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Annual Conference on Trace Substances in Environmental Health, June 23-25, 1970, D. D. Hemphill (ed). University of Missouri, Columbia. pp. 186-193. Mitchell, R. L., J. W. S. Reith, and I. M. Johnston. 1957. Trace- element uptake in relation to soil content. J. Sci. Food Apic. 8:51-59. Money, D. F. L. 1970. Vitamin E and selenium deficiencies and their possible aetiological role in the sudden death infants syn- drome. New Zealand Meet. J. 71 :32-34. Parker, R. L. 1967. Composition of the earth's crust. In Data of geo- chemistry, M. Fleischer (ed). U.S. Geol. Surv. Prof. Pap. No. 440.D. U.S. Government Printing Office, Washington, D.C. pp. 1-19. Pope, A. L. 1971. A review of recent mineral research with sheep. J. Anirn. Sci. 33:1332-1343. Pratt, P. F., and F. L. Blair. 1964. Depletion and accumulation of trace elements in irrigated soils. Agric. Olem. 19:39. Price, N. 0 ., W. M. Linkous, and R. W. Engel. 1955. Minor element content of forage plants and soils. Apic. Food Chern. 3:226-229. Raymond, W. F., and C. R. W. Spedding. 1966. Paper in Nitrogen and grassland, P. F. J. VanBurg and G. H. Arnold (eds). Proceedings of the First General European Meeting of the European Grass- land Federation, Wagerungen. Centre for Apicultural Publica- tions and Documentation, Wageningen, Netherlands. pp. 151- 160. Reid, R. L., G. A Jung, R. Weiss, A. J. Post, F . P. Hom, E. B. Kahle, and C. E. Carlson. 1969. Performance of ewes on nitrogen- fertilized orchardgrass putures. J. Anirn. Sci. 29:181-182. Rhode, G. 1962. The effects of trace elements on the exhaustion of sewage-irrigated land. J. lost. Sewage Purif. (Pt. 6):581-585. Robinson, W. 0., and G. Edgington. 1945. Minor elements in plants and some accumulator plants. Soil Sci. 60:15-28. Overview 21 Robinson, W. 0., and G. Edgington. 1946. Fluorine in soils. Soil Sci. 61(5):341-353. Schafer, K., and H. Kick. 1970. Die Nachwirkung von Schwermet- allhaltigen Abwasser-Klarschlamm in einem Feldversuch. Land- wirtsch. Forsch. 23:152-161. Schneider, B. H., K. C. Beeson, and H. L. Lucas. 1953. Composi- tion of com in the United States: A report of the Apicultural Board. Nat. Acad. Sci. Publ. No. 258. National Academy of Sciences, Washington, D.C. 26 pp. Schwarz, K., and D. B. Milne. 1972. Fluorine requirement for growth in the rat. Bioinorg. Olem. I :331-338. Swaine, D. J. 1955. The trace element content of soils. Commonw. Bur. Soil Sci. Tech. Commun. No. 48. Herald Printing Works, York, England. 167 pp. Swaine, D. J. 1962. The trace-element content of fertilizers. Commonw. Apic. Bur. Tech. Commun. No. 52. FAO and Commonwealth Apicultural Bureaux, Farnham Royal, Bucks, England. Turelcian, K. K., and K. H. Wedepohl. 1961. Distribution of the elements in some major units of the earth's crust. Geol. Soc. Am. Bull. 72:175-191. Underwood, E. J. 1966. The mineral nutrition of livestock. FAO and Commonwealth Apicultural Bureaux, Farnham Royal, Bucks, England. Underwood, E. J. 1971. Trace elements in human and animal nu- trition (3rd ed.). Academic Press, New York. 543 pp. U.S. Geological Survey. 1972. Southwest energy study, Coal Re- sources Working Group. Appendix J, U.S. Geol. Surv. Open- File Rept. U.S. Geological Survey, Denver, Colo. Wedepohl, K. H. 1970. Geochemical data on sedimentary carbon- ates and carbonate rocks and their facies and petrogenic evaluation. Verb. Geol. Bundesanst. 4:692-705. (In German.) Chern. Abstr. 75(7):71(1971).
