Environmental Life Cycle Costing - Chapter 10 pptx

123 CHAPTER 10 Environmental Fluoride 10.1 INTRODUCTION 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. Although fluoride is not listed as one of the “Criteria Air Pollutants” regulated by the EPA, it is nevertheless a very important gaseous air pollutant. Indeed, fluoride (F) is the most phytotoxic air pollutant because it can damage plants at extremely low concentrations. Furthermore, adverse effects of F are not limited to airborne F; waterborne F at high levels is also injurious to both human and animal health. For example, in China and India millions of people are suffering from dental and skeletal fluorosis, an abnormal or poisoned condition caused by F. 10.2 OCCURRENCE AND FORMS OF FLUORIDE Fluoride is ubiquitous: it occurs in minerals and soils, air, natural waters, and foods. The F content in rocks is about 0.06 to 0.09% (by weight). The most important F-containing minerals and soils are fluorspar or fluorite (CaF 2 ), cryolite (Na 3 AlF 6 ), and fluorapatite (Ca 10 F 2 (PO 4 ) 6 ). The air in U.S. residential and/or rural communities contains less than 0.04 to 1.2 ppb (0.03 to 0.90 mg F/m 3 ). Fluoride content in natural waters in the U.S. ranges from 0.02 to 0.2 ppm. In 1969, there were 2630 commu- nities in the United States with a drinking water supply with a natural F concentration of 0.7 ppm or more (Figure 10.1). 1 River waters contain 0.0 to 6.5 ppm, with an average of 0.2 ppm. Ground waters contain from 0.1 to 8.7 ppm, depending on the rocks from which the waters flow. The F level in seawater is about 1.4 ppm. Virtually all foods contain trace amounts of F. Fluoride-containing foods and beverages are, therefore, the most important sources of F. The adult intake of F from LA4154/frame/C10 Page 123 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC 124 ENVIRONMENTAL TOXICOLOGY foods in the U.S. is about 0.2 to 0.3 mg per day. The intake from drinking water ranges from 0.1 to 0.5 mg in nonfluoridated communities, while in fluoridated communities the intake may amount to 1 to 2 mg/day. The F contents in plants vary with plant species. Most plants contain 0.1 to 10 ppm F (dry basis), but several species are known as F accumulators. For instance, tea leaves may contain as high as 760 ppm F (dry basis). Tea beverage, however, may contain less than 0.5 mg F per cup. The F contents of some foods are shown in Table 10.1. 10.3 SOURCES OF ENVIRONMENTAL FLUORIDE Natural sources of waterborne F include volcanism, aerosols from ocean spray, soil dust blown into the atmosphere, and others. Fluoride emitted into the atmosphere from volcanoes, industries, and other sources is in both gaseous and particulate forms. These sources also contribute F to surface waters. Natural waters in some parts of the world contain high levels of F (from several ppm to more than 20 ppm). Anthropogenic sources of F emission include a variety of industries, such as primary aluminum production, phosphate fertilizer and elemental phosphorus plants, primary iron and steel production, the ceramic industry (tile, brick, glass works, etc.), and others. In addition, fuel combustion (F in coal: 0.001 to 0.048% in US; average, 0.008%) and solid waste incineration also result in F emission. The forms of F emitted from industrial processes include hydrogen fluoride (HF), fluorspar, cryolite, and silicon tetrafluoride (SiF 4 ). In addition to deposition into surface waters, airborne Figure 10.1 Distribution of communities in the United States with 0.7 ppm or more natural fluoride in community water supply. (Adapted from National Academy of Sci- ences/National Research Council, Effects of Fluorides in Animals, NAS Subcom- mittee on Fluorosis, Washington, DC, 1974.) LA4154/frame/C10 Page 124 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC ENVIRONMENTAL FLUORIDE 125 F may eventually be deposited onto the ground and taken up by soils, plants, and animals (Figure 10.2). 