Water Quality Ambient Water Quality Criteria for Fluoride 1. Introduction Major reviews of the literature on fluoride, with respect to its role as a nutrient or as a toxin, its effect on teeth and bones, its effect on metabolism, its occurrence in air, food and water, its effects on wildlife, livestock and vegetation, and occupational exposure, have been carried out periodically. Some of these reviews are (McKee and Wolf, 1963; Underwood, 1971; Anon, 1968; Cholak, 1959; Anon (WHO), 1986; Ericsson (Editor), 1970; Princi, 1960; Cass, 1961; Campbell et al., 1958 & 1974; Suttie, 1977; Roholm, 1937; Hodge and Smith, 1965; Anon, 1966/1970; Davis, 1961; Rose and Marier, 1977; Anon, 1971a; Smith and Cox, 1952; Maynard et al., 1958; Anon, 1970; Farkas, 1975b; Weinstein, 1977; and Anon, 1974). There is also a journal, 'Fluoride', which publishes papers exclusively on fluoride and its effects. Techniques for sampling, sample preparation and measurement of fluoride in plant tissue, animal tissue, soil and rock, food and beverages, air and water are described by Jacobson and Weinstein (1977). The use of fluoridated drinking water has been attacked on many fronts by an active anti-fluoridation lobby; however, most such attacks have neither been objective nor backed by scientifically acceptable evidence. Seven of these common attacks have been outlined and refuted in two brief reviews, Anon (1978a) and Anon (1978b). There are also professional scientists who have reservations about fluoride use. Generally, while they do not believe that the 1.0 mg/L level is harmful, they think that there is not enough safety margin between the recommended level, and levels, less than 1 order of magnitude higher, which cause harmful effects. They are not convinced that the benefits of fluoridation are as great as the pro-fluoridation lobby indicates (Hileman, 1988). Ambient Water Quality Criteria for Fluoride 2.0 Occurrence 2.1 Natural Occurrence Fluorine is the 17th (McNeely et al. , 1979), or 13th (Anon, 1971) most abundant element in the earth's crust. It is present as a fluoride since fluorine is the most reactive element (McNeely et al. , 1979; Sawyer and McCarty, 1967; and McKee and Wolf, 1963). Detectable fluoride levels occur in almost all minerals Ministry of Environment Water Protection and Sustainability Branch Mailing Address: Telephone: 250 387-9481 Environmental Sustainability PO Box 9362 Facsimile: 250 356-1202 and Strategic Policy Division Stn Prov Govt Website: www.gov.bc.ca/water Victoria BC V8W 9M2 (McNeely et al. , 1979; Anon, 1980; and Anon, 1977). The main minerals are fluorspar-CaF , Cryolite- 2 Na AlF and fluorapatite-Ca F (PO4) (McNeely et al., 1979; Anon, 1971; Weber, 1966; and Dave, 3 6 10 2 6 1984). Fluorapatite is a complex mineral and has several different formulae given in the literature. Topaz- Al SiO (F, OH) is also a fluoride mineral (Norrish, 1975). Fluoride in soils ranges from 76 mg fluoride/kg 2 4 for sandy soils to 2640 mg fluoride/kg for heavy clays (Gisiger, 1968). Most of this is insoluble, especially at the higher concentrations. Soils in British Columbia have not been systematically surveyed and analyzed for fluoride and little is known of the available fluoride concentrations. The weathering of alkalic and silicic igneous and sedimentary rocks, primarily shales, contributes much of the fluoride to natural waters. Volcanic emissions also supply fluoride (McNeely et al. , 1979; Underwood, 1971) and precipitation may contain up to 1.0 mg/L of fluoride (McNeely et al. , 1979). Most fluorides associated with monovalent cations are very water soluble, 10's of grams per litre; while salts of divalent cations are relatively insoluble, 10's of milligrams per litre. Table 2.1 gives the solubilities of some fluoride salts in cold water (Weast, 1968). Seawater Seawater fluoride levels are usually in the range of 0.86 to 1.4 mg/L (McNeely et al. , 1979; Benefield et al.., 1982; Bewers, 1971; Warner et al., 1975; Thompson and Taylor, 1933; Dave, 1984; Barbaro et al., 1981). Brines may reach 600 mg/L (McNeely et al. , 1979). The mean chloride to fluoride ratio in natural seawater is generally 14903.13 to 1, range 14749.26 to 1 up to 15060.24 to 1 (Moore, 1971; and Barbaro et al.., 1981). This is usually quoted as a fluoride to chloride ratio of 0.0000671 to 1. The correlation of fluoride to chloride is positive and linear (Franco et al.., 1978; and Barbaro et al. , In Press). Deviations from these narrow concentration ranges or ratios generally indicate that