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Fluoride

3. How are humans exposed to fluorides?

  • 3.1 How much fluoride is there in drinking water?
  • 3.2 How much fluoride is there in food?
  • 3.3 How much fluoride is there in toothpaste?
  • 3.4 How much fluoride are humans exposed to?
  • 3.5 What happens to fluorides absorbed by the body?

3.1 How much fluoride is there in drinking water?

The source document for this Digest states:

Fluoride is ubiquitous in the environment; therefore, sources of drinking-water are likely to contain at least some small amount of fluoride. The amount of fluoride present naturally in non-fluoridated drinking-water (i.e., drinking-water to which fluoride has not been intentionally added for the prevention of dental caries) is highly variable, being dependent upon the individual geological environment from which the water is obtained. Levels may range up to approximately 2.0 mg/litre; however, in areas of the world in which endemic fluorosis of the skeleton and/or teeth has been well documented, levels of fluoride in drinking-water supplies range from 3 to more than 20 mg/litre. In areas in which drinking-water is fluoridated (i.e., fluoride is intentionally added for the prevention of dental caries), the concentration of fluoride in drinking-water generally ranges from 0.7 to 1.2 mg/litre.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Chapter 1.4: Environmental levels and human exposure 

For more information, see the full IPCS document:
Chapter 5.2.1 Drinking-water 

3.2 How much fluoride is there in food?

The source document for this Digest states:

Virtually all foodstuffs contain at least trace amounts of fluoride. Elevated levels are present in fish. Tea leaves are particularly rich in fluoride; the amount of fluoride in brewed tea is dependent upon the concentration of soluble fluoride in the tea leaves, the level of fluoride in the water used in its preparation and the length of the brewing period. The concentration of fluoride in food products is not significantly increased by the addition of superphosphate fertilizers, which contain significant concentrations of fluoride (1–3%) as impurities, to agricultural soil, due to the generally low transfer coefficient from soil to plant material. However, a recent study suggests that, given the right soil conditions and application of sufficient fluoride as an impurity in phosphate fertilizers to soils, plant uptake of fluoride can be increased. The use of water containing relatively low (<3.1 mg/litre) levels of fluoride for crop irrigation generally does not increase fluoride concentrations in foodstuffs. However, this is dependent on plant species and fluoride concentrations in soil and water. The level of fluoride in foods is significantly affected by the fluoride content of the water used in preparation or processing, most notably in beverages and dry foodstuffs — for example, powdered baby formula — to which water is added prior to consumption. The concentrations of fluoride in unwashed or unprocessed foods grown in the vicinity of industrial sources (emissions) of fluoride may be greater than the levels in the same foods grown in other non-industrially exposed areas. In commercially available infant formulas sold in the USA, soy-based ready-to-use and liquid concentrate formulas contained higher levels of fluoride than the equivalent milk-based products; however, no significant difference was observed between soy- and milk-based powdered infant formulas. Fluoride has been detected in breast milk; reported levels range from <2 to about 100 µg/litre, with most values being between 5 and 10 µg/litre.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", EHC 227, 
Chapter 1: Summary and Conclusions, p. 5-6, section 1.4 

For more information, see the full IPCS document:
Chapter 5.2.2: Food 

3.3 How much fluoride is there in toothpaste?

The source document for this Digest states:

Dentifrice products for adults that are commercially available in many countries generally contain fluoride at concentrations ranging from 1000 to 1500 µg/g; some products designed for use by children contain lower levels, ranging from 250 to 500 µg/g. Dental products such as toothpaste, mouthwash and fluoride supplements have been identified as significant sources of fluoride. Mouth rinses marketed for daily home use usually contain between 230 and 500 mg fluoride/litre, whereas mouthwash products intended for weekly or biweekly use may contain 900–1000 mg fluoride/litre.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Chapter 1.4: Environmental levels and human exposure 

For more information, see the full IPCS document:
Chapter 5.2.4: Consumer 

3.4 How much fluoride are humans exposed to?

The source document for this Digest states:

Although individual exposure to fluoride is likely to be highly variable, the inhalation of airborne fluoride generally makes a minor contribution to the total intake of this substance. For adults, the consumption of foodstuffs and drinking-water is the principal route for the intake of fluoride. In areas of the world in which coal rich in fluoride is used for heating and food preparation, the inhalation of indoor air and consumption of foodstuffs containing increased levels of fluoride also contribute to elevated intakes. Infants fed formula receive 50–100 times more fluoride than exclusively breast-fed infants. The ingestion of dentifrice by young children makes a significant contribution to their total intake of fluoride. In general, estimated intakes of fluoride in children and adolescents do not exceed approximately 2 mg/day. Although adults may have a higher absolute daily intake of fluoride in milligrams, the daily intake of fluoride by children, expressed on a milligram per kilogram body weight basis, may exceed that of adults. In certain areas worldwide in which the concentration of fluoride in the surrounding environment may be exceedingly high and/or where diets are composed of foodstuffs rich in fluoride, estimated intakes of fluoride in adults as high as 27 mg/day have been reported, the principal source being drinking-water obtained from groundwater sources located in geological areas rich in fluoride.