10.4 INDUSTRIAL SOURCES OF FLUORIDE IN THE ENVIRONMENT Several representative industrial sources of F contributing to environment fluo- ride are discussed here. 10.4.1 Manufacture of Phosphate Fertilizers The starting material for manufacture of normal superphosphate fertilizer is phosphate rock composed mainly of fluorapatite. In this process, fluorapatite reacts with H 2 SO 4 and water, producing CaH 4 (PO 4 ) 2 . The overall chemical reaction for the manufacture is shown in Equation 10.1. Since the F content of the ore is approxi- mately 3%, a substantial quantity of HF is produced. HF reacts with SiO 2 in the fluorapatite to form SiF 4 (gas), as shown in Equation 10.2. Ca 10 F 2 (PO 4 ) 6 + 7H 2 SO 4 + 3H 2 O → 3CaH 4 (PO 4 ) 2 · H 2 O + 7CaSO 4 + 2HF (10.1) SiO 2 + 4HF → SiF 4 + 2H 2 O (10.2) (gas) In the wet scrubber, SiF 4 readily reacts with water, forming fluorosilicic acid: SiF 4 e + H 2 O → H 2 SiF 6 (10.3) Table 10.1 Fluoride Content of Selected Foods (ppm on dry basis) Milk 0.04–0.55 Meats 0.01–7.7 Fish 0.10–24 Cheese 0.13–1.62 Butter 0.4–1.50 Rice and peas 10 Cereal and cereal products 0.10–0.20 Vegetables and tubers 0.10–2.05 Citrus fruits 0.04–0.36 Sugar 0.10–0.32 Coffee 0.2–1.6 Tea infusion 0.1–2.0 Instant (solution) 0.2 Adapted from National Academy of Sci- ences/National Research Council, Committee on Biologic Effects of Atmospheric Pollutants, Fluorides, Washington DC, 1971. LA4154/frame/C10 Page 125 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC 126 ENVIRONMENTAL TOXICOLOGY Figure 10.2 Environmental transfer of fluoride. (Adapted from National Academ y of Sciences/National Research Council, Committee on Biologic Effects of Atmospheric Pollutants, Fluorides, Washington DC, 1971.) LA4154/frame/C10 Page 126 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC ENVIRONMENTAL FLUORIDE 127 10.4.2 Manufacture of Aluminum Manufacture of aluminum is almost exclusively by the Hall–Herouet process, in which alumina (Al 2 O 3 ) is dissolved in molten cryolite and reduced electrolytically. The electrolytic cell contains a carbon lining, serving as both the cathode and the container for the melt. Equation 10.4 shows the chemical reaction: (10.4) As seen in the equation, CO and CO 2 are the two gases emitted in the process; it shows no emission of any F-containing substances. In actuality, however, a number of those substances are emitted. The reason for this apparent discrepancy is that various catalysts, including CaF 2 , AlF 3 , and cryolite, are used in the electrolysis of alumina, and as they are heated to high temperatures, some will escape from the cells and are emitted into the surrounding atmosphere. In addition to CO and CO 2 shown in Equation 10.4, several other gases such as SO 2 , SiF 4 , HF, COS, CS 2 , He, and water vapor, are also emitted from the electrolysis cells. A large number of particulates are also emitted. Examples of the particulates include Al 2 O 3 , carbon, cryolite, AlF 3 , CaF 2 , Fe 2 O 3 , and chiolite (Na 5 Al 3 F 14 ). 10.4.3 Manufacture of Steel In the process of manufacturing steel, CaF 2 is used as a flux (a substance used to promote fusion) in an open-hearth oven to increase the fluidity of the slags and enhance the removal of impurities, such as phosphorus and sulfur, from the melts. Fluoride compounds emitted from this operation include HF and CaF 2 . 10.5 EFFECTS ON PLANTS 10.5.1 Toxicological Effects Hydrogen fluoride is the most phytotoxic air pollutant. It can cause injury to susceptible plants at concentrations below 1 ppb (0.8 µ g/m 3 ) for exposure periods of 7 days or fewer. 2,3 Fluoride-induced effects in plants may be considered on four levels of biologic organization: cellular, tissue or organ, organism, and ecosystem (Table 10.2). 4 Fluoride accumulates in plant leaves mainly as a result of diffusion through the stomata from the atmosphere or through absorption from the soil by the roots. In contrast to other major air pollutants, such as SO 2 , NO 2 , and O 3 discussed in Chapter 8, F accumulates in the foliage of plants, which serves as a vehicle for its transfer to herbivores with the potential for inducing dental and skeletal fluorosis. Fluoride induces both structural and functional changes in plant cells. Changes occur in cellular and subcellular membranes with subsequent injuries. Although plants differ widely in their susceptibility to F injury, accumulation of high levels of F in leaves normally leads to chlorosis and necrosis. Chlorosis is associated with Al O C Catalysts Al CO CO 23 2 22+ →++ LA4154/frame/C10 Page 127 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC 128 ENVIRONMENTAL