man-made pollution is occurring or that seawater is mixing with fresh water in estuarine areas. Freshwater Fluoride is considered to be the main ion responsible for dissolving iron, tin, tantalum, niobium, scandium, berylium and aluminum in natural waters (Anon, 1976). Fluoride levels in lakes are likely regulated by the calcium-carbonate-phosphate-fluoride system which tends to maintain uniform fluoride levels with depth (Kramer, 1964). Natural concentrations of fluoride in surface waters may exeed 50 mg/L (McNeely et al. , 1979), but are typically less than 1.0 mg/L (McNeely et al. , 1979; Livingstone, 1963; Wetzel, 1975; Cholak, 1959; Anon, 1980). Fluoride levels in the Great Lakes range from 0.05 to 0.14 mg/L (Anon, 1977) and in major rivers, world-wide, the range is 0.01 to 0.02 mg/L (Anon, 1987). Many natural streams are below 0.2 mg/L (McNeely et al. , 1979; Neuhold and Sigler, 1960; Anon, 1980; Dave, 1984). In the western US, fluoride is commonly found at 0.1 mg/L and 1.0 mg/L is not rare. Walker and Pyramid Lakes in Nevada contain 13 mg/L and the Madison and Firehole Rivers in Yellowstone Park contain 12 to 14 mg/L (Anon, 1957). Natural thermal waters in New Zealand, pH 5-9, contain 1 to 12 mg/L (Mahon, 1964). Wells in Japan may contain 1.5 to 5.5 mg/L (Kobayashi, 1951). Ground water throughout British Columbia is generally higher in fluoride than surface water, and regularly exceeds 0.2 mg/L (MOE). Ground water concentrations of fluoride may reach detrimental levels (Anon, 1950). They have been recorded at 9 to 15 mg/L (Benefield et al.., 1982; Messer et al.., 1972; and Underwood, 1971), and are often above 10 mg/L (McNeely et al. , 1979). In dry seasons when proportionately more of a river's flow comes from ground water sources, the river levels of fluoride may rise (McNeely et al. , 1979). Such fluctuations in fluoride levels can cause problems for water treatment plants trying to maintain uniform fluoride levels in treated drinking water (McNeely et al. , 1979). British Columbia coastal lakes and streams are low in fluoride and interior waters are somewhat higher. It is difficult to decide what is background in British Columbia over much of the southern interior since air and water emissions of fluoride are substantial from Cominco operations in Trail and Kimberley and affect levels in two large drainage basins. On the coast, the area around Kitimat is affected by the Alcan Aluminum Smelter and true background levels are difficult to determine. Another factor affecting background fluoride levels throughout much of the interior of British Columbia, but not on the coast, is fluoridation of drinking waters and its subsequent discharge to streams. Only a few coastal communities fluoridate and their discharges are generally to the sea. Mean fluoride levels found in lakes and streams in British Columbia which have not been heavily polluted are well below values which would cause health concerns. All natural levels are, in fact, too low in fluoride for good dental protection, and need to be supplemented with fluoride if the optimum tooth protection level is to be achieved in drinking waters. The whole Okanagan Valley drainage basin appears to have naturally high fluoride with levels generally in the 0.2 to 0.3 mg/L range; otherwise, apart from areas around Kimberley and Trail affected by high fluoride discharges, only one coastal and three interior water samples exceeded the aquatic life criterion of 0.2 mg/L when no known source of pollution was present. 2.2 Anthropogenic Sources Municipal Sewage Sewage effluents from municipalities using fluoridated drinking water discharge significant amounts of fluoride to the environment (McNeely et al. , 1979; and Anon, 1985). The average concentration of fluoride in 57 Ontario municipal sewage plants surveyed in 1976 was 1.0 mg/L (Anon, 1978). In 1985, 53.7% of Alberta's population received fluoridated drinking water; the total volume being 186 X 106 m3 of water. Once used, this becomes fluoridated wastewater with maximum, minimum and mean concentrations of fluoride being 1.21, 0.74 and 1.03 mg/L, respectively (Anon, 1985). These fluoride levels are at least one order of magnitude above the usual background levels in the streams and rivers to which this wastewater is discharged. The excess concentration of fluoride in raw sewage effluent, over the water supply levels for the four cities analyzed, was 1.30 mg/L. Excess fluoride decreased to 1.28 mg/L after primary treatment in 23 cities and to 0.39 mg/L after secondary