Fluoride

Guideline

The maximum acceptable concentration (MAC) for fluoride in drinking water is 1.5 mg/L.

Identity, Use and Sources in the Environment

In the free state, fluorine is a pale yellow diatomic gas. Fluorine is never found in this form in nature, because it is very chemically reactive and combines with every other element except the inert gases. It is the 13th most abundant element, commonly occurring in the minerals fluorspar (CaF₂), cryolite (Na₃AlF₆) and fluorapatite 1,2 (3Ca₃(PO₄)₂-Ca(F,Cl)₂). Fluorine is used in aluminum, steel, glass, enamel, brick, tile, pottery and cement manufacturing; fluorinated chemical and phosphate fertilizer production; and metal casting, welding and brazing.^3,4 Sodium fluoride (NaF) is used in various pesticide formulations, including insecticides and wood preservatives.⁵ Fluoride-containing compounds are employed in the artificial fluoridation of drinking water for the prevention of dental caries.⁶ Fluoride-containing dental products are now widely available, including toothpaste, supplements, mouth rinses and professionally applied gels and varnishes.⁷ Fluoride (primarily as NaF) has also been used in the treatment of osteoporosis.⁸ Both natural and anthropogenic sources can contribute fluoride to soil, air, water and food. About 23 500 t of inorganic fluorides are released from anthropogenic sources in Canada each year,⁴ whereas global volcanic sources are estimated to release 60-6000 kt annually.⁹ Fluoride can occur naturally in surface waters as a result of the deposition of particulates from the atmosphere and the weathering of fluoride-containing rocks and soils. Groundwater can also contain high concentrations of fluoride owing to leaching from rocks. Chemical manufacturing plants and waste ponds can contribute fluoride to raw water sources directly through effluents or indirectly through volatilization.^3,10 Free fluoride ions predominate in aqueous solutions, but both ionic (i.e., inorganic) and nonionic forms of fluoride can be present in plant and animal tissues.^8,11

Exposure*

Surveys conducted in 1984-1989 in several provinces found mean concentrations of fluoride** in non-fluoridated drinking water ranging from <50 µg/L (detection limit) in British Columbia (not detected in three locations) and Prince Edward Island (detected in four of 13 locations; <50-70 µg/L) to 210 µg/L in the Yukon (<30-650 µg/L; detection limit <30 µg/L).^12-14 Elevated levels of naturally occurring fluoride in drinking water are relatively infrequent in Canada, although communities in Quebec, Saskatchewan and Alberta have recorded concentrations as high as 2520-4350 µg/L.¹⁵ In 1986, artificially fluoridated drinking water was supplied to approximately 38% of the Canadian population.¹⁵ Between 1986 and 1989, average fluoride concentrations in fluoridated drinking water across Canada ranged from 730 µg/L (600-800 µg/L) in Newfoundland and Labrador (three locations) to 1250 µg/L (1200-1300 µg/L) in the Yukon (two locations).^15-18 Typical fluoride concentrations in fresh and cooked foods from Canada and the United States include 0.01-0.80 µg/g for dairy products; 0.01-0.58 µg/g for fruit; 0.04-4.57 µg/g for meats, fish and eggs; 0.05-0.13 µg/g for fats; and 0.02-0.86 µg/g for sugar-based foods.^19,20 A mean fluoride concentration of 0.54 µg/g (543 µg/L; range <0.05-5.85 µg/g) was recorded in a 1990 survey of 172 bottled waters obtained across Canada.²¹ The fluoride concentration of water used to reconstitute or prepare beverages and dry concentrates can greatly influence their fluoride content.^22-24 In the United States, fluoride concentrations in infant formulas were found to range from 0.127 mg/L for ready-to-use milk-based formulas to 0.854 mg/L for soy-based powdered formula prepared using water containing fluoride at a concentration of 1.0 mg/L.²⁵ A Canadian survey found that women consuming non-fluoridated drinking water (<0.16 ppm [mg/L] fluoride) produced milk with a mean fluoride concentration of 4.4 ng/g (µg/L), whereas breast milk from women consuming fluoridated drinking water (1 mg/L fluoride) contained fluoride at a concentration of 9.8 ng/g.²⁶ No Canadian data are available on fluoride concentrations in indoor air. Average monthly concentrations of fluoride (gaseous and particulate) in ambient air reported for a residential area of Toronto (Ontario) in 1981 ranged from 0.01 to 0.05 µg/m³, with a mean of 0.03 µg/m³.²⁷ Canadian estimates of mean fluoride concentrations in soil range from 6 ppm (µg/g) for a forest in Newfoundland (depth and range not specified) to 309 ppm (63-1000 ppm at depths of 0-130 cm) for 23 Canadian Soil Survey Committee (CSSC) reference samples.^28,29 The most commonly used fluoride-containing dental product is toothpaste. At least 95% of the toothpastes sold in North America contain fluoride as NaF and/or disodium monofluorophosphate (MFP, or Na₂PO₄F), with an effective fluoride concentration of approximately 1000 ppm (µg/g).^30-34 The mean amount of tooth-paste ingested per brushing by children 1-4 years of age ranges from 0.13 to 0.39 g. In contrast, adults 20-35 years of age ingest an average of 0.04 g toothpaste per brushing.³⁵ Other fluoride-containing dental products include fluoride supplements (NaF tablets or drops) for children residing in non-fluoridated communities,^36,37 fluoride mouth rinses, which are generally used in school'based programs in areas with high caries rates,³⁸ and topical fluoride gels, which are usually applied once or twice a year by dentists.³³