TOXICOLOGY lowered chlorophyll content in the leaf and thus leads to lowered photosynthesis. Similarly, the destruction of part of the leaf resulting from necrosis will cause a comparable reduction in photosynthesis. Both chlorosis and necrosis lead to reduced growth and yield. Tree death could result when the injuries are severe (Figure 10.3A). Unlike NO 2 or SO 2 , F accumulation occurs in the leaf tips and margins of many plant species (Figures 10.3B and C). In germinating mung bean seedlings exposed to varying concentrations of NaF, a concentration-dependent growth inhibition was observed (Figure 10.4). During the past several decades, numerous field and laboratory studies have been conducted on the phytotoxicity of F throughout the world. An interesting case study is presented here to serve as an example. In 1979 researchers in Taiwan observed a previously unknown foliage disease on rice plants grown in northern Taiwan. Leaves of the plants grown in an area adjacent to ceramic and brick industrial facilities manifested acute symptoms of chlorosis and tip necrosis. Studies done in 1983 showed that ambient F concentration in the area ranged from 0.4 to 15 µ g/kg (average, 4.5 µ g/kg). Analyses of leaf F content in rice leaves grown in the area revealed marked increases with the increasing severity of the leaf injuries. The severely injured leaves contained 80 times as much F as the healthy leaves. Subse- quent laboratory experiments involving fumigation of rice seedlings with HF showed leaf symptoms similar to those observed in the field. These results suggested to the researchers that F emitted from the ceramic and brick factories was the cause of the new rice disease. 5 10.5.2 Biochemical Effect Fluoride is widely known as a metabolic inhibitor. As such, F affects many biological processes including glycolysis, Krebs cycle reactions, photosynthesis, 6 protein synthesis, lipid metabolism, and others. Much of the action of F on these processes can be attributed to F-dependent inhibition of enzymes. Enzymes that are Table 10.2 Nature of Fluoride-Induced Effects in Plants at Four Levels of Biologic Organization Cellular Tissue Organism Ecosystem Effects on enzymes and metabolites Decreased assimilation Altered respiration Increased F in ecosystem Modification of cell organelles and metabolism Altered growth and development Modified growth Increased F burden of animals Pathway disruption Chlorotic lesions Reduced reproduction Fluorosis in animals Cellular modification Necrotic lesions Decreased fitness for environment Disruption and death of cell Death or abscission of leaf Death of plants Desolation Adapted from National Academy of Sciences/National Research Council, Committee on Biologic Effects of Atmospheric Pollutants, Fluorides, Washington DC, 1971. LA4154/frame/C10 Page 128 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC ENVIRONMENTAL FLUORIDE 129 inhibited include enolase, phosphoglucomutase, phosphatase, hexokinase, PEP car- boxylase, pyruvate kinase, succinic dehydrogenase, malic dehydrogenase, pyrophos- phatase, phytase, nitrate reductase, mitochondrial ATPase, and urease. 7 In germinat- ing mung bean seedlings exposed to NaF at 1 m M and above, inhibition of lipase, 8 amylase (Table 10.3), 9 and invertase 10 activities in vivo has been observed. Fluoride- induced inhibition of amylase and invertase appears to involve the removal of cofactor Ca 2+ by F – . Seedlings exposed to 1 m M NaF inhibited [2- 14 C]thymidine incorporation into DNA. The inhibition suggests concomitant changes in protein synthesis. 11 Inhibition of enzymes such as these is often reflected by compositional changes in plant tissue. For instance, soybean leaves exposed to 30 ppb HF exhibited lowered sucrose content, while the levels of both glucose and fructose were elevated. 12 In addition, marked increases in organic acids, such as malic, malonic, succinic, and citric acids, occurred. 