ORNL
Oak Ridge
National
Laboratory
Operated by
Union Carbide Corporation for the
Department of Energy
Oak Ridge, Tennessee 37830
ORNL/EIS-85
EPA
United States
Environmental Protection
Agency
Office of Research and Development
Health Effects Research Laboratory
Cincinnati, Ohio 45268
EPA-600/1-78-050
REVIEWS OF THE ENVIRONMENTAL
EFFECTS OF POLLUTANTS:
IX. FLUORIDE
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS RE-
SEARCH series. This series describes projects and studies relating to the toler-
ances of man for unhealthful substances or conditions. This work is generally
assessed from a medical viewpoint, including physiological or psychological
studies. In addition to toxicology and other medical specialities, study areas in-
clude biomedical instrumentation and health research techniques utilizing ani-
mals but always with intended application to human health measures.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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ORNL/EIS-85
EPA-600/1-78-050
REVIEWS OF THE ENVIRONMENTAL EFFECTS OF POLLUTANTS: IX. FLUORIDE
by
John S. Drury, John T. Ensminger, Anna S. Hammons, James W. Holleman,
Eric B. Lewis, Elizabeth L. Preston, Carole R. Shriner, and
Leigh E. Towill
Information Center Complex, Information Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
operated by
Union Carbide Corporation
for the
Department of Energy
Reviewers and Assessment Chapter Authors
James L. Shupe, A. E. Olson, and H. B. Peterson
Utah State University
Logan, Utah
Interagency Agreement No. D5-0403
Project Officer
Jerry F. Stara
Office of Program Operations
Health Effects Research Laboratory
Cincinnati, Ohio 45268
Date Published: September 1980
Prepared for
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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This report was prepared as an account of work sponsored by an agency
of the United States Government. Neither the United States Government nor
any agency thereof, nor any of their employees, contractors, subcontractors,
or their employees, makes any warranty, express or implied, nor assumes any
legal liability or responsibility for any third party's use or the results
of such use of any information, apparatus, product or process disclosed in
this report, nor represents that its use by such third party would not
infringe privately owned rights.
This report has been reviewed by the Health Effects Research Labora-
tory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views
and policies of the U.S. Environmental Protection Agency, nor does mention
of trade names or commercial products constitute endorsement or recommenda-
tion of use.
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CONTENTS
Figures vii
Tables xiii
Foreword xxi
Acknowledgments xxiii
Abstract xxv
1. Summary 1
1.1 Discussion of Findings 1
1.1.1 Chemical and Physical Properties and
Analytical Techniques 1
1.1.2 Environmental Occurrence 2
1.1.3 Environmental Cycling and Fate 3
1.1.4 Biological Aspects in Microorganisms 4
1.1.5 Biological Aspects in Plants 5
1.1.6 Biological Aspects in Animals 6
1.1.7 Biological Aspects in Humans 7
1.1.8 Food Web Interactions 8
1.2 Conclusions 9
2. Chemical and Physical Properties and Analysis 12
2.1 Summary 12
2.2 Physical and Chemical Properties 13
2.2.1 Fluorine 13
2.2.2 Hydrogen Fluoride 16
2.2.3 Fluorspar, Cryolite, and Fluorapatite 20
2.2.4 Alkali Fluorides 23
2.2.5 Silicon Tetrafluoride and Fluorosilicic Acid . . 23
2.2.6 Halogen Fluorides 25
2.2.7 Group VIA Fluorides 27
2.2.8 Organic Fluorides 29
2.2.9 Uranium Hexafluoride 33
2.3 Analysis for Fluoride 35
2.3.1 Sampling and Sample Preparation 35
2.3.2 Separation of Fluoride 39
2.3.3 Methods of Analysis 42
2.3.4 Comparison of Analytical Procedures 49
3. Biological Aspects in Microorganisms 59
3.1 Summary 59
3.2 Metabolism 59
3.2.1 Uptake and Accumulation 60
3.2.2 Biotransformation 66
3.3 Effects 68
3.3.1 Toxic Effects 68
3.3.2 Metabolic Effects 79
3.4 Prospects for Future Research 91
3.4.1 Inorganic Fluorides 91
3.4.2 Organic Fluorocompounds 93
4. Biological Aspects in Plants 106
4.1 Summary 106
4.2 Metabolism 108
4.2.1 Uptake and Absorption 108
iii
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4.2.2 Translocation 113
4.2.3 Cellular Metabolism of Fluoride 114
4.2.4 Distribution 118
4.2.5 Bioelimination 135
4.3 Effects 137
4.3.1 Metabolic Effects 138
4.3.2 Symptoms of Fluoride Accumulation 146
4.3.3 Effects of Fluoride on Growth and
Productivity 152
4.3.4 Cytogenetic Effects 162
5. Biological Aspects in Domestic and Wild Animals 176
5.1 Summary 176
5.2 Insects 177
5.2.1 Metabolism 177
5.2.2 Effects 178
5.3 Aquatic Organisms 185
5.3.1 Metabolism 185
5.3.2 Effects 190
5.4 Birds 195
5.4.1 Metabolism 195
5.4.2 Effects 197
5.5 Domestic and Wild Mammals 201
5.5.1 Metabolism 201
5.5.2 Effects 212
6. Biological Aspects in Humans 242
6.1 Summary 242
6.2 Essentiality of Fluoride 244
6.3 Metabolism 246
6.3.1 Uptake 246
6.3.2 Distribution and Balance 249
6.4 Effects 265
6.4.1 Effects on Enzymes and Cell Systems 265
6.4.2 Fluoride and Teeth 281
6.4.3 Toxicity of Fluorine and Fluorine Compounds . . . 291
6.4.4 Teratogenesis, Mutagenesis, and
Carcinogenesis 320
7. Environmental Distribution and Transformation 349
7.1 Summary 349
7.2 Production and Usage 350
7.3 Distribution of Fluoride in the Environment 350
7.3.1 Sources of Pollution 350
7.3.2 Distribution in Rocks and Soils 360
7.3.3 Distribution in Water 368
7.3.4 Distribution in Air 375
7.4 Environmental Fate 380
7.4.1 Mobility and Persistence in Soils 380
7.4.2 Mobility and Persistence in Water 381
7.4.3 Mobility and Persistence in Air 382
7.5 Waste Management 382
8. Environmental Interactions and Their Consequences 392
8.1 Summary 392
8.2 Environmental Cycling of Fluoride 392
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8.3 Fluoride in Foods 393
8.4 Bioaccumulation in Food Chains 397
Environmental Assessment of Fluoride 406
9.1 Introduction 406
9.2 Properties and Environmental Occurrences 406
9.2.1 Soils 406
9.2.2 Water 407
9.2.3 Air 407
9-3 Environmental Interactions 408
9.3.1 Soils 408
9.3.2 Water 409
9.3.3 Air 409
9.3.4 Industrial Effluents 409
9.3.5 General Biological Aspects 409
9.4 Microorganisms 410
9.5 Vegetation 410
9.5.1 Sources of Fluorides to Vegetation 411
9.5.2 Fluoroorganic Compounds 412
9.5.3 Symptoms and Susceptibility 412
9.5.4 Effects on Vegetation 412
9.6 Domestic and Wild Animals 414
9.6.1 Sources of Fluorides to Animals 414
9.6.2 Fluoride Toxicosis 415
9.6.3 Signs and Lesions 415
9.6.4 Diagnosis 421
9.6.5 Treatment 423
9.6.6 Species Tolerances 423
9.6.7 Prevention of Fluoride Toxicosis 425
9.7 Humans 425
9.8 Research Needs 431
9.8.1 Properties and Environmental Occurrences .... 431
9.8.2 Environmental Interactions 431
9.8.3 Microorganisms 431
9.8.4 Vegetation 432
9.8.5 Domestic and Wild Animals 432
9.8.6 Humans 434
9.9 Conclusions 434
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FIGURES
2.1 Typical wet-impinger collector 36
2.2 Types of dry, cascade impingers 37
2.3 Apparatus for distillation of fluoride 40
2.4 Diffusion apparatus: (a) vaseline seal, (2?) acidified
sample (a) plastic cup, (d) trapping solution, and
(e) lid 41
2.5 Cross sections of typical selective ion electrodes 45
2.6 Potentiometric measuring circuit showing measuring (M)
and reference (R) electrodes and potentiometers 45
3.1 Growth of Pseudomonas sp. on 0.1% p-fluorophenylacetic
acid 60
3.2 Structures of metabolites isolated from medium after
incubation of Pseudomonas sp. with p-fluorophenyl-
acetic acid 66
3.3 Release of F~ ion by a Pseudomonas sp. from racemic
ert/tTiro-fluorocitric acid in two experiments 67
3.4 The effect of the duration of 50 mftf NaF treatment on
production of conidia; initial treatment was to
4-hr-old Neurospora crassa cultures 70
3.5 Oxygen uptake during NaF treatment of Neurospora crassa ... 80
3.6 Effect of fluoride at pH 5.2 on photosynthesis (left)
and on the Hill reaction (right) in Plectonema
boryanwn cell suspensions 81
3.7 Effect of fluoride on an actively synthesizing
polysaccharide system of Streptococcus mitis 84
3.8 Effect of the phosphorylation uncoupler carbonylcyanide-
p-trifluoromethoxy-phenylhydrazone (FCCP) on replica-
tion of RC1 phage in photosynthetically grown cells of
Rhodopseudomonas capsulata Z-l incubated under photo-
synthetic conditions 86
3.9 Effect of NaF treatment on protein, RNA, and DNA
synthesis of Neurospora crassa 87
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4.1 Comparison of the amounts of fluoride taken up by Acacia
georginae from solutions of sodium fluoride, 300 yg/ml
(15.75 mW) at pH 6.6 and pH 4.0 (acidification with
nitric acid) 109
4.2 Fluorine content of washed (solid) and unwashed (shaded)
leaves of six citrus varieties as affected by gaseous
hydrogen fluoride exposure 130
4.3 Fluorine content of washed (solid) and unwashed (shaded)
leaves of six ornamental species as affected by
gaseous hydrogen fluoride exposure 131
4.4 Comparison of uptake by grass of fluoride from hydrogen
fluoride and from submicron particulate fluoride 133
4.5 Fluoride accumulation in mixed planting of timothy and
red clover with intermittent (solid symbols) and
continuous (open symbols) fumigations 134
4.6 Inhibition of apparent photosynthetic rates of barley
and oat canopies by 2-hr air pollution fumigations .... 140
4.7 Possible effects of fluoride on agriculture 152
4.8 Relation of concentration and duration of exposure to
effects of atmospheric fluoride on tomato 154
4.9 Relation of concentration and duration of exposure to
effects of atmospheric fluoride on alfalfa 155
4.10 Relation of concentration and duration of exposure to
effects of atmospheric fluoride on gladiolus 156
4.11 Relation of concentration and duration of exposure to
effects of atmospheric fluoride on sorghum (Milo
maize) 157
5.1 The amount of 3SS02F2 present in the eggs of
Schistocerca gregaria and Tenebrio molitor at
different stages of embryonic development 177
5.2 Uptake and removal of fluoride from the (a) exoskeleton,
(b) gills, (
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5.5 Fluorine-18 concentration in blood of lambs following
oral administration 206
5.6 Diurnal variation in plasma fluoride in sheep 206
5.7 Fluorine-18 levels in blood from mature cows after
intravenous dosing 207
5.8 Effect of fluoride source on fluoride deposition
(expressed as percentage of bone ash) in three
sections of the metacarpal bones of cattle 208
5.9 Average fluoride-18 concentration in excreta and
saliva from mature cows 211
5.10 Relationship of urinary fluoride level to the fluoride
in dry matter consumed by cows 212
5.11 Variation of incisor classification of 4 or 5 with
distance from industrial plants in annular segments .... 223
5.12 Calving rate of cows on three levels of fluorine
intake 229
6.1 Urinary fluoride excretions during fluoride supplemental
intake of 45 mg/day 250
6.2 Skeletal concentrations of fluoride in residents of
West Hartlepool, South Shields, and Leeds, England,
and Rochester, New York 252
6.3 Mobilization of fluoride from the human skeleton 253
6.4 The compartment-system model and differential equations
for calculation of bone and urinary 18F clearance
after a single intravenous injection 255
6.5 Percentage of radiologically detectable calcification
of abdominal aorta in males and females residing in
high- and low-fluoride areas 260
6.6 Maternal-fetal transfer of X8F in the human and in the
rabbit 261
6.7 Scatter diagram of the maternal versus the cord serum
fluoride values taken at the time of delivery 261
6.8 Inorganic plasma fluoride related to duration of
pregnancy 263
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6.9 Effect of varying concentrations of ATP and Mga+ on
adenyl cyclase activity in fat cell ghosts: (a)
activities are measured at fixed concentration of
Mg"1"1" (5 mM); (Z>) activities are measured at fixed
concentration of ATP (5.84 mW) 270
6.10 Loss of adenyl cyclase activity in a rabbit skeletal
muscle homogenate at 4°C 271
6.11 Effect of increasing concentrations of sodium fluoride
on brain adenyl cyclase activity in rats 272
6.12 The proposed mechanism of activation of adenylate
cyclase system 274
6.13 A schematic representation of the adenylate cyclase of
the cyclase-PDE model cyclic AMP generating system .... 275
6.14 Effect of pyruvate on 22Na release and cellular NAD
concentration in fluoride-treated and control
erythrocytes 278
6.15 Effect of fluoride at two concentration levels on the
regeneration of skin in the rabbit ear 280
6.16 Relation between decayed, missing, and filled teeth
(broken line at left), severity of fluorosis (solid
lines), and fluoride concentration in water
(logarithmic scale) 282
6.17 Relationship among fluoride levels, fluorosis, and
ambient temperatures 283
6.18 Fluoride concentrations in portions of alveolar bone
and teeth 286
6.19 The relationship between age and the fluoride content of
human premolar (a) enamel and (2?) dentin 287
6.20 Communities, water-supply systems, and population served
with fluoridated water, 1960-1970 288
6.21 Relationship between fluoride concentration of public
water supply and number of dental caries in
permanent teeth of children 288
6.22 Relationship between dental caries prevalence
(permanent teeth) and fluoride ingestion as
measured by percentage of children showing dental
fluorosis in 8576 selected 12- to 14-year-old
children in 27 cities 289
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6.23 Reduction in caries incidence in permanent teeth of
children from Grand Rapids, Michigan, after 10 and
15 years of fluoridation 290
6.24 Relationship between fluoride concentration of drinking
water and fluoride concentration of the urine 296
6.25 Scheme of the effects of fluoride on calcium homeo-
stasis (osteocytic resorption) and bone metabolism
(osteoclastic resorption) 296
6.26 Effect of Freon 11 on cardiac conduction in dogs 308
6.27 Freon 11 results: note narrow margin between concen-
tration eliciting earliest detectable yet reversible
change and concentration of the first lethal result .... 309
6.28 Serum fluoride and "organic acidlabile fluoride"
(OALF) concentrations of all samples taken from 15
patients at various times after the end of
anesthesia 312
6.29 Mean serum inorganic fluoride levels for all three
patient groups combined plotted against time in hours . . . 314
6.30 Plasma fluoride levels following methoxyflurane
analgesia for (a) delivery only, (b) for labor and
delivery, and (c) for caesarean section (* indicates
significant change from control) 315
7.1 Supply-demand relationships for fluoride (all forms) .... 353
7.2 Fluorine concentrations in surficial materials of the
conterminious United States 363
7.3 Maximum fluoride content of U.S. waters (by counties) .... 374
7.4 U.S. production and environmental release of
fluorocarbons 379
8.1 Environmental transfer of fluoride 392
8.2 Dispersion of fluoride in the biosphere 393
9.1 Routes of fluorides in the environment 408
9.2 Apricot leaves showing various degrees of necrosis
caused by excessive levels of atmospheric fluoride .... 413
9.3 Classification of representative incisor teeth from
cattle from 0 to 5 reading left to right in A and B . . . . 416
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9.4 Permanent bovine Incisor teeth 417
9.5 Metatarsal bones from two cows of the same breed, size,
and age: left normal bone; right severe
osteofluorosis 418
9.6 Cross sections of the two metatarsal bones shown in
Figure 9.5 419
9.7 Water intake by beef cattle at different ambient air
temperatures 422
9.8 Permanent human teeth of a 55-year-old man 430
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TABLES
2.1 Physical properties of fluorine 14
2.2 Properties of some ionic fluorides 15
2.3 Properties of some covalent fluorides 17
2.4 Some physical properties of anhydrous hydrogen fluoride ... 18
2.5 Physical properties of calcium fluoride 21
2.6 Physical properties of cryolite 22
2.7 Some physical properties of silicon tetrafluoride 24
2.8 Solubility of silicon tetrafluoride in various solvents ... 25
2.9 Physical properties of some inorganic fluorosilicates .... 26
2.10 Halogen fluorides: types and boiling points 27
2.11 Some physical properties of oxygen difluoride 28
2.12 Selected physical properties of sulfur tetrafluoride .... 28
2.13 Some physical properties of disulfur decafluoride 29
2.14 Properties of sulfur hexafluoride 30
2.15 Some physical properties of aliphatic fluorocarbons 32
2.16 Some physical properties of uranium hexafluoride 34
2.17 Methods for determining fluoride 43
3.1 Incorporation of 5-fluorouracil into RNA of various
microbial species 61
3.2 Fluoride concentration in a Streptococcus isolated
from human plaque and grown on media containing a
range of fluoride with final pH reached after
incubation with sucrose for 18 hr 62
3.3 Accumulation of fluoride by lichens exposed to four
days of uniform ambient fluoride levels (5 yg of
fluoride per cubic meter) but under varying relative
humidity regimes 63
3.4 Fluoride concentrations of transplanted lichens 63
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3.5 Fluoride concentrations in lichens 64
3.6 Fluoride concentrations in washed and unwashed yeast
after successive fermentation series 65
3.7 Effects of sodium fluoride on growth and sporulation
of pathogenic fungi 71
3.8 Effects of fluorocarbon aerosol propellants on
microorganisms 73
3.9 Survival of a coagulase-positive (Giorgio) strain and
two coagulase-negative strains (Guinn and ATCC 6020)
of Staphylococcus aureus as determined by colony
counts after exposing the bacterial cells to 5-min
gassing treatment (30 ml/min) and a subsequent 24 hr
in the gaseous atmosphere 76
3.10 Effects of fluoride on respiration of the aquatic fungi
Allomyces javaniaits and Brevilegnia itnisperma var.
delioa 80
3.11 Effects of fluoride (NaF) on microbial carbohydrate
metabolism 82
3.12 Enzyme inhibition by soluble fluorides 88
3.13 Effects of fluoride on microbial enzymatic activity 89
3.14 Influence of sodium fluoride on the enzymes involved in
the synthesis and degradation of glycogen in crude
extracts of Streptococcus salivarius 90
3.15 Effects of 5-fluorouracil incorporation of enzymatic
activity 90
4.1 Effect of 50 ppm fluorine (as NaF) in nutrient solution
(series A and B) and of HF fumigation (series C and D)
on the degree of injury and fluoride levels in tissues
of tomato plants grown with different levels of
nitrogen, calcium, and phosphorus Ill
4.2 Changes in fluoride concentrations in different sections
of snow princess gladiolus leaves following fumigation
with hydrogen fluoride 112
4.3 Fluoride content and fresh weights of mature navel orange
trees grown for 18 months in solution cultures with and
without fluoride present in the nutrient solutions .... 114
4.4 Distribution of fluorine in tropical plants 117
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4.5 Fluoride concentrations in selected plants 119
4.6 Fluoride values in tissues of various plants 122
4.7 Treatments and tissue fluoride concentrations for
bean experiments 132
4.8 Concentrations of fluoride in plants near the Anaconda
Aluminum Company smelter in northwest Montana 136
4.9 Distribution of 19F and *8F in various cellular
constituents of tomato leaves treated through the
aerial portions of the plant 137
4.10 Nature of fluoride-induced effects in plants at
different levels of biological organization 138
4.11 Seasonal effects of fluoride (1 mA/ NaF) on photo-
synthesis and respiration of foliage from three
species of pines and six species of hardwood 139
4.12 The Q02 ratio (water infiltrated to fluoride infiltrated)
of bean seedlings at three growth stages 141
4.13 Sensitivity of selected plants to fluoride 148
4.14 Effect of fumigation with relatively low concentrations
of hydrogen fluoride on the photosynthesis of plants . . . 161
5.1 Fluoride levels in control insects 178
5.2 Fluoride levels in test insects 179
5.3 Sodium fluoride toxicity to selected insect species 180
5.4 LTso values computed for various doses of sodium
fluoride and development stages of selected
insect species 180
5.5 Mortality of Cryptotermes brevis exposed to sulfuryl
fluoride for 3 hr in temperature-controlled
fumigation chambers 181
5.6 Toxicity of inorganic fluoride compounds to Bonibyx mori
and Apis mellifera 182
5.7 Egg production by Tribolium confusion per five-day
interval after exposure to sodium fluoride levels
varying from 0 to 0.1% 183
5.8 Mean values of biological parameter response in
Drosophila melanogaster to atmospheric contamination
by hydrogen fluoride 183
xv
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5.9 Recessive mutation rate in Drosophila melanogaster
exposed to perfluorobutene-2 and perfluorobutene-2
in combination with oxygen, carbon dioxide, nitro-
gen, and compressed air 184
5.10 Fluoride concentrations in dried tissues of crabs
from natural, unpolluted waters 186
5.11 Fluoride analysis of tissues from aquatic species
collected from Lynemouth Power Station (England)
inflow filter and from offshore sites 188
5.12 Toxicity of fluorides to aquatic species 192
5.13 The effect of increased fluoride (as sodium fluoride)
in artificial seawater of various marine, intertidal
animals of the Northumbrian coast 194
5.14 Femur fluoride levels in birds collected from
uncontaminated ecosystems 195
5.15 Bone and gizzard fluoride concentrations in birds in
an uncontaminated area of New Zealand 196
5.16 Tissue fluoride levels of seabirds from the coast of
Great Britain 197
5.17 Fluoride levels in tissues of turkeys fed various
amounts of sodium fluoride 198
5.18 The effect of dietary fluoride on enzyme systems of
chicks 199
5.19 Fluoride concentrations in bones of wild and
domestic animals 202
5.20 Fluoride levels in femurs of wild animals 203
5.21 The effect of added dietary increments of fluoride
(as sodium fluoride) on soft tissue fluoride
concentrations in dairy cows 210
5.22 Fluoride concentration in metacarpal bones of newborn
calves 210
5.23 Response of domestic animals to various levels of
fluoride dosage: minimal response 214
5.24 Response of domestic animals to various levels of
fluoride dosage: acute response 215
5.25 Response of domestic animals to various levels of
fluoride dosage: lethal doses 216
xvi
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5.26 Dental lesions associated with exposure of livestock
to elevated fluoride levels 219
5.27 Skeletal lesions associated with exposure of livestock
to elevated fluoride levels 224
5.28 The effects of added dietary increments of fluoride
(as sodium fluoride) on the calcification of bones
and joints of dairy cows 226
5.29 Lameness associated with exposure of livestock to
elevated fluoride levels 227
5.30 Nutritional signs associated with exposure of
livestock to elevated fluoride levels 230
5.31 Dietary fluoride tolerances for domestic animals 232
5.32 Tolerance of animals for fluoride 233
6.1 Fluoride balances before, during, and after sodium
fluoride (NaF) supplementation 250
6.2 Fluoride levels in soft tissues of animals 257
6.3 The concentration of fluoride in human soft tissues
in relation to that in the water supply 258
6.4 Concentrations of fluoride in human soft tissues,
normal deaths 258
6.5 Fluoride content of human tissues following fluoride
poisoning fatalities 259
6.6 Fluoride concentration in placenta 262
6.7 Fluoride content of ashed fetal bones and teeth 263
6.8 Concentrations of fluoride found in human milk 264
6.9 Calculated distribution of total body fluoride in
human tissues 265
6.10 Summary of effects of fluoride on enzyme systems 267
6.11 Effects of inorganic fluoride compounds on enzyme
systems 268
6.12 Effect of epinephrine and fluoride on cyclic AMP
formation by adipocytes before and after
homogenization 271
xvii
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6.13 Threshold limit values of various fluorine compounds .... 294
6.14 Olefin toxicities 304
6.15 Inhalation toxicity of fluoromethanes 305
6.16 Classification of propellants based on toxicity to
respiratory and circulatory systems 306
6.17 Comparative life hazard of gases and vapors 307
6.18 Lethal concentrations of several fire-extinguishing
agents 317
6.19 Toxicities of various gases encountered in fire
fighting 318
6.20 Minimal concentrations of halogenated fire-
extinguishing agents required to produce
characteristic reactions in rats 318
6.21 Toxicities of fire-extinguishing agents 319
6.22 Mortality and response of several mammalian species
to pyrolyzed bromotrifluoromethane (CF3Br) 319
7.1 Uses of selected fluoride compounds 351
7.2 Summary of forecasts of U.S. and world fluorine demand,
1973-2000 354
7.3 Soluble fluoride emissions 355
7.4 Fluorine emissions from processing phosphates 358
7.5 Fluoride concentrations in atmospheric precipitation .... 361
7.6 Fluoride content of certain micaceous clays 362
7.7 Fluoride in soils 364
7.8 Fluoride content of principal German fertilizers 368
7.9 Fluoride in North American waters 369
7.10 The occurrence of fluoride in drinking water from
various countries 372
7.11 U.S. Public Health Service recommended limits for
fluoride concentration 373
7.12 Fluoride in particulate matter collected from the
air of U.S. cities 376
xviii
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7.13 The occurrence of fluoride in the atmosphere of some
U.S. communities 376
7.14 Fluoride in urban and nonurban U.S. air, 1966-1968 377
7.15 Fluorides in air near industrial operations 378
7.16 Fluoride retention from 200- and 800-lb applications
of hydrofluoric acid in four soils 381
7.17 Rates of removal of fluoride from seawater due to
incorporation into various minerals 382
7.18 Fluoride waste treatment processes 383
8.1 Fluoride content of various foods and beverages 394
8.2 Fluoride content of various foods and beverages
processed in either fluoridated or unfluoridated
water 396
8.3 Estimated daily fluoride intake from food and
drinking water 397
8.4 Daily dietary fluoride intake for various countries 398
8.5 Estimates of total daily fluoride intake in the United
States, the United Kingdom, Russia, and Japan 399
8.6 Fluoride in diets in North American 400
8.7 Bioaccumulation of fluoride in selected plants and
animals 401
9.1 Guide to diagnosis and evaluation of fluoride effects
in dairy cattle 420
9.2 Fluoride tolerance levels in feed and water for
domestic animals based on clinical signs and lesions . . . 424
9.3 Fluoride content of various foods 427
xix
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FOREWORD
A vast amount of published material is accumulating as numerous
research investigations are conducted to develop a data base on the adverse
effects of environmental pollution. As this information is amassed, it
becomes continually more critical to focus on pertinent, well-designed
studies. Research data must be summarized and interpreted in order to
adequately evaluate the potential hazards of these substances to ecosystems
and ultimately to public health. The Reviews of the Environmental Effects
of Pollutants (REEPs) series represents an extensive compilation of rele-
vant research and forms an up-to-date compendium of the environmental
effect data on selected pollutants.