treatment in 29 cities (Masuda, 1964). In British Columbia the two major population centers, Greater Victoria and Greater Vancouver, do not fluoridate their water supplies. However, 22 smaller communities, with a total population of approximately 321 000, currently add fluoride in the form of NaF, Na SiF or H SiF , to their water supply (Gunther and 2 6 2 6 Gray, 1988). Industrial Fluorides are used in a number of industries including tile, glass, adhesives, ceramics, herbicides, insecticides, metal fluxes, brick, aluminum, steel, brazing, welding, plating, electronics and smelting (McNeely et al. , 1979; Anon, 1980; Benefield et al., 1982; Anon, 1976; Anon, 1981; Anon, 1960; Schwartz, 1973; and Connell and Miller, 1984). Fluorides are released from coal-burning thermo-electric generating stations, but environmental damage is not usually severe. Insecticides and herbicides containing fluorides reach water sources through agricultural runoff (McNeely et al. , 1979; and Benefield et al., 1982). Fertilizer production from fluorapitite-containing phosphate rock releases large amounts of fluoride to the environment (Benefield et al., 1982; and Schwartz, 1973). As indicated below, Cominco operations in Trail and Kimberley released large amounts of fluoride to the environment from such processes. The resulting high fluoride levels in the lakes and streams affected are quite apparent, but are not above drinking water supply levels except in the most polluted ditches and small streams. Wastewater from aluminum, stainless steel and phosphate fertilizer plants can contain 8-70 mg/L of fluoride (Rose and Marier, 1977). Stack emissions, spillage and fugitive dust from these various industries release fluoride to the environment (McNeely et al. , 1979; and McKee and Wolf, 1963) and very high local concentrations may occur as a result (Warrington, 1987), causing damage to forests, grazing lands and aquatic habitats (Hindawa, 1970; Treshaw and Pack, 1970; and Anon, 1971a). Aluminum smelters, phosphate fertilizer plants and welding operations are the main sources of occupational exposure to fluoride and have been reviewed by Hodge and Smith (1977) and Dinman et al. (1976a, b, c, and d). Alcan Aluminum Smelter - Kitimat There are abundant data from the period 1975 to 1983 on fluoride emission levels and ambient environmental levels in the Kitimat area associated with the Alcan Aluminum Smelter (Warrington, 1987; MOE; and Remington, 1987). Stack emissions are not discussed here, but much of this fluoride will fall out in the watershed and find its way into water and sediments. Direct loading of fluoride to Moore Creek, a tributary of the lower Kitimat River, averaged 13.5 kg/d while diffuse loads averaged 23.2 kg/d. Direct loading to marine waters averaged 1 395 kg/d over a 7-year period. Effluent concentration of fluoride over an 8-year period, both to Moore Creek and to the sea, ranged from 410 mg/L to 0.1 mg/L, with a mean of 25.4 mg/L in 876 samples. These effluent concentrations and loadings resulted in a mean of 0.307 mg/g dry weight in seven marine sediments, a mean of 0.894 mg/L in marine waters at various depths and a mean of 0.970 mg/L in Moore Creek. Background levels in the Kitimat River were less than 0.1 mg/L and included stack-emission fallout in the watershed(Warrington, 1987). The fluoride: chloride ratio in the harbour ranged from 13 to 1500 x 10-5 with a mean of 158 x 10-5. This is about 20 times the natural mean background ratio mentioned in Section 2.1. Fluoride levels in Kitimat Harbour can not be directly compared to the world-wide mean of 1.4 mg/L for open ocean sites for several reasons. The harbour is at the head of a long inlet and is diluted with large amounts of fresh water, amounts which vary seasonally. There is a large fresh water lens floating on the marine water in the harbour and the location, boundaries and depth of this lens are not fixed. Variable, but substantial amounts of fluoride are discharged to the inlet by the smelter operations. There were 296 samples taken at six sites in the Bay at various distances and depths from the discharge. The maximum fluoride level recorded was 50.6 mg/L at a surface site and the mean was 1.82 mg/L at that site. Cominco Fertilizer Operations - Trail and Kimberley There are abundant data on fluoride emission levels and ambient environmental levels in the Trail and Kimberley areas associated with the fertilizer operations (MOE). Stack emissions are not discussed here, but much of this fluoride will fall out in the watershed and find its way into water and sediments. Sewers from the Trail fertilizer plant showed a fluoride maximum of 277 mg/L and a mean of 98.9 mg/L in 27 samples for one sewer, and a maximum of 78 mg/L and a mean of 7.08 mg/L in 19 samples for a second sewer. The Columbia River at Waneta had 53 fluoride measurements in the 1978-1987 period with a mean of 0.167 and maximum of 0.3 mg/L. More recent data have a mean of 0.11 mg/L in 175 samples, of which only 12 exceeded 0. 