12 The inhibition of amylase 9 and invertase 10 in the germinating mung bean seedling exposed to NaF, mentioned above, is often accompanied by an increase in sucrose levels in the root. Figure 10.3 (Left) An injured fir tree growing in an area adjacent to an aluminum manufac- turing plant. Analysis of needles from adjacent trees showed F levels at approx- imately 500 ppm, on dry wt basis. (Top) Pear leaves with tip and marginal necrosis. (Bottom) Gladiolus leaves with tip necrosis. LA4154/frame/C10 Page 129 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC 130 ENVIRONMENTAL TOXICOLOGY While it is clear that the action of F on plant metabolism is complex and involves a variety of enzymes, the mode of action of fluoride ion on these enzymes is not so clear. The principal mechanisms that have been suggested earlier include: (a) for- mation of complex with metalloenzymes; (b) removal of a metal cofactor such as Ca or Mg from an enzyme system; and (c) binding to the free enzyme or to the enzyme substrate complex. 7 Using a model system Edwards et al. 13 showed that F could disrupt the hydrogen bonding of protein molecules. Because hydrogen bonding is important in the maintenance of the tertiary structure of protein molecules, dis- ruption of an enzyme protein by F would lead to enzyme inhibition. As shown in Chapter 5, SOD is an important antioxidant enzyme. Field and laboratory studies have shown that SOD activities in different plant tissues exposed to F were either enhanced or lowered. For instance, mung bean seedlings exposed to 0.2 m M NaF showed increased SOD activity, whereas exposure to 1 m M NaF and above resulted in depressed SOD activity. 14 10.6 EFFECTS ON ANIMALS Animals normally ingest small amounts of F in their rations without observable adverse effects, but excessive intake can be detrimental. Fluoride intake increases Figure 10.4 Effect of NaF on mung bean germination. Seedlings were exposed to 0 (control), 0.1, 1.0, and 5.0 m M NaF for 24, 48, and 72 h, respectively. (Yu, M H., unpub- lished data, 2000.) Table 10.3 Effects of NaF on α -Amylase from Mung Bean Cotyledon Specific Activity (nmol/mg/min) NaF, m M 48 h Percent of Control 72 h Percent of Control 0.0 13.1 — 27.8 — 0.1 14.6 111 24.4 88 1.0 11.3 86 24.2 87 5.0 8.3 63 22.2 80            'XUDWLRQRI7UHDWPHQWK 5DGLFOHOHQJWKPP &RQWURO P0 P0 P0 LA4154/frame/C10 Page 130 Friday, May 19, 2000 9:51 AM © 2001 by CRC Press LLC ENVIRONMENTAL FLUORIDE 131 when animals ingest vegetation or hay contaminated by elevated levels of airborne F. The effect of F on domestic animals may be acute or chronic, depending on F concentrations. 10.6.1 Acute Effects Fluoride and arsenic have caused detrimental effects on livestock in the U.S. and other industrialized countries. The sources of F pollution are limited mostly to phosphate-fertilizer manufacturing, aluminum production, fluorohydrocarbon, and heavy metal production. Safe levels of soluble F in animal rations range from 30 to 50 mg/kg for cattle and from 70 to 100 mg/kg for sheep and swine. Such physio- logical effects as gastroenteritis, muscular weakness, pulmonary congestion, nausea, vomiting, diarrhea, chronic convulsions, necrosis of the mucosa of the digestive tract, anorexia, cramping, collapse, and respiratory and cardiac failure may occur, followed by death. 10.6.2 Chronic Effects The two most conspicuous and thoroughly studied manifestations of chronic F poisoning are dental and skeletal fluorosis. Once absorbed into the animal body, F has a great affinity for developing and mineralizing teeth. Such affinity of fluorides can either enhance tooth development or induce dental lesions, depending on the amount of fluorides ingested. Dental lesions are manifested by abnormal enamel matrix, such as in chalkiness, mottling, and hypoplasia (a thin enamel). An affected tooth is also subject to more rapid wear and to erosion of the enamel away from the dentin. It is noteworthy that dental lesions will not be seen in animals brought into endemic fluorosis areas after their permanent teeth have erupted. 15 Recent studies indicate a widespread chronic effect of environmental fluoride on wildlife. Fluoride contamination of vegetation has arisen from various industrial activities and the combustion of coal. Studies done by European scientists indicate a large number of deer in various European countries suffer from both dental and skeletal fluorosis. 