Reviews of the Environmental Effects of Pollutants: IX. Fluoride
includes information on chemical and physical properties; pertinent ana-
lytical techniques; transport processes to the environment and subsequent
distribution and deposition; impact on microorganisms, plants, and wild-
life; toxicologic data in experimental animals including metabolism, tox-
icity, mutagenicity, teratogenicity, and carcinogenicity; and an assessment
of its health effects in man. The large volume of factual information
presented in this document is summarized and interpreted in the final
chapter, "Environmental Assessment," which presents an overall evaluation
of the potential hazard resulting from present concentrations of fluoride
in the environment. This final chapter represents a major contribution by
James L. Shupe, A. E. Olson, and H. B. Peterson of Utah State University.
The REEPs are intended to serve various technical and administrative
personnel within the Agency in the decision-making processes, i.e., in
the development of criteria documents and environmental standards, and
for other regulatory actions. The breadth of these documents makes them
a useful resource for public health personnel, environmental specialists,
and control officers. Upon request these documents will be made available
to any interested individuals or firms, both in and out of the government.
Depending on the supply, the document can be obtained directly by writing
to:
Dr. Jerry F. Stara
U.S. Environmental Protection Agency
Health Effects Research Laboratory
26 W. St. Clair Street
Cincinnati, Ohio 45268
R. J. Garner
Director
Health Effects Research Laboratory
xxi
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ACKNOWLEDGMENTS
The authors are particularly grateful to W. R. Laing and S. B.
Mclaughlin, Oak Ridge National Laboratory (ORNL), for reviewing prelimi-
nary drafts of this report and for offering helpful comments and sugges-
tions. The advice and support of Helga B. Gerstner, Manager, Information
Center Complex, and Jerry F. Stara, EPA Project Officer, and the coopera-
tion of the Toxicology Information Response Center, the Environmental
Mutagen Information Center, and the Environmental Resource Center of the
Information Center Complex, Information Division, ORNL, are gratefully
acknowledged. The authors also thank Carol McGlothin and Maureen Hafford,
editors, and Donna Stokes and Patricia Hartman, typists, for preparing
the manuscript for publication.
Appreciation is also expressed to Bonita M. Smith, Karen L. Blackburn,
and Donna J. Sivulka for EPA in-house reviews and editing and for coordi-
nating contractual arrangements. The efforts of Allan Susten and Rosa
Raskin in coordinating early processing of the reviews were important in
laying the groundwork for document preparation. The support of R. John
Garner, Director of Health Effects Research Laboratory, is much appreciated.
Thanks are also expressed to Carol A. Haynes for typing correspondence
and corrected reviews.
xxiii
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ABSTRACT
This study is a comprehensive, multidisciplinary review of the health
and environmental effects of fluoride on microorganisms, plants, wild and
domestic animals, and humans. More than 1000 references are cited.
Fluoride is widely distributed in the environment, occurring in
igneous rocks (210 to 1000 ppm) , sedimentary rocks (180 to 940 ppm),
normal soils (200 to 300 ppm), surface waters (uncontaminated lakes and
streams, <0.3 ppm), seawater (approximately 1.5 ppm), and air (nonindus-
trial areas, <0.05 ug/m3). Most fluoride emissions to the atmosphere
occur during the manufacture of phosphorus and phosphate fertilizer, the
operation of aluminum- and steel-producing furnaces, the production of
brick and tile products, and the combustion of coal. Liquid-fluoride
wastes are generated primarily during the production of glass products,
pesticides, fertilizers, aluminum, steel and inorganic chemicals, and in
metal-processing industries.
Human intake of fluoride is chiefly through the diet; drinking water
is normally the largest single source. Low concentrations of fluoride
in water (approximately 1 ppm) benefit mammalian systems, making bone
and tooth apatite less soluble, but long-term ingestion of water contain-
ing more than 8 ppm fluoride causes fluorosis in humans. Fluoride salts
are lethal to humans when ingested in doses of about 3 g or more. At
concentrations normally encountered by the general public, fluoride is
not teratogenic, mutagenic, or carcinogenic to humans, but chronic fluo-
ride toxicosis of both livestock and wildlife is an important problem in
many areas of the United States. The principal manifestations of chronic
fluoride toxicosis in livestock are dental fluorosis, osteofluorosis,
lameness, and impaired performance. Among domestic animals, dairy cattle
are the most sensitive to excessive fluoride exposure.
This report was submitted in partial fulfillment of Interagency
Agreement No. D5-0403 between the Department of Energy and the U.S.
Environmental Protection Agency. The report was completed in December
1979.
XXV
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SECTION 1
SUMMARY
1.1 DISCUSSION OF FINDINGS
1.1.1 Chemical and Physical Properties and Analytical Techniques
Fluorine is a pale yellow acrid gas that freezes to a colorless
solid at -219.6°C and boils at -188.2°C; it is a common element, ranking
13th in abundance and constituting 0.06% to 0.09% of the earth's crust.
Fluorine is highly reactive and rarely exists in the elementary state in
nature. It usually occurs as ionic or covalently bonded fluoride. The
most common chemical forms are hydrogen fluoride, alkali fluorides, sili-
con tetrafluoride, sodium fluorosilicate, fluorocarbons, uranium hexaflu-
oride, chalcogen and halogen fluorides, and the minerals cryolite,
fluorapatite, and fluorspar (Section 2.2).
Techniques for sampling environmental sources for fluoride are well
established, except for the partitioning of airborne gaseous and particu-
late fluorides. A variety of good analytical methods are available for
determining fluoride in environmental media. The widely used spectrophoto-
metric procedure based on the zirconyl-SPADNS reagent is now being rapidly
superseded by the relatively new fluoride ion electrode. The latter tech-
nique has comparable, or better, sensitivity (1 to 100 ng/g), precision
(1% to 10%), and accuracy (1% to 5%) and is quicker and more convenient
than other methods for most types of fluoride samples. Fluoride in envi-
ronmental samples can also be determined by polarographic, enzymatic, and
activation analyses techniques, but these methods are competitive with the
fluoride ion electrode method only under special circumstances (Section
2.3.3).
The biochemistry of fluorides is complex. Drinking water concentra-
tions of about 1 ppm fluoride are beneficial to mammals, reducing the dis-
solution of hydroxyapatite crystals in teeth and bone through the formation
of the less soluble fluorapatite. About 99% of the fluoride retained in
the human body is localized in this fashion. However, higher levels of
fluoride are toxic to all biological systems. The manner in which excess
fluoride interferes with biochemical processes is not well understood at
the molecular level. It is known, nevertheless, that excess fluoride pre-
vents oxidative metabolism by inhibiting the action of enzymes that depend
on polyvalent cations such as magnesium, calcium, iron, and manganese. In
addition, other body functions that require complexable polyvalent metal
ions (e.g., membrane transport, nerve conduction, muscle contraction, and
blood clotting) are also disrupted. It is apparent that the fluoride ion,
per se, is responsible for the toxic effects. Accordingly, soluble inor-
ganic fluoride salts are more toxic than insoluble salts, and most organic
compounds that do not yield free fluoride ions in body fluids have little
or no toxicity. The naturally occurring organic compounds fluoroacetic
acid and to-fluorooleic acid are exceptions to this rule; their highly toxic
effect is due not to free fluoride ion but to their metabolic conversion
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to fluorocitric acid, which interferes with the chemistry of the Krebs
cycle, causing metabolic death of the cell. Treatment of acute fluoride
intoxication is based on reducing the cellular availability of fluoride
through the formation of complexes or precipitates in the intestinal tract
or in the bloodstream.
1.1.2 Environmental Occurrence
Fluoride is widely distributed in the environment. It occurs most
abundantly in ores, such as fluorspar (CaF2); in phosphate and silicate
minerals, such as fluorapatite [CaF2*3Ca3(PO*,)2]; and in topaz [Al2SiOt,
(F,OH)2]. It is also present in lesser amounts in most igneous (210 to
1000 ppm) and sedimentary (180 to 940 ppm) rocks. Normal mineral soils
average 200 to 300 ppm fluoride. Generally, sandy soils contain less
than average amounts of fluoride while heavier soils contain more. Soils
naturally rich in phosphorus tend to contain above-average fluoride con-
centrations in extreme cases, levels of 7000 to 8000 ppm are observed
(Section 7.3.2.2).
Fluoride is a normal constituent of natural waters. The fluoride
content of surface water depends on the water source and the amount of
precipitation received; normally, fluoride in uncontaminated lakes and
streams does not exceed 0.3 ppm. Seawater usually contains more fluoride
than fresh surface water about 1.4 to 1.5 ppm in waters of normal salin-
ity. Highly saline waters have increased concentrations of fluoride; the
Great Salt Lake in Utah and certain lakes in Kenya, Africa, contain 14 and
1600 ppm fluoride respectively. Fluoride in groundwaters, such as springs,
wells, and infiltration galleries, varies greatly depending on the type
of rock the water flows through. Groundwaters associated with alkalic
igneous rock, dolomite, phosphorite, and volcanic glasses contain fluoride
concentrations that usually do not exceed 10 ppm but may occasionally reach
60 to 70 ppm. Large areas of the world have local groundwaters with more
than 1.5 ppm fluoride. Limits set by the U.S. Public Health Service for
fluoride in drinking water vary from 0.6 to 1.7 mg/liter, depending on
local air temperatures. Nearly all U.S. public water supply systems meet
this standard (Section 7.3.3).
Fluorides occur naturally in the atmosphere; soluble gaseous fluorides
and soluble and insoluble dusts are formed as a result of the weathering
of rocks and minerals, volcanic activities, and precipitation. The concen-
trations of these materials in ambient air depend on the amount of fluoride
emitted, the distance from the source, meteorological conditions, and the
topography of the area. In both rural and urban areas, atmospheric fluo-
ride concentrations are typically reported as less than 0.05 ug/m3, the
limit of detection of the analytical method used in the survey. However,
higher localized atmospheric concentrations of fluoride frequently result
from industrial activities, particularly the combustion of coal, the manu-
facturing of aluminum and steel, and the production of phosphate fertil-
izer. U.S. coals contain about 60 ppm fluoride. Half of this fluoride
escapes to the atmosphere during combustion as hydrogen fluoride, silicon
tetrafluoride, or fluoride particulates. Similar contaminants are released
during phosphate fertilizer production, and average fluoride concentrations
-------
in excess of 3 yg/m3 have been reported in the air near older phosphate
fertilizer manufacturing plants. These concentrations are well below the
threshold limit values of 2.5 and 0.2 mg/m3 set for fluoride and fluorine
in the workplace, respectively, by the American Conference of Governmental
Industrial Hygienists (Section 7.3.4).
Hydrogen fluoride is the most important manufactured fluoride; it is
the intermediate from which all other fluorides are prepared. In 1974,
the U.S. consumption of all forms of fluorides amounted to 625,100 metric
tons (689,000 short tons), computed as fluorine. About one-third of this
total (32.5%) was consumed in synthesizing organic compounds and products
such as dichlorodifluoromethane, trichlorofluoromethane, tetrafluorometh-
ane, tetrafluoroethylene, vinyl fluoride, and hexafluoropropene, which
were used for aerosol propellants, refrigerants, and fluorinated plastics.
The remaining fluoride was used primarily by metal producing or processing
industries; steel and electrometallurgical fluxing, 44%; nonferrous metal
production, 22%; ceramics and glass manufacture, 1.3%; and other processes,
0.2% (Section 7.2).
Large quantities of chlorine-containing fluorocarbons released to the
atmosphere in recent years as aerosol propellants or refrigerants raised
questions about destruction of stratospheric ozone and ensuing health haz-
ards from increased ultraviolet radiation. The extent to which this reac-
tion occurs is uncertain, but studies to establish the significance of the
reaction are in progress. As a precautionary measure all nonessential
aerosol propellant uses of fluorocarbons were banned by federal regulations
in 1978.
Consumption of fluorine in the United States is increasing rapidly
and is expected to more than triple by the year 2000 (Section 7.2).
1.1.3 Environmental Cycling and Fate
Fluoride cycles naturally through the environment. It moves from the
lithosphere to the atmosphere primarily by volcanism and entrainment of
soil particles (Section 8.2), but manufacturing activities are becoming
increasingly significant. Volcanism is estimated to transfer 109 kg of
fluoride per year to the atmosphere. In 1970, emissions from U.S. indus-
trial activities amounted to an additional 1.5 * 10° kg of fluoride.
Atmospheric fluoride returns to the hydrosphere and lithosphere in
precipitation and by deposition of particulates. Rainfall, which averages
0 to 0.02 ppm fluoride in uncontaminated areas, contains 0.2 to 14 ppm
fluoride in areas near urban and industrial sources. In one location where
much coal is burned, rainwater is estimated to add 170 g of fluoride per
hectare annually. Global precipitation is estimated to deposit 1.2 * 10l°
kg of fluoride per year (Section 7.3.1.2.2).
Fluoride tends to persist in most soils. It is strongly absorbed by
soil colloids and is not easily displaced by common anions. In alkaline
soils fluoride is usually fixed as the insoluble calcium salt, or, if ade-
quate calcium is not present, as aluminum silicofluoride. In very alkaline
-------
soils the sodium salt may be formed. Losses from runoff and leaching are
relatively small averaging 0.5% to 6% annually in typical forest and agri-
cultural areas (Section 7.4.1).
Dissolved and particulate fluorides from natural and industrial
sources are transported to the sea primarily by flowing water; as a con-
sequence, world rivers average about 0.09 to 0.2 ppm fluoride (Section
7.3.3). Seawater contains ten times as much fluoride as rivers. Oceanic
sediments are richer still, averaging about 730 ppm. Some 4 to 6 * 1011
g of fluoride is withdrawn from the sea annually by incorporation into
calcium carbonate or calcium phosphate. This removal results in an aver-
age fluoride residence time in the ocean of 2 to 3 million years. There
is no apparent difference in the fluoride content of sediments from the
Atlantic, Pacific, and Indian oceans (Section 7.4.2).
Several effective and economical treatments exist for removing
fluoride from gaseous- and liquid-waste streams. Fluorides are usually
scrubbed from gaseous wastes with water or caustic solutions. The most
commonly used methods for removing fluoride from liquid wastes involve
precipitation of calcium or aluminum fluoride by addition of lime or alum,
followed by filtration or settling (Section 7.5). Another frequently used
waste management technique involves absorption of ionic fluoride on ion
exchangers or alumina. The fluoride sludge resulting from these opera-
tions is normally disposed of as landfill. Adequate precautions against
acidification of these landfill sites are necessary to avoid inadvertent
release of solubilized or vaporized fluorides.
1.1.4 Biological Aspects in Microorganisms
Many microorganisms, such as bacteria, fungi, yeast, algae, protozoa,
and viruses, are known to metabolize fluoride or fluoride-containing com-
pounds. A few strains of bacteria can utilize fluoride compounds as
catabolites. Microorganisms may contain relatively high concentrations
of fluoride. Some samples of oral bacteria contain up to 134 ppm, and
accumulations up to 900 ppm fluoride may occur in lichens grown near an
industrial pollution source such as an aluminum smelter. In most in-
stances, fluoride appears to be only loosely bound to microbe cells and
can be removed or reduced in concentration by washing with water or other
solvents (Section 3.2). There is no evidence that fluoride is essential
to microorganisms. In fact, excessive concentrations are toxic, but dif-
ferent species exhibit different tolerances. Toxic effects of fluoride
on microorganisms include developmental and morphological alterations,
growth inhibition, and reduction in infectivity. These effects occur
primarily through interference with respiratory, photosynthetic, ionic
transport, and glycolysis processes. Higher molecular weight compounds
and compounds containing more chlorine than fluorine seem to be most toxic
to microorganisms. Dormant bacterial spores are more resistant than vege-
tative cells to fluoride aerosols (Section 3.3). The laboratory substi-
tution of p-fluorophenylalanine and 5-fluorouracil for their unfluorinated
analogs in bacterial proteins and nucleic acids interferes with subsequent
vital biological processes, such as protein reduction, RNA and DNA syn-
thesis, and cell differentiation; it also causes chromosomal alterations,
-------
changes in ribosomal composition and properties, and modification in func-
tions of messenger RNA. There is no evidence, however, that mutagenic
effects to microorganisms occur by chance, from simple fluoride compounds
normally encountered in the environment (Section 3.3.1).
1.1.5 Biological Aspects in Plants
Fluoride is found in virtually all plants. In unpolluted areas,
fluoride concentrations normally range from about 2 to 20 yg per gram of
dried plant matter. Near industrial pollution sources, such as aluminum
or phosphate fertilizer producers or in soils of high fluoride content,
concentrations of fluorides in plants may be 10 to 100 times greater
(Section 4.2.4.2). Although plants can absorb fluoride from soil, levels
of major nutrients in the soil affect the amount of fluoride absorbed
through roots, and there is not necessarily a simple direct relationship
between concentrations of fluoride in soil and plant tissues. Uptake of
fluoride by plants is strongly pH dependent (Section 4.2.1.1). Plants
absorb gaseous and airborne particulate fluorides via leaves; in areas
with polluted atmospheres most of the fluoride in the plant is probably
supplied in this manner. Gaseous fluorides are more effectively absorbed
than particulate forms and lead to greater plant injury. Tissue fluorides
increase with increased length of exposure and with increased atmospheric
concentrations. Existing data are inadequate to determine subcellular
sites of localization; however, some evidence suggests that chloroplasts
accumulate fluoride to a greater extent than mitochondria or cell walls.
Mobility of fluoride within the plant is limited fluoride is translocated
upward from root to shoot, but leaf fluoride is essentially fixed. Bio-
elimination occurs through loss of leaves, twigs, and roots, leaching by
rain, and in certain plants possibly by volatilization of organofluorides
(Section 4.2.5).
The metabolism of organic fluoride by plants is not well understood.
Some plant species synthesize and accumulate large amounts of compounds
such as fluoroacetate. A variety of plants form trace amounts of fluoro-
acetate and fluorocitrate, but no information is available concerning
enzyme systems necessary to synthesize or degrade these organofluorides.
It is also uncertain if all plants can synthesize carbon-fluorine bonds
(Section 4.2.3).
Although the linear growth of selected plants may be enhanced by
exposure to a few parts per billion of airborne fluoride, the presence of
fluoride in plant tissue in abnormal concentrations is generally detri-
mental. All plants are not equally susceptible; gladiolus, apricot, and
Douglas fir are exceptionally sensitive while cherry, tomato, and wheat
are resistant. Excess fluoride causes growth inhibition, tip and marginal
necrosis of foliage, chlorosis, wilting, and eventually death of the plant.
Fruit quality and yield can be impaired. Inhibition of seed germination
also occurs. Fluoride causes these effects by altering photosynthesis,
carbohydrate metabolism, respiratory and oxidative processes, RNA metabo-
lism, and calcium nutrition. The mechanisms involved are complex and
largely unresolved in vivo, but in vitro studies suggest that many effects
result from fluoride inhibition of essential enzymatic reactions or effects
on the structural integrity of the cell (Section 4.3.1).
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Fluoride appears to be mutagenic in plants. Chromosomal abnormali-
ties, such as breakage, bridging, and stickiness, occur in a variety of
plants after treatment with concentrations of gaseous hydrogen fluoride
or aqueous sodium fluoride too low to induce immediate .visible injury.
The mechanisms by which fluoride induces chromosomal aberrations are not
known (Section 4.3.4).
1.1.6 Biological Aspects in Animals
Animals are exposed to a variety of forms and concentrations of flu-
oride through ingestion of food and water and from the atmosphere. Inges-
tion is the principal form of uptake by insects, aquatic and terrestrial
animals, and birds; inhalation and skin absorption contribute only negli-
gible amounts. Fluorides are metabolized and accumulate in mineralizing
tissues of animals. Usually, 96% to 98% of the fluoride in the body is
located in bones and teeth. Although most mammals normally accumulate
fluoride in mineralizing tissues with age, the major portion of that
assimilated is rapidly excreted in urine. Smaller amounts are eliminated
in feces, saliva, and perspiration (Section 5.5.1.3).
Tolerance to fluoride differs among various animal species and among
individuals of the same species. Birds tolerate fluorides better than
mammals (Section 5.4.2.2.4). Based on performance, growing chicks accept
up to 300 ppm fluoride in their diet without difficulty; turkeys up to
400 ppm. However, teratogenic effects occur when fluoride-containing
compounds (e.g., 5-fluorouracil, 5-fluoro-2'-deoxyuridine, and 5-fluoro-
orotic acid) are injected into the yolk sac during the first four days
of development of chicken embryos. Skeletal deformation, microphthalmia,
retardation of growth of extremities, and abnormal bill development are
common malformations caused by intrayolk injections (Section 5.4.2).
Fluoride toxicosis of livestock usually occurs only in areas with a
fluoride pollution problem, but significant exposures can result from the
ingestion of excessive raw rock phosphate and geothermal waters rich in
fluorides (Section 5.5.1). Acute fluoride toxicosis is rare, but chronic
fluoride toxicosis occurs in both livestock and wildlife and is an impor-
tant problem in the United States. Dental and bone lesions, lameness, and
impaired performance are the principal manifestations of chronic fluoride
toxicosis in livestock. Sheep and horses are more tolerant to fluoride
than cattle. Based on chemical signs and lesions, safe levels of fluoride
in the feed of these animals are 60 ppm to 30 ppm, respectively, under
breeding or lactating conditions. Swine appear to be the most tolerant
among domesticated mammals, tolerating up to 70 ppm fluoride in their feed
(dry basis) without apparent injury (Section 5.5.2.4). Feed values should
be reduced proportionally when water contains appreciable amounts of flu-
oride. Available scientific data do not support carcinogenic effects of
fluorides in wild or domestic animals. Water characteristics, such as pH,
hardness, and contaminants, influence the tolerance of aquatic animals to
fluoride; sensitivity is also related to environmental acclimatization
and species of animal. In general, however, concentrations of 1.5 ppm
fluoride appear not to have harmful effects, although slightly higher
levels may be detrimental to some aquatic species. For example, the 20-day
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median tolerance limit for some Salmo flngerlings is 2.7 to 4.7 ppm sodium
fluoride at 12.8°C, under constant-flow conditions. Filter-feeding mol-
luscs are also very sensitive to fluoride. Mussels subjected to seawater
containing 10 ppm fluoride die after five-week exposures. Growth of crus-
taceans (e.g., the crab) is reduced by exposure to water containing 20
ppm fluoride. Muscle tissue of such animals can accumulate up to 50 ppm
fluoride a level potentially hazardous for continual human use. Since
fluoride concentrations of 20 ppm have been reported in estuaries where
phosphate mining operations occur, such operations can have adverse effects
on the crabbing industry. It is worth noting, however, that the accumula-
tion of fluoride in crustaceans is reversible: both hard and soft tissue
concentrations approach near-normal levels following exposure of these
animals to fluoride-free water for a time comparable with the contamina-
tion period (Section 5.3.2.1).
Both inorganic and organic fluorides produce lethal and sublethal
toxicity in insects. The LD30 for many different species varies from 100
to 300 mg of sodium fluoride per kilogram of living weight. Exposure to
fluoride causes either a stimulation or an inhibition of egg production
in insects, depending on the length of exposure and concentration of the
poison. For example, seven-day exposure of some Tribolium larvae to flour
containing 0.01% sodium fluoride stimulated egg production, compared with
controls, but a similar exposure to flour containing 0.1% sodium fluoride
inhibited egg production. Sublethal exposures of fluoride may also cause
mutagenic effects in some insects; thus increased sex-linked recessive
lethal mutations occur in DrosophiZa melanogas'bev males after exposure
to a mixture of gas containing 10% perfluorobutene-2 and 90% air (Section
5.2.2.1.3).
1.1.7 Biological Aspects in Humans
The biological response of humans to fluoride depends on many factors,
such as the chemical form and concentrations involved. At trace levels
ionic fluoride may be essential; at intermediate concentrations (approxi-
mately 1 ppm) it appears beneficial; and at higher levels it is toxic. The
essentiality of fluoride is difficult to show experimentally because of
its ubiquity and the resulting difficulty in removing fluoride from the
diet; nonetheless, trace levels of this substance may be necessary for
nucleation of crystalline material in bone (Section 6.2). Although fluo-
ridation of public water supplies has caused controversy, most evidence
indicates that this step is beneficial and is the most cost-effective and
safest procedure of improving dental health (Section 6.4.2). An even
higher level of fluoride than the 1.0 ppm considered optimum for caries
resistance may enable older persons to better resist osteoporosis (Section
6.4.2.3).
Human intake of fluoride is chiefly through the diet, drinking water
usually furnishing the largest share. Absorption of fluoride is largely
passive; the amounts retained depend on the solubility of the fluoride
compound (Section 6.3.1.2). Absorbed fluoride is rapidly distributed
across membranes and into tissues; however, bone is the major storage site.
Bones accumulate fluoride as fluorapatite or possibly, to a lesser extent,
-------
as magnesium fluoride, throughout the lifetime of an individual. The rate
decreases with age (Section 6.3.2.2). Fluoride sequestered by bone during
periods of excess intake is released to the blood and excreted through the
kidneys when the level of intake subsides. Some fluoride is eliminated in
sweat, and small amounts pass through the mucosa of the intestines into
the gut.
Long-term ingestion of water containing fluoride at levels above 8
ppm causes skeletal fluorosis osteofluorosis, in about one in ten persons.