Table 1. Estimated daily intake of fluoride for the 7 month to 4 year and 20+ year age groups in the general population of Canada^a

		Daily intake of fluoride from various sources (µg/kg bw per day)						Proportion of total daily intake allocated to drinking waterg
Age group	Type of Community	Drinking waterb	Airc	Soild	Foode	Toothpastef	Total
Daily intakes derived from data presented in Table 11 of reference 39. Estimated using mean fluoride concentration ranges for non-fluoridated (i.e., <50 µg/L for British Columbia and Prince Edward Island to 210 µg/L in the Yukon)12-14 and fluoridated (i.e., 730 µg/L in Newfoundland and Labrador to 1250 µg/L in the Yukon )15-18 communities in Canada, assuming that individuals from the 7 month to 4 year and 20+ year age groups consume 0.8 and 1.5 L of drinking water per day, respectively.40 Combined intake from both indoor and ambient air. Indoor air concentrations assumed to be equivalent to ambient air concentrations.39 Estimated intakes calculated from the mean ambient air concentration in Toronto (0.03 µg/m3),27 assuming that individuals from the 7 month to 4 year and 20+ year age groups breathe 5 and 20 m3 of air per day, respectively.40 Estimated from the range of mean fluoride concentrations in soil recorded for a forest soil in Newfoundland and 23 Canadian Soil Survey Committee (CSSC) reference soil samples (6-309 µg/g),28,29 assuming that individuals from the 7 month to 4 year and 20+ year age groups consume 50 and 20 mg of soil per day, respectively.40 Estimated using survey data on the concentrations of fluoride in various food groups in Canada and the United States19,20 and estimates of the daily consumption of those food groups by the 7 month to 4 year and 20+ year age groups.40 Calculated from the estimates of mean amounts of toothpaste ingested per brushing (i.e., 0.13-0.39 g and 0.04 g for the 7 month to 4 year and 20+ year age groups, respectively),35 an effective fluoride concentration of 1000 µg/g for fluoridated toothpastes sold in Canada34,41 and the assumption that both age groups brush their teeth an average of twice a day.39 Calculated as follows: Minimum allocation to drinking water = lowest daily intake from drinking water ÷ (lowest daily intake from drinking water + daily intake from air + highest daily intake from soil + daily intake from food + highest daily intake from toothpaste) Maximum allocation to drinking water = highest daily intake from drinking water ÷ (highest daily intake from drinking water + daily intake from air + lowest daily intake from soil + daily intake from food + lowest daily intake from toothpaste) Assumed body weights: 7 month to 4 year age group, 13 kg bw; 20+ year age group, 70 kg bw. 40 Average.
7 months - 4 yearsh	Non-fluoridated	3.08-12.92	0.01	0.02-1.19	22.30	20.00 -60.00	45.41-96.42	0.04-0.23 (0.15)i
	Fluoridated	44.92-76.92	0.01	0.02-1.19	22.30	20.00-60.00	87.25-160.42	0.35-0.65 (0.50)i
20+ yearsh	Non-fluoridated	1.07-4.50	0.01	0.002-0.09	30.08	1.14	32.30-35.82	0.03-0.13 (0.08)i
	Fluoridated	15.64-26.79	0.01	0.002-0.09	30.08	1.14	46.87-58.11	0.33-0.46 (0.40)i

The estimated daily intake of fluoride from drinking water, air, soil, food and toothpaste for two age groups -- 7 months to 4 years and 20+ years -- in the general Canadian population is shown in Table 1. Daily fluoride intakes from supplements, mouth rinses and gels were not estimated, as the available data on the proportion of the general population using these products or the amount of fluoride ingested from them were considered inadequate. However, regular supplement use in accordance with either Canadian Paediatric Society or Canadian Dental Association recommendations could add as much as 19-76 µg/kg bw per day to the daily fluoride intakes of preschool children in non-fluoridated communities.^36,37 For children less than 6 months of age with a body weight of 7 kg and a daily consumption of 0.75 L of formula or breast milk, daily fluoride intake can be estimated to range from 13.6 to 91.5 µg/kg bw for formula and from 0.47 to 1.05 µg/kg bw per day for breast milk.³⁹

Analytical Methods and Treatment Technology

Several methods are available for measuring fluoride in drinking water, including ion-selective electrode, SPADNS colorimetric, complexone and ion chromatographic methods. The ion-selective electrode (suitable for 0.1->10 mg/L)⁴² and SPADNS colorimetric (suitable for 0.05-1.4 mg/L)⁴² methods are most often employed for routine monitoring. The analytical range of the complexone method is 0.1-2.0 mg/L. Ion chromatography is not usually recommended for routine fluoride measurements because of difficulties with quantitation at low concentrations and interferences from simple organic acids, but it may be satisfactory if special techniques are employed, such as dilute eluent or gradient elution.⁴² Methods to remove fluoride from drinking water include adding chemicals during coagulation or softening to remove fluoride in the flocs, ion exchange or adsorption processes and demineralization techniques, such as reverse osmosis and electrodialysis.⁴³ Adsorption with activated alumina is probably the most effective and frequently used technique in municipal treatment systems.^43-45 Effluents of <1 mg/L have been obtained from raw water containing 5-8 mg/L at full'scale facilities using this technique; in practice, the upper limit for influent fluoride concentration is 10 mg/L.⁴³ Bone char is also used for adsorption, but the medium is more expensive, has a lower adsorption capacity and is less stable in continuous use than activated alumina.^43,45 In Canada, artificial fluoridation is generally carried out by supplementing raw water with NaF, hydro- fluosilicic acid (H₂SiF₆) or sodium silicofluoride (Na SiF ).^44,46