16,17 Improvement has been made in controlling F emission in the past three decades. Comparative field studies show that F contamination of vegetation in recent years has decreased significantly, with concomitant decreases in F levels in dental and skeletal samples from wild animals. Studies on deer populations affected by F are relatively limited in the United States. Perhaps there is little active research in this area because atmospheric F pollution is not considered a serious environmental pollution problem in the U.S. Nevertheless, one study has indicated the impact of airborne F on wildlife. Figures 10.4A and B show a comparison between marked dental disfigurement and the abnormal tooth wear pattern of a female black-tailed deer (deer A) (Figure 10.4A) and the normal tooth wear pattern of another deer (deer B) (Figure 10.4B). Deer A was killed on a road near an aluminum manufacturing plant, whereas deer B was killed on a road in an area with no industrial facilities. Analysis of the F content in bone samples from these two animals showed that the F levels of the bone from deer A were 15 to 20 times higher than those of the bone from deer B. 18 LA4154/frame/C10 Page 131 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC 132 ENVIRONMENTAL TOXICOLOGY In addition to inducing tooth mottling, F can also cause skeletal fluorosis. In this case, the affected bones lose their normal, hard, smooth luster and appear rough, porous, and chalky white. A generalized hyperostosis (excessive formation of bone tissue, especially in the skull) and, in some cases, exostotic lesions of the otherwise smooth, long bones may be observed ( Note: Exostosis is a spur or bony outgrowth from a bone.) Lameness or stiffness is an intermittent sign of F toxicity. The clinical basis for the lameness is not well understood. Appetite is normally impaired, and this may result in decreased weight gain, cachexia, and lower milk yield. Decline in milk production may be secondary to appetite impairment or other responses. Evidence that animals may be suffering chronic F effect may be obtained from chemical analysis of the feed and elevated levels of F in urine and body tissues. 19 Other effects include increased susceptibility to other environmental stresses and decrease in longevity. A number of factors influence the manifestation of dental and skeletal fluorosis. For example, the amount and the bioavailability of F ingested; duration of ingestion; species of animals involved (Table 10.4); age at time of excessive F ingestion; nutritional and general health status of animals; mode of F exposure (e.g., contin- uous or intermittent); presence of synergistic or antagonistic substances; presence of other stress factors, such as those caused by poor management; and individual biologic response. Fluoride inhibits the metabolism of carbohydrates, lipids, and proteins. In ani- mals and humans, a large number of enzymes are depressed by F, including enolase, adenylcyclase, lipase, and cholinesterase. Inhibition of glycolysis, due in part to decreased enolase activity, may be responsible for the hyperglycemia observed in experimental animals. Several nutrients, such as proteins, Ca, and vitamin C, influ- ence the severity of F toxicity. The adverse effect of F is often alleviated by these nutrients. For example, both vitamin C and Ca have been shown to decrease the toxicity in guinea pigs. 20 Protein nutrition is also important in affecting F accumu- lation in experimental animals. Mice fed a low-protein (4%) diet deposited 500% more F in tibia than did control animals fed a regular diet containing 27% protein. Furthermore, supplemental vitamin C greatly lowered F deposition in the bone. 21 It Table 10.4 Fluoride Tolerances (in ppm) in Livestock Diets Breeding or Lactating Animals Finishing Animals Dairy and beef heifers 30 100 Dairy cows 30 100 Beef cows 40 100 Sheep 50 160 Horses 60 — Swine 70 — Turkeys — 100 Chickens 150 — Adapted from National Academy of Sciences/National Research Council, Committee on Biologic Effects of Atmospheric Pollutants, Fluorides, Washington DC, 1971. LA4154/frame/C10 Page 132 Friday, May 19, 2000 9:27 AM © 2001 by CRC Press LLC [...]... Press LLC LA4154/frame/C10 Page 134 Friday, May 19, 2000 9:27 AM 134 Figure 10. 5 ENVIRONMENTAL TOXICOLOGY (A) Dental disfigurement and abnormal tooth wear patterns in a black-tailed deer killed in an area adjacent to an aluminum plant (Female, ca 1.5 yr old.) (B) Normal tooth wear patterns of a black-tailed deer killed in an area with no industrial facilities (Male, ca 2.5 yr old.) 10. 