In most cases, the skeleton does not deteriorate and functions normally,
both structurally and metabolically. When fluorosis is severe, bone
changes occur and may be accompanied by crippling, impaired locomotion,
and pain. Fluoride salts are lethal when taken orally in doses of about
3 g (Section 6.4.3). Aspects of fluoride poisoning leading to death are
blockage of respiratory enzymes, interference with necessary body functions
controlled by calcium, specific organ damage, and general collapse (Section
6.4.3.2). Some of these effects are reversible. If proper prompt treat-
ment is provided, not only may the patient be saved, but recovery without
sequelae is possible. In the case of exposure to HF or F2, the extremely
corrosive nature of these substances adds further damaging effects to their
general fluoride toxicity (Section 6.4.3.3). Absorbed as fumes or vapors,
they cause extreme irritation to the lungs, resulting in edema and tissue
damage as well as systemic toxic effects.
Except for accidental ingestion of fluoride salts, most U.S. residents
are exposed to fluorides chiefly from industrial or occupational contacts.
Usually, threshold limit values have been established for such exposures,
and exposure levels are monitored by air, food, and water sampling, and
urine analyses. At concentrations normally encountered by the general
public, fluoride is not teratogenic, mutagenic, or carcinogenic (Section
6.4.4). However, some concern exists over possible teratogenic or other
reproductive effects of fluorinated anesthetics among chronically exposed
persons such as operating room personnel (Section 6.4.3.6.2). Continued
study of the risk-benefit factors for such uses appears warranted.
1.1.8 Food Web Interactions
The movement of natural fluorides in the food chain has been exam-
ined only in a very preliminary manner and is not well established. The
available data indicate a 20- to 50-fold increase of fluoride in the femurs
of herbivores (e.g., deer mice) relative to forage values, and smaller
increases perhaps 2- to 5-fold in skeletons of predators of these
herbivores. The increased uptake of fluoride in the diets of predators
presumably results from consumption of prey skeletons since only trace
levels of fluoride occur in the soft tissues. Because the fractional
consumption of skeletal tissues by predators decreases higher in the food
chain, localization of fluoride in skeletal tissues effectively limits
the transfer of fluoride in most species, and biomagnification is not a
serious problem. Thus animals grown for human consumption generally do
not significantly increase human uptake of fluoride.
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1.2 CONCLUSIONS
1. Fluoride occurs in detectable concentrations in most rocks,
soils, and waters, as well as plant and animal tissues.
2. Normal mineral soils contain 200 to 300 ppm fluoride.
3. Uncontaminated surface waters usually contain no more than 0.3
ppm, but seawater of normal salinity averages 1.4 to 1.5 ppm
fluoride.
4. Most urban and almost all nonurban air contains environmentally
insignificant amounts of fluoride (<0.05 vig/m3).
5. Fluorite (CaF2) is the most abundant and economically important
fluoride mineral.
6. Hydrogen fluoride (HF) is the most important manufactured fluo-
ride and is probably the greatest single industrial fluoride
contaminant of the atmosphere.
7. Most fluoride emissions to the atmosphere occur in the manu-
facturing of phosphorus and phosphate fertilizer, the operation
of aluminum- and steel-producing furnaces, the production of
brick and tile products, and the combustion of coal.
8. Liquid-fluoride wastes are generated primarily in the production
of glass products, pesticides, fertilizers, aluminum, steel and
inorganic chemicals, and in metal-processing industries.
9. Fluoride is usually removed from aqueous wastes by the addition
of lime or alum, followed by filtration of the resulting calcium
or aluminum precipitate, or by absorption on ion exchangers or
alumina.
10. Volatile fluorides are usually fixed by scrubbing gaseous wastes
with water or caustic solutions.
11. Good analytical methods are available for determining fluoride
in environmental samples at concentrations down to the parts-
per-billion level.
12. Low concentrations of fluoride in water (approximately 1 ppm)
benefit mammalian systems, making bone and tooth apatite less
soluble.
13. Excess fluoride reacts with some complexable polyvalent cations
in biological systems, preventing normal enzymatic reactions
and causing cellular death.
14. Ingestion is the principal form of uptake of fluoride by
insects, aquatic and terrestrial animals, and birds; inhalation
and skin absorption contribute only negligible amounts.
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10
15. Acute fluoride toxicosis of livestock is rare, but chronic
fluoride toxicosis of both livestock and wildlife is an impor-
tant problem in many areas of the United States.
16. The principal manifestations of chronic fluoride toxicosis in
livestock are dental fluorosis, osteofluorosis, lameness, and
impaired performance among domestic animals. Dairy cattle are
the most sensitive to excessive fluorides.
17. Fluoride accumulates in the hard tissues of animals approxi-
mately 98% of the body burden is incorporated in teeth and bones.
18. Concentrations of 1.5 ppm fluoride in seawater appear not to
have harmful effects on marine animals, but higher levels are
frequently detrimental.
19. Plants absorb some soluble fluoride from the soil via roots,
while atmospheric gases and particulates are absorbed in and
collected on leaves and stems. The latter mechanism predomi-
nates in areas near aluminum, steel, and fertilizer manufacturers.
20. Excess fluoride in or on plants causes growth inhibition, plant
damage, reduced quality and yield of fruit, and fluoride toxi-
cosis in grazing animals.
21. The metabolism of fluoride by plants is not well understood;
however, it is established that excess fluoride in plants inter-
feres with photosynthesis, carbohydrate metabolism, respiratory
and oxidative processes, KNA metabolism, and calcium nutrition.
22. There is not necessarily a simple, direct correlation of fluo-
ride in soil and plant tissues. Uptake is strongly pH dependent.
23. The LD30 for many species of insects ranges between 100 and 300
mg of sodium fluoride per kilogram of living weight.
24. Biomagnification of fluoride occurs at the lower end of the food
chain but is limited by localization of fluoride in skeletal tis-
sues. Therefore, it does not significantly increase human uptake.
25. Human intake of fluoride is chiefly through the diet (drinking
water).
26. Water containing approximately 1 ppm of fluoride appears bene-
ficial to human life, but higher concentrations may be toxic.
27. Long-term ingestion of water containing more than 8 ppm of
fluoride causes fluorosis in humans.
28. Fluoride salts are lethal to humans when ingested in doses of
about 3 g.
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11
29. Except for accidental ingestion of salts, most U.S. residents
are exposed to fluorides chiefly from industrial or occupational
contacts. However, waters with high fluoride content are impor-
tant sources of exposure in some countries such as India and
Africa.
30. At concentrations normally encountered by the general public,
fluoride is not teratogenic, mutagenic, or carcinogenic to
humans.
31. Continued study of the risk-benefit factors for the use of
fluorinated anesthetics is warranted.
-------
SECTION 2
CHEMICAL AND PHYSICAL PROPERTIES AND ANALYSIS
2.1 SUMMARY
Fluorine is a common element, ranking 13th in abundance and consti-
tuting 0.06% to 0.09% of the earth's crust. Because of its small atomic
radius and large number of electrons, fluorine has the greatest surface
charge density of any element; consequently, it is highly reactive and
only rarely occurs naturally in elemental form. Fluorine is widely dis-
seminated, however, in ionic or combined forms; it appears in detectable
concentrations in most rocks, soils, waters, and plant and animal tissues.
Even rural air samples normally carry traces of fluoride.
Fluorine and its derivatives have large and growing uses in many
industrial processes and products, and various fluorides occur as by-
products or wastes. The chemical forms most frequently encountered are
fluorine gas, hydrogen fluoride, alkali fluorides, silicon tetrafluoride,
sodium fluorosilicate, fluorocarbons, uranium hexafluoride, Group VIA
element fluorides, halogen fluorides, and the minerals cryolite, fluor-
apatite, and fluorspar.
On the basis of quantity produced, hydrogen fluoride is the most
important manufactured fluoride (292,000 metric tons in 1977); it is the
intermediate from which all other fluoride compounds, including fluorine,
are prepared. Hydrogen fluoride is obtained by treating the mineral fluor-
spar with sulfuric acid. Because of its extensive use, hydrogen fluoride
is probably the greatest primary fluoride contaminant of the atmosphere.
Owing to its great reactivity, however, it is unlikely to remain in this
form very long.
Fluorination of organic compounds and products constitutes the
greatest single use of fluorides in the United States. In 1977, approx-
imately 108,000 metric tons of hydrogen fluoride was used in the synthesis
of dichlorodifluoromethane, trichlorofluoromethane, tetrafluoromethane,
tetrafluoroethylene, vinyl fluoride, hexafluoropropene, and similar prod-
ucts. These compounds are used chiefly for aerosol propellants, refriger-
ants, and fluorinated plastics. In 1978, nonessential uses of fluorocarbon
propellants were banned, and this segment of the fluorocarbon market shrank
to about 2% of its previous value. Smaller quantities of other fluorocar-
bons find specialized uses as inhalation anesthetics, fire extinguishing
agents, cleaners, and degreasers. Other large users of hydrogen fluoride
include the aluminum industry, uranium isotope enrichment plants, the
petroleum industry, and stainless steel pickling operations.
Most fluoride emissions to the atmosphere occur in the manufactur-
ing of fertilizer and phosphorus from rock phosphate^ the operation of
aluminum- and steel-producing furnaces, the*manufacturing of brick and
tile products, and the combustion of coal. In general, these wastes take
the form of hydrogen fluoride, fluorine, boron trifluoride, fluorosilicic
12
-------
13
acid, sodium fluorosilicate, aluminum fluoride, calcium fluoride, lead
difluoride, fluorapatite, silicon tetrafluoride, and fluoride particulates,
Liquid-waste streams containing appreciable quantities of fluoride are
generated by glass manufacturers, pesticide and fertilizer producers,
steel and aluminum makers, metal processing industries, and inorganic
chemical producers. Usually this fluoride is in the form of hydrogen
fluoride or fluoride ion, depending on the pH of the waste stream.
Techniques for sampling environmental sources for fluoride are reason-
ably well established, except for the partitioning of airborne gaseous and
particulate fluorides. A variety of good analytical methods are available
for determining fluoride in these samples. The widely used spectrophoto-
metric procedures based on the zirconyl-SPADNS, or similar, reagent are
now being rapidly superseded by the relatively new fluoride ion electrode.
The latter technique has comparable or better precision and accuracy and
is more rapid and convenient than previous analytical methods for most
types of fluoride samples. Fluoride in environmental samples can also be
determined by polarographic, enzymatic, and activation analysis techniques.
However, these methods are competitive with the electrode technique only
under specialized circumstances.
2.2 PHYSICAL AND CHEMICAL PROPERTIES
Fluorine is unique among the elements in the variety of forms its
compounds can take; many inorganic gases and salts exist, as well as a
large and growing number of organic compounds. Some of these compounds
interact significantly with the environment (Cholak, 1959a, 19592?) and
are pertinent to this study; the most important of these are fluorine,
hydrogen fluoride, alkali fluorides, fluorspar, cryolite, fluorapatite,
silicon tetrafluoride, sodium fluorosilicate, fluorocarbons, organic
fluorides, and Group VIA fluorides. Pertinent physical and chemical
properties of these compounds are discussed in the following sections.
2.2.1 Fluorine
Fluorine ranks 13th in abundance among the elements and constitutes
0.06% to 0.09% of the earth's crust (Leech, 1956, p. 3). First isolated
in 1886 by Moissan, elemental fluorine remained largely a laboratory curi-
osity until World War II, when nuclear energy requirements stimulated
commerical production (Weast, 1978). It is now produced in high tonnages.
2.2.1.1 Physical Properties Fluorine (F2) is a pale yellow acrid gas
that freezes to a colorless solid at -219.6°C and boils at -188.2°C; its
heat of formation and energy of dissociation are 18.9 and 37.7 kcal/mole
respectively (Nikolaev et al., 1972). The density of the gas is 1.69 g/
liter (15°C, 1 atm); at -188°C, the density of the liquid is 1.51 (Weast,
1978), and the dielectric constant is 1.517 at -189.95°C (Neumark and
Siegmund, 1966). Physical properties of fluorine are listed in Table 2.1.
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14
TABLE 2.1. PHYSICAL PROPERTIES OF FLUORINE
Property
Value
Melting point (mp)
Boiling point (bp)
Transition temperature, solid
Critical temperature
Critical pressure
Density, solid
Refractive index, liquid at bp
Surface tension, liquid
At -193.26°C
At -206.95eC
Heat of transition, solid
Heat of fusion
Heat of vaporization at bp
Viscosity, liquid
At -187.96°C
At -203.96°C
Viscosity, vapor
At 0°C, 760 mm Hg
Dielectric constant
At -189.95eC
At -215.76"C
Thermal conductivity, gas
At 0°C, 760 mm Hg
-219.62°C
-188.14°C
-227.61°C
-129.00°C
55 atm
1.90 g/cm*
1.2
14.81 dynes/cm
18.85 dynes/cm
173.90 cal/g-mole
121.98 cal/g-mole
1561.3 cal/R-mole
0.257 cP
0.414 cP
0.0218 cP
1.517 e
1.567 e
5.92 x 1Q-3 cal/(sec)(cma)(°C/cm)
Source: Adapted from Neumark and Siegmund, 1966, Table 1,
p. 506. Reprinted by permission of the publisher.
2.2.1.2 Chemical Properties Although the effective nuclear charge of
the fluorine atom is not as great as that for some other elements, the
effective surface charge density of the fluorine atoms is greater than
that of any other element because of its small radius (Durrant and Durrant,
1962). As a result, fluorine is the most electronegative and reactive of
all elements (Weast, 1978).
The standard oxidation potential for the reaction
2F
F2 + 2e
is -2.85 V vs the normal hydrogen electrode (Horton, 1961). Fluorine
combines directly at ordinary or elevated temperatures with all elements
other than oxygen and nitrogen (Banks and Goldwhite, 1966). When finely
dispersed, water, glass, ceramics, carbon, and metals all burn in fluorine
with a bright flame (Weast, 1978). Fluorine reacts with water to form
hydrogen fluoride and oxygen difluoride, with nitric acid to yield the
-------
15
explosive gas fluorine nitrate, and with sulfuric acid to form fluoro-
sulfuric acid. It reacts violently with most organic molecules, usually
with dissociation (Merck, 1976).
Because of the low quantum number and the simple electronic config-
uration of the fluorine atom, its ability to form diverse bond formations
is restricted; the only common states for the fluorine atom in combination
are the ionic form, F~, and the covalent tetrahedral form (Durrant and
Durrant, 1962). Some characteristics of these forms are described below.
2.2.1.2.1 Ionic fluorides Fluorine reacts with metallic elements to
form compounds which are usually ionic, both in the crystalline state and
in solution; they have characteristically high melting and boiling points
(Table 2.2). Most of these salts are readily soluble in water; however,
lithium, aluminum, strontium, barium, magnesium, calcium, and manganese
fluorides are sparingly soluble or insoluble (Latimer and Hildebrand,
1951). The poor solubility of the last three salts has important phys-
iological consequences in cases of acute fluorosis.
TABLE 2.2. PROPERTIES OF SOME IONIC FLUORIDES
Substance
Aluminum fluoride
Calcium fluoride
Cesium fluoride
Lithium fluoride
Magnesium fluoride
Manganese fluoride
Potassium fluoride
Rubidium fluoride
Sodium fluoride
Sodium fluoroalumlnate
Sodium fluorosllicate
Uranium tetrafluorlde
Formula
A1F,
CaFa
CsF
L1F
MgF,
MnF,
KF
RbF
NaF
NajAlF.
NaaSiF,
UF»
Color
White
White
White
White
White
Red
White
White
White
White
White
Green
Melting
point
<°C)
1040
1360
682
842
1225
856
846
775
988
1000
Decomposes
960
Boiling
point
(°C)
1291
2500
1251
1676
2260
1505
1410
1695
Density,
25eC
(g/ml)
3.07
3.18
4.115
2.601
3.0
3.98
2.48
3.557
2.558
2.90
2.679
6.7
Solubility
In water, 18°C
(g/100 ml)
0.559 (25°C)
0.0016
367
0.133 (25"C)
0.0076
0.66 (40"C)
92.3
130.6
4.22
0.034 (15°C)
0.652 (17eC)
Slightly soluble
Source: Compiled from Horton, 1961, and Weast, 1978.
Fluoride ion also has a strong tendency to form complexes with heavy
polyvalent cations in aqueous solution (Horton, 1961; Thomas and Alther,
1966):
Fe
Al
Mn
Mn
3 +
3 +
3 +
2 +
6F
6F
5F
3F
3-
FeF6- ,
A1F63- ,
MnF32~ ,
MnF
2-
-------
16
This behavior, and the previously mentioned formation of insoluble fluo-
rides, are chiefly responsible for the biological toxicity of inorganic
fluorides.
2.2.1.2.2 Covalent fluorides Fluorine and hydrogen fluoride react
with nonmetallic elements to form covalent compounds, such as hydrogen
fluoride, fluorine monoxide, silicon tetrafluoride, sulfur hexafluoride,
organic compounds containing fluorine, and complex anionic forms. Because
of the small size of the fluorine atom and its high electronegativity,
most elements exhibit their highest oxidation state as fluorides. When
all valence-shell electrons of such atoms form covalent bonds with fluo-
rine, increase in coordination number by the formation of ionic crystals
is impossible. Crystals of such compounds consist of simple molecules
held together by van der Waals forces. Accordingly, in contrast to ionic
fluoride compounds, covalent compounds of fluorine tend to have low melt-
ing points and high volatility (Durrant and Durrant, 1962). The melting
points, boiling points, and other physical properties of a wide variety
of covalent fluorides are given in Table 2.3.
2.2.1.3 Occurrence and Synthesis Because of its great reactivity, ele-
mental fluorine does not usually occur free in the environment and, when
introduced, does not long persist unreacted; its occurrence is soon marked
by the formation of fluorinated reaction products.
Elemental fluorine is produced on a commercial scale by the elec-
trolysis of a molten solution of potassium fluoride in anhydrous hydrogen
fluoride. Fluorine gas is formed at the anode, and hydrogen is formed
at the cathode:
2HF -» H2
Some fluorocarbons are also produced during the electrolysis because the
anode is made of carbon; however, the main impurity in the product is
normally hydrogen fluoride. The latter is removed by passing the product
through absorption towers packed with sodium fluoride (National Academy
of Sciences, 1971).
2.2.2 Hydrogen Fluoride
First prepared in the anhydrous state by Fremy in 1856 (Gall, 1966),
hydrogen fluoride (HF) is now a widely used industrial chemical. Because
of this extensive use, hydrogen fluoride is probably the greatest single
atmospheric fluoride contaminant. Due to its great reactivity, however,
hydrogen fluoride is unlikely to remain in its original form very long.
2.2.2.1 Physical Properties Hydrogen fluoride is a colorless, pungent
liquid or gas that boils at 19.5°C and freezes near -83°C (Weast, 1978).
Its heat of formation and energy of dissociation are 64.5 and 140 kcal/mole
respectively (Nikolaev et al., 1972). Hydrogen fluoride is highly soluble
in water and alcohol and fumes strongly in contact with the atmosphere.
-------
TABLE 2.3. PROPERTIES OF SOME COVALENT FLUORIDES
Substance
Ammonium fluoride
Chlorine tri fluoride
Dichlorodifluoromethane
Disulfur decafluoride
Fluoroacetic acid
Hexafluoropropene
Hydrogen fluoride
Oxygen di fluoride
Silicon tetrafluoride
Sulfur hexafluoride
Sulfur tetrafluoride
Tetrafluoroethylene
Tetrafluoromethane
Trichlorofluoromethane
Uranium hexafluoride
Vinyl fluoride
Formula
NHi,F
C1F9
CClaFa
SaFio
FCHaCOOH
C9F6
HF
OF a
SiF«,
SF6
SF*
C2F<,
CF<,
CClaF
UF6
CaH3F
Color
White
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Melting
point
(°C)
a
-82.6
-158
-92
35.2
-156.2
-83.1
-223.8
-90
-50.4
-125.0
-142.5
-150
-111
69.5
-160.5
Boiling
point
(°c)
12.0
-30
29
165
-29.4
19.5
-144.8
-86
-65a
-40.0
-76.3
-129
23.7
56*
-72.2
Density
(g/ml)
1.009 (25°C)
2.04 (-50°C)
1.75 (-115°C)
2.08 (0°C)
1.369 (36°C)
1.583 (-40°C)
1.0015 (0°C)
1.90 (-233°C)
1.66 (-95°C)
1.88 (-50°C)
1.519 (-76°C)
3.034 (0°C)
1.49 (17°C)
4.68 (21°C)
Solubility
in water
(g/100 ml)
100 (0°C)
Reacts
Soluble
Reacts
Soluble
Miscible
Slightly soluble,
reacts
Reacts
Slightly soluble
Reacts
Insoluble
Slightly soluble
Insoluble
Reacts
Insoluble
a
Sublimes.
Source: Compiled from Weast, 1978; Horton, 1961; and Merck, 1976.
-------
18
The density of the liquid is 1.0015 at 0°C (Horton, 1961). The dielectric
constant of liquid hydrogen fluoride is near 84 at 0°C; accordingly, its
solvent power rivals that of water (Moeller, 1952). The formula weight
of hydrogen fluoride is 20.006, but hydrogen bonding between molecules
causes a high degree of association, and both the liquid and gas show
large departures from ideal behavior (Gall, 1966). Other physical prop-
erties of hydrogen fluoride are listed in Table 2.4.
TABLE 2.4. SOME PHYSICAL PROPERTIES OF ANHYDROUS HYDROGEN FLUORIDE
Property
Value
Formula weight, calculated
Molecular weight
Saturated vapor at boiling point (bp)
Saturated vapor at 100°C
Boiling point at 1 atm
Melting point (mp)
Density
Liquid at 25°C
Vapor, saturated, at 25°C
Vapor pressure at 25°C
Heat of vaporization
bp at 1 atm
Heat of fusion at mp
Heat capacity at constant pressure
Liquid at bp
Vapor at 25°C, 1 atm
Heat of formation, ideal gas at 25°C
Free energy of formation, ideal gas at 25°C
Entropy, ideal gas, at 25°C
Critical temperature
Critical pressure
Critical density
Viscosity at 0"C
Surface tension at bp
Refractive index, 5893 A", at 25°C
Molar refractivity, 5893 X, formula weight
Conductivity at 0°C
Dielectric constant at 0°C
Dipole moment, HF molecule
20.006
78.24
49.08
19.51°C
-83.37°C
0.9576 g/cms
3.553 g/liter
17.8 psia
1609 cal/20.01 gfl
1785*
46.93 cal/g
12.2 cal/(20.01 g)(°C)
143 cal/(20.01 g)(°C)
-64.9 kcal/20.01 g
-65.0 kcal/20.01 g
41.5 cal/(20.01 g)(°C)
188°C
941 psia
0.29 g/cm3
0.26 cP
8.6 dynes/cm
1.1574
2.13 cm3
<1.6 * 10"* mho/cm
83.6
1.83 D
.From vapor pressure vs temperature.
From calorimetry.
Source: Adapted from Gall, 1966, Table 1, p. 611. Reprinted by
permission of the publisher.
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19
2.2.2.2 Chemical Properties Anhydrous hydrogen fluoride is one of the
most acidic substances known (Horton, 1961). It readily protonates and
dissolves even nonbasic compounds such as alcohols, ketones, and mineral
acids:
2HF 4- ROH -v ROH2+ + HF2~ ,
2HF + R2CO * R2COH+ + HF2~
2HF + HN03 -v H2N03+ + HF2
Fluorides of the alkali metals, silver, barium, ammonia, and thallium
dissolve in anhydrous hydrogen fluoride and behave as strong electrolytes.
Other metal salts, such as the halides, cyanides, and azides, react with
anhydrous hydrogen fluoride to form the fluoride and the corresponding
acid. The latter is insoluble in hydrogen fluoride and is expelled (Banks
and Goldwhite, 1966):
NaCl + HF -> NaF + HC1 .
Anhydrous hydrogen fluoride reacts with metals more positive than hydrogen
in the electromotive series, providing they do not form insoluble fluoride
films, as aluminum does. Anhydrous hydrogen fluoride is also a strong
dehydrating agent; wood and paper are charred on contact, and aldehydes
undergo condensation by elimination of water (Gall, 1966).
In dilute aqueous solution, hydrogen fluoride is a weak acid; only
about 10% is ionized in 0.1 M solutions. This behavior is unusual com-
pared with the other hydrogen halides and is attributed to the high bond
strength in hydrogen fluoride (Banks and Goldwhite, 1966) (bond energies:
hydrogen fluoride, 135; hydrogen chloride, 103; hydrogen bromide, 87;
hydrogen iodide, 71 kcal/mole). Aqueous hydrogen fluoride (hydrofluoric
acid) is best known for its ability to dissolve glass:
4HF + Si02 * SiFi, + 2H20 .
Anhydrous hydrogen fluoride, both gaseous and liquid, and higher
concentrations of aqueous hydrofluoric acid are all very corrosive to
skin, eyes, lungs, and mucous membrane; extreme care should be taken to
avoid contact with these materials. With dilute solutions of hydrofluo-
ric acid, burns of the skin may not be evident when exposure occurs but
may later become apparent by deep-seated ulceration (Gall, 1966).
2.2.2.3 Synthesis and Use Based on quantity of production, hydrogen
fluoride is the most important manufactured compound of fluorine; it is
used directly or as an intermediate in the preparation of almost every
-------
20
fluoride-containing product (Gall, 1966). Hydrogen fluoride is made in-
dustrially by treating the mineral fluorspar with concentrated sulfuric
acid:
CaF2 + HaSO*. -» CaSO« + 2HF .
The volatile gas is condensed, purified by distillation, and stored in
steel tanks and cylinders (Gall, 1966). About 292,000 metric tons were
produced in the United States in 1977, primarily as anhydrous liquid or
gas (Chemical Marketing Reporter, 1978Z?) . Approximately 40% of this total
was used to manufacture aluminum, and 37% was converted into fluorocarbon
compounds and products. The remainder was used chiefly in processing ura-
nium (7%), in alkylation catalysts in petroleum refining (5%), in manufac-
turing fluoride salts (4%), and in stainless steel pickling operations
(4%). Smaller quantities were used as fluxes in metal casting, welding,
and brazing operations; etching agents in the glass and ceramics indus-
tries; cleaners in metal finishing processes; pesticides; and, of course,
for fluoridation of water, toothpaste, and other products.