2 mg/L (MOE). Three creeks downstream from the Kimberley operations showed a maximum of 33.0 mg/L and a mean of 2.46 mg/L of fluoride for 286 samples. As far downstream as Lake Koocanusa or Kootenay Lake the fluoride levels were still at a maximum of 0.96 mg/L and a mean of 0 20 mg/L for 141 samples. These records were from the 1973 to 1987 period. Fluoride levels dropped about one order of magnitude after 1975 at the St. Mary River (Wycliffe) site. St. Mary River data at Wycliffe for the period 1985 to 1988 still show a mean of 0.29 mg/L for 14 samples with a maximum of 0.42 and a minimum of 0.23 (MOE). The Kootenay River at Fenwick Station downstream from the St. Mary River had a maximum of 0.2 mg/L in 74 measurements made between May 1985 and May 1988. Ambient Water Quality Criteria for Fluoride 3.0 Fluoride Metabolism Table 2.1 gives the solubilities of some fluoride salts in cold water. This information should be referred to when reviewing papers on the effects of various doses and concentrations of fluoride on organisms. For example, Simonin and Pierron (1937), in Table 5.2, report effects of fluoride at concentrations in excess of the solubility of the salt at physiological temperatures. It is not always clear in some papers whether the concentration referred to is the concentration of the salt or only of the fluoride component. Table 2.1 also gives the percentage of fluoride in the common fluoride salts used in physiological experiments. Dietary Intake All food contains some fluoride, generally between 0.1 and 10 mg/kg (Nommik, 1953). Some examples are given in Table 3.1. Fish, tea and some vegetables have much higher fluoride levels than other common foods. Some fish can reach 100 mg/kg and tea generally ranges from 8-400 mg/kg (McClure, 1949; Anon, 1970; Nommik, 1953; Matuura et al.., 1954 ; Reid, 1936; Wang et al.., 1949); however, considerably higher levels of 1758 to 1900 mg/kg are reported in some teas (Matuura et al.., 1954; Reid, 1936). About two-thirds of the fluoride in tea leaves dissolves in tea so that one cup of tea made from 100 mg/kg tea leaves would add about 0.1 to 0.2 mg of fluoride to the daily fluoride intake (Tarzwell, 1957; Underwood, 1971; and Reid, 1936). Two cups of tea made from the highest fluoride level tea leaves would exceed the recommended daily fluoride intake. The use of fluoridated water supplies in food preparation can double the level of fluoride in prepared foods. Vitamins, toothpaste and pharmaceuticals also add to the daily fluoride dose. The use of bone meal supplements, more common in pet and livestock feeds, can add quite large amounts of fluoride to the diet. Estimates of the daily dietary intake of fluoride by adults are 0.2 to 3.1 mg (Anon, 1980; Rose and Marier, 1977; and Anon, 1970), in areas where the water is not fluoridated, but 3.5 to 5.5 mg (Rose and Marier, 1977), when water is fluoridated at 1.0 mg/L. For children, the estimates are 0.5 mg (Anon, 1970), and <2.0 mg (Anon, 1980), respectively. Table 3.2 gives more specific examples. Daily intake levels will be exceeded in hot climates where fluoridated water is available, and by those individuals who drink tea (Rose and Marier, 1977). Assuming a 70 kg adult, the estimates of acceptable daily fluoride intake are 0.033 to 0.073 mg/kg (Rose and Marier, 1977; Farkas, 1975b; Farkas, 1975a; Toth, 1975), based on levels in bones and 0.053 to 0.076 mg/kg (Rose and Marier, 1977), based on levels in blood plasma. The 3.5 to 5.5 mg/d intake estimates in areas with fluoridated water corresponds to a 0.05 to 0.08 mg/kg daily intake. Thus, to remain within the acceptable daily intake levels of fluoride from all sources, the water supplies should not exceed 1.0 mg/L. Hard water confers some protection from fluorosis (Herbert and Shurben, 1964; and Neuhold and Sigler, 1960). Chronic fluoride intake increases the need for calcium, magnesium, manganese and vitamin C (Rose and Marier, 1977). Fluoride as an Essential Element Due to the ubiquitous nature of fluoride it is very difficult