7.4 Chronic Effects... 20, 1999 © 2001 by CRC Press LLC LA4154/frame/C10 Page 137 Friday, May 19, 2000 9:27 AM ENVIRONMENTAL FLUORIDE 137 23 Yu, M.H and Tsunoda, H., Environmental fluoride problems in China, Fluoride, 21, 163, 1988 10. 9 REVIEW QUESTIONS 1 2 3 4 5 6 7 8 9 10 11 12 Why is fluoride the most phytotoxic among the major air pollutants? What are the most important F-containing minerals? List three industrial operations...LA4154/frame/C10 Page 133 Friday, May 19, 2000 9:27 AM ENVIRONMENTAL FLUORIDE 133 should be mentioned that mice produce vitamin C as well The effect of fluoride on a number of enzymes is markedly influenced by the nutritional status of the exposed animals For instance, da Motta et al.22 studied the effects of subtoxic dose of a NaF (10 mg F/kg body weight) on the activities of glucose-6-phosphate dehydrogenase... Chronic Effects Fluoride accumulates in the skeleton during prolonged, high-level exposures Radiological evidence of hypermineralization (osteofluorosis) is shown when bone © 2001 by CRC Press LLC LA4154/frame/C10 Page 135 Friday, May 19, 2000 9:27 AM ENVIRONMENTAL FLUORIDE 135 concentrations reach about 5000 ppm F.19 Coupled with other environmental factors, such as nutrition and health status, patients... to 0.55 ppm) The amount of F inhaled from air is about 0.05 mg/day 10. 7.2 Absorption Absorption of F from the gastrointestinal tract occurs through a passive process; it does not involve active transport Absorption is rapid and probably occurs in the lumen The rate of absorption depends on the F-compounds involved, e.g., NaF, 97%; Ca10F2(PO4)6, 87%; Na3AlF6, 77%; and CaF2, 62% About 50% of the absorbed... functions, and cholinesterase activity Inhibitory effects of F in many reactions involving Ca are generally considered to be due to CaF2 formation, as depicted below: [Protein-Ca] ↔ Protein + Ca2+ (10. 5) Ca2+ + F– ↔ [CaF]+ + F– ↔ CaF2 (10. 6) Fluoride also mediates enzyme systems requiring Mg, or in reactions involving phosphorus In this case, it is suggested that F forms a magnesium–fluorophosphate complex... human tissues Inhibition of one or more of these enzymes may allow more free radical-induced reactions to occur, leading to cellular and tissue damage As noted earlier, a number of researchers have used antioxidants, such as vitamins E and C, β-carotene, and GSH, to ameliorate injuries induced by excessive levels of F 10. 8 REFERENCES AND SUGGESTED READINGS 1 National Academy of Sciences/National Research... 17 Vikoren, T., Stuve, G., and Froslie, A., Fluoride exposure in cervids inhabiting areas adjacent to aluminum smelters in Norway 1 Residue levels, J Wildlife Dis., 32, 169, 1996 18 Newman, J.R and Yu, M.H., Fluorosis in black-tailed deer, J Wildlife Dis., 12, 39, 1976 19 Parker, C.M., Sharma, R.P., and Shupe, J.L., The interaction of dietary vitamin C, protein, and calcium with fluoride: effects in... weight) on the activities of glucose-6-phosphate dehydrogenase (G6PD) in the submandibular glands of fed and overnight-fasted rats and observed that the enzyme activities in the fasted animals were significantly decreased, but the fed animals did not manifest the decreases 10. 7 EFFECTS ON HUMANS 10. 7.1 Daily Intake Daily intake of F from food is about 0.2 to 0.3 mg; from water 0.1 to 0.5 mg (1 to 2 mg if water... Weinstein, L.H., Effects of hydrogen fluoride on incorporation and transport of photoassimilates in soybean, Environ Toxicol Chem., 6, 627, 1987 © 2001 by CRC Press LLC LA4154/frame/C10 Page 136 Friday, May 19, 2000 9:27 AM 136 ENVIRONMENTAL TOXICOLOGY 4 National Academy of Sciences/National Research Council, Committee on Biologic Effects of Atmospheric Pollutants, Fluorides, Washington DC, 1971, 295 5 . 0.04–0.55 Meats 0.01–7.7 Fish 0 .10 24 Cheese 0.13–1.62 Butter 0.4–1.50 Rice and peas 10 Cereal and cereal products 0 .10 0.20 Vegetables and tubers 0 .10 2.05 Citrus fruits 0.04–0.36 Sugar 0 .10 0.32 Coffee 0.2–1.6 Tea. and animals (Figure 10. 2). 10. 4 INDUSTRIAL SOURCES OF FLUORIDE IN THE ENVIRONMENT Several representative industrial sources of F contributing to environment fluo- ride are discussed here. 10. 4.1 Manufacture. 123 CHAPTER 10 Environmental Fluoride 10. 1 INTRODUCTION Fluorine is the lightest element in Group VII of the periodic