2.2.3 Fluorspar, Cryolite, and Fluorapatite
The principal fluoride-containing minerals are fluorspar (CaF2), cry-
olite (3NaF»AlF3), and fluorapatite [CaF2»3Ca3(P0ll)2]. Their theoretical
fluoride contents are 48.5%, 54.5%, and 3.8% respectively. Commercially,
fluorspar is the most important mineral with workable deposits occurring
in all major countries. World production in 1975 exceeded 4,150,000 metric
tons (Quan, 1976). Almost 29% of this amount (1.2 million metric tons)
was consumed in the United States. Physical properties of the purified
form of the mineral are listed in Table 2.5. Cryolite is a relatively
rare mineral which is an essential raw material in the aluminum industry;
its chief physical characteristics are given in Table 2.6. Commercially
important deposits of this material were found only in Greenland, and these
are now exhausted; present supplies are prepared synthetically (National
Academy of Sciences, 1971). Fluorapatite is a constituent of rock phos-
phate; it contains only a small percentage of fluoride and is presently
unimportant as a commercial source of fluorine. Rock phosphate has great
environmental significance, however, as well as potential commercial impor-
tance in the future, because it is mined and consumed in vast quantities
in the production of elemental phosphorus and phosphate fertilizers. Wood
(1975) estimated the fluorine content of the phosphate rock mined annually
in the United States as 729,000 metric tons. It is estimated that all
forms of fluoride emissions to the atmosphere from phosphorus and phosphate
fertilizer production in the United States amounted to more than 16,300
metric tons in 1968 (National Academy of Sciences, 1971, p. 9).
Fluorspar, cryolite, and fluorapatite are essentially insoluble in
water; accordingly, the mammalian toxicity of these compounds is moderate
to low. Their toxicity toward insects is much more pronounced, however,
and synthetic cryolite is sometimes used as an insecticide for the control
of chewing insects, such as the codling moth, the Mexican bean beetle,
flea beetles, and tomato worms (Metcalf, 1966).
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21
TABLE 2.5. PHYSICAL PROPERTIES OF CALCIUM FLUORIDE
Property
Value
Melting point (mp)
Boiling point (bp)
Heat of fusion
Heat of vaporization at bp
Vapor pressure at 2100"C
Specific heat at constant pressure
Solid at 25°C
Solid at op
Liquid at mp
Entropy at 25"C
Heat of formation, solid at 25°C
Free energy of formation, solid at 25"C
Thermal conductivity, crystal at 25°C
Density
Solid at 25*C
Liquid at mp
Thermal expansion, average, at 25°C to 300°C
Compressibility at 25°C, 1 atm
Hardness
Mohs scale
Knoop, SOO-g load
Solubility In water
At 25eC
At 175"C
Refractive index at 24°C, 5893 A
Dielectric constant at 30°C
Electrical conductivity
Solid at 20°C
Solid at 650°C
Solid at mp
1402*C
2513"C
5.5 kcal/mole
80 kcal/mole
7.6 nnn
16.02 cal/(mole)(°C)
30.0 cal/dnoleX'C)
23.9 cal/(mole)(°C)
16.46 cal/(mole)("C)
-290.3 kcal/mole
-278.1 kcal/mole
0.0262 cal/sec(cma)(°C/an)
3.181 g/cms
2.52 g/cm*
22.3 x 10-*/eC
1.24 x lO-'/atm
4
158
0.0017 g/100 g water
0.0018 g/100 g water
1.43382
6.64
1.3 x 1Q-li mho/cm
6 x 10"s mho/cm
3.45 mho/cm
Source: Adapted from Gall, 1966, Table 1, p. 574. Reprinted by
permission of the publisher.
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22
TABLE 2.6. PHYSICAL PROPERTIES OF CRYOLITE
Property
Value
Formula weight
Composition, calculated
Fluorine
Aluminum
Sodium
Melting point (mp)
Transition temperature
Monoclinic to cubic
Second-order
Vapor pressure, liquid, at 1009°C
Heat of fusion at 1009°C
Heat of vaporization at 1009°C
Heat of transition
Monoclinic to cubic at 560°C
Second-order at 880°C
Heat capacity
Monoclinic crystal at 25°C
Cubic crystal at 560"C
Liquid at 1009"C
Entropy, monoclinic crystal at 25°C
Heat of formation, monoclinic crystal at 25°C
Free energy of formation, monoclinic crystal at 25°C
Density
Monoclinic crystal at 25°C
Cubic crystal from x-ray data, at 560"C
Solid at 1009"C
Liquid at 1009°C
Hardness, Mohs scale
Optical properties
Refractive index
Alpha form
Beta form
Gamma form
Biaxial character
Axial plane
Angle of acute bisectrix to C axis
Electrical conductivity
Liquid at 1009°C
Solid at 400°C
Viscosity, liquid, at 1009°C
Surface tension, liquid in air, at 1019°C
Solubility in water
At 25°C
At 100"C
209.94
54.30*
12.85Z
32.85Z
1009
560eC
881 °C
1.9 mm Hg
26.7 kcal/mole
54
2.22 kcal/mole
<0.2 kcal/mole
51.6 cal/(mole)(°C)
65.0 cal/(mole)(eC)
96.8 cal/(mole)(°C)
57.0 cal/(mole)(°C)
-788.9 kcal/mole
-750.1 kcal/mole
2.97 g/cm*
2.77 g/cm*
2.62 g/cms
2.087 g/cms
2.5
1.3385
1.3389
1.3396
Positive
Perpendicular to (010)
43°54'
2.83 IT* cm"1
4.0 x ID'* n" cm'1
6.7 cP
125 dynes/cm
0.042 g/100 g
0.135 g/100 g
Source: Adapted from Call, 1966, Table 2, p. 536. Reprinted by
permission of Che publisher.
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23
2.2.4 Alkali Fluorides
The alkali fluorides have the formula MF, where M represents lithium,
sodium, potassium, rubidium, or cesium. The alkali fluorides are typical
salts; they have high melting and boiling points and, except for the lith-
ium and sodium compounds, are fairly soluble in water. Other physical
properties are listed in Table 2.2. All of the fluorides, except lithium,
absorb hydrogen fluoride to give acid fluorides of the type MHF2 (Banks
and Goldwhite, 1966). This reaction is reversible for the sodium and
potassium salts; on strong heating they dissociate to yield the normal
salt (Durrant and Durrant, 1962):
KHF2 = KF + HF .
This reaction is often used to produce small quantities of anhydrous
hydrogen fluoride in the laboratory.
Sodium fluoride is the most important member of the alkali fluoride
group. It is a white crystalline powder that melts at 988°C and boils at
1695°C (Weast, 1978). It is prepared by neutralizing aqueous hydrofluoric
acid with sodium carbonate. The commercial product is only 90% to 95%
pure because of the presence of fluorosilicates and other impurities
derived from the aqueous hydrofluoric acid (Merck, 1976).
Sodium fluoride is widely used in fluxes, for fluoridation of water
supplies, and for scrubbing hydrogen fluoride from fluorine; it is also
occasionally used as an insecticide and a wood preservative (Rudge, 1962).
Documentation of fatalities caused by accidental fluoride poisonings
shows that sodium fluoride, more than any other compound, is the toxic
agent (Eagers, 1969). To prevent the confusion of sodium fluoride with
common edible materials such as flour, powdered milk, and baking powder,
some states require insecticidal grades of sodium fluoride to be tinted
blue green (Merck, 1976).
2.2.5 Silicon Tetrafluoride and Fluorosilicic Acid
Silicon tetrafluoride is a colorless gas that melts at -90°C, boils
at -86°C (Weast, 1978), and has a pungent odor reminiscent of hydrogen
chloride (Merck, 1976); it is very toxic (Roholm, 1938). Other properties
are listed in Tables 2.7 and 2.8. The gas has little utilitarian value;
its environmental significance is due to its formation in large quantities
during the combustion of coal and the manufacture of normal and triple
superphosphate fertilizers, elemental phosphorus, wet-process phosphoric
acid, aluminum metal, and brick and tile products. The total fluoride
emission to the atmosphere in the United States in 1968 from the above
sources, was estimated to be nearly 63,500 metric tons (National Academy
of Sciences, 1971). The exact fraction of the total attributed to sili-
con tetrafluoride is difficult to determine with certainty, but silicon
tetrafluoride is known to be the chief gaseous pollutant in many of the
-------
24
manufacturing steps. For example, normal and triple superphosphate fer-
tilizers are prepared by treating rock phosphate with sulfuric acid and
phosphoric acid respectively:
CaF2«3Ca3(PO<,)2 + 7H2SO<, + 3H20 > 3CaH<,(PO«)2«H20 + 7CaSO<, + 2HF
and
CaF2«3Ca3(PO<,)2 + 14H3PO<, + 10H20
2»H20 + 2HF .
In each instance, the resulting hydrofluoric acid reacts further with
silica in the rock phosphate to produce silicon tetrafluoride:
4HF + Si0
2H20 .
In modern production plants, off-gases are scrubbed with water, and most
of the silicon tetrafluoride is removed as fluorosilicic acid (Banks and
Goldwhite, 1966):
3SiF<, + 2H20 -+ 2H2SiF6 + Si02
However, large quantities of silicon tetrafluoride and hydrogen fluoride
escape to the atmosphere in older manufacturing plants.
TABLE 2.7. SOME PHYSICAL PROPERTIES OF SILICON TETRAFLUORIDE
Property
Value
Melting point (triple point), 1318 mm
Boiling point
Density of gas at 0°C and 1 atm
Molar refraction
Heat of capacity at constant pressure
Critical temperature
Critical pressure
Heat of formation at 25°C
Heat of sublimation at 177.7"K and 1 atm
Heat of fusion at 182.9°K and 1320 mm
Heat of vaporization at 182.9°K and 1320 nan
Heat of dissociation
Vapor pressure, log p, mm
Sublimation pressure, log p, mm
-90.2°C
-95.0'C
4.69 g/liter
8.40
18.2 cal/(mole)(°C)
14.15 ± 0.02°C
36.66 ± 0.05 atm
-370 kcal/g-mole
6.15 kcal/g-mole
1.69 kcal/g-mole
4.46 kcal/g-mole
232 kcal/g-mole
8.453-957.0/T
10.469-1352.8/T
Source: Adapted from Byrns, 1966, Table 1, p. 651.
Reprinted by permission of the publisher.
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25
TABLE 2.8. SOLUBILITY OF SILICON TETRAFLUORIDE
IN VARIOUS SOLVENTS
Silicon tetrafluoride
Solvent content
(g/100 g solvent)
Acetic acid 1.1
Acetone 3.1
Butyl alcohol 23.4
Ethyl alcohol, absolute 36.4
Ethyl alcohol, 95X 38.1
Glycerol 5.7
Glycol 26.2
Isopropyl alcohol 28.2
Methanol 32.8
Source: Adapted from Byrns, 1966, Table 2,
p. 651. Reprinted by permission of the publisher.
Fluorosilicic acid (H2SiF6), which is formed from the reaction of
silicon tetrafluoride and water, is extremely toxic (Waldbott, 1963). The
acid is very water-soluble and is readily absorbed by vegetation. Concen-
trated solutions are corrosive to glass, ceramics, some metals, and metal
oxides (National Academy of Sciences, 1971). Fluorosilicic acid is some-
times used in hardening cement, preserving timber, manufacturing enamels,
and preserving oil pigments (Merck, 1976). Small amounts of the sodium
salt of fluorosilicic acid (Na2SiF6) are used as an insecticide; it is
said to be more potent as an insecticide and less toxic to higher animals
than sodium fluoride (Metcalf, 1966; Rudge, 1962). The physical properties
of some inorganic fluorosilicates are shown in Table 2.9.
2.2.6 Halogen Fluorides
Fluorine reacts with other halogens to form the interhalogen compounds
shown in Table 2.10. Although some interhalogen compounds have been known
for well over a hundred years, those containing fluorine are relatively
new and are still the objects of considerable research (Emeleus, 1969).
The halogen fluorides are very active compounds that react with
most metals and nonmetals as vigorously as elemental fluorine (Banks and
Goldwhite, 1966); consequently, they are not normally present in the envi-
ronment. They are occasionally released, however, in chemical laboratories
and in certain rocket-engine jtest firings (National Academy of Sciences,
1971). Such gases are rapidly hydrolyzed by moisture in the air to form
hydrogen fluoride, oxygen, and other products.
Halogen fluorides are synthesized in the laboratory by direct union
of the elements, variations in reaction conditions determining the partic-
ular species formed when alternative combinations are possible. Chlorine
-------
TABLE 2.9. PHYSICAL PROPERTIES OF SOME INORGANIC FLUOROSILIGATES
Fluorosillcate
Aluminum
Ammonium
Barium
Calcium
Cuprlc
Ferrous
Lithium
Potassium
Sodium
Formula
Ala(SlF.),.9H,0
(NH*)»S1F.
BaSiF,
CaSiF.«2HaO
CuSiF«-6HjO
FeSiF..6H,0
Li,SiF«.2H,0
K,SiF«
Na,SlF«
Appearance
Hexagonal prisms
Colorless, cubic
Colorless, rhombic needles
White, tetragonal
Blue, rhombic, efflorescent
Pale blue green, trigonal
White, monoclinic
Colorless, cubic
Colorless, hexagonal
Specific
gravity
2.011
4.279
2.662
2.270
1.961
2.33
2.746
2.755
Refractive Index Solubility
u E (g/100 ml)
Very soluble
(cold)
1.3692 18.58 (17.5°C)
0.025 (25eC)
10.58 (22°C),
decomposes
1.4092 1.4080 233 (17"C)
1.3638 1.3848 128.2
1.300 1.296 73 (17°C)
1.339 0.177 (25°C)
1.312 1.309 0.762 (25°C)
Solubility
In alcohol
Soluble
Insoluble
Soluble
Slightly
soluble
Insoluble
Soluble
Insoluble
Insoluble
In acetone
Insoluble
Insoluble
Insoluble
Insoluble
Source: Adapted from Byrns, 1966, Table 3, p. 658. Reprinted by permission of the publisher.
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27
TABLE 2.10. HALOGEN FLUORIDES: TYPES AND BOILING POINTS
AB ABS AB, AB7
C1F (-101°C) GIF, (12eC) C1F5 IF7 (277°C, sublimes)
BrF (20°C) BrF, (126°C) BrFs (41°C)
IFS
Source: Adapted from Emele'us, 1969, p. 11. Reprinted by
permission of the publisher.
trifluoride (C1F3) is probably the most frequently used halogen fluoride.
It is colorless as a gas, yellow green as a liquid, and white as a solid.
Chlorine trifluoride boils near 12°C and melts at -83°C; its odor is sweet
and suffocating. The specific gravity of chlorine trifluoride is 1.82 at
20°C (Bryce, 1964). Glass wool and organic matter burst into flames on
contact with chlorine trifluoride, and even quartz is attacked if traces
of moisture are present. Chlorine trifluoride is used in nuclear reactor
fuel processing, as a fluorinating agent in chemical reactions, and as an
igniter and propellant for rockets (Merck, 1976).
2.2.7 Group VIA Fluorides
Fluorine reacts with the Group VIA elements to form a variety of
fluorides. Most of these compounds are infrequent contaminants of the
environment. Only the following compounds are of interest here: oxygen
difluoride, sulfur tetrafluoride, disulfur decafluoride, and sulfur
hexafluoride.
Oxygen difluoride (OF2) is a toxic, colorless gas sometimes used as
a high-energy oxidizer in rocket-propulsion systems. Oxygen difluoride
can also occur in laboratory or manufacturing operations when fluorine
reacts with dilute aqueous sodium hydroxide solutions (Emele'us, 1969) or
when halogen fluorides are hydrolyzed (National Academy of Sciences, 1971).
Oxygen difluoride melts at -223.8°C and boils at -145.3°C (Streng, 1963).
It does not attack glass in the cold, reacts only slowly with water, but
corrodes mercury. Unlike fluorine and hydrogen fluoride, oxygen difluoride
is not readily detectable by smell and causes no immediate discomfort even
in potentially lethal concentrations; however, it is considered the most
dangerous of the gaseous inorganic fluorine compounds (Lester and Adams,
1965). Other properties of oxygen difluoride are listed in Table 2.11.
Sulfur tetrafluoride (SF*) is a colorless gas that reacts violently
with water and attacks glass but not quartz or mercury. It melts at
-121°C, boils at -40.4°C, and is thermostable to 600°C; other physical
properties are given in Table 2.12. It is prepared on an industrial scale
by treating sodium fluoride with sulfur dichloride in acetonitrile at 70
to 80°C (Merck, 1976). Sulfur tetrafluoride is a unique fluorinating agent
for organic compounds; it directly replaces carbonyl oxygen with fluorine.
Accordingly, sulfur tetrafluoride is mainly used in the laboratory and
-------
28
TABLE 2.11. SOME PHYSICAL PROPERTIES OF
OXYGEN DIFLUORIDE
Property
Value
Formula
Formula weight
Color
Freezing point
Boiling point
Critical temperature
Critical pressure
Critical density
Heat of formation
Heat of vaporization
Dipole moment
Density
Gas, normal temperature
and pressure
Liquid at melting point
OFa
54.0
Colorless (gas), pale
yellow (liquid)
-223.8CC
-145.3°C
-58.0'C
48.9 atm
0.553 g/ml
7.6 kcal/mole
2.65 kcal/mole
0.1759 D
2.41 mg/ml
1.932 g/ml
Source: Adapted from Streng, 1963, Table I,
pp. 608-609. Reprinted by permission of the
publisher.
TABLE 2.12. SELECTED PHYSICAL PROPERTIES OF
SULFUR TETRAFLUORIDE
Property
Value
Melting point (rap)
Boiling point (bp)
Critical temperature
Surface tension at bp
Dipole moment
Heat of formation
Molar heat of vaporization
Trouton's constant
-40.4°C
90.9°C
19.85 dynes/cm
0.632 D
-171.7 i 2.5 kcal/g-mole
6320 cal
27.1
Source: Adapted from Brown, 1966, Table 5, p.
671. Reprinted by permission of the publisher.
chemical manufacturing operations to prepare gem-d±fluorides from aldehydes
and ketones and to convert carboxylic acids to trifluoromethyl compounds
(Banks and Goldwhite, 1966). Sulfur tetrafluoride is very poisonous; its
toxicity is comparable with that of phosgene (Merck, 1976).
Disulfur decafluoride (S2F10) is a dense colorless liquid that melts
at -92°C and boils at 29°C (Weast, 1978). Other physical properties are
listed in Table 2.13. Disulfur decafluoride occurs as a toxic by-product
-------
29
TABLE 2.13. SOME PHYSICAL PROPERTIES OF
DISULFUR DECAFLUORIDE
Property Value
Melting point -92°C
Boiling point 29°C
Trouton's constant 23.0
Surface tension at 0°C 13.9 dynes/cm
Liquid density at 0°C 2.08 g/ml
Specific electrical conductivity 10"" mho/ml
Dielectric constant at 10°C 2.030
Heat of vaporization 7 kcal/g-nole
Source: Adapted from Brown, 1966, Table 6,
p. 673. Reprinted by permission of the publisher.
when sulfur is treated with fluorine; it can also be formed by the partial
decomposition of sulfur hexafluoride in high-voltage electric discharges
(National Academy of Sciences, 1971). Disulfur decafluoride is very reac-
tive and is considered more toxic than fluorine (Eagers, 1969).
Unlike sulfur tetrafluoride and disulfur decafluoride, sulfur hexaflu-
oride (SF6) is nontoxic and chemically inert (Banks and Goldwhite, 1966).
It is prepared by burning sulfur in fluorine and washing the product with
aqueous alkali to remove the unwanted tetrafluorides and decafluorides.
The colorless gas, which melts at -50.4°C and sublimes at -65°C under 2.21
atm absolute pressure, is widely used as a dielectric in high-voltage elec-
trical equipment (National Academy of Sciences, 1971). Several additional
properties of this compound are listed in Table 2.14.
2.2.8 Organic Fluorides
Covalently bound fluorine so closely resembles hydrogen that it
is possible, in principle, to synthesize fluorine analogs for almost all
of the presently known hydrocarbons and their derivatives; already, sev-
eral thousand fluorine-containing organic compounds have been prepared
(Banks and Goldwhite, 1966). The chemical and physiological properties
of many of these compounds differ greatly from those of their hydrocarbon
counterparts. These differences stem largely from the greater electro-
negativity of fluorine, compared with hydrogen, which makes the covalent
carbon-fluorine bond much stronger (approximately 116 kcal/mole) than
the similar carbon-hydrogen bond (approximately 99 kcal/mole) (Barry and
Norbury, 1974). Of the many potentially interesting organic fluorides,
this report can consider.here only two classes: fluorocarbons and natur-
ally occurring monofluoro aliphatic compounds.
2.2.8.1 Fluorocarbons Technically, the term fluorocarbon refers to
compounds containing only carbon and fluorine. It is used here, however,
in its popular sense which encompasses, additionally, compounds contain-
ing the other halogens or hydrogen or both.
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30
TABLE 2. lit. PROPERTIES OF SULFUR HEXAFLUORIDE
Property
Value
Chemical formula
Molecular weight
Critical temperature
Critical pressure
Critical density
Triple-point temperature
Triple-point pressure
Boiling point at 1.0133 x 10s N/ma
Melting point
Transition temperature
Density of solid at -91.15°C
Coefficient of thermal expansion of
liquid at melting point
Heat of formation of gas at 25°C
Free energy of formation of gas at 25°C
Heat of sublimation at -63.7°C
Heat of fusion
Heat of transition
Entropy of gas at 25°C
Heat capacity ratio of gas at 25°C
and 1.0133 x 10s N/m3
Velocity of sound at 0°C and
1.0133 x 10s N/ma
Dielectric constant of gas at 25°C
and 1.0133 x 10s N/ma
Refractive index of gas at 2S°C and
1.0133 x ios N/ma
Threshold limit value
SF.
146.0504
45.54°C
37.600 x 10s N/ma
736.0 kg/m'
-50.0°C
2.3267 x 10s N/ma
-68.0°C
-50.7°C
-179.15°C
2550.0 kg/ms
-1.2217 x io» J kg-mole"1
-1.1177 x 10' J kg-mole'1
2.2860 x 107 J kg-mole'1
5.0242 x io4 J kg-mole'1
1.6077 x io« J kg-mole"1
2.9187 x io5 J kg-mole'1 C"1
1.29
131.2 m/sec
1.002049
1.000766
1000 ppm (6 x 10~S kg/ms)
Source: Adapted from Horvath, 1975, Table 9.1, p. 118. Reprinted
by permission of the publisher.
Fluorocarbons are prepared by various techniques. The most direct
method is based on fluorination of a vaporized hydrocarbon using elemental
fluorine. The reaction is highly exothermic and must be performed in the
presence of inert gas diluent in a metal-packed reactor that can remove
excess heat before thermal dissociation of the product occurs. Less ener-
getic reaction conditions are possible in certain instances, by replacing
the fluorine gas with less potent fluorinating agents, such as hydrogen
fluoride, cobalt(III) fluoride, silver(II) fluoride, antimony(III) fluo-
ride, chlorine monofluoride, or chlorine trifluoride. For some products,
the method of choice involves an entirely different technique the elec-
trolysis between nickel electrodes of a solution of the organic compound in
anhydrous hydrogen fluoride. A potential of 5 to 6 V is usually applied.
-------
31
Hydrogen is evolved at the cathode, and fluorination of the dissolved com-
pound takes place at the anode; no anodic gas is formed. Usually, all
hydrogen atoms in the dissolved compound are replaced with fluorine, double
bonds are saturated, fragmentation of the molecule occurs, and functional
groups are retained. See Banks and Goldwhite (1966), Emeleus (1969), Fed-
eral Task Force on Inadvertant Modification of the Stratosphere (1975),
Rudge (1962), and Sargent and Seff1 (1970) for extensive discussions of
these preparatory procedures.
Fluorination of organic compounds and products constituted the great-
est single use of hydrogen fluoride in the United States in 1968; about
90,700 metric tons was used that year for that purpose (National Academy
of Sciences, 1971). By 1977, U.S. consumption of hydrogen fluoride had
grown to 108,000 metric tons, resulting in the production of 386,000 met-
ric tons of fluorocarbons (Chemical Marketing Reporter, 1978a, 1978£>).
The fluorocarbons, which were used chiefly for aerosol propellants (24%),
refrigerants (39%), solvents (11%), and blowing agents (12%), included
dichlorodifluoromethane, trichlorofluoromethane, tetrafluoromethane, tet-
rafluoroethene, vinyl fluoride, and hexafluoropropene. The first three
compounds of this group have high chemical stability, low toxicity, low
boiling points, and vapor pressures suitable for propellants or refriger-
ants. The last three compounds are unsaturated and can be polymerized into
solids that have exceptionally low coefficients of friction and remarkable
chemical inertness. The physical properties of these and related compounds
are summarized in Table 2.15. In 1978, nonessential uses of fluorocarbon
propellants were banned by the U.S. Environmental Protection Agency, and
this segment of the fluorocarbon market shrank to about 2% of its former
value. As a consequence, the total U.S. market for fluorocarbons was
expected to decline to about 309,000 metric tons in 1978 and perhaps even
further in 1979. However, annual increases of 5% to 6% are projected for
overall fluorocarbon demand from 1980 through 1983 (Chemical Marketing
Reporter, 1978a).
In addition to the major uses of fluorocarbons cited above, numerous
minor applications also exist such as fire extinguishing agents (CF3Br,
CF2Br2, and CF2BrCl), inhalation anesthetics (CF3CHBrCl), and specialized
cleaners and degreasers (CF2C1CFC12) (Banks and Goldwhite, 1966; Rudge,
1962).
Although saturated compounds of carbon and fluorine are neither toxic
nor narcotic, many of the higher unsaturated compounds of carbon and fluo-
rine or of carbon, hydrogen, fluorine, and other halogens are very toxic
(Rudge, 1962).
2.2.8.2 Fluoroacetate and Fluorooleic Acid Thousands of synthetically
prepared organic compounds containing fluorine are known, but only a few
occur naturally. Historically and physiologically, the most important of
these are the monofluoroaliphatic compounds, fluoroacetic acid (FCH2COOH)
and u-fluorooleic acid [F(GH2)8CH=CH(CH2)7COOH(<2£s) ]. Fluoroacetic acid
is the toxic principle in the leaves of various species of Dichapetalum,
Acaciat Gastrolobiwn, and Palicourea (Smith, 1970); it melts at 35.2°C,
boils at 165°C, and is soluble in water and alcohol (Weast, 1978). At
the pH of cell sap, the compound presumably exists as the fluoroacetate.
