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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 amount of fluoride present naturally in drinking water is highly variable, depending on the specific geological environment from which the water is obtained. In non-fluoridated drinking water (i.e., drinking water to which fluoride has not been intentionally added for the prevention of dental caries) levels may reach up to about 2.0 mg/litre. However, some places can have fluoride levels in drinking water of up to 20 mg/litre. In areas in which drinking water is fluoridated, the concentration of fluoride in drinking water generally ranges from 0.7 to 1.2 mg/litre. More...

3.2 How much fluoride is there in food?

Virtually all foodstuffs contain at least trace amounts of fluoride. Elevated levels are present in fish and in tea leaves, which are particularly rich in fluoride. Although the concentration of fluoride in food products is not significantly increased by the addition of superphosphate fertilizers (containing fluorides as impurities) to agricultural soil, a recent study shows that plant uptake of fluoride could increase given certain conditions. The use of water containing relatively low levels (less than about 3 mg/litre) of fluoride for crop irrigation generally does not increase fluoride concentrations in foodstuffs, but this depends on plant species and fluoride concentrations in soil and water. However, the level of fluoride in foods is significantly affected by the fluoride content of the water used in food preparation or processing, particularly in beverages and dry foodstuffs to which water is added prior to consumption, such as powdered baby formula. The concentrations of fluoride in unwashed or unprocessed foods grown near industrial fluoride sources may be greater than the levels in the same foods grown in other non-industrially exposed areas. Fluoride has been detected in breast milk at concentrations up to 100 µg /litre, with most measurements ranging between 5 and 10 µg/litre. More...

3.3 How much fluoride is there in toothpaste?

Dental products such as toothpaste, mouthwash and fluoride supplements have been identified as significant sources of fluoride. Toothpastes for adults that are commercially available generally contain fluoride at concentrations ranging from 1000 to 1500 µg/g, whereas those designed for children contain 250 to 500 µg. The concentration of fluoride in mouth rinses varies with the recommended frequency of use from 230 to 1000 mg/litre. More...

3.4 How much fluoride are humans exposed to?

Individual exposure to fluoride is highly variable depending on the levels of fluoride in foodstuffs and drinking water, on the use of fluoridated dental preparations, and in certain cases on the levels of fluoride in indoor air.

For adults, the consumption of foodstuffs and drinking water is the principal route of exposure to fluoride. Formula-fed infants receive 50–100 times more fluoride than exclusively breast-fed infants. The ingestion of toothpaste by young children makes a significant contribution to their total intake of fluoride. In general, estimated intakes of fluoride by children and adolescents do not exceed about 2 mg/day. Although adults may have a higher absolute daily intake of fluoride in milligrams, the daily fluoride intake of children, expressed on a milligram per kilogram body weight basis, may exceed that of adults. In geological areas rich in fluoride, drinking water obtained from groundwater wells can be the principal source, leading to estimated intakes of fluorides in adults up to 27 mg/day.

The inhalation of airborne fluoride generally does not contribute much to the total intake of this substance, save in areas of the world in which coal rich in fluoride is used indoors on open fires for heating and cooking or where certain wood preservatives are used.

Workers in the aluminium, iron ore or phosphate ore processing industry may be exposed via inhalation or dermal contact. More...

3.5 What happens to fluorides absorbed by the body?

When fluorides are ingested by humans or laboratory animals, they are absorbed in the stomach and/or the intestine. Fluoride from soluble fluorides is almost completely absorbed (either as HF or F-, depending on stomach acidity). However, when fluoride is bound to aluminium, calcium etc., its release and subsequent absorption may be reduced because this combination is less soluble. When fluorides in gaseous or particulate form are breathed in, the respiratory tract, they are partially or completely absorbed depending on how soluble they are or on how big the fluoride-containing particles are.

Fluoride is then rapidly distributed in tissues. In humans and laboratory animals, fluorides mostly build up in bones and teeth, which retain about 99% of the total fluoride body burden.

Fluoride is eliminated from the body primarily through the urine. Infants retain 80 to 90% of fluoride ingested, while adults retain approximately 60%.

However, the balance of fluoride in the body (i.e. the difference between the amount of fluoride ingested and the amount excreted) can be positive or negative. This physiological balance is determined by earlier fluoride exposure, the degree of accumulation in bone, the rate at which it is released from bone and the efficiency of the kidneys in excreting fluoride. When fluoride intakes are low excretion through urine can exceed intake.

Fluoride can be transferred from mother to foetus through the placenta. More...

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