,000 titles, keywords, and abstracts. Fluoride has a Gmelin reference of 14905.

What are the use cases of fluoride?

Fluoride has a number of uses as discussed below:

  • Water fluoridation: Fluoride is mainly used as an additive to public drinking water after water treatment in a process called municipal water fluoridation to reduce tooth decay. Fluorosilicic acid, sodium hexafluorosilicate, sodium silicofluoride, or sodium fluoride are some of the commonly used fluorine compounds used during water fluoridation. The benefits of municipal water fluoridation are mainly realized in children around 8 years of age when the milk teeth fall off and permanent teeth come out and need strengthening. In adults, the consumption of water-rich in fluoride supports tooth enamel resulting in healthy and strong teeth. Fluoride was scientifically proven to reduce tooth decay by up to 25%. The dental benefits of the consumption of water with fluoride get realized through mechanisms like fewer caries or cavities, less serious cavities, reduced cases of tooth fillings and removals as well as fewer toothaches and misery associated with teeth decay. This has a net positive effect on people, public health systems, and economies saving millions of dollars by preventing tooth decay.
  • Dental products: Fluoride is widely used in the manufacturing of tooth care products like toothpaste, gels, and mouthwashes. These are all products effective in reducing tooth decay.
  • Nutrient supplements: Fluoride is also used as a nutrient supplement mostly in the form of tablets where water fluoridation cannot be undertaken.
  • Industrial applications: Inorganic fluoride compounds are commonly used in different industrial uses spanning from the production of aluminum and as a purifying agent in metallurgical applications in steel and glass fiber industries. Fluoride compounds are also used in the manufacturing of phosphate fertilizers that contain about 3.8% fluorine.
  • Building and construction industry: Fluoride compounds are widely used in the manufacturing of products used in the building and construction industries like bricks, tiles, and ceramics.


The use of fluoride compounds is diverse from the addition of fluoride in domestic water, industrial uses in the steel industry, manufacturing of fertilizer compounds in the chemical industry, and in the manufacturing of some construction industry raw materials.

Cavity prevention

Cavity prevention refers to the avoidance of the formation of caries or holes in a person’s teeth. These holes are called cavities and are caused by the presence of acids in plaque from foodstuffs or sweet beverages that cause the demineralization of teeth. Demineralization is the loss of minerals from the teeth’ enamel.

Fluoride is important because it minimizes or reverses the cavity formation and subsequently reduces tooth decay through the process of remineralization (the deposition or addition of fluoride onto the tooth’s enamel) and the following mechanisms. Fluoride prevents tooth decay by changing the structure of the developing enamel in children with milk teeth (under the age of 7 years), providing a conducive atmosphere where better quality enamel that is more resistant to acid attacks is formed and reducing the ability of bacteria in plaque to produce acid.

Biochemical reagent

Fluoride salts are widely used in biological analysis processing to inhibit the activity of phosphatases, such as serine or threonine phosphatases. Fluoride is important because it stimulates the nucleophilic hydroxide ion in these enzymes’ active sites.

Fluoride-ion battery

A Fluoride-Ion Battery (FIB) is a newly developed battery that is able to generate electricity through the transportation of fluoride ions from one electrode to another via an electrolyte that conducts fluoride ions. The FIB is rechargeable and is effective in combating greenhouse gas emissions. Fluoride ions play a vital role in generating electricity because it is one of the most stable anions that are highly mobile.

What is the difference between naked fluoride?

Naked fluoride comprises relative unsolvated fluoride salts that exist in aprotic solvents. Such aprotic solvents do not have protons or hydrogen atoms. Naked fluoride is a strong Lewis base and a powerful nucleophile. Examples of ammonium salts of naked fluoride include tetramethylammonium fluoride and tetrabutylammonium fluoride.  One common characteristic of naked fluorides is that they all lack structural characterization in aprotic solvents and because they are highly basic, many naked fluoride sources are in reality bifluoride salts.

Naked fluorides like Tetra-n-butylammonium fluoride (TBAF) are commercially available as a white solid trihydrate and as a solution in tetrahydrofuran. TBAF is used as a source of fluoride ions in organic solvents and specifically as a phase transfer catalyst and as a mild base.

What are the dietary recommendations for fluoride?