-------
TABLE 2.15. SOME PHYSICAL PROPERTIES OF ALIPHATIC FLUOROCARBONS
Compound
Trichlorofluoromethane
Dichlorodif luorome thane
Chlorotrlfluoronethane
Dlchlorofluo rone thane
Chlorodif luororae thane
Chlorofluoromethane
Tetraf luorome thane
Tr if luorome thane
Dif luorome thane
Fluoromethane
Hexaf luoroethane
Pen taf luoroethane
1,1,1 ,2-Tetraf luoroethane
1 , 1 ,1-Trif luoroethane
1 ,1-Dif luoroethane
Fluoroethane
Tetraf luoroethene
1,1, 2-Trif luoroethene
1 , 1 -Dif luoroethene
Fluoroethene (vinyl fluoride)
Octafluoropropane
Hezafluoropropene
Formula
CC1,F
CClaF,
CC1F,
CHClaF
CHClFa
CHaCIF
CF.
CHF,
CH,Fa
CHjF
CF»-CF»
CHFa-CF,
CHaF-CF,
CHa-CF,
CHs-CHFa
CHa-CHaF
CFa-CFa
CHF-CFa
CHa~CF»
CHa^HF
CF,-CTa-CF»
CFaCF-CFa
Molecular
weight
137.38
120.93
104.47
102.93
86.48
68.48
88.01
70.02
52.03
34.03
138.02
120.03
102.04
84.04
66.05
48.06
100.02
82.03
64.04
46.05
188.03
150.02
Boiling
point
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33
Unlike inorganic fluorides, fluoroacetic acid is not poisonous, per
se; it has little or no effect on isolated enzymes or those organized in
mitochondria (Bartlett and Barron, 1947). However, fluoroacetic acid is
readily metabolized to fluorocitric acid. One of the isomers of fluoro-
citric acid irreversibly complexes aconitase which prevents the conversion
of citric acid to aconitate, disrupts the Krebs cycle, and causes metabolic
death of the cell (Goldman, 1969). Fluoroethanol (FCH2CH2OH), which also
is not intrinsically toxic, has an apparent odor of toxicity as great as
fluoroacetate because of its metabolic conversion to the latter (Pattison
and Peters, 1966). The sodium salt of synthetically produced fluoroacetic
acid was formerly used extensively in the United States for the control of
rats and other mammalian pests ("rodenticide 1080"). However, its manu-
facture and use in interstate commerce for predator control was banned by
the U.S. Environmental Protection Agency (1972). Accidental ingestion of
this compound has resulted in several human fatalities (Sollmann, 1957)
(see Section 6).
(D-Fluorooleic acid occurs in the seeds of Dionapetalwn toxicarium,
along with traces of lower u-fluorocarboxylic acids containing an even
number of carbon atoms in their chain. The presence of these trace com-
pounds suggests that a>-fluorooleic acid is built up in steps of two carbon
atoms from the lower fatty acids, beginning with fluoroacetate (Pattison
and Peters, 1966). Like fluoroacetate, u-fluorooleic acid inhibits aco-
nitase in kidney mitochondrial preparations, causes citrate accumulation
in the tissues, and is toxic to mammals. Although the lower odd-numbered
carbon acids show little or no toxicity, all the lower even-numbered car-
bon acids are poisonous. These circumstances correspond to the Knoop rule
for the degradation of fatty acids and suggest that the toxicity of the
even-numbered carbon compounds is due to their ultimate degradation to
fluoroacetate (Pattison, 1959).
2.2.9 Uranium Hexafluoride
In the United States, isotopically enriched uranium required for
nuclear reactor fuel and nuclear weapons is obtained by processing uranium
hexafluoride in gaseous diffusion plants (Drury, 1967, p. 85). Preparation
of the necessary uranium hexafluoride requires large amounts of hydrogen
fluoride; in 1974 about 9000 metric tons was used for this purpose (Ck&n-
iedl and Engineering News, 1975).
Uranium hexafluoride can be prepared from naturally occurring uranium
oxides by a variety of processes; the method used for large-scale produc-
tion is dictated by economic considerations. Currently, a series of chem-
ical steps are employed. The trioxide is first reduced to the dioxide by
treatment with hydrogen gas at 700°C:
H2 * U02 + HaO
-------
34
The resulting dioxide is converted to the tetrafluoride with hydrogen
fluoride at 500°C:
U02 + 4HF * UFA + 2H20 .
The latter is then converted to the final product by treatment with fluo-
rine at 350°C:
UF
F2 -* UF6
The intermediate product, uranium tetrafluoride, is a green crystalline
solid that melts at 960°C. It is only poorly soluble in water and is
relatively inert chemically (Simons, 1964).
Uranium hexafluoride is a colorless, extremely corrosive, crystal-
line solid that sublimes at 56°C and melts at 69.2°C under 2 atm pressure
(Rudge, 1962). Other physical properties are listed in Table 2.16. Ura-
nium hexafluoride is a very reactive, toxic compound, a powerful oxidizer,
and a strong fluorinating agent (Banks and Goldwhite, 1966; Eagers, 1969).
Uranium hexafluoride attacks glass and quartz, but not copper, nickel,
aluminum, or silver; it is also unreactive to oxygen, nitrogen, chlorine,
bromine, and saturated fluorocarbons (Simons, 1964).
TABLE 2.16. SOME PHYSICAL PROPERTIES OF
URANIUM HEXAFLUORIDE
Formula
Formula weight
Color
Melting point
Boiling point
Density
Dipole moment
Dielectric constant
Surface tension
Heat of formation
Solid
Heat of vaporization
Heat of fusion
Heat of sublimation
UF.
352.07 g
Colorless to pale yellow
69.5°C
56°C (sublimes)
4.68 g/ml at 21°C
0.0 D
4.2 x 10" e'1
15.6 dynes/cm at 80eC
-516 kcal/mole at 25°C
6.907 kcal/mole at 64"C
4.588 kcal/mole at 64°C
11.495 kcal/mole at 64°C
Source: Compiled from Horton, 1961, and
Mattson, 1970.
-------
35
Although large quantities of uranium hexafluoride are handled at
atomic energy installations and industrial plants, stringent control
measures are applied because of the radioactivity of the uranium, and as
a result few emissions to the environment occur (National Academy of
Sciences, 1971).
2.3 ANALYSIS FOR FLUORIDE
2.3.1 Sampling and Sample Preparation
Fluorides occur in the environment as organic and inorganic gases,
liquids, and solids. Specialized techniques are required to obtain repre-
sentative samples of the various forms, and certain precautions are neces-
sary to avoid contamination of, or loss of fluoride from, these samples.
The principal requirements for handling the various sample types are dis-
cussed in the following sections.
2.3.1.1 Fluoride in Air Hydrogen fluoride, silicon tetrafluoride, and
particulates such as sodium and calcium fluorides constitute the chief
inorganic fluoride contaminants of air (National Academy of Sciences,
1971). Fluorine, because of its great reactivity, is rarely present in
elemental form. Concentrations of fluoride in excess of 1.5 yg/m3 seldom
occur in nonindustrial atmospheres; the usual range is from less than 0.05
to 0.5 yg/m9 (Katz, 1968; Thompson, McMullen, and Morgan, 1971). Higher
concentrations are found near facilities manufacturing steel, aluminum,
phosphorus, phosphate fertilizers, bricks, pottery, and ceramics, as well
as near large coal-fired power plants. Samples may be collected manually
or automatically. Manual techniques include sorption of fluorides on
beads or tubing coated with sodium bicarbonate or other basis compounds,
or use of a liquid-filled bubbler (Figure 2.1) or impinger-type collector
(Figure 2.2) with or without a prefilter to remove particulate fluorides
(Jacobson and Weinstein, 1977). Countercurrent scrubbers and spray col-
umns are also utilized. Usually, at least 1 to 10 m3 of air are processed.
Bubblers and scrubbers normally contain water or a solution of sodium or
potassium hydroxide; the resulting fluoride solution may be further proc-
essed, prior to analysis, as decribed in Section 2.3.1.2. Automated equip-
ment for determining gaseous fluorides in air are also available. These
instruments extract gaseous fluoride constituents from air with absorbing
liquids or solids during a specified sampling period, then flush the sample
into a cell where the fluoride ion concentration is measured by a specific
ion electrode whose signal is amplified and displayed on a recording device
(Jacobson and Weinstein, 1977). Particulate fluorides are prefiltered and
are not determined in presently available instruments. When it is impor-
tant to determine particulate fractions of the sample, fractionation is
usually accomplished by prefiltering the air sample (Mandl et al., 1971;
Pack et al., 1959). The partl'culate matter generally requires fusion with
alkali hydroxide to convert it into a soluble form prior to separating the
fluoride for analysis (Intersociety Committee on Methods for Ambient Air
Sampling and Analysis, 1969). Sampling devices and procedures are dis-
cussed in detail by the American Industrial Hygiene Association (1972) ,
Hendrickson (1968), Israel (1974), Jacobson and Weinstein (1977), MacDonald
(1970), Marshall and Wood (1968), and Thompson, McMullen, and Morgan (1971).
-------
36
ORNL-OWG 77-9689R
27
cm
275ml
225
175
125
75
5 mm-
BAFFLE
2.3-mm
/ HOLE
5 mm
30ml
16
cm
20
CENTERING
LUGS
10
1-mm HOLE
WATER. ETHYL, NORMAL PROPYL. OR
ISOPROPYL ALCOHOL
Figure 2.1. Typical wet-impinger collector. Source: Adapted from
American Industrial Hygiene Association, 1972, Figure 9-22, p. 133.
Reprinted by permission of the publisher.
-------
37
ORHL-DWO 77-12899
AEROSOL
INLET
IMPACT ION
SLIDES
AEROSOL
INLET
IMPACTION
SLIDE
CLEANED AIR
OUTLET
LARGE JET.
LARGE
PARTICLE
IMPACTION
SLIDE
CLEANED AIR
OUTLET
SMALL
'PARTICLE
SMALL
'JET
SMALL
"PARTICLE
IMPACTION
SLIDE
IMPACTION
SLIDE
Figure 2.2. Types of dry, cascade Impingers. Source: Adapted from
American Industrial Hygiene Association, 1972, Figure 9-23, p. 134.
Reprinted by permission of the publisher.
2.3.1.2 Fluoride in Water Fluoride usually occurs in water in the ionic
state. Except for unusual circumstances, the concentration of fluoride in
natural waters is low usually less than 1 ppm (Cholak, 1959a). However,
the concentration of fluoride in Industrial waste streams depends on the
chemical process involved; for example, typical processing solutions from
-------
38
the chemical milling of titanium metal contain about 100,000 ppm fluoride
(Staebler, 1975). Samples are normally taken in glass or, preferably,
polyethylene containers. Typically, storage losses are not troublesome
(Sholtes et al., 1973), but acidic samples should be handled in plastic
or other inert containers and should be treated with a known excess of
base or fixative (Horton, 1961). When interfering ions are absent, the
fluoride determination can be made directly; however, polyvalent complex-
able cations, such as aluminum, silicon(IV), and iron(III), interfere; so
do chloride, sulfate, and phosphate (American Public Health Association,
American Water Works Association, and Water Pollution Control Federation,
1971). For colorimetric analysis a preliminary acid distillation is rec-
ommended to free the sample of contaminants. If the resulting distillate
is colored or turbid, the solution is made alkaline, the fluoride is
adsorbed on magnesium oxide which is removed by centrifugation, and the
preliminary distillation step is repeated with the purified product
(American Public Health Association, American Water Works Association,
and Water Pollution Control Federation, 1971). When fluoride is deter-
mined by the electrode technique, the distillation step can usually be
eliminated [even when the sample contains such ions as aluminum, hexamet-
aphosphate, iron(III), and orthophosphate] if a citrate buffer solution
is added to the sample. The citrate complexes the interfering cations,
releasing fluoride ion for analysis (American Public Health Association,
American Water Works Association, and Water Pollution Control Federation,
1971).
2.3.1.3 Fluoride in Soils and Minerals This class of samples often
requires extensive preanalysis preparation, and careful manipulation is
required to avoid loss or contamination of the sample. Samples are usu-
ally homogenized in ball or hammer mills. Organic matter, if present,
is removed by ashing. For soil samples, ashing is normally performed at
about 575°C, using fluoride-free calcium oxide as a fixative (Horton,
1961). Refractory materials that do not easily dissolve in sulfuric or
perchloric acid are fused with alkali carbonate or hydroxide to convert
them to a soluble form. Jacobson and Weinstein (1977) and Brewer (1965)
reviewed in detail the various aspects of preparing soil and mineral
samples.
2.3.1.4 Fluoride in Plant Tissues Representative sampling of plant
material is difficult to accomplish. Variations in composition occur,
not only in different parts of the plant but also diurnally and season-
ally. Additionally, it is necessary to distinguish surface fluoride on
the plant from fluoride in the plant. In general, field errors greatly
exceed laboratory errors in the analysis of plant materials; only by tak-
ing relatively large numbers of samples can the population variability
be adequately measured (Allen et al., 1974; Jacobson and Weinstein, 1977).
When collected, the samples are usually washed, dried, ashed, and fused
with alkali before the fluoride is separated for analysis. If samples
are not to be processed immediately, they are frequently stored in a
frozen state with fluoride-free calcium oxide added to prevent loss of
fluoride.
-------
39
Various washing techniques are used. The Intersociety Committee on
Methods for Ambient Air Sampling and Analysis (1969) recommends a gentle
30-sec bath in a polyethylene vessel containing a solution 0.05% in Alco-
nox and 0.05% in sodium ethylenediaminetetraacetate, followed by 10-sec
rinses in each of three beakers of deionized water. Typically, drying
is performed in an oven at 70 to 80°C for 24 to 48 hr, usually without a
lime fixative. Ashing is accomplished by heating the plant material in
a nickel, Inconel, or platinum crucible to 400 to 600°C for 2 hr. In
many plant samples this ashing step results in refractory fluorides that
do not readily dissolve in subsequent operations; it is therefore good
technique to fuse the ashed sample with alkali carbonate or hydroxide to
ensure solubility of the residue (National Academy of Sciences, 1971).
After fusion, the melt is dissolved and the fluoride is separated for
analysis. Also see Jacobson and McCune (1969), Jacobson and Weinstein
(1977), and Kakabadse et al. (1971) for additional discussion of sample
handling techniques.
2.3.1.5 Fluoride in Animal Tissues The procedures described for plant
samples are generally applicable to animal tissues, except that rapid
freezing prior to storage is desirable because of the lower stability
of animal tissues. Also, since most soft tissues contain little silica
or aluminum, they seldom form refractory fluorides, and fusing the ashes
of these tissues with alkali carbonate or hydroxide is generally unnec-
essary. Samples of skeletal tissues are simply prepared; they are freed
from flesh, dried, and ashed at 500 to 600°C. The fluoride in the residue
is then ready for separation and analysis. After gentle evaporation to
dryness, body fluids (e.g., blood, serum, and urine) are treated similarly
(National Academy of Sciences, 1971); however, this procedure is not always
necessary if the specific ion electrode or diffusion methods are used to
determine fluoride concentrations. Venkateswarlu (1975) compared ten dif-
ferent procedures for determining fluoride in unwashed bovine and human
sera; he found results for nonionic fluoride and total fluoride erratic,
especially by diffusion methods, and recommended ashing such samples prior
to analysis.
Reagents commonly used in large amounts in preparing plant and animal
tissue for analysis, such as alkaline fixatives, often contain sufficient
fluoride to alter the subsequent analysis drastically. If realiable assays
are to be obtained, the utmost caution must be exercised to use fluoride-
free materials (Weddle and Maurer, 1954).
2.3.2 Separation of Fluoride
Substances are present in many analytical samples that interfere
in the subsequent determination of fluoride. Accordingly, except for
specific ion electrode analysis, it is common practice to isolate the
fluoride from other constituents of analytical samples (Horton, 1961;
Jacobson and Weinstein, 1977). Distillation, diffusion, ion exchange,
and precipitation techniques are most frequently used.
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40
2.3.2.1 Distillation - Until recently, distillation was the most widely
used technique for separating fluoride from other constituents of analyt-
ical samples (Jacobson and Weinstein, 1977; MacDonald, 1970; National Acad-
emy of Sciences, 1971; Nikolaev et al., 1972). Many variants of the method
exist, but the basic procedure (Willard and Winter, 1933) consists of vol-
atilizing hexafluorosilicic acid from an acid solution in the presence of
glass or quartz, with steam vapor as the carrier. A representative dis-
tillation apparatus is shown in Figure 2.3. Recovery of fluoride depends
on the geometry of the container, temperature, acid, and impurities; gen-
erally, distillation from perchloric acid at 135°C is preferred. Chloride
in the distillate interferes but can be fixed by addition of a soluble
silver salt. Similarly, small amounts of interfering sulfate can be fixed
with a soluble barium salt; however, excess barium must be avoided since
insoluble barium fluoride may be precipitated (Horton, 1961).
ORNL-DWG 79-20895
A - STEAM GENERATOR
B - DISTILLING FLASK
C - CONDENSER
0 - STEAM RELEASE TUBE
E - THERMOMETER
f - PLATE
G - RECEIVER
H - SAFETY TUBE
I - RUBBER TUBING
J- SOFT GLASS BEADS
K - BOILING CHIPS
Figure 2.3. Apparatus for distillation of fluoride. Source:
Adapted from Katz, 1977, Figure 203.1, p. 388. Reprinted by permission
of the publisher.
-------
41
2.3.2.2 Diffusion The isolation of fluoride in microsamples is often
accomplished by the diffusion method (National Academy of Sciences, 1971).
In this simple technique, an aliquot of the prepared sample is mixed with
acid and sealed in a vessel containing an alkali, which absorbs the liber-
ated hydrogen fluoride gas. Typically, the sample aliquot contains 30 yg
of fluoride, or less, in a volume of 1 ml. It is placed in a polyethylene
container (Conway diffusion dish) and mixed with 2 ml of concentrated per-
chloric acid. The microdiffusion dish is then quickly sealed with a lid
on whose inner surface 0.05 ml of alcoholic sodium hydroxide solution has
been deposited and dried. The sealed dish is heated in a 60°C oven for 16
to 20 hr, after which the alkaline absorbent is removed for fluoride anal-
ysis by the desired analytical method. An alternative arrangement is shown
in Figure 2.4. Interfering materials that volatilize under the described
conditions must be fixed or eliminated prior to the diffusion process.
Sulfites are converted to nonvolatile sulfates by treatment with hydrogen
peroxide, and chlorides are fixed by adding silver perchlorate (Intersoci-
ety Committee on Methods for Ambient Air Sampling and Analysis, 1969, p.
72). Because the required diffusing time increases with fluoride concen-
tration, this method of isolating fluoride from the sample matrix is only
used for samples containing small amounts of fluoride (Horton, 1961).
Obviously, only acid-labile fluoride is collected in the diffusion method.
If other forms of fluoride are present, previously described preanalysis
procedures must be used to convert them to the acid-labile form. See
Jacobson and Weinstein (1977), MacDonald (1970), Nicholson (1966), Singer
and Armstrong (1965), and Taves (19682?) for further discussion of the
separation of fluoride by the diffusion technique.
ORNL-OWG 79-20894
B .C ^D ^E
Figure 2.4. Diffusion apparatus: (a) vaseline seal, (2?) acidified
sample, (0) plastic cup, (d) trapping solution, and (e) lid. Source:
Adapted from Taves, 19682?, Figure 1, p. 970. Reprinted by permission of
the publisher.
2.3.2.3 Ion Exchange Samples may be freed of cationic contaminants by
preferentially absorbing the fluoride species on an ion exchange resin,
followed by desorption in a small volume of eluant (Jacobson and Weinstein,
1977; MacDonald, 1970; Nielsen, 1960; Nikolaev et al., 1972). A typical
-------
42
chromatographic column consists of a borosilicate tube that has an inside
diameter of 10 mm and is 16 cm long, with a fritted glass disk and a stop-
cock sealed in the base and a 100-ml reservoir attached to the top. The
column is filled to a height of 10 to 12 cm with preconditioned 60 to 100
mesh anion exchange resin, such as Duolite A-A1, lonac A 302, Permutit A,
or Rexyn 205. Fluoride is fixed on the resin when the acidified sample is
passed through the column; interfering cations are not absorbed and are
discarded. The fluoride is eluted from the resin with 0.1 N sodium hydrox-
ide, and the purified fluoride solution is analyzed by a convenient method
(Intersociety Committee on Methods for Ambient Air Sampling and Analysis,
1969). Ion exchange methods are also useful for concentrating dilute solu-
tions of fluoride. Despite its usefulness, however, the ion exchange
method of separating fluoride appears to be little used, compared with
the distillation and diffusion techniques.
2.3.2.4 Precipitation In general, fluoride compounds are more soluble
than salts conventionally used as precipitates in analytical chemistry
(Nikolaev et al., 1972); consequently, precipitation is now used only in-
frequently to isolate fluoride from other elements in the sample. When
the technique is used, the precipitated species is usually calcium fluoride
or lead chlorofluoride (Horton, 1961; MacDonald, 1970; McKenna, 1951a).
2.3.2.5 Solvent Extraction Venkateswarlu (1974) isolated and concen-
trated fluoride from a variety of biological materials by equilibrating
acidified samples with diphenylsilanediol dissolved in toluene; the fluo-
ride is extracted into the immiscible organic solvent as fluorosilane.
The latter is then back-extracted into an aqueous sodium hydroxide solu-
tion as fluoride ion, which can be analyzed with the fluoride ion elec-
trode or other convenient technique. Good recoveries are obtained, and
a 30- to 50-fold increase in fluoride concentration is possible by reduc-
ing the volume of the back extract. However, separation of fluoride by
solvent extraction sometimes yields negatively biased results (Jacobson
and Weinstein, 1977) , and the technique does not appear to be used
extensively.
2.3.3 Methods of Analysis
Fluoride in environmental samples can be determined by a variety
of procedures; those which are currently important or show promise of
future usefulness are described in this section. The performance and
limitations of each method are emphasized rather than minute operational
details. Summaries of the methods are given in Table 2.17. It is impor-
tant to realize that variations in sensitivity, precision, and accuracy
occur, not only among different methods but also among various models of
analytical instruments and among different operators (Karasek, 1975):
the tabulated data should therefore be considered representative rather
than definitive. Performance data obtained from sources interested in
developing a new method usually reflect optimized conditions. Interlab-
oratory comparisons, when they exist, offer more realistic comparisons
of the various methods.
-------
TABLE 2.17. METHODS FOR DETERMINING FLUORIDE
Analytical method
SpectrophoCometry
Fluoride ion electrode
Titrimetry
Important application
Limit of detection
Precision (relative
standard deviation)
Accuracy (relative
error)
Interfering substances
Selectivity
Comments
Samples from air, water, soil, and
biological sources
0.2 ug/ml (zirconyl-SPADNS, zirconyl
eriochrome, cyanine R)a
0.015 ug/ml (lanthanum alizarin
complexone)a
8.0% (830 ug/liter, zirconyl-SPADNS,
no Interferants)/
12.8% (680 wg/liter, zirconyl-SPADNS,
with interferants)/
1.2% (830 ug/liter, zirconyl-SPADNS,
no interferants)/
5.9% (680 yg/liter, zirconyl-SPADNS,
with interferants)/
Aluminum, iron(III), silicon(IV),
chloride, sulfate, and phosphate
Ionic fluoride is determined.
Used extensively in field applica-
tions and is well seasoned
Natural fresh and saline waters,
industrial waste solutions,
atmospheric gases, mists and
particulates, soils and min-
erals, biological fluids and
solids
0.04 ng/ml (rainwater)*
40 ug/g (rock)tf
0.25 ng/g (air)d
0.1 ug/g (water)6
2.9% (900 ug/liter) (water)/
3.4% (1.7 ug/g) (standard
solution)"
1.0% (684 pg/liter) (seawater)?
9.8% (94 ng/g) (rabbit plasma)1
4.9% (900 pg/liter) (water)/
2.9% (1.7 yg/g) (standard
solution)"
0.9% (684 yg/llter) (seawater)^
2,6% (94 ng/g) (rabbit plasma)1
Extremes of pH and polyvalent
cations, such as silicon(IV),
iron(III), and aluminum
Only ionic fluoride is determined.
Rapidly becoming the method of
choice for virtually all types
of fluoride samples
Minerals, water, air, urine,
and blood
5 to 50 yga
5% to 10% (30
1% (1
10% to 20% (50 ug)
Co
Aluminum, barium, calcium,
iron(III), thorium,
titanyl, vanadyl, zirco-
nium, phosphate, and
sulfate ions
Only fluoride is determined.
Older method largely super-
seded by more recent
techniques
jjlntersociety Committee on Methods for Ambient Air Sampling and Analysis, 1969.
Warner and Bressan, 1973.
^Ficklin, 1970.
Elfers and Decker, 1968.
llJ.S. Environmental Protection Agency, 1974.
'American Public Health Association, American Water Works Association, and Water Pollution Control Federation, 1971.
fWdin, 1953.
^Warner, 1971.
*.Hall et al., 1972.
?McKenna, 1951a and 1951*.
*Nikolaev et al., 1972.
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44
2.3.3.1 Spectrophotometry This analytical method is based on the in-
creased or decreased absorbance of monochromatic light by a metal-dye
complex when the metal ion of the dye reacts with fluoride. The amount
of absorbed light is measured with a spectrophotometer and is compared
with a previously determined calibration plot that relates light absorp-
tion to the concentration of fluoride in the sample. Various absorption
complexes are used by different analysts; those most commonly used are the
zirconyl alizarin, the zirconyl-SPADNS or the zirconyl Eriochrome Cyanine
R compounds, and the lanthanum or cerium alizarin complexones (Jacobson
and Weinstein, 1977; MacDonald, 1970; National Academy of Sciences, 1971).
The three complexes first mentioned are highly colored initially but are
decolorized by reaction with fluoride; the initially red complexones are
converted to new, stable, blue-colored forms in the presence of fluoride
ion. The effective range of the zirconyl-SPADNS and the zirconyl Erio-
chrome Cyanine R systems is 0.00 to 1.40 yg of fluoride per milliliter,
and the detection limit is 0.02 yg/ml. For the lanthanum alizarin com-
plexone, these quantities are 0.00 to 0.5 ug of fluoride per milliliter
and 0.015 yg/ml respectively (Intersociety Committee on Methods for Ambi-
ent Air Sampling and Analysis, 1969, p. 79). In a comparison involving
53 laboratories, a synthetic unknown sample containing 830 yg/liter of
fluoride and no interfering ions was determined without distillation by
the SPADNS method with a relative standard deviation of 8.0% and a rela-
tive error of 1.2%. With distillation, the relative standard deviation
increased to 11.0% and the relative error to 2.4%. In a similar synthetic
sample that contained appreciable quantities of interfering constituents,
the 53 laboratories determined fluoride with a relative standard deviation
of 12.8% and a relative error of 5.9% (American Public Health Association,
American Water Works Association, and Water Pollution Control Federation,
1971). In general, aluminum, iron, phosphate, and sulfate interfere, and
their effects must be eliminated by one of the preanalysis treatments
discussed in Section 2.3.2.