to prepare fluoride-free diets to test the hypothesis that fluorine is an essential element. If it is essential only very low levels are required (Anon, 1980). In 1972 it was claimed that fluoride was essential for the growth of rats (Schwarz, 1973), and fluoride was shown to enhance fertility and growth of rats in small doses (Underwood, 1971). There are other studies claiming that fluorine is essential for animals (Messer et al., 1972; and Underwood, 1975); however, there is no consensus yet on its status as an essential element, since other studies did not find any effects over several generations, when fluoride levels in diets were as low as 5 µg/kg of fluoride (Weber, 1966; Doberanz et al., 1963; and Maurer and Day, 1957). Metabolism The general systemic effects of fluoride are remarkably similar from species to species; only dose rates and the time required to achieve any effect vary. Thus the fluoride ion must exert its effect upon some basic physiologic process common to mammalian life. Enzyme systems and the central nervous system are affected very early in the process of fluorosis. Due to rapid excretion and active scavenging by bones and teeth, soft tissue damage is relatively difficult to achieve and requires repetitive high doses (Davis, 1961). Fluoride ingested in water is almost completely absorbed. Up to 97% of a dose of 12 to 25 mg/day will be absorbed (Sargent and Heyroth, 1949). Absorption efficiency of fluoride from foods is somewhat lower, but still quite high, with the exception of fish and some meats which may have absorption efficiencies as low as 25%. Fluoride passes via the placenta to the fetus and passes through the milk to nursing young (Zipkin and Likins, 1957; Wallace, 1953; and Anon, 1974). Distribution of absorbed fluoride is rapid with most retained in the skeleton and the teeth (Underwood, 1971). While the fluoride retention rate decreases with age (Anon., 1980), bone fluoride increases up to about age 55 (Jackson and Weidmans, 1958). Excretion of fluoride is primarily in the urine and is affected by health and previous fluoride history. At high doses, fluoride interferes with carbohydrate, lipid, protein, vitamin, enzyme and mineral metabolism (Anon, 1970). Many symptoms of acute fluoride intoxication are a result of the calcium in the body being bound as CaF . The body attempts to prevent accumulation of toxic fluorides in the tissues 2 by increased renal excretion of 52 to 63% of the absorbed fluoride (Pantucek, 1975; and Sargent and Heyroth, 1949), or permanent sequestration in the bones and teeth. The acute lethal doses for humans cited in the literature are 2 g of fluoride or 5 g of NaF (Anon, 1980), 0.5 g/kg (Greenwood, 1940), 2.5 g (Forrest et al., 1957), or 4.0 g (Anon, 1960). Severe symptoms occur at 250 to 450 mg (Anon, 1960). Initial signs and symptoms of fluoride intoxication include vomiting, nausea, abdominal pain, diarrhea and convulsions (Anon, 1977). Pathological changes due to high doses include gastric hemorrhaging, kidney damage and injury to the liver and heart (Anon, 1970). Gastric and intestinal mucosa are severely affected by large oral doses of fluoride (Suttie, 1977). High fluoride levels cause cell damage and necrosis which affect organ function. Enzymes, including cholinesterase, are inhibited, and hyperglycemia may occur. The decrease in plasma calcium may be responsible for the effects on the nervous system, blood clotting and membrane permeability. In spite of various prior claims to the contrary, it is generally agreed that there is no acceptable evidence that fluoride in water is carcinogenic to people (Anon, 1980; Anon, 1970; Clemmesen, 1983; and Anon, 1982. Suggestions that fluoride is mutagenic, teratogenic or in any way related to birth defects has also been reviewed and proven to be groundless (Anon, 1970). It is probable, but not proven, that it is the gross disturbance of calcium metabolism that leads to death in acute fluoride intoxication (Davis, 1961). Adults, not subject to occupational high fluoride levels, may use drinking and cooking water with up to 5 mg/L without cosmetic or harmful effects. Generally, if urinary excretion rates do not exceed 5 to 8 mg/day (5 to 10 mg/L of urine), there is no deleterious effect on health (Princi, 1960). Teeth and Bones Fluoride, when incorporated into the teeth, reduces the solubility of the enamel under acidic conditions and prevents dental caries. The incidence of caries decreases as fluoride in the water rises to about 1 mg/L (Anon, 1980). Mottling of teeth may occur when fluoride levels rise to about 1.5 to 2.0 mg/L or at 1.0 mg/L under long-term consumption by children up to 7 years old with kidney diseases. Once teeth have matured and mineralization has ceased, mottling will not occur (Anon, 1977; and Anon, 1968). Thus adults can be exposed to higher fluoride levels than young children without risk of tooth mottling. Skeletal fluorosis occurs at about 3 to 6 mg/L depending upon additional sources of fluoride intake (Anon, 1977). Bone damage in children and adults is reported to occur when fluoride levels reach 8 to 20 mg/L over long periods of time or when intakes reach 20 to 40 mg/day. The damage consists of depressed collagen formation, bone resorption and an increase in bone crystal (Anon, 1977; Anon, 1970; Hodge and Smith, 1954; and Neer et al., 1966). High Risk Groups Some portions of the population are more at risk from high fluoride levels than others; they include: workers in welding, aluminum smelter and phosphate fertilizer industries; people living near such industries where water and air are subject to pollution: people living in areas where goiter is endemic; people with kidney disfunction, polydipsia or diabetes insipidus; those whose diets are deficient in iodine, calcium, manganese or vitamin-C; and those with low calcium to phosphorus ratios in their diet (Rose and Marier, 1977). Hemodialysis treatments require very low fluoride water since increased plasma fluoride levels may occur in patients when water containing as little as 1.0 mg/L is used. Such increases in plasma fluoride may be as much as 2 to 4 times normal at a 1.0 mg/L fluoride concentration. Such patients tend to already have higher than normal plasma fluoride levels due to their kidney insufficiency, and can ill-afford further increases (Posen et al., 1971; Cordy et al., 1974; Seidenberg et al., 1976; and Hahijarvi, 1971). Table 3.3 gives some effects of various fluoride doses on mammals, including man. The effects are arranged in increasing dose size. The fluoride dose given is expressed in several ways and a separate increasing dose section of the table is provided for doses on a mg/kg, mg/day, mg/animal and mg/litre basis. Synergistic Responses When Chlorella vulgaris is grown in 759 mg/L fluoride and 635 mg/L copper (as NaF and CuS0 4 respectively), respiration is almost completely arrested, while neither compound alone had much affect on respiration. These copper levels are three orders of magnitude higher than those reported to affect growth, photosynthesis and respiration in algae and Chlorella in particular (Singleton, 1987). If, instead of simultaneous treatment, the algal cells were pretreated with copper before adding fluoride, respiratory inhibition was found to increase with pretreatment time. Pretreating with fluoride produces less inhibition as the pretreatment time increases. Presumably fluoride blocks the main respiratory pathway and copper blocks the hexose monophosphate shunt (Hassel, 1969). The significance of these responses at very high copper and fluoride levels, compared to normal metabolic responses found in other organisms at much lower copper and fluoride levels, is not known. Ambient Water Quality Criteria for Fluoride 4.0 Drinking Water Water Treatment Some water supplies may have excessive fluoride levels which need to be reduced before delivery to the consumer. There are a number of processes which will do this, but all are expensive and few jurisdictions carry them out (Benefield et al., 1982; and Sawyer and McCarty, 1967). Precipitation of CaF by adding calcium salts such as Ca(OH) , CaS0 or CaCl is one method and adsorption to the 2 2 4 2 insoluble compound Al(OH) which is produced by adding alum, Al (S0 ) .14H 0, to the water is another 3 2 4 3 2 method. Ion exchange and sorption on bone char, synthetic ion exchange media and activated alumina (Al 0 ) are also practiced (Benefield et al., 1982). Activated alumina defluoridation can reduce fluorides 2 3 from 8 to 1 mg/L (Sorg, 1978; Bishop and Sansoucy, 1978; and Choi and Chen, 1979). Caustic soda is a better regenerant than alum in ion exchange methods. Silicate and hydroxyl compete for exchange sites when the pH is over 7, but between pH 5 and pH 6 fluoride is preferentially adsorbed. The acidic water resulting from this process needs to be neutralized with limestone to reduce its corrosiveness and a 96% water recovery is possible (Anon, 1985). Reverse osmosis can also reduce fluoride from 2.2 to less than 1.0 mg/L (Naylor