The dietary recommendations for fluoride intake in human beings generally increase with an individual’s age from infancy to adulthood. Results from studies conducted by the United States National Institutes of Health show that the daily adequate intake of fluoride ranges between 0.01 mg in infants (from birth to 6 months) to 4 mg and 3 mg for male and female adults respectively aged 19 years and above. The adequate intake rates indicate what is adequate for daily fluoride needs from all sources like food, water, and nutrient supplements.

What is the prominence of fluoride for dental health?

Fluoride is vital in the protection of teeth because it minimizes cavity formation and also reduces tooth decay through the process of remineralization.  Remineralization is the deposition or addition of fluoride onto the tooth’s enamel thus the teeth become more resistant to acid attacks that are formed through bacterial plaque and sweet beverages.

Scientific studies have revealed that about 0.7 mg/l of fluoride in water is good enough to prevent tooth decay. However, the WHO GDWQ prescribes a limit of 1.5 mg/l of fluoride in drinking water. In the US, the EPA has set an enforceable Maximum Contaminant Level (MCL) for fluoride at 4 mg/l and an unenforceable Secondary Maximum Contaminant Level (SMCL) was set at 2 mg/l to guard against aesthetic or cosmetic dangers of fluoride. Levels above 4 mg/l are categorized as hazardous. Where other significant sources of fluoride are available like in food, it becomes necessary to reduce the intake of fluoride in drinking water so as to prevent overexposure to the mineral.

When is fluoride critical to consume?

Fluoride can be consumed under a number of situations:

  • Low fluoride in drinking water: When the fluoride concentration in drinking water is low, it becomes critical to supplement fluoride intake through other mechanisms like consumption of vegetables rich in fluoride or taking supplements.
  • Where there is no water fluoridation: Where there are no fluoridation schemes during potable water treatment, it is necessary to consume more fluoride from other sources like dietary sources.
  • High fluoride diet: Under circumstances where someone has a fluoride deficiency in his/her diet and has been prescribed by a medical doctor to consume more fluoride it becomes vital to consume more fluoride.

How does fluoride affect tooth decay?

Fluoride can affect teeth in 2 ways, namely through preventing tooth decay or it can cause dental fluorosis. At low levels of fluoride in water (up to 0.7 mg/l), fluoride is able to prevent tooth decay through changing the structure of the developing enamel in children with milk teeth, remineralization that strengthens teeth enamel such that the teeth are able to withstand the acid attacks from plaque and sweet foodstuffs and beverages.

However, overexposure to fluoride in drinking water results in a side effect is a condition called dental fluorosis. This is a condition that is characterized by whitish, yellowish to brownish discoloration of teeth, tooth surface irregularities, and pits on teeth that are very noticeable.

What is the daily fluoride intake?

The adequate intake rates are the adequate amount for daily fluoride needs from all sources like food, water fluoridation, and supplements. The adequate fluoride intake in human beings generally is the same for both genders except for adults but varies according to the age of the person. According to the United States National Institutes of Health, the daily adequate intake of fluoride for infants (from birth to 6 months) is 0.01 mg, infants of 7 to 12 months is 0.5mg, for toddlers (1 to 3 years) is 0.7 mg, for children of 4 to 8 years the adequate fluoride rate is 1 mg/day. The adequate daily intake of fluoride for children aged 9 to 13 years is 2 mg, whilst for teenagers between 14 and 18 years is 3mg. For adults aged 19 years and above, the adequate intake rate of fluoride for males is 4 mg and for females is 3mg.

However, the daily tolerable fluoride rates are higher than the adequate intake rates because the tolerable rates indicate how much a body can tolerate before fluoride becomes hazardous.

How to measure the fluoride within the water?

monitoring of fluoride in waterAlthough the procedures of testing for fluoride in water are relatively similar, some steps are different depending on whether home water test kits or accredited water quality laboratories are used for testing for fluoride.  The procedures to measure the fluoride level in water are the same for any water resource like well water, tap water, or river water.

Home water test kits

  • Sample collection: Rinse an open water container with the water to be tested 3 times or with distilled water to prevent cross-contamination and then collect a water sample.
  • Testing: For test strips, one needs to dip the test strip in the water for the prescribed amount of time. For color disks, one needs to add a reagent to the water sample.
  • Results interpretation: For test strips compare the new color of the test strip with the color of the chart supplied. For color disks, one needs to spin the color disk until the color of the disk matches the new color of the water sample. The results need to be compared against the relevant guidelines.