The level of precision attainable by the various modifications of the
spectrophotometric method is adequate for most environmental and industrial
applications; consequently, it has been widely used for the analysis of
samples derived from air, water, soil, and biological sources (Ashley,
1960; Bethea, 1974; Hargreaves, Ingram, and Cox, 1970; Megregian, 1954).
Now, however, it is being replaced by the more convenient fluoride ion
electrode technique (Jacobson and Weinstein, 1977; MacDonald, 1970).
2.3.3.2 Fluoride Ion Electrode Fluoride ion concentrations can be
rapidly and precisely determined in a wide variety of samples, often
without elaborate sample preparation, by means of the fluoride ion elec-
trode. The fluoride ion electrode (Figure 2.5) is somewhat similar to
the familiar glass pH electrode, except that the membrane is a disk of
single-crystal rare earth fluoride, such as lanthanum, praseodymium, or
neodymium fluoride (Frant and Ross, 1966). The electrode is filled with
a solution containing both fluoride and chloride ions, and an electrical
contact is provided by a silver-silver chloride wire; it is used with a
pH meter and an external reference electrode, such as the standard satu-
rated potassium chloride-calomel type (Figure 2.6). The crystal membrane
of the fluoride ion electrode is appreciably permeable only to the fluo-
ride ions, and the cell potential follows the Nernst equation relationship
-------
45
ORNL-DWG 79-20893
INTERNAL
FILLING
SOLUTION*
Ag-Ag Cl
! INTERNAL
REFERENCE
ELECTRODE*
INTERNAL
FILLING
SOLUTION
»Ag-Ag Cl
INTERNAL
REFERENCE
ELECTRODE
s^-
GLASS MEMBRANE
LIQUID JUNCTION
CRYSTALLINE
MEMBRANE
Figure 2.5. Cross sections of typical selective ion electrodes.
Source: Babcock and Johnson, 1968, Figure 1, p. 954. Reprinted from
JOURNAL American Water Works Association Volume 60 by permission of the
Association. Copyrighted 1968 by the American Water Works Association,
Inc., 6666 W. Quincy Avenue, Denver, Colorado 80235.
ORNL-DWG 79-2O892
MILLIVOLTMETER
EXTERNAL REFERENCE
ELECTRODE
R
TEST SOLUTION
LIQUID
JUNCTION
INTERNAL
REFERENCE
ELECTRODE
INTERNAL
REFERENCE
SOLUTION
ION-SELECTIVE (MEASURING)
ELECTRODE
M
ION-
SELECTIVE
MEMBRANE
Figure 2.6. Potentiometric measuring circuit showing measuring (M)
and reference (R) electrodes and potentiometers. Source: Adapted from
Light and Cappuccino, 1975, Figure 1, p. 247. Reprinted by permission
of the publisher.
-------
46
over more than five orders of magnitude of fluoride ion activity. The
electrode is unresponsive to most other common anions; interference by
hydroxide ion occurs, but only at concentrations equal to or greater than
the fluoride ion concentration. This interference by hydroxide can be
minimized by controlling the pH of the sample; it causes no difficulty
at pH 5.
The fluoride electrode measures fluoride activity, rather than con-
centration; it is therefore necessary to ensure that samples and reference
solutions are at equal ionic strengths if measurements interpretable in
terms of concentration are to be obtained (Frant and Ross, 1968). The pH
and ionic strength requirements of the electrode are satisfied by adding
to the samples and standards a high-ionic-strength buffer that also con-
tains citrate ion or other complexing agents to preferentially complex
metal ions such as iron or aluminum, and assure that the fluoride in the
samples is available in the free, uncomplexed form (Light and Cappuccino,
1975).
The fluoride in a sample is measured by immersing the fluoride and
reference electrodes in a solution of the dissolved sample containing the
total ionic strength adjustment buffer. When a steady potential is estab-
lished, a meter reading is made and confirmed; if the method of standard
additions is used for calibration (Fuchs et al., 1975; Warner, 1973) addi-
tional spikes are added, new readings are made, and the original sample
concentration is determined from the response curve. Alternatively, the
electrode potential can be converted to the fluoride concentration in the
sample by use of standard reference solutions or a previously determined
calibration curve.
The range of the fluoride ion electrode is normally considered to be
from about 0.2 to 2.0 mg of fluoride per liter (American Public Health
Association, American Water Works Association, and Water Pollution Control
Federation, 1971); progressively longer times are required to achieve
steady readings as the lower concentration limit is approached. However,
with proper electrode conditioning and a specialized technique, the lower
fluoride concentration limit can be reduced to less than a part per bil-
lion (Warner and Bressan, 1973). In an interlaboratory comparison involv-
ing 111 analysts, a synthetic unknown sample containing 850 yg of fluoride
per liter and no interferants was determined by the electrode method with
an average relative standard deviation of 3.6% and an average relative
error of 0.7%. A second unknown sample containing 750 yg of fluoride per
liter with added phosphate and carbonate interferants was determined by
the electrode method with a relative standard deviation of 4.8% and a
relative error of 0.2%. Precision and accuracy are adequate for almost
all environmental and industrial applications.
Because of its excellent performance, speed, and general convenience,
the fluoride ion electrode is rapidly becoming the method of choice for
determining fluoride in a wide variety of environmental and industrial sam-
ples (Devine and Partington, 1975; Erdmann, 1975; Jacobson and Weinstein,
1977; MacDonald, 1970; Melton, Hoover, and Ayers, 1974; Torma, 1975). See
Andelman (1968) for an extensive discussion of the theory and application
of ion-selective electrodes in general.
-------
47
2.3.3.3 Titrimetry In titrimetric methods, a solution containing fluo-
ride ion and an indicating agent is titrated with a standard solution
containing an ion that forms a complex with fluoride. When the end point
is reached and all of the fluoride is reacted, additional titrant reacts
with the indicator, producing a color change that signals completion of
this titration. The quantity of fluoride in the sample is determined from
the volume and concentration of the titrant consumed, and the stoichiometry
of the reaction. Thorium nitrate is the most commonly used titrant for
fluoride ion (Horton, 1961); it is useful in determining microgram to mil-
ligram quantities of fluoride. Alizarin Red S is the most widely used
indicator for this reaction; it has a light yellow color in dilute acid
solutions that contain only alkali metal ions and fluoride ion but forms
a pink lake in the presence of uncomplexed thorium. Ions that complex
or form insoluble compounds with fluoride or thorium interfere with the
titration and must be removed in preliminary treatments. Aluminum, bar-
ium, calcium, iron(III), thorium, vanadyl, zirconium, titanyl, phosphate,
and sulfate ions are the principal offenders (Intersociety Committee on
Methods for Ambient Air Sampling and Analysis, 1969, p. 74). Zirconium,
iron, aluminum, cerium, silver, and uranium(IV) solutions may also be
used as titrants (Horton, 1961).
The precision of titrimetric methods varies in different systems;
typically, relative standard deviations of 5% to 10% are obtained with
samples containing about 30 yg of fluoride (Horton, 1961, p. 260). Rela-
tive errors of 1% to 20% are reported for samples containing 1 to 700 yg
of fluoride (McKenna, 1951a; Nikolaev et al., 1972).
Formerly, titrimetric methods were used extensively for the deter-
mination of fluoride in all types of samples. During the last decade,
however, these methods have been largely superseded by the spectrophoto-
metric and fluoride ion electrode techniques.
2.3.3.4 Other Methods Several analytical methods for determining fluo-
ride are not widely used; some have limited applications while others are
less convenient, precise, or economical than methods now in use. These
methods are briefly described and referenced below.
Gravimetric methods are based on the precipitation of fluoride as
the sparingly soluble calcium fluoride or lead chlorofluoride. The dried
precipitates are weighed, and the fluoride content of the sample is cal-
culated from the weight and gravimetric factor of the precipitate. The
method is useful for fluoride-rich minerals or compounds but is not suf-
ficiently sensitive for general environmental use. McKenna (1951&) dis-
cussed the technique in detail.
The activity of some enzymes is inhibited by fluoride ion, for exam-
ple, the conversion of ethyl butyrate to butyric acid by liver esterase.
Linde (1951) used this effect to determine fluoride at the microgram level
in body fluids by adding liver esterase to the sample, incubating it for
5 hr, and titrating the liberated acid with sodium hydroxide. He observed
a sensitivity of about 0.1 yg of fluoride per gram and a reproducibility
of about 0.1 to 0.2 yg of fluoride for samples containing 0.5 to 5 yg of
-------
48
fluoride. The method was later adapted to the determination of nanogram
quantities of fluoride by McGaughey and Stowell (1964).
Direct polarographic measurement of fluoride is not feasible; how-
ever, several cations that form well-defined fluoride complexes (such as
aluminum and iron) can be determined by this technique and can provide a
basis for indirect determination of fluoride. MacNulty, Reynolds, and
Terry (1952) developed such a method based on complexing fluoride with
excess aluminum, followed by polarographic determination of the unused
aluminum. Concentrations of fluoride as low as 0.2 yg/g were satisfac-
torily measured. Shoemaker (1955) also developed an indirect method of
determining fluoride polarographically, based on the reduction of the
diffusion current of a standard iron solution owing to complexation by
fluoride ion. The procedure determines 1 yg of fluoride with a relative
error of about 15% (also see Gawargious, Besada, and Faltaoos, 1975).
Several fluorometric techniques are based on quenching the fluores-
cence of metal-dye complexes by fluoride (Horton, 1961; Taves, 1968a);
although ultrasensitive their detection limit is about 20 yg of fluo-
ride they are all seriously affected by extraneous ions and are not
used much today.
Fluoride can also be determined by indirect atomic absorption spec-
trometry techniques. Bond and O'Donnell (1968) developed two such methods,
The first is based on depressing the absorption of magnesium in an air-
coal-gas flame with fluoride; the second depends on enhancing the absorp-
tion of zirconium with fluoride ion. In the absence of interfering ions,
the first method is useful over the range of 0.2 to 20 yg of fluoride
per milliliter. The second method is applicable to the concentration
range from 5 to 200 yg of fluoride per milliliter. Gutsche, Kleinoeder,
and Herrmann (1975) also reported a sensitive indirect atomic absorption
spectrometric method for fluoride; it is based on reacting excess sodium
vapor with the sample and measuring the resulting decrease in atomic
sodium concentration. A detection limit of 0.8 yg of fluoride is claimed.
A variety of nuclear activation methods have been developed to
determine fluorine. Feldman and Battistone (1966) measured fluoride in
bacteriological media by monitoring the 10.7-sec activity from fluorine-
20 produced in the l9F(o),Y)20F reaction. The method is applicable to
fluoride concentrations down to about 5 yg/ml.
Jeffery and Bakes (1967) analyzed fluorite ores and concentrates by
irradiating samples with fast neutrons and measuring the activity of the
resulting nitrogen-16. No sample preparation, other than crushing, is
required. The technique is not suitable for trace analysis. Ohno et al.
(1970) used a photonuclear activation technique to measure fluoride in
urine. They observed a detection limit of about 0.01 yg of fluoride and
a precision of about 10% in the range from 1 to 2 ppm. Other nuclear
activation methods are discussed by Bressan et al. (1974), Fiarman and
Schneier (1972), Lauff, Champlin, and Przybylowicz (1973), and Nikolaev
et al. (1972).
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49
2.3.4 Comparison of Analytical Procedures
There are many analytical procedures for determining fluoride; the
standard technique by which other methods are usually judged consists
of isolating the fluoride by a Willard-Winter distillation and analyzing
the resulting solution by the zirconium-SPADNS spectrophotometric method.
This well-seasoned procedure has a detection limit of about 20 yg of flu-
oride per milliliter, a characteristic precision of about 10%, and an
accuracy of about 5%; it is thus quite adequate for use with most envi-
ronmental samples (American Public Health Association, American Water
Works Association, and Water Pollution Control Federation, 1971; Inter-
society Committee on Methods for Ambient Air Sampling and Analysis, 1969:
McFarren, Moorman, and Parker, 1969).
Despite the attractive features of the standard zirconium-SPADNS
spectrophotometric technique, it is not the method of choice for deter-
mining fluoride in most environmental and industrial samples today. That
distinction belongs to the fluoride ion electrode method. The popularity
and effectiveness of the fluoride ion electrode has steadily increased
since it was introduced by Frant and Ross in 1966. Generally speaking,
no pretreatment is required for dissolved samples other than the addition
of the total-ionic-strength adjustment buffer. However, care is required
on this point because the electrode monitors only fluoride ion activity
bound or complexed fluoride is not detected. The normal detection limit
of the electrode (about 0.2 mg of fluoride per liter) (American Public
Health Association, American Water Works Association, and Water Pollution
Control Federation, 1971) can be extended to less than a part per billion
by special procedures (Warner and Bressan, 1973). The precision and accu-
racy of the electrode method equal or somewhat exceed those of the spec-
trophotometric or titrimetrie techniques for most samples. These factors,
along with demonstrated speed and convenience, ensure the future dominance
of this method.
In earlier years, titrimetric methods were extensively used for
determining fluoride. In capable and experienced hands, some of the pro-
cedures, especially the thorium nitrate-alizarin Red S titration, still
produce good results. They are, however, a great deal more time consuming
than the electrode method and are subject to greater operator variance;
consequently, they are infrequently used.
The remaining methods of determining fluoride are mostly specialized
procedures that are appropriate for selected samples or that make use of
specialized facilities; they seem unlikely to find widespread, generalized
application.
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50
SECTION 2
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SECTION 3
BIOLOGICAL ASPECTS IN MICROORGANISMS
3.1 SUMMARY
Some microorganisms are capable of interacting with fluoride-
containing pollutants in the environment, altering the form, concen-
tration, and potential hazard of the compounds. The types of fluoride
compounds to which microorganisms are exposed are those used in water
fluorination, dentifrices, aerosols, pesticides, and compounds associated
with industrial air pollution. Fluoride and fluoroorganic compounds are
also used as a biochemical tool for investigating microbial metabolism.
A few strains of bacteria utilize fluoride compounds as catabolites. Sev-
eral fluorocarbohydrate intermediates have been isolated. Up to 900 ppm
fluoride (47.4 micromoles per gram wet weight) has been reported in lichens
and as much as 180 ppm (8.9 micromoles per gram) in oral bacteria. In
some cases, fluoride accumulation can be reversed by a recuperation per-
iod or by washing the cells.
Toxic and metabolic effects from fluoride exposure are reported
for bacteria, yeast, fungi, algae, protozoa, and viruses. Toxic effects
include developmental and morphological alterations, growth inhibition,
and reduction in infectivity. Dormant bacterial spores are more resist-
ant than vegetative cells to fluoride aerosols; higher molecular weight
compounds and compounds containing more chlorine than fluoride seem to
be the most toxic to some microorganisms (e.g., StaphyloooccuB aweus).
Fluoride acts as a metabolic inhibitor altering such processes as respir-
ation, photosynthesis, carbohydrate metabolism (e.g., sugar uptake, ion
transport, acid production, and glycolysis), and enzyme activity. A sub-
strate analog of phenylalanine, p-fluorophenylalanine, and an analog of
uracil, 5-fluorouracil, can be incorporated into protein and nucleic acids.
Some effects of these compounds are: reduction of synthesis of protein,
RNA, and DNA; interference with cell differentiation, chromosomal altera-
tions, and changes in ribosomal composition and properties; and modifica-
tion of messenger RNA functions.
3.2 METABOLISM
Uptake, accumulation, and biotransformation of fluoride and fluoro-
organic compounds by microorganisms are the subjects of this section.
Studies of microbial metabolism of fluoride compounds have involved sev-
eral types of organisms under diverse sets of objectives. Strains of
bacteria capable of metabolizing fluoride compounds are important because
of their possible degradation of fluoride-containing pollutants in streams
and soils. Accumulation of fluoride in microorganisms is discussed in
terms of uptake in laboratory cultures and in natural environments, in-
cluding those in human saliva and dental plaque.
59
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60
3.2.1 Uptake and Accumulation
Several strains of bacteria that can metabolize fluorocarbons have
been isolated. From creek water, Kelly (1965) isolated a gram-negative
rod (National Collection of Industrial Bacteria No. 9562) capable of
growing very slowly with fluoroacetate (40 mW) or fluoroacetamide (40 mW)
as the sole carbon and fuel source. (Fluoroacetamide also served as a
nitrogen source.) The growth was linear rather than exponential, sug-
gesting inhibition due to the accumulation of toxic fluoride by-products.
Goldman (1965) isolated a pseudomonad from Potomac River mud which used
fluoroacetate (50 mW) as its sole carbon source, and Goldman, Milne, and
Pignataro (1967) isolated Pseudomonas species that utilized 2-fluorobenzoic
acid as its sole carbon source. A Pseudomanas species isolated by Harper
and Blakley (1971) used p-fluorophenylacetic acid as its sole carbon and
fuel source (Figure 3.1). However, a Vibrio 01 strain exhibited no growth
in 48 hr in a medium containing p-fluorobenzoate even when inoculated with
cells adapted to benzoate (Ali, Callely, and Hayes, 1962). Bowman et al.
(1964) and Bowman and Mallette (1966) found that Esoheviohia ooli could
degrade p-fluorophenylamine by a process that involves an initial deami-
nation; products included a number of fluoride-containing compounds in
addition to fluorophenylacetate.
Examples of microbial incorporation of fluoride compounds into pro-
tein and nucleic acids are numerous. Effects of such incorporated flu-
oride are given in Section 3.3.2.3. Fluoride can be incorporated into
fc 180
o»
£
Z
O 120
t-
Z
UJ
o
Z 60
O
O
UJ
O
0:
i o
ORNL-DWG 76-16552R
0.9
e
FLUORIDE IN
MEDIUM
I
I
I
I
0.6
0.3
<0
OT
UJ
O
CL
O
"- O 20 40 60 80
INCUBATION TIME (hr)
Figure 3.1. Growth of PeettdomonoB sp. on 0.1% p-fluorophenylacetic
acid. Source: Adapted from Harper and Blakley, 1971, Figure 1, p. 636.
Reproduced by permission of the National Research Council of Canada from
the Canadian Journal of Microbiology, Volume 17.
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61
microbial protein via metabolism of fluoridated amino acids (Browne,
Kenyon, and Hegeman, 1970; Dunn and Leach, 1967; Pine, 1978; Rennert and
Anker, 1963). For example, a leucine-requiring mutant of E. coli, (strain
B 615 F) substituted 5',5',5'-trifluoroleucine for leucine in proteins
(Rennert and Anker, 1963). Similarly, a cell-free E. coli (strain Crookes)
system incorporated p-fluorophenylalanine into protein (Dunn and Leach,
1967) , and an E. coli, mutant strain lacking tryptophanase and tryptophan
synthetase incorporated DL-tryptophan substituted with fluorine in either
the 4, 5, or 6 position (Browne, Kenyon, and Hegeman, 1970).
5-Fluorouracil (FU) has been used extensively in the study of nucleic
acid metabolism. Mandel (1969) reviewed the incorporation of FU into RNA
and its molecular consequences. Table 3.1 shows the percent replacement
TABLE 3.1. INCORPORATION OF 5-FLUOROURACIL INTO RNA OF
VARIOUS MICROBIAL SPECIES
Species
Uracil
replaced
Comment
Bacteria
Escherichia coli B 70
Escherichia coli, uracil 25
auxotroph
Bacillus subtilis 40-60
Bacillus cereus 15
Staphylococcus aureus 5
Leuconostoc cerevisiae a
Partially reversed by uracil
Essentially unchanged by addition of
uracil; 5-fluorouracil partially
replaced uracil requirement
Reversed by uracil; enhanced by
deoxythymidine
Tested only in presence of uracil
Reversed by uracil
Fungi
Saccharomyces aarlsbergensis 70
Candida utilis 10
Trichoderma viride
Reversed by uracil
Reversed by uracil; incorporation of
5-fluorouracil, equal to that of
uracil
Virus
Tobacco mosaic virus
Polio virus
Phage MS2
Phage R 17
Phage f2
56
36
80
28
c
Reversed by uridine
Reversed by uridine
Reversed by uracil
?6.9 wg 5-fluorouracil per milligram dry weight.
Tritiated 5-fluorouracil incorporated into RNA.
ClilC-labeled 5-fluorouracil incorporated into phage RNA.
Source: Adapted from Mandel, 1969, Table 1, p.
of the publisher.
85. Reprinted by permission
-------
62
of uracil by FU in several bacteria, fungi, and viruses. Kaiser (1969)
reported that E. coli B grown in the presence of FU-RNA contained a mix-
ture of normal and FU-containing transfer ribonucleic acids (FU-tRNA). Up
to 65% to 70% replacement of uracil residues by FU was detected in the
£RNA. Similarly, Viriyanondha and Baxter (1970) grew Staphylococcus aureus
ATCC 6538P in a complex medium with 300 vg per milliliter of fluoroacetate.
Approximately 50% of the acetate in #-acylamino sugar-containing uridine
nucleotides, excreted in response to penicillin, was substituted with
fluoride.
Jenkins, Edgar, and Ferguson (1969) reported that plaque bacteria
grown on fluoride-rich media contained high levels (up to 134 ppm) of flu-
oride (Table 3.2). (Data are for a Streptococcus strain; similar results
were obtained for another Streptococcus and an organism tentatively iden-
tified as a Staphylococcus.) Dental plaque, which is mainly amassed
bacteria, may contain as much as 180 ppm fluoride (Hardwick and Leach,
1963).
TABLE 3.2. FLUORIDE CONCENTRATION IN A STREPTOCOCCUS ISOLATED
FROM HUMAN PLAQUE AND GROWN ON MEDIA CONTAINING A RANGE OF
FLUORIDE WITH FINAL pH REACHED AFTER INCUBATION WITH
SUCROSE FOR 18 hra
Fluoride
added to
media
(ppm)
0
2
5
10
Fluoride in
suspension
(jig/ml)
0.8
2.0
4.5
5.0
Nitrogen in
suspension
(mg/ml)
0.46
0.51
0.58
0.59
Estimated
fluoride
in washed
bacteria
(ppm)
27
62
124
134
pH after
incubation
4.72
5.00
5.16
5.43
aThese figures on fluoride concentration were obtained before
the advent of the fluoride electrode and are now thought to be too
high; however, later work has confirmed that bacteria take up
fluoride and are inhibited as a result.
Source: Adapted from Jenkins, Edgar, and Ferguson, 1969,
Table 4, p. 112. Reprinted by permission of the publisher.
High levels of fluoride can also be accumulated by certain species
of lichens. Lichen thalli accumulated fluoride from exposure to ambient
fluoride at a level of 4 yg of fluoride per cubic meter of air (Nash,
1971). This ability to accumulate fluoride was thought to be a function
of relative humidity as indicated by the data in Table 3.3. These data
show that an increase in fluoride levels in two species, Cladonia cpistat-
ella and Parmelia caperata, occurred with an increase in relative humidity.
Concentrations of fluoride in Cladonia and Paxmelia species, transplanted
near a chemical factory known to be a source of ambient fluoride, ranged
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63
TABLE 3.3. ACCUMULATION OF FLUORIDE BY LICHENS
EXPOSED TO FOUR DAYS OF UNIFORM AMBIENT FLUORIDE
LEVELS (5 gg OF FLUORIDE PER CUBIC METER) BUT
UNDER VARYING RELATIVE HUMIDITY REGIMES
(ppm dry weight)
Accumulation at
relative humidity of
Species
40%
63%
87%
Ctadonia cristatella
Parmelia cccperata
10
11
32
26
82
89
Source: Adapted from Nash, 1971, Table 3,
p. 105. Reprinted by permission of the publisher.
from 100 to 200 yg of fluoride per gram dry weight (100 to 200 ppm), com-
pared with 8 to 28 ppm fluoride in controls (Table 3.4). Laboratory re-
sults also revealed that lichens accumulated fluoride: lichens exposed to
4 ug of fluoride per cubic meter of air accumulated 84 to 115 ppm fluoride
after a nine-day exposure period, as compared with 14 to 25 ppm fluoride
accumulated in lichens in control chambers. Fluoride concentrations noted
in several other lichens are given in Table 3.5.
TABLE 3.4. FLUORIDE CONCENTRATIONS OF TRANSPLANTED LICHENS*1
(ppm dry weight)
Exposure time
Species
Concentration
at distance
from factory of
100 m
6000 m
One-month exposure
June
July
August
September
October
Three-month exposure
(July to September)
Cladonia criatatella
Cladonia polyaarpoides
Cladonia orietatella
Parmelia plittii
,
138?
164?
180*
220*
100*
>220*
>220J
174°
23
28
24
20
8
18
21
22
°T)ata are means of two subsamples. Values that exceeded the
calibration scale are indicated by >.
^Significantly different from the control at the 1% level.
Source: Adapted from Nash, 1971, Table 1, p. 105. Reprinted
by permission of the publisher.
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64
TABLE 3.5. FLUORIDE CONCENTRATIONS IN LICHENS
Species
Dermatocarpon rtiniatwn
Peltigera rufesaens
Parmelia saxatilis
Uanea aubfloridana
Ramalina fmxinea
Usnea subfloridana
Parmelia sulcata
Sample description
Saxicolous, collected near aluminum
smelter
Terricolous, collected near aluminum
smelter
Saxicolous, collected downwind of
aluminum smelter
Lignicolous , collected downwind of
aluminum smelter
Trees, Invergordon, Scotland, 1969°
Trees, Invergordon, Scotland, 1969
Corticolous, field transplant, E and
NE of smelter, four months
Corticolous , field transplant , E and
NE of smelter, 12 months
Distance
from smelter
(km)
1.6
2.1
3
7
11
1.6
2.1
3
7
12
1
2
4
8
15
40
1
2
4
8
15
Fluoride
content
(ppm)
199
184
47
18
17
19
14
20
7
2
2
<1
0
0
990
750
570
475
190
70
900
700
516
500
134
Aluminum smelter began operation in spring 1971.
Source: Adapted from Gilbert, 1973, Table 2, p. 179.
sources. Reprinted by permission of the publisher.
Data collected from several
Although fluoride can be accumulated by some microorganisms, experi-
mental evidence shows that in some instances the fluoride-cell bond is weak
and that fluoride accumulation can be reversed. Comeau and LeBlanc (1972)
found that three weeks after fumigating Hypogymnia physodes with 65 ppb
fluoride for 2 hr, 36% and 47% of the accumulated fluoride was lost. No
mechanism for the loss was postulated. Birkeland and Rolla (1972) found
that StreptocoactiB strains OMZ 52-3, GS 5, and ATCC 10558 had negligible
or no affinity for fluoride, either when standing in phosphate buffer (10
\iM sodium fluoride) or grown in 5% sucrose broth containing 10 ]iM fluo-
ride. This lack of bacterial affinity suggests that if fluoride is bound
within oral bacteria, it is probably associated with a low-molecular--weight
compound. Accumulation of fluoride in a beer culture after successive
fermentations was studied by Klopper and Jongeling-Eijndhoven (1971).
Concentrations up to 29.89 ppm fluoride occurred in SaccharomyeeB caple-
bergensis cells after six successive fermentations when 10 ppm fluoride
was added to the wort (Table 3.6). However, washing the cells removed
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65
TABLE 3.6. FLUORIDE CONCENTRATIONS IN WASHED AND UNWASHED
YEAST AFTER SUCCESSIVE FERMENTATION SERIES
Yeast
preparation
Unwashed
Washed
Series
number
1
2
3
4
5
6
I
2
3
4
5
6
Fluoride content (ppm dry weight)
for added fluoride concentration of
0
0.15
0.11
0.22
2.14
0.76
0.06
0.02
0.00
0.04
0.10
1
1.41
2.23
3.01
2.92
3.89
0.05
0.08
0.42
0.05
0.06
2
1.51
3.72
4.82
5.59
7.26
0.08
0.14
0.43
0.11
0.37
5
7.40
7.83
8.41
10.47
20.53
0.35
0.19
0.66
0.13
10
12.18
24.67
19.79
16.14
29.89
0.12
0.19
0.43
0.12
0.19
Source: Adapted from Klopper and Jongeling-Eijndhoven,
1971, Tables II and III, p. 260. Reprinted by permission of
the publisher.
most of the fluoride, suggesting that the fluoride was loosely bound to
the cells. Kashket and Rodriguez (1976) found that Streptococcus sanguia
could concentrate fluoride from dilute solutions and that part of the
accumulated fluoride could be readily removed by simple washing of the
cells; however, part of it was tightly bound. Because uptake was not
inhibited by iodoacetamide or lack of glucose, they concluded that it
was a passive process.
It is becoming clear that a large part of fluoride uptake by micro-
organisms can be related to the weak-acid character of hydrogen fluoride.
For example, Whitford et al. (1977) concluded from their study of fluoride
uptake by Streptococcus mutans strain 6715 that "fluoride uptake occurs
by the diffusion of hydrogen fluoride and subsequent trapping of ionic
fluoride." It is well known that bacteria maintain a difference in pH
across the cell membrane during growth and metabolism. This difference
results from: (1) the action of a membrane ATPase, which moves protons
out of the cell; and (2) the proton barrier function of the membrane.
Therefore, when a compound such as sodium fluoride is added to a bacterial
cell suspension, it will dissociate, and depending on the pH, some of the
fluoride will be in the form of hydrogen fluoride, which passes readily
across the membrane. Since the cell interior is alkaline, the hydrogen
fluoride will dissociate. The F~ ion cannot pass back across the membrane,
therefore it is trapped within the cell. This mechanism for fluoride up-
take is probably the major basis for the common finding that fluoride is
more potent at lower pH values. Eisenberg et al. (1978) found that fluo-
ride can act as a transmembrane-proton conductor to discharge the pH dif-
ference across the cell membranes of streptococci, thereby rendering them
more acid sensitive.
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66
3.2.2 Biotransformation
Many oxidation products of fluorocarbohydrates have been identified
from studies of bacterial carbohydrate metabolism. Several examples of
fluorocarbohydrate biotransformation by Pseudomonas bacteria are cited.
1. The following fluorinated intermediates were detected in the
medium of a Pseudomonas species using p-fluorophenylacetic acid as its
sole carbon source: (a) D(+)-monofluorosuccinic acid, (b) tvans-3-f.luoro-
3-hexenedioic acid, (c) (-)-4-carboxymethyl-4-fluorobutanolide, (d) 4-
fluoro-2-hydroxyphenylacetic acid, and (e) 4-fluoro-3-hydroxyphenylacetic
acid (Harper and Blakley, 1971). The structures of these compounds are
shown in Figure 3.2.
ORNL-DWG 76-I6553R
COOH
HaCHb
HCF
COOH
A
COOH
CHz
CH
II
FC
CH2
COOH
B
COOH
CH2
I
CH2
I >
V
0
C
CHeCOOH
CH2COOH
A - D(+)-monofluorosuccinic acid
B trans-3-f luoro-3-hexenedioic acid
C ()-4-carboxymethyl-4-fluorobutanolide
D 4-fluoro-3-hydroxyphenylacetic acid
E 4-fluoro-2-hydroxyphenylacetic acid
Figure 3.2. Structures of metabolites isolated from medium after
incubation of Pseudomonas sp. with p-fluorophenylacetic acid. Source:
Adapted from Harper and Blakley, 1971, Figure 3, p. 638. Reproduced by
permission of the National Research Council of Canada from the Canadian
Journal of Microbiology, Volume 17.
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67
2. White and Taylor (1970) reported that resting whole-cell suspen-
sions of Pseudomonas fluoveseene would metabolize 3-deoxy-3-fluoro-D-
glucose (3FG) to 3-deoxy-3-fluoro-D-gluconic acid (3FGA). A further
oxidation product was obtained and tentatively assigned the structure of
3-deoxy-3-fluoro-2-keto-D-gluconic acid (3F2KGA). Taylor, White, and
Eisenthal (1972) found that P. fiuoveecens cell-free extracts immediately
oxidized 3FG to 3F2KGA. Using partially purified enzyme preparations of
P. fluorescens cell-free extracts, Taylor, Hill, and Eisenthal (1975)
found that 3FG and 3FGA were substrates for glucose oxidase and gluconate
dehydrogenase. Thus it seems that the same enzymes that oxidize glucose
and gluconic acid also oxidize 3FG and 3FGA.
3. 3-Fluorocatechol, 2-fluoromuconic acid, and fluoride ion were
identified in the growth medium of a Pseudomonas species which was sup-
plied with 2-fluorobenzoic acid as its sole carbon source (Goldman, Milne,
and Fignataro, 1967). The presence of the first two oxidation products
suggests the following metabolic pathway:
COOH
4. A Pseudomonas species isolated from mud was found to selectively
degrade the enantiomer of fluorocitrate that inhibits the tricarboxylic
acid-cycle enzyme aconitase (Kirk and Goldman, 1970). Figure 3.3 shows the
course of fluoride release due to the bacterial degradation of fluorocit-
rate. The concentrations of fluoride (2.1 mM and 2.4 wM in two different
experiments) represent approximately half the amount of racemic evythro-
fluorocitric acid that was added to the medium, suggesting the selective
degradation of one isomer.
ORNL-DWG 76-16554
40 60
TIME (hr)
Figure 3.3. Release of F~ ion by a Pseudomonas sp. from racemic
eryt/iro-fluorocitric acid in two experiments. Source: Adapted from
Kirk and Goldman, 1970, Figure 1, p. 410. Reprinted by permission of the
publisher.
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68
5. Washed cells of the actinomycete Noaardia erytkpopolie can oxidize
2-fluoro-4-nitrobenzoate to fluoroacetate, which is enzymatically converted
to fluorocitrate (Cain, Tranter, and Darrah, 1968).
Although present data make it impossible to assess the relative tox-
icities of these fluorinated carbohydrates and ionic fluorides, organisms
such as the Pseudomonas species discussed in example 4, which can degrade
an inhibitor of aconitase, may play a role in detoxifying fluorine pollut-
ants in the environment. For additional information on microbial biotrans-
formation of fluorocarbohydrates see Taylor (1972) and Goldman (1972).
3.3 EFFECTS
Toxic and metabolic effects of fluoride compounds have been observed
in bacteria, yeast, fungi, protozoa, algae, and viruses. Toxic effects
reported include developmental and morphological alterations, growth in-
hibition, and reduction in infectivity. Metabolic effects include inhibi-
tion of energy-transferring mechanisms such as respiration, photosynthesis,
and carbohydrate catabolism; inhibition of substrate uptake and transport;
inhibition of many enzymes; and interference with protein synthesis and
nucleic acid metabolism. Most of the data presented are from studies on
lichen sensitivity to pollutants, the cariostatic activity of fluoride,
the effects of aerosols, and the use of fluoride as an enzymatic and
metabolic probe.
3.3.1 Toxic Effects
Since many lichens are sensitive to airborne fluorides, they are
frequently used as indicators of fluoride air pollution (Gilbert, 1973;
Hawksworth, 1971). Injury to lichen flora in the vicinity of aluminum
smelters and chemical factories has been reported by several authors
(LeBlanc, Comeau, and Rao, 1971; LeBlanc and De Sloover, 1970; LeBlanc,
Rao, and Comeau, 1972; Pistit and Lisicka-JelfnkovS, 1974). Severity of
injury depends on distance from the fluoride source, topography, and wind
direction. Toxic symptoms resulting from fluoride pollution include:
chlorosis; necrosis; curled margins; white, pink, or gray colors; disin-
tegration of the thallus; microscopically observed plasmolysis; and loss
of color in the algae cells (Comeau and LeBlanc, 1972; Gilbert, 1973;
Nash, 1971). In a laboratory fumigation experiment, Comeau and LeBlanc
(1972) exposed Hypogymnia phyeodee to concentrations of hydrogen fluoride
ranging from 13 to 130 ppb. Fumigation with 13 ppb for 8 hr caused no
observable symptoms. However, 36-, 72-, and 108-hr exposures caused
chlorosis and curling of the margins; so did a 12-hr exposure to 65 ppb.
The authors noted that fluoride was accumulated even when no symptoms
could be observed. Nash (1971) reported that lichens fumigated with fluo-
ride invariably became chlorotic upon fluoride accumulation, and that a
critical level of F~ in the thallus was 30 to 80 ppm. He concluded that
the algal component of the lichen was more sensitive to hydrogen fluoride
than the fungal component, since the morphological form of the lichen was
maintained for several weeks after the appearance of total chlorosis.
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69
Some toxic effects of fluorine compounds on protozoa have been
observed; however, exact mechanisms of action are not known. The amino
acid analog DL-p-fluorophenylalanine (p-FPhe) inhibits division in cells
selected from exponentially growing populations of Tetrdhymena pyriformis
(Rasmussen and Zeuthen, 1962) and Paramea-iiffn aurelia (Rasmussen, 1967).
In P. aurelia., 16 vcM p-FPhe inhibited cell division when applied up to
4.5 hr after the previous cell division. After that time (the sensitivity
transition point), p-FPhe did not block cell division. For both organisms,
this transition point occurred about 1 hr before completion of the cell
cycle (i.e., cytokinesis) and roughly coincided with the termination of
macronuclear DNA synthesis. In a study of various chemicals associated
with operation and maintenance of nuclear power plants and cooling tower
structures, Becker and Thatcher (1973) reported that although fluoride
ions apparently have direct toxic properties toward aquatic life, concen-
trations of 1.5 ppm fluoride did not appear to be harmful to aquatic orga-
nisms under most conditions. The toxic threshold of Mierovegma heterostoma
occurred after a 28-hr incubation period at 27°C with 226 ppm fluoride
(Bringmann and Kuhn, 1959, as cited in Becker and Thatcher, 1973).
Bean plants (Phaseolus vulgaon-s L.) showed increased numbers of
lesions with increasing foliar fluoride concentrations (up to 500 ppm)
after inoculation with tobacco mosaic virus (TMV) (Treshow, Dean, and
Harner, 1967). Above 500 ppm fluoride the number of lesions decreased.
Although fluoride did increase the virulence of TMV in this controlled
situation, the authors suggested that, due to many environmental factors
(e.g., light, temperature, and moisture) this increased virulence may go
undetected in the field.
Effects of p-fluorophenylalanine on nitrous acid mutagenesis in bac-
teriophage T* r mutants were studied by Johnson (1975Z>). The frequency
of nitrous acid-induced forward r mutations was approximately doubled
when the phage-infected E. aoli B cells were held in the presence of p-
FPhe. However, spontaneous forward mutation frequency and the nitrous
acid specificity were not affected by p-FPhe. The frequencies of sponta-
neous and nitrous acid-induced reversion of rll transition mutants were
unaffected by p-FPhe when the phage was plated on the restrictive host
after mutagenesis. However, compared with the control phage, the induced
reversion frequency was approximately tripled when the mutagenized phage
first underwent a cycle of replication in the presence of p-FPhe. In
contrast, Johnston (1975a) reported that p-FPhe depressed 5-bromouracil
induced frequencies in both forward and reverse mutation. Davies and
Parry (1978) found that p-fluorophenylalanine at growth-inhibitory con-
centrations increased the frequency of mitotic gene conversion in haploid
yeast cultures and enhanced the mutagenicity of nitrous oxide, mitomycin
C, ethylmethane-sulphonate, and uv light. They suggested that p-fluoro-
phenylalanine became incorporated into the enzymes involved in DNA repli-
cation with the net result of lower fidelity of replication and increased
errors in base incorporation.
Haploidization in yeast can be induced by p-FPhe. Gutz (1966) re-
ported that p-FPhe treatment resulted in haploidization of diploid Sehizo-
sacoharomyces parribe strains when plated on yeast extract glucose agar
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70
gradient plates (0.06% to 0.1% p-FPhe). DL-p-Fluorophenylalanine also
induced haploidization in Aspergillus rriger diploids (Lhoas, 1961). Con-
idia were plated onto standard complete medium containing 0.01% p-FPhe.
The viable counts were the same as controls; however, the growth was
slower (reduced colony diameters), and sporulation was poor.
Fluoride can interfere with fungal sporulation, germination, and
growth. Lukens and Horsfall (1973), studying effects of several respira-
tory inhibitors on the sporulation process of Alternaria solani, found that
5.96 wM sodium fluoride reduced stalk formation by 50%. The effective
concentration for 50% inhibition of conidial formation (EDSO) was greater
than 20 voM and for stalk collapse, greater than 100 mW. Inhibition of
spore germination in the dermatophyte Microsporum gypsewn resulted from
the addition of 0.1 mM phenylmethylsulfonyl fluoride to the germination
medium (Leighton and Stock, 1970). No effect on growth occurred if phenyl-
methylsulfonyl fluoride was added after the emergence of the germ tube.
The compound was found to specifically inhibit the release of free amino
nitrogen by the macroconidia. Sodium fluoride at a concentration of 50
mM and administered to spores which had been cultured for 4 hr at 30°C,
affected conidia production of Neidfospora orassa strain 853 A (Figure 3.4)
(Timberlake and Turian, 1975). The effects were time-dependent. Conidia-
tion increased with length of treatment up to 2 hr, stabilized from 2 hr
ORNL-DWG 76-16555
75
ro
CM
o: *"
uj T
°- t
$
01234
NaF TREATMENT (hr)
Figure 3.4. The effect of the duration of 50 wM NaF treatment on
production of conidia; initial treatment was to 4-hr-old Neurospora orassa
cultures. Source: Adapted from Timberlake and Turian, 1975, Figure 1,
p. 152. Reprinted by permission of the publisher.
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71
to 3 hr, and then decreased after 3 hr. The growth of the treated cultures
was as rapid as that of the untreated, until the 3-hr treatment period.
The inhibition could be reversed by washing or by the addition of magnesium
chloride. Treshow (1965) found varying effects on fungal growth and spor-
ulation from concentrations of 0.1 to 50 mM sodium fluoride. Verticillium
albo-atrum growth was completely inhibited by 50 mW fluoride, and Colleto-
trichum lindemuthianum was the only fungus that grew at all in this con-
centration. Table 3.7 shows other reported effects (Treshow, 1965).
Leslie and Parbery (1972) found that VertiailHwn leaanii grew readily
on 211 roAf fluoride, a tolerable concentration four times that reported by
Treshow (1965) for V. albo-atrum. No differences in the morphology of V.
leoani-iy resulting from growth on fluoride-containing medium, were noted
by Leslie and Parbery. However, spore length increased with increasing
fluoride concentrations. Fluoroamino acids such as DL-p-fluorophenyl-
alanine (p-FPhe) can also inhibit bacterial sporulation (Hardwick and
Foster, 1952), even at concentrations that have little effect on growth
(Marquis, 1970).
TABLE 3.7. EFFECTS OF SODIUM FLUORIDE ON GROWTH AND SPORULATION OF PATHOGENIC FUNGI
Species
NaF
concentration
Effect on growth rate
Effect on sporulation
Alternaria oleraceae
Botrytis ainerea
Colletotnahum Hndemuthianum
Cytoepora rubescena
Helnrinthoeporium sativum
Pythium debaryanum
VePticillium albo-atrwn
25, 50
2.5
0.1, 0.5, 1
5
10
1
50
1
5
>10
<25
0.5
10
25
25
1
Significantly suppressed
at 21'C
Complete Inhibition
Significantly suppressed
Significant stimulation
Stimulated at 24°C
Suppressed at 21°C and
24 "C
Significantly suppressed
at 24°C
Significantly suppressed
at 21eC
Complete inhibition
No effect
Significantly inhibited
at 27"C
Significantly inhibited
at 24°C
Significantly Inhibited
at 21"C
Significantly inhibited
at 27"C
Stimulated at 18°C or
27°C; not stimulated
at 21°C or 24"C
No effect at <1 mW
Reduced sporulation; only
a few conidiospores
matured
Fewer conidiospores
matured than at 5 mW
No effect
No effect
No effect until complete
growth inhibition
Source: Adapted from Treshow, 1965, Figure 1, p. 217. Reprinted with permission from Mycologia
57:216-221, 1965.
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72
With the increased use of aerosol propellants, the amount of fluoro-
carbons in the atmosphere has increased (Section 7.3.4). It is impor-
tant to know the effects of these propellants on microorganisms and also
to know if these compounds might be useful as disinfectants for use in
foods or for human infections. Effects of some of these fluorocarbons
on microorganisms are listed in Table 3.8. Bacterial spores seem to be
more resistant than vegetative cells. Some treatments have resulted in
increased survival rates or only slight toxicity. Oujesky and Bhagat
(1973) examined the effects of several Freons and Genetrons on both
coagulase-positive and coagulase-negative strains of S. aureus. The most
effective gas tested was dichlorofluoromethane (Genetron-21, Freon-21),
which inhibited both coagulase-positive and coagulase-negative strains
(Table 3.9). The coagulase-negative strains (Guinn and ATCC 6020) were
more sensitive than the coagulase-positive (Giorgio) strain. There was
no apparent effect on deoxyribonuclease and gelatinase production by the
three strains. The higher molecular-weight ethane and methane compounds
and those containing more chloride than fluoride appeared to be the most
toxic. Thus, the toxicity of chloride-containing fluorocarbon propellants
may be enhanced by chloride substitution for fluoride (Section 7.3.4).
From their results, Prior et al. (1975) suggested that the death of E.
aoli, cells, caused by dichlorodifluoromethane, involved increased permea-
bility, leakage of cell constituents, and lysis. The fluorocarbon liquids
used in experiments on liquid breathing and for formulations of artificial
blood do not appear to be toxic to microorganisms and have been used to
supply oxygen to pressurized cultures (Marquis, 1976).
The physiological effects on E. aoli of incorporated amino acid anal-
ogues were described by Pine (1978). He determined a toxicity series with
canavanine > azetidine-2-carboxylate > p-fluorophenylalanine > ethionine >
norleucine or o-fluorophenylalanine > /n-fluorophenylalanine or 2,5-dihydro-
phenylalanine > selenomethionine. Kay and Cameron (1978a, 19782?) used the
fluoridated acids fluorocitrate and fluoromalate to isolate transport-
negative mutants of 5. typhirmari-um for citrate and dicarboxylic acids
respectively.
Gallon, Ul-Haque, and Chaplin (1978) found that among the pleiotrophic
effects of fluorocitrate on the blue-green bacterium Gloeoaapsa sp. was an
inhibition of nitrogen fixation, especially under aerobic conditions. Ammo-
nium ion accumulated within the organism apparently because of the reduced
synthesis of ketoglutarate needed for its assimilation. The lipid content
of the organism was also altered.
A new fluoroacid, flumequine, has the following structure:
Greenwood (1978) found that flumequine was active against E. coli and
could possibly be used in place of nalidixic acid for treatment of urinary
tract infections.
-------
TABLE 3.8. EFFECTS OF FLUOROCARBON AEROSOL PROPELLANTS ON MICROORGANISMS
Coapound
Treatment
Species
Effect
Reference
Fluorocarbon-12 and
fluorocarbon-114*
(mixture)
Fluorocarbon-12,
fluorocarbon-142b
40/60 propellent blend
(12/114)
Vapor and liquid states
Vapor state
Vapor state
Vapor and liquid states
Vapor state
Vapor and liquid states
Vapor and liquid states
Vapor state
Vapor and liquid states
Vapor state
Vapor and liquid states
Vapor and liquid states
Vapor and liquid states
Vapor state
Vapor state
Vapor state
Pseudomonas aeruginoaa
StaphyloaoccuB aureua
Streptococcus agalaotiae
(microaerophlle)
Aepergillua niger (fungus)
Paecilomycea varioti
(fungus)
StaphlococcuB aureue
MicrocoaouB conglomerate
Streptococcus oremorig
Streptococcus loctia
Leuconoetoc citrovorun
Leuconostoo dextronioum
Bacillus aereue (spores)
Bacillus polymyxa (spores)
Eecheriahia coli
Eecherichia intermedia
Salmonella typhimtrium
Peeudomonae aemginoea
Paeudomonae fluoreaceno
Paeudomonae fragi
Aakfomobacter butyri
Flavobacterium devorane
Growth not affected at 37°C
for 48 hr
Growth not affected at 37°C
for 48 hr
Growth inhibited
Growth inhibited
Growth inhibited
Growth inhibited
Growth inhibited
Growth Inhibited
Growth inhibited
Growth inhibited
Growth Inhibited
Growth
Growth
Growth
Growth
Growth
Growth
Growth
Growth
inhibited
Inhibited
inhibited
inhibited
inhibited
inhibited
Inhibited
inhibited
Reed and Dychdala,
1964
Reed and Dychdala,
1964
Reed and Dychdala,
1964
Reed and Dychdala,
1964
Reed and Dychdala,
1964
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
U>
-------
TABLE 3.8 (continued)
Compound
Treatment
Species
Effect
Reference
Fluorocarbon-11 and
fluoYocarbon-12
(mixture)
Genetron-2r
Genetron-23^
Genetron-152A"
Fluorocarbon-12
Vapor and liquid states
Vapor state
Vapor mixture (60:40)
S-min gassing treatment
(30 ml/min); then 24 hr
In gaseous atmosphere
S-min gassing treatment
(30 mg/min); then 24 hr
In gaseous atmosphere
S-min gassing treatment
(30 ml/min); then 24 hr
In gaseous atmosphere
S-min gassing treatment
(30 mg/min); then 24 hr
in gaseous atmosphere
S-min gassing treatment
(30 ml/min); then 24 hr
in gaseous atmosphere
5-mln gassing treatment
(30 mg/min); then 24 hr
in gaseous atmosphere
S-min gassing treatment
(30 ml/min); then 24 hr
in gaseous atmosphere
5-mln gassing treatment
(30 mg/min); then 24 hr
in gaseous atmosphere
Liquid, 2 hr, 22°C
Saaoharantyaee cereviaiae
Candida utilia
Eeaheriakia soli.
Bacillus eubtilie var. niger
Staphylocoacua aureua,
coagulaae positive strain
Staphylococcue aureua,
coagulase negative strain
Staphylococcue aureua,
coagulase positive strain
Stophyloooccue aureua,
coagulase negative strain
StophylococcuB aureua,
coagulase positive strain
StophylocoacuB aureua,
coagulase negative strain
StophylococouB aureua,
coagulase positive strain
Stophyloooccua aureua,
coagulase negative strain
Eaoheriohia aoli HS2
Growth inhibited
Growth inhibited
Rate of inactlvation slower
than Prior et al. (1970)
results; slowly lethal
l.OZ survivors after treat-
ment for three weeks
Spores more resistant than
E. coli vegetative cells
Decreased survival rate
Decreased survival rate
Increased survival rate and
coagulase production
Decreased survival rate
Increased survival rate and
coagulase production
Increased cell viability
Increased survival rate and
coagulase production
Increased cell viability
Inactivated young cells more
rapidly than old cells;
clumping; cytoplasm light
and grainy less dense and
less uniform than control
Prior, Pennema, and
Marth, 1970
Prior, Fennema, and
Marth, 1970
Stretton, Gretton,
and Watson-Walker,
1971
Stretton, Gretton,
and Watson-Walker,
1971
Ouj esky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Prior, Fennema, and
Pate, 1975
-------
TABLE 3.8 (continued)
Compound
Treatment
Species
Effect
Reference
Fluoro_carbon-114
Fluorocarbon-21
1.25 x saturation for up
to 1200 mln, 22°C
5-mln gassing treatment
(30 ml/min); then 24 hr
In gaseous atmosphere
5-mln gassing treatment
(30 rag/rain); then 24 hr
In gaseous atmosphere
0.5Z to 1.5Z (wt/wt)
Eecherichia ooli ML30
Staphylococcua aureua,
coagulase positive strain
Stophylocoecus aureus,
coagulase negative strain
Saaoharomyaee cerevisiae
Decreased viability; 50Z loss
of compounds absorbing at
260 ran; 32% lysis; most
changes in first 300 rain
Enhanced coagulase production
and mannitol fermentation;
decreased survival rate
Decreased survival rate
Inactivation greatest with (1)
increasing concentrations,
(2) increasing volume of
medium, (3) Increasing tem-
perature from 7°C to 47°C,
(4) agitation, (5) young
cells (8 hr) rather than old
(36 hr or 10 days), and (6)
cells grown without glucose;
treated cells resistant to
lysis by sonication
Prior, Pennema, and
Pate, 1975
Oujesky and Bhagat,
1973
Oujesky and Bhagat,
1973
Middleton, Marth,
and Fennema, 1975
Ui
.Freon-12, dichlorodifluoromethane.