and Dague, 1975). Fluoride is added to water as sodium fluoride (NaF), sodium silicofluoride (Na SiF ) or fluorosilicic acid 2 6 (H SiF ) where water fluoridation is practiced (Anon, 1971; Sawyer and McCarty, 1967; and Gunther and 2 6 Gray, 1988). In 1987, 53.7% of Alberta's population received fluoridated water amounting to 186 X 106 m3 of water with a mean fluoride level of 1.03 mg/L (Anon, 1985). In 1985, only 11.1% of British Columbia's population received fluoridated water. The fluoride content of natural water supplies in Canada varies between 0.01 and 4.5 mg/L. Ground water infiltration is suspected of being the major source of fluoride in surface water with high fluoride concentrations (Anon, 1980). Since some natural supplies exceed the fluoride drinking water objective of 1.0 mg/L, they need to be treated to remove excess fluoride. Other supplies are below the objective and need to have fluoride added since too little has detrimental effects on teeth. As of 1985 there were 22 communities in British Columbia where fluoridation of the drinking water was carried out. These were all smaller communities with a total population of about 330 000. The start dates of these water treatments ranged from 1955 to 1975. The raw water supplies in these communities, before fluoridation, had natural fluoride levels ranging from 0.01 to 0.95 mg/L. Fluoride was added as NaF, H SiF or Na SiF . With never more than 13% of the provinces' population drinking fluoridated 2 6 2 6 water, British Columbia has traditionally had the lowest percentage of any provincial population in Canada being served by fluoridated water supplies. The two largest population centres in British Columbia, Greater Victoria and Greater Vancouver, do not fluoridate their water. They draw water from large watershed reserves and the water is virtually all recent rainfall or snowmelt and low in fluoride. Fluoridation would likely decrease dental caries in children living in these communities. Studies done in several cities where fluoridation occurs have shown the expected 60% reduction in tooth decay. A comparison of 13-year-old students in British Columbia, exclusive of those in Victoria and Vancouver areas, showed a significant decrease in the dental caries index of up to 19% in students living in communities with fluoridated water as opposed to those in communities which did not practice fluoridation. This difference showed up in spite of the complexities, described in the next paragraph, which were not accounted for in a study designed for other purposes. If a study was designed specifically to determine the effects of water fluoridation and these variables were controlled, one would expect to see a better percentage improvement. Much of the population uses fluoride toothpastes, fluoride rinses, fluoride supplements and topical fluoride applications. Few students were born and remained in either a fluoridated or non-fluoridated community; mobility is quite high, estimated at around 50% for 13-year-old students. Thus 13-year-old students may well have been brought up in a different community than that in which they were tested. Even communities classified as fluoridated had children in their schools who came from outlying areas not under fluoridation. The differences are smaller in younger children and become more pronounced with age as cumulative effects begin to appear (Gunther and Gray, 1988; and Gray and Gunther, 1987). Effects The effects of excessive fluoride have been covered in Chapter 3 and can be found in more detail in the review articles referenced in Chapter 1. High dental caries levels may occur if fluoride levels are below 0.5 mg/L (Anon, 1982). Small amounts of fluoride reduce dental caries, especially in children, while excessive levels cause mottling of teeth (McNeely et al., 1979; Anon, 1982; Anon, 1983; and Anon, 1986). Dental fluorosis is not considered an adverse health effect, but due to cosmetic effects, fluoride should not be allowed to rise above 2.4 to 4.0 mg/L (Anon, 1958). Water with less than 0.9 to 1.0 mg/L fluoride will seldom cause mottled tooth enamel in children, and there is abundant literature to show the advantages of maintaining a fluoride level of 0.8 to 1.5 mg/L. In adults, less than 3.0 to 4.0 mg/L will not cause endemic cumulative skeletal effects (McKee and Wolf, 1963; McClure et al., 1945; and McClure and Kinser, 1944); fluorides up to 5.0 mg/L cause no effects except mottling of tooth enamel (Smith and Cox, 1952; Heyroth, 1952; and Hillboe and Ast, 1951).