Laboratory analysis

  • Sample collection: Rinse the sampling bottle supplied by the laboratory with the water to be tested 3 times or with distilled water to prevent cross-contamination and then collect a water sample.
  • Sample preparation: Where necessary add the preservative to the water sample and immediately close the bottle tightly with the lid and store it in a cooler box before shipment to the laboratory.
  • Transportation: Send the water sample to the laboratory for analysis.
  • Results interpretation: After getting the numerical results from the laboratory, one can compare them against the relevant guidelines.

How to know whether tap water contains fluoride?

Due to the fact that public or municipal water supply systems regularly test their water quality in order to comply with the applicable water quality guidelines like the WHO DWQG and the USEPA guidelines, such authorities normally keep those records and can avail them to different stakeholders including the public. As a starting point, one can check with the water authority or municipality about whether the treated water being distributed has fluoride and at what levels.

The best strategy to test for fluoride in tap water is to use home water testing kits. This is because municipal water supply systems regularly test their water quality in order to comply with the applicable water quality guidelines like the WHO DWQG, USEPA guidelines. One can buy a home water test kit that can test for fluoride like test strips or alternatively color disks that are quite accurate. Home water testing kits are cheap to buy and provide rapid results that come out in a few minutes.

How to know whether the toothpaste contains fluoride?

By law, toothpaste manufacturers are required to indicate the active ingredients in the toothpaste on the toothpaste tube. As such one can check on the side of the toothpaste tube whether fluoride is indicated as an ingredient in the toothpaste or not. Some toothpaste brands do not have fluoride and they are normally indicated as being “fluoride-free” on the toothpaste tube.

Do water filters remove fluoride from water?

A number of water filters are effective in the removal of fluoride from water as discussed below:

Yes, water filters are able to remove fluoride from water. The following are some of the Fluoride Water Filters and a brief explanation of how they are able to reduce or remove fluoride.

  • Reverse Osmosis: The most effective way of reducing or removing fluoride from drinking water is Reverse Osmosis (RO). RO is able to remove or reduce fluoride through the physical process of filtration using the semipermeable membrane in the pressurized water chamber. The removal occurs because most mineral constituents or contaminants get trapped by the semi-permeable membrane that allows water to pass through.
  • Distillation: Distillation involves boiling water until it evaporates. The steam rises and it condenses in the cooling chamber where pure water will get collected in a separate container. During this process, contaminants like fluoride remain in the boiling chamber during evaporation and are washed out during cleaning. The distilled water that gets collected in the container after cooling is pure and devoid of dissolved minerals, contaminants, and any other impurities.
  • Anion exchange: Anion or Ion exchange replaces (or exchanges) undesired minerals in water (like fluoride) with less objectionable ones (salt). Chloride and hydroxide ions are the most commonly used materials on the resin beads. As water passes through the device, the resin adsorbs anions such as sulfate, nitrate, arsenic, and bicarbonates and releases chloride into the water. The exchange occurs in a fiberglass tank or plastic-lined steel tank filled with either the resin or a synthetic zeolite.
  • Carbon filter: A carbon water filter is a water purification system that uses a highly porous carbon-based medium to retain contaminants like fluoride using the physical process of adsorption thereby purifying the water that passes through the media. The carbon medium can be granular, carbon blocks or radial flow carbon filters in nature. Due to the highly porous nature of activated carbon media, it is estimated that 1 gram of activated carbon has a surface area ranging between 300 and 2000 m2. The higher the surface area of the carbon media, the higher the capacity of adsorbing contaminants and also the higher the capacity of water filtration.
  • Adsorptive media filtration: Fluoride can be removed from water by passing untreated water through adsorptive media contained in a pressure vessel. As the water passes through the media, the ions of the opposite charge (contaminants) get attracted to the positively charged media particles. In this case, the negatively charged fluoride ions are adsorbed onto the surfaces of the positively charged media particles thus get removed from the water. The common media used for the adsorption of fluoride is activated alumina.

Is fluoride a water pollutant?

Yes, fluoride is regarded as a water pollutant. The USEPA has set an enforceable Maximum Contaminant Level (MCL) of 4 mg / l for fluoride. Above this concentration, the consumption of water with fluoride is deemed to be hazardous to human health. Additionally, levels above the MCL are considered as causing water pollution.

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