II Fluorine MICHAEL FLEISCHER, Chairman Richard M. Forbes, Robert C. Harriss, Lennart Krook, Joe Kubota The major known role of fluorine in health is the beneficial effect of its compound-fluoride-on the incidence of den- tal caries in children. Preliminary studies indicate that fluo- rine may be an essential element for animal growth (Schwarz, 1971; Schwarz and Milne, 1972; Messer et al., 1972). High levels of dietary fluoride cause fluorosis (bone disease) and mottling of teeth. CHARACTERISTIC GEOCHEMISTRY AND SOURCES Fluorine, a relatively abundant element of the earth's crust (average content 650 ppm; Committee on Biologic Effects of Atmospheric Pollutants, 1971; Fleischer and Robinson, 1963), is concentrated in silicic igneous rocks (about 750 ppm), shales and oceanic sediments (700-800 ppm), and in volcanic ash and bentonites (750 ppm). Phosphorites are of special interest because they contain 3-3.5 percent fluorine, which is retained in superphosphate fertilizer. Fluorine is emitted into the atmosphere in volcanic and fumarolic gases and from hot springs associated with volcanism. Fluorine is the lightest element in Group VII of the periodic table, with atomic number 9 and an atomic weight of 18.998. It has a single isotope and its valence in all naturally occurring compounds is 1-. The fluoride ion has the radius 1.36 A and is therefore isomorphous with the hydroxyl ion (OHr in many silicate and phos- 22 phate minerals. (The radius of the hydroxyl ion is 1.40 A.) Fluoride occurs mainly in silicate minerals. Fluorine is concentrated in the last stages of crystallizing magmas and in the residual solutions and vapors; hence, its con- centration is increased in highly siliceous igneous rocks, alkalic rocks, and hydrothermal solutions. Table 7 sum- marizes the fluoride contents of igneous and sedimentary rocks. Groundwaters (Figure 2) may average as much as 8 ppm of fluoride (Table 8); surface water generally contains less, but fluoride levels tend to increase in dry seasons. Closed basins in areas of high evaporation, such as Great Salt Lake, accumulate up to 14 ppm of fluoride; groundwater from the Willcox Basin, Arizona, has been reported to contain 106,000 ppm dissolved solids and 282 ppm fluoride (Kister et al., 1966). Seawater contains about 1.2 ppm. Most of the fluoride that reaches the ocean precipitates in the oceanic sediments. Lakes in East Africa formed by leaching of alkalic rocks contain 1,000-1,600 ppm fluoride. Fluoride contents of natural waters are listed in Table 8. Calculation shows that the concentration listed for seawater represents only 0.35 percent of the total amount eroded from the land; i.e., 99.65 percent has precipitated in ma- rine sediments. Volcanic gases are rich in fluorine, mainly as HF, but also as SiF4 , H2 SiF 6 , and F 2 ⢠The ratio of fluorine/chlorine, commonly 2:1 in rocks, is lower in most fumarolic gases and as low as 0.0006 in waters of hot springs, where the fluoride is deposited while the chlorine remains in solution.
TABLE 7 Fluoride Content of Igneous and Sedimentary Rocks Fluoride Content, ppm Rock Type Range Average Igneous Basalts and gabbros 20-1100 400 Silicic rocks, granites 0-2700 750 Alkalic rocks 200-2200 950 Sedimentary limestones and dolomites 0-1210 230 Sandstones 10-880 180 Shales 10-7600 800 Oceanic sediments 100-1600 730 Volcanic ash 10-2900 750 Soils 10-7000 280 Plants can take up fluoride from soil, water, or air. Most plants contain 0.1-10 ppm (dry wt) fluoride; forage plants generally contain 5-10 ppm (dry wt), but the range is much greater-<1-300 ppm. Plant contents are not appreciably affected by soil content except for a few fluoride accumu- lators; tea may contain 760 ppm, elderberry 3,600, and - 1 5 ppm For hâ¢---r fa 1G-1 .⢠ppmF c:Jo~e"""'F ~ o-o .⢠PQmF 0 nodlll Fluorine 23 camellia 620 ppm (all dry weight). The older the tea plant the more fluoride in the leaves. Commercial tea leaves aver- age about 100 ppm (dry wt), about 90 percent of which is extracted by hot water. Another plant of interest is the epiphyte Spanish moss, Tillandasill usneoides L., reported to contain up to 624 ppm (dry wt) fluoride. There is no evidence that fluoride is essential for plant growth. The effects on plants vary greatly from species to TABLE 8 Fluoride in Waters Water Type Seawater Groundwaters from granitic rocks alkalic rocks basaltic rocks limestones and dolomites shales and clays Surface waters rivers lakes 100 200 300 400 500MILES 0 100 200 300 400 600 KILOMETERS Fluoride Content, ppm Range Average 1.2 0.0-9 1.2 0.7-35.1 8.7 0.0-0.5 0.1 0.0-1.7 0.3 0.0-2.8 0.4 0.0-6.5 0.2 up to 1627 FIGURE 2 Fluoride content of groundwater in the conterminous United States, maximum reported value for each county, 1972 (U.S. Geological Survey, 1964 ).