Occupational exposure to fluoride via inhalation or dermal contact likely occurs in individuals involved in the operation of welding equipment or in the processing of aluminium, iron ore or phosphate ore. In relatively recent studies, reported concentrations of airborne fluoride in the potrooms of aluminium smelters have been in the order of 1 mg/m3.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Summary of the Report, Chapter 1.4: Environmental levels and humans exposure 

Available data on the concentrations of fluoride in indoor air are limited. In the Netherlands, concentrations of gaseous fluoride ranged from <2 to 49 µg/m3 in the indoor air of five homes constructed with wood treated with a preservative containing 56% fluoride. In China, concentrations as high as 155 µg/m have been reported for samples of indoor air collected from homes where coal containing high amounts of fluoride was burned indoors.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Summary of the Report, Chapter 1.4: Environmental levels and humans exposure 

For more information, see the full IPCS document:
Chapter 5.2.3: Indoor air 
Chapter 5.2.5: Intake estimates 
Chapter 5.3: Occupational exposure 

3.5 What happens to fluorides absorbed by the body?

The source document for this Digest states:

In humans and laboratory animals, the absorption of ingested fluoride into the general circulation occurs primarily in the stomach and intestine and is dependent upon the relative aqueous solubility of the form consumed. Soluble fluorides are almost completely absorbed from the gastrointestinal tract; however, the extent of absorption may be reduced by complex formation with aluminium, phosphorus, magnesium or calcium. There is partial to complete absorption of gaseous and particulate fluorides from the respiratory tract, with the extent of absorption dependent upon solubility and particle size.

Fluoride is rapidly distributed by the systemic circulation to the intracellular and extracellular water of tissues; however, in humans and laboratory animals, approximately 99% of the total body burden of fluoride is retained in bones and teeth. In teeth and skeletal tissue, fluoride becomes incorporated into the crystal lattice.

Fluoride crosses the placenta and is transferred from mother to fetus. Fluoride is eliminated from the body primarily in the urine. In infants, about 80–90% of a fluoride dose is retained; in adults, the corresponding figure is approximately 60%. These values can be altered by alterations in urinary flow and urinary pH.

Fluoride is present in body organs, tissues and fluids. Concentrations of fluoride in whole blood of individuals residing in a community in the USA receiving fluoridated drinking-water ranged from 20 to 60 µg/litre. The mean plasma level in 127 subjects with 5.03 mg fluoride/litre in their drinking-water was 106 ± 76 (SD) µg/litre. Serum and plasma contain virtually the same amount of fluoride. Levels of fluoride in calcified tissues are generally highest in bone, dentine and enamel. The concentration of fluoride in bone varies with age, sex and the type and specific part of bone and is believed to reflect an individual’s long-term exposure to fluoride. The concentration of fluoride in dental enamel decreases exponentially with the distance from the surface and varies with site, surface attrition, systemic exposure and exposure to topically applied fluoride. The concentration of fluoride in soft tissues is reflected by that in blood. Levels of fluoride in the urine of healthy individuals are related to the intake of fluoride. Increased levels of urinary fluoride have been measured in individuals following occupational exposure to airborne fluoride and among those residing in areas associated with endemic fluorosis.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Chapter 1.5: Kinetics and metabolism in humans and laboratory animals 

The "balance" of fluoride in the body (i.e., the difference between the amount of fluoride ingested and the amount of fluoride excreted in the urine and the faeces) can be positive or negative. When the fluoride is derived from human milk or cow’s milk, biological fluids with a low fluoride content, urinary excretion generally exceeds intake (i.e., there is a negative fluoride balance). In infants, when fluoride intakes are low, sufficient fluoride is released from bone to extracellular fluid to result in urinary excretion being higher than intake (Ekstrand et al., 1994).

Hence, the plasma concentrations and the urinary excretions mirror a physiological balance that is determined by earlier fluoride exposure, the degree of accumulation of the ion in bone, the mobilization rate from bone and the efficiency of the kidneys in excreting fluoride.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Chapter 6: Kinetics and metabolism in humans and laboratory animals, Section 6.2.3, Districbution to calcified tissues 

For more information, see the full:
Chapter 6: Kinetics and metabolism in humans and laboratory animals 


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