Freon-114, 1,2-dichlorotetrafluoroethane.
,1,1-Dif luoro-1-chloroe thane.
Agitated for 48 hr at 21°C. Vapor state: vapor space saturated at 21°C, but amount insufficient to cause condensation. Liquid
state (partial): vapor space saturated; at low level, few drops of condensate in medium; at high level enough condensate In medium to bind
all water.
SXrichlorofluoromethane.
'Fluorocarbon-21, dichlorofluoromethane.
f Trlfluoromethane.
1,1-Difluoroethane.
-------
76
TABLE 3.9. SURVIVAL OF A COAGULASE-POSITIVE (GIORGIO) STRAIN AND TWO
COAGULASE-NEGATIVE STRAINS (GUINN AND ATCC 6020) OF STAPHYLOCOCCUS AUREUS AS
DETERMINED BY COLONY COUNTS AFTER EXPOSING THE BACTERIAL CELLS TO 5-min GASSING
TREATMENT (30 ml/min) AND A SUBSEQUENT 24 hr IN THE GASEOUS ATMOSPHERE0
Gas used
for treatment
Air , compressed
Genetron-152A
Genetron-23
Genetron-21
Freon-12
Freon-114
Air
Genetron-152A
Genetron-23
Genetron-21
Freon-12
Freon-114
Strain
Guinn
ATCC 6020
Guinn
ATCC 6020
Guinn
ATCC 6020
Guinn
ATCC 6020
Guinn
ATCC 6020
Guinn
ATCC 6020
Untreated
controls
(cells/ml)
Coagulase
1.6 * 10*
1.0 x 10*
0.8 x 10*
1.7 x 10*
1.1 x 10*
1.2 x 10"
Coagulase
1.8 - 10*
1.9 x 107
1.5 x io»
1.9 x io7
1.3 « 10*
1.2 x io7
1.4 x ioa
2.7 x io7
1.0 x 10'
1.9 x io7
1.1 x 10*
1.6 x io7
Viable gas-
treated cells
(cells/ml)
positive
1.8 x 10*
1.0 x 10*
1.4 x io8
0.4 x io6
1.6 x 10*
1.0 x 10"
negative
1.9 x 10"
2.3 x io7
1.8 x io8
1.8 x io7
0.9 x 10'
1.0 x io7
0.3 x 10*
0
1.3 x 10*
2.4 x io7
0.9 x 10*
0.9 x io7
Survivors from
gas-treated cells
(Z i std deviation)
115.0 ± 14.0
106.0 ± 26.0
185.0 ± 19.0
0.2 ± 0.09
148.0 ± 5.0
84.3 ± 4.9
108.0 ± 9.0
121.0 ± 2.8
118.4 ± 13.6
95.0 ± 17.3
71.6 ± 19.4
85.0 ± 12.05
0.0024 i 0.0016
0
126.0 ± 18.4
124.5 ± 5.5
80.0 ± 7.0
55.9 ± 4.1
Coagulase-posltive organisms were incubated on coagulase mannitol agar for
24 hr at 37°C; coagulase-negative organisms were incubated on brain heart Infu-
sion agar for 24 hr at 37°C.
Source: Adapted from Oujesky and Bhagat, 1973, Table 3, p. 232, and Table
6, p. 234. Reprinted by permission of the publisher.
Some fluorinated bases are used as antimicrobial, and often anti-
tumor, agents. For example, 5-trifluoromethyl-2'-deoxyuridine has been
used to treat herpes virus infections. It appears (Clough, Wigdahl, and
Parkhurst, 1978) that this compound is hydrolyzed to yield S-carboxy-21-
deoxyuridine, which is the active agent that upsets DNA synthesis at the
level of the de novo biosynthetic pathway for pyrimidine biosynthesis.
Fluoridated compounds are also widely used as anesthetics. Among the
best known ones are halothane (2-bromo-2-chloro-l,l,l trifluoroethane)
and methoxyflurane (CHC13-CF2-OCH3). These agents are active against
microorganisms and microbial responses. Many of these responses seem to
involve the loss of normal microtubular structure as shown in the follow-
ing examples: loss of motility of Tetrdhymena pyriformis (Nunn, Dixon,
and Moore, 1968); immobilization and stoppage of cytoplasmic streaming
in amoebae (Bruce and Christiansen, 1965); collapse of heliozoan axopods
(Allison et al., 1970); inhibition of cell division of Tetrahymena
(Kirkness and MacDonald, 1972); and inhibition of bacterial luminescence
(Halsey and Smith, 1970).
A very dramatic bacterial response to growth in fluoridated media
was described by Lesher, Bender, and Marquis (1977). Massive lysis
occurred in cultures of Bacillus subtilis, Neisseria aitbflava, and a
micrococcus called LYT following growth in the presence of 5 or 10 mAf
sodium fluoride. The action appeared to be the result of activation of
-------
77
autqlytic enzymes rather than to any restriction in the supply of phos-
phoenolpyruvate, the production of the enolase reaction needed for the
synthesis of the cell-wall structural polymer peptidoglycan. Only bacte-
ria with active autolytic systems underwent lysis, but increased turnover
of peptidoglycan occurred in other organisms during growth in fluoridated
media. Therefore, in some instances, it is evident that fluoride can be
bactericidal instead of only bacteriostatic.
It appears also that some fluoride preparations can actually kill
bacteria and serve as deplaquing agents as well as cariostatic agents.
For example, Mtlhlemann and Strub (1975) reported a 21.5% reduction in the
sulcular plaque index due to daily rinsing by human subjects with 0.025%
amine fluoride solution. Andres, Shaeffer, and Windeler (1974) found
that mouth washing with 0.5% SnF2 solution, but not 0.27% sodium fluoride
solution, reduced the number of viable bacteria in saliva. Tinanoff,
Brady, and Gross (1976) showed that daily mouth rinsing with SnFa solution
(100 ppm fluoride) reduced early plaque formation, while sodium fluoride
at an equivalent fluoride concentration was ineffective with once-a-day
application but effective when used twice a day.
The antiplaque activity of topical fluoride preparations apparently
has a number of bases. For one, it appears that fluoride can inhibit
initial colonization of hydroxyapatite by oral bacteria (Rolla, 1977).
In addition, the counterion for fluoride may cause more damage than the
fluoride itself. Thus, Sna+, alkyl amines, and a pH of 3.2 are all very
damaging to bacterial cells. However, it should be pointed out that
sodium fluoride or potassium fluoride solutions can act as deplaquing
agents when they are used frequently, and it seems that it must be the
fluoride in those solutions that is the active agent.
There has been considerable use in caries prevention of monofluoro-
phosphate, especially in fluoride toothpastes. However, recent studies
by Pearce and Jenkins (1976, 1977) indicated that fluorophosphate was no
more effective than sodium fluoride in reducing acid production in human
saliva and that, in fact, it is decomposed by saliva to yield fluoride,
which is probably the active inhibitory agent.
Many strains of oral bacteria can become acclimatized to fluoride.
This acclimation process was studied in several oral streptococcal strains
(Williams, 1964, 1967, 1968). Williams (1964) found that several strains
of Streptococcus faecalis adapted to sodium fluoride (concentrations not
reported). These fluoride-adapted cells exhibited a longer lag phase
than control cells, whether in the presence or absence of fluoride. Five
strains of Lancefield group D streptococci HT25 and 680 (isolated from
human dental plaque), Streptococcus zymogenes NCIB 8886, Streptococcus
faecalis NCDO 580, and Streptococcus faecalis NCTC 370 were "fluoride
trained" by growing in 2 mW fluoride for four days, then for four days in
10 mW, 33 vM, and 100 mW fluoride successively. The adapted cultures grew
more successfully in high fluoride concentrations than control strains in
the absence of fluoride. If these cultures were grown for two to three
days in fluoride-free medium, they lost their fluoride resistance. Using
strain HT25, Williams (1968) found that both fluoride-acclimated cells and
-------
78
control cells were quite permeable to fluoride; however, the acclimated
cells appeared to be less permeable. Perhaps the difference was due to
factors such as differences in culture, pH, and growth phase. The bacte-
ria were grown overnight in 8.5 ppm fluoride at 37°C, and the volume of
cell protoplasts was estimated using a radioactive sulfate technique.
Permanent or genotypic resistance to fluoride in S. sdlivarius was
studied by Hamilton (1977). Hamilton also noted that slowly metabolizing
bacteria are more fluoride resistant than rapidly metabolizing bacteria.
Hamilton and Ellwood (1978) found that cells of 5. mutans strain Ingbritt,
grown anaerobically in a chemostat at pH 5.5, were more fluoride resistant
and had higher glycolytic capacities than cells grown at higher pH values
of 6.0 or 6.5.
Frostell and Ericsson (1978) stated that bacteria readily became
resistant to fluoride when grown in its presence and that dental-plaque
bacteria in areas with fluoridated water acquired fluoride tolerance. It
should be noted that fluoride intake in areas of the United States without
water fluoridation may be nearly as great as that in fluoridated areas
because of consumption of foods and beverages processed with fluoridated
water. Rosen, Frea, and Hsu (1978) indicated that fluoride-resistant var-
iants of 5. nrutans were less cariogenic than parent strains, and that the
carious process produced by the variants could be suppressed by fluoride.
They concluded that their findings favored a mechanism for the anticaries
activity of fluoride that does not involve direct inhibition of bacterial
metabolism. However, some caution is needed because many fluoride-resist-
ant mutants, for example those studied by Hamilton (1977), are resistant
at pH values near neutrality but are still sensitive at lower pH values.
Clearly, dental-plaque bacteria have had to adapt to the presence of mil-
limolar levels of fluoride.
Herbison and Handelman (1975) tested the effects of fluoride on five
antigenic strains (AHT, BHT, GS-5, LM-7, and SLIR; antigenic types a, b3 c,
d, and E respectively) of Streptococcus mutccns in vitro. Fluoride (0.15,
1.5, and 15 ppm) reduced hydroxyapatite solubility in three strains. In
combination with strontium (1.7, 17.0, and 170 ppm), solubilization was
reduced even further. Fluoride at 1.5 ppm reduced acid production in the
five strains. This reduction was negated by the addition of 17 ppm stron-
tium. No significant effect was observed in four strains grown on agar
plates that were treated with fluoride at concentrations of 0.15, 1.5,
and 15 ppm.
The cariogenic K-l strain of S. mutans has been the subject of much
study on the anticaries effect of fluoride (Luoma, 1972a, 19722?, 1973;
Luoma, Ranta, and Turtola, 1971). The addition of fluoride causes leakage
of potassium and phosphorus from both fermenting and nonfermenting cells
and reduces acid production. The current opinion by many researchers is
that fluoride does not directly inhibit the phosphotransferase system for
sugar uptake. Schachtele and Mayo (1973) found no such inhibition. How-
ever, fluoride can indirectly inhibit the system by inhibiting the enolase
reaction. Also, Marquis (1977) found that fluoride could inhibit strepto-
coccal membrane ATPase. This inhibition could reduce potassium uptake by
the cells.
-------
79
At pH values of 5.2 and 5.8, 50 ppm fluoride caused leakage of cel-
lular potassium in fermenting systems (Luoma, 1972a). At higher pH levels
(6.8 and 8.4), 100 ppm fluoride slightly reduced cellular potassium leak-
age. Twenty-five ppm fluoride, alone or in combination with 6% ethanol,
reduced the cellular potassium and phosphorus levels in nonfermenting
cells. The concentration of phosphorus was less affected. Chlorhexidine,
a compound used effectively to remove dental plaque (Gjermo and RSlla,
1971, as cited in Luoma, 19722)), had previously been found to cause leak-
age of cellular phosphorus in micrococci (Rye and Wiseman, 1964, as cited
in Luoma, 1972a). Luoma (1972Z?) tested the action of fluoride on strain
K-l of S. mutans at concentrations of 25, 50, 75, and 100 ppm alone or
in combination with chlorhexidine (12.5 to 50.0 ppm). He found reduced
cellular potassium and phosphorus concentrations in fermenting cells.
Sodium levels increased in cells incubated without sucrose at 50 ppm flu-
oride, 12.5 ppm chlorhexidine, or a combination of both. If the incuba-
tion mixture contained sucrose, cells treated with 50 ppm fluoride or 50
ppm fluoride plus 12.5 ppm chlorhexidine had about the same sodium concen-
tration as untreated systems. A pretreatment with 50 ppm fluoride had
little effect on acid production by strain K-l; however, 50 ppm fluoride
plus 50 ppm chlorhexidine completely inhibited acid production. Further
testing (Luoma, 1973) showed that fluoride in combination with chlorhexi-
dine and propanol produced the greatest reductions in potassium and phos-
phorus concentrations in the cells and the greatest reduction in acid
production. The results of Luoma1s research are interesting, but they
have not been fully interpreted.
Loesche et al. (1975) found that acidulated phosphate fluoride gel
may be an effective oral antimicrobial agent. They compared the percent-
age of S. mutans and S. sanguis present in dental plaque samples before
and after treatment with acidulated phosphate fluoride. Prior to treat-
ment, 5. mutans comprised about 9% of the colony-forming units in the
occlusal plaque and 1% in the approximal plaque. 5. sanguis comprised
about 5% of the colony-forming units in the approximal plaque and 8% in
the occlusal plaque. In the test, 10 ml of gel containing 1.23% fluoride
ion in 0.1 M phosphoric acid solution at pH 3.2 was applied 8 to 10 times
daily for 8 to 10 days to 44 boys, 14 to 16 years old. The acidulated
phosphate fluoride caused reductions of 45% to 75% of 5. mutans in occlu-
sal samples but had no effect in approximal samples. No effect was
observed on S. sanguis populations.
3.3.2 Metabolic Effects
This discussion on microbial metabolic effects caused by fluoride
compounds deals with four topics: (1) energy transfer, (2) carbohydrate
metabolism, (3) protein synthesis and nucleic acid metabolism, and (4)
enzymatic activity.
3.3.2.1 Energy Transfer Inorganic fluoride can interfere with microbial
energy-transfer processes. Examples are inhibition of respiration, photo-
synthesis, and carbohydrate metabolism (Section 3.3.2.2). Effects of
sodium fluoride on respiration of the aquatic fungi Allomyces javanicus
-------
80
and Brevilegnia unisperma var. delioa in the presence and absence of glu-
cose are shown in Table 3.10 (Thakur and Dayal, 1971); inhibition was
greatest in the presence of glucose. A concentration of 10 wM fluoride
caused 95% inhibition of A. javanicus respiration. Studies involving the
green algae Chlorella vulgaris and Chlorella pyrenoidoea showed that endog-
enous respiration rates were not decreased by the individual addition of
40 mW sodium fluoride or 8 wM copper sulfate. However, if both agents
were added simultaneously, oxygen uptake was almost completely inhibited
(Hassall, 1967; Sargent and Taylor, 1972). Sodium fluoride (50 roAf) treat-
ment of dormant conidia of N. ovassa induced premature conidia germination
and also decreased the rate of respiration (Figure 3.5) (Timberlake and
Turian, 1975).
TABLE 3.10. EFFECTS OF FLUORIDE ON RESPIRATION OF THE AQUATIC FUNGI
ALLOMYCES JAVANICUS AND BREVTLECNIA UHISPEPHA VAR. DELICA
Allomjcee javanicua
Brevilegnia unieperma
Treatment
Molecular
oxygen
as percent
of control
Percent
inhibition
Molecular
oxygen
as percent
of control
Percent
inhibition
Control
175
110
In absence of glucose
0.01 M fluoride
0.005 H fluoride
In presence of glucose
0.01 M fluoride
0.005 M fluoride
127
148
80
137
48
27
95
38
80
93
66
83
30
17
44
27
Source: Adapted from Thakur and Dayal, 1971, Table 2, p. 467.
by permission of the publisher.
Reprinted
90
80
70
3.
Q M
tu
N
_J 40
I-
oN301
20
10
ORNL-DWG 76-16556R
/-NoF
NoF
0123
NoF TREATMENT (hr)
Figure 3.5. Oxygen uptake during NaF treatment of Neurospora
Source: Adapted from Timberlake and Turian, 1975, Figure 5, p. 153.
Reprinted by permission of the publisher.
-------
81
Fluoride has been used as an inhibitor of photosynthesis in the
green alga Chlorella (Warburg, 1962) and of photosynthesis and the quinone
Hill reaction in the blue-green bacteria Plectonema boryanian and Andbaena
vandbiHs (Vennesland and Turkington, 1966a, 19662>). Potassium fluoride
at a concentration of 20 mM in the absence of carbon dioxide and at pH 5.8
almost completely inhibited the quinone Hill reaction in washed suspensions
of P. bopyamon and A. variabiHs. Fluoride inhibition increased with de-
creasing pH. Figure 3.6 illustrates the effect of fluoride at pH 5.2
on photosynthesis and on the Hill reaction in P. boryanum cell suspensions.
Photosynthesis was more sensitive to fluoride than was the Hill reaction.
ORNL-DWG 76H6557R
100
_ 80
60
o"
40
20
/
/No KF
- /
/ 0.001 M KF
/ ( / ^
./6.003>t/KF
^ / S 1
/ * I ^/«^^^^5 ^n K r
NoKF
/ /O.OOI/l/KF
//. 0.003 A/KF
_ //. 0.005 MKf
>l ' ' ^
~ ////
://'
7 , i
20 40 0 20
TIME (min)
40
Figure 3.6. Effect of fluoride at pH 5.2 on photosynthesis (left)
and on the Hill reaction (right) in Plectonema boryanum cell suspensions,
Source: Adapted from Vennesland and Turkington, 1966a, Figure 2, p. 154,
Reprinted by permission of the publisher.
3.3.2.2 Carbohydrate Metabolism Fluoride influences several aspects
of carbohydrate metabolism, including sugar uptake, acid production, and
enzyme activities. Many of these studies have involved cariogenic bacteria
and attempts at elucidating the mode of action of fluoride in reduction
of caries. Information indicates that the effect of fluoride on sugar
metabolism involves bacterial membranes (Luoma and Tuompo, 1975; Schachtele
and Mayo, 1973). Table 3.11 lists some effects of fluorides on several
aspects of microbial carbohydrate metabolism. The concentrations tested
ranged from 0.01 to 47.5 mW sodium fluoride. At low fluoride concentra-
tions, stimulation of phosphqrylase and carbon dioxide formation in sali-
vary organisms and of glucose fermentation by E. coli are reported (Table
3.11).
Weiss et al. (1965) found that fluoride at concentrations as low as 1
to 10 ppm affected the rate of synthesis of iodophilic polysaccharides from
glucose, maltose, and sucrose by Streptococcus mitis; fluoride inhibition
was reversed with time. Figure 3.7 shows the rapid effect of fluoride at
-------
TABLE 3.11. EFFECTS OF FLUORIDE (NaF) ON MICROBIAL CARBOHYDRATE METABOLISM
Organism
Concentration
(mW)
Effect
Reference
Eacherichia aoli
Yeast
Aepergillua niger
Streptococcus and
LactobacilluB sp.
Yeast
Streptococcus
aalivarius
Eaaherichia coli
Salivary sediment
mixtures
0.01
0.05
0.05
0.01
0.1
2.4
0.06
1.2
2.4
4.8
9.6
50
1.0
£0.22
0.22, 1.0
Activation of glucose fermentation
Activation of fermentation
Inhibition of citric acid production
Inhibition of acid production
Inhibition of pyrophosphatase
Inhibition of glucose uptake; reduction in
cellular glucose-6-P; inhibition of intra-
cellular enolase activity
Decrease in cellular glucose-6-P in cells
metabolizing glucose if added before or
after substrate
Stimulation of phosphorylase activity
Stimulation of phosphorylase activity; imme-
diate decrease in cellular glucose-6-P and
ATP in cells actively degrading glucose;
complete inhibition of glucose uptake and
glycogen synthesis
Inhibition of ADPG pyrophosphorylase
Inhibition of ADPG glucan transferase
Inhibition of phosphoglucomutase
Inhibition of phosphatases that hydrolyze
o-methyl-D-glucose-6-P; inhibition strong
at acid pH, but no inhibition at alkaline
pH; in vivo phosphorylation and dephosphor-
ylation inhibited at acid pH
Stimulation of C02 formation from glucose at
acid pH
No effect on C0a formation
Inhibition of lactic acid and total acid
production
Venkateswarlu, 1970
Venkateswarlu, 1970
Venkateswarlu, 1970
Venkateswarlu, 1970
Venkateswarlu, 1970
Kanapka and Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Kanapka, Khandelwal, and
Hamilton, 1971
Haguenauer and Kepes, 1972
oo
ts>
Sandham and Kleinberg, 1973
Sandham and Kleinberg, 1973
Sandham and Kleinberg, 1973
-------
TABLE 3.11 (continued)
Organism
Concentration
(mW)
Effect
Reference
Entamoeba hietolytiaa 25
Bacillus a
atearothermophilus
Streptococcus mutans
47.5
Blocking of glycolysis; no effect on initial
transport rate of 10 mW 3-0-methylglucose
Inhibition of a-methyl-D-glucoside accumulation
in presence of ATP and Embden-Meyerhoff-
Parnas pathway Intermediates; fluoride plus
sodium azide almost completely inhibited
transport of a-methyl-D-glucoside with NADH
as cosubstrate
Inhibition of sugar uptake, partially allevi-
ated by potassium; potassium extruded from
both fermenting and nonfermenting cells
accompanied by rapid F~ uptake by ferment-
ing cells, then immediate release of F"
back into the medium; intracellular sugar
changes slight; complete inhibition of acid
production
Serrano and Reeves, 1974
O'Leary, Busta, and McKay,
1975
Luoma and Tuorapo, 1975
CO
co
Fluoride concentration not given.
-------
84
700
600
GJ 500
u
o>
E 400
g 300
O
200
100
0
FLUORIDE
ADDITION
ORNL-OWG 76-I65S8R
CONTROL
^_ 10 ppm F"
"~-« 15 ppm F"
~ - 20 ppm F"
50 ppm F"
30 60 90 120
TIME (min)
150
Figure 3.7. Effect of fluoride on an. actively synthesizing poly-
saccharide system of Streptococcus mitis. Source: Adapted from Weiss
et al., 1965, Figure 3, p. 842. Reprinted by permission of the publisher,
concentrations of 15 ppm and higher on glucose incorporation. At 50 ppm
fluoride, bacterial incorporation of sugar ceased about 2 hr after fluoride
addition and degradation of intracellular polysaccharide occurred. Sodium
monofluorophosphate (Na2F09F) was also tested and was found to be less in-
hibitory to polysaccharide synthesis than sodium fluoride. Inhibition of
polysaccharide synthesis, especially synthesis of capsular dextrans and
levans, also occurred in the cariogenic bacterium S. mutccns (Bowen and
Hewitt, 1974). The production of dextran (polyglucan) and levan (poly-
fructan) was altered by 70 ppm fluoride in five different strains of S.
mutone. The ratio of fructose to glucose was significantly higher in cul-
tures grown in the presence of 70 ppm fluoride than in control cultures
grown in the absence of fluoride. However, Schachtele (1977) was unable
to show inhibition of various forms of the enzyme glucosyl transferase,
even at fluoride concentrations as high as 26.3 mW. He also indicated a
high level of resistance for other enzymes involved in metabolism of dex-
trans and levans.
Yost and VanDemark (1978) found that Leuconoatoc mesenteroides,
which does not transport sugars by the phosphoenolpyruvate-requiring
phosphotransferase system, was less sensitive to fluoride in terms of
growth inhibition than S. mutons, which does have the phosphotransferase
system.
In addition, Kashket, Rodriguez, and Bunick (1977) found that very
low levels of fluoride inhibit glucose utilization by oral streptococci
and do not have any stimulatory action. The whole subject of the effects
of fluoride on carbohydrate uptake and metabolism was reviewed by Hamilton
(1977).
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85
3.3.2.3 Protein Synthesis and Nucleic Acid Metabolism Of the fluorinated
compounds that can alter protein synthesis and nucleic acid metabolism of
microorganisms, the substrate analogs p-fluorophenylalanine (p-FPhe), 5-
fluorodeoxyuridine (FdUrd), and 5-fluorouracil (FU) have been the most
widely studied. Their incorporation into biopolymers and the resulting
metabolic effects were reviewed by Heidelberger (1972) and Fowden (1972).
Mandel (1969) extensively reviewed data on the incorporation of FU
into RNA. Table 3.1 (Section 3.2.1) shows that 5% to 80% of the original
uracil in several bacterial and fungal species and viruses can be replaced
by FU. In most cases the incorporation could be reversed by the addition
of uracil. Subcellular effects of FU replacement of uracil included alter-
ations in ribosomal composition and properties; changes in the functions,
properties, and base composition of transfer RNA (£RNA); and modifications
in the functions of messenger RNA. Recently, more work has been done using
E. coli B tRNA. Lowrie and Bergquist (1968) obtained up to 100% replace-
ment of uracil by FU in tRNA, and Kaiser (1969, 1971) obtained 80% to 84%
replacement. Lowrie and Bergquist found that the secondary structure of
FU-tRNA was altered. However, Kaiser (1971) reported that fluorouridine
replacement of uridine and uridine-related minor base components had only
minor effects on secondary and tertiary properties, especially in the pres-
ence of Mg2+. The FU-tRNA retained about 90% of its ability to accept
amino acids (Kaiser, 1969).
Cohen et al. (1958) determined that the inhibitory effect of FdUrd
on DNA synthesis in E. eoli was due to the inhibition of thymidylate syn-
thetase by the phosphorylated 5*-monophosphate of FdUrd. In this case,
the fluorinated pyrimidine is not incorporated into the nucleic acid but
rather prevents the synthesis of a component (thymidylate) essential for
DNA replication.
The enzyme thymidylate synthetase can be inhibited in some micro-
organism cells by the fluorinated base 5-fluorocytosine. The major source
of deoxythymidylate for DNA synthesis is thus suppressed. Inhibition ap-
pears to result from formation of 5-fluorodeoxyuridylate which can irre-
versibly bind to thymidylate synthetase to inactivate it. The kinetics
of the reaction with the enzyme from Lactobacillus casei were described
(Danenberg and Danenberg, 1978).
Mandelbaum-Shavit and Kisliuk (1