24 THE RELATION OF SELECTED TRACE ELEMENTS TO HEALTH AND DISEASE species and the form in which fluoride occurs. Some plants show foliar lesions at tissue fluoride concentrations of 20- 150 ppm, but more tolerant species may have as much as 4,000 ppm or more without apparent injury. Plants appear to be more sensitive to injurious effects of fluoride from airborne sources than from sources in soil and water. Fluo- ride accumulates preferentially in leaves, with associated necrotic foliar lesions, decrease in chlorophyll, and de- creased growth rates when accumulations are excessive. Studies on distribution of fluoride in man and animals indicate that 99 percent is in bones and teeth. EFFECTS ON HEALTH Experimental evidence for a role for fluorine in the vital biological processes of mammalian systems has been lacking until recently, when preliminary evidence has been pre- sented to indicate that fluorine influences the growth and reproductive capacity of animals (Schwarz, 1971 ; Schwarz and Milne, 1972; Messer et aL, 1972). Fluorine has profound anti-enzyme properties, and the effectiveness of fluoride in prevention of dental caries in children is well established. It must be remembered, how- ever, that fluoride confers protection against caries during the period when tooth enamel is being formed. There is some evidence that fluoride decreases caries by decreasing the rate of conversion of sugars to acids in the oral cavity. Daily dietary intake of fluoride by man ranges from 0.2 to 1 mg. Larger amounts are present in diets rich in fish or fish products; fish protein concentrate contains from 20 to 760 ppm (dry wt) fluoride (Ke et al., 1970) and drinking water generally contains about 1 ppm. Tea drinkers may take in an additional 1 mg daily, on the average. Because an absolute requirement for fluorine in man has not been es- tablished, deficiency effects have been associated only with increased dental caries. High levels of fluoride cause dental lesions, periosteal hy- perostasis, calciflcation of ligaments, and lameness. Crippl- ing fluorosis in humans has been observed in persons ex- posed to very high intake (probably more than 20 mg/day) over periods of several years, such as workers in the cryolite industry (World Health Organization, 1970). Safe levels of soluble fluoride in animal rations range from 30 to 50 mg/kg for cattle and from 70 to 100 mg/kg for sheep and swine. Osteoporosis, a condition of too little bone mass per unit volume, is relatively common in postmenopausal women and in some men. Bone tissue is in constant turnover, continu- ously reabsorbed. Too little bone mass can, obviously, re- sult from either too little formation or too much resorption. The latter mechanism appears to be the decisive one in osteoporosis (Dymling, 1964). When fluoride is available during osteogenesis, the fluoride ion replaces the hydroxyl ion and the resulting fluorapatite [Cas (P04 ) 3 F) is more resistant to resorption than hydroxylapatite (Ca5 (P04 ) 3 OH]. This is presumably the basis for fluoride serving as a prophy- lactic and therapeutic agent in osteoporosis; however, neither the treatment nor the rationale has been accepted by all in the scientific community. Some experiments indicate a progressive bone loss that in some ways resembles human osteopenic conditions (Saville and Krook, 1969). Feeding adult beagles a low cal- cium, high phosphorus diet for about 40 weeks causes a bone-mass loss of about 20 percent in the vertebrae and 12- 15 percent in the long bones (Saville and Krook, 1969; Krook et aL, 1971 ). The synthetic diet, with a fluoride con- tent of less than 1 ppm, was used in an experiment by Hen- rikson et aL ( 1970) to evaluate the influence of added fluo- ride on the progressive bone loss. One group of dogs was fed the basal diet; the diets of four other groups were sup- plemented with sodium fluoride at levels of 1, 3, 9, and 27 ppm. Examination of bones after 42 weeks on the diets in- cluded measurements of specific gravity; ash per cubic centimeter of bone; fluoride, calcium, and phosphorus in ash; radiography and microradiography; 1251 densitometry; and biomechanical testing. The addition of fluoride had no beneficial effects on any of the bone components tested; however, densitometry of the mandible, which is the most probable site of nutritionally induced osteoporosis in ani- mals, showed that the degree of bone loss increased signif- icantly with increasing dietary fluoride. Ash fluoride in- creased in proportion to dietary fluoride and reached 6,000 ppm in vertebrae after 42 weeks at highest levels. A 1-year study of 11 human osteoporotics has shown that a combined treatment of 50 mg of sodium fluoride and 900 mg of calcium per day, and 50,000 IU of vitamin D twice a week, increased new bone formation without pro- ducing biochemical, roentgenographic, or microscopic evidence of fluorosis (Jowsey et al., 1972). POLLUTION Table 9 lists the major sources of fluoride emissions into the atmosphere from industrial sources. These same sources contribute fluoride to surface waters, as do industrial oper- ations such as plating. Combustion of fluorine-bearing plas- tics of the Teflon type releases fluoride into the atmosphere as well as into surface waters. Some heavy discharges of flu- orine into waters have occurred in connection with the phos- phate and aluminum industries. Some fluoride has been traced to runoff from application of insecticides and weed killers. Phosphate mining operations release waste water contain· ing large quantities of fluoride into several watersheds in North Carolina and Florida. Organisms in the streams and estuaries receiving phosphate mining wastes are subjected to continuous exposure of slightly elevated concentrations of fluoride (range of 2-20 mg/1) and occasional large doses (20-1 00 mg/1) as a result of a breakdown in waste-treatment
