Ambient Water Quality Criteria for Fluoride

Water Quality

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 (McNeely et al. , 1979; Anon, 1980; and Anon, 1977). The main minerals are fluorspar-CaF₂, Cryolite-Na₃AlF₆ and fluorapatite-Ca₁₀F₂(PO4)₆ (McNeely et al., 1979; Anon, 1971; Weber, 1966; and Dave, 1984). Fluorapatite is a complex mineral and has several different formulae given in the literature. Topaz-Al₂SiO₄(F, OH) is also a fluoride mineral (Norrish, 1975). Fluoride in soils ranges from 76 mg fluoride/kg 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, Na₂SiF₆ or H₂SiF₆, to their water supply (Gunther and 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.


	Water Quality 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 (McNeely et al. , 1979; Anon, 1980; and Anon, 1977). The main minerals are fluorspar-CaF₂, Cryolite-Na₃AlF₆ and fluorapatite-Ca₁₀F₂(PO4)₆ (McNeely et al., 1979; Anon, 1971; Weber, 1966; and Dave, 1984). Fluorapatite is a complex mineral and has several different formulae given in the literature. Topaz-Al₂SiO₄(F, OH) is also a fluoride mineral (Norrish, 1975). Fluoride in soils ranges from 76 mg fluoride/kg 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, Na₂SiF₆ or H₂SiF₆, to their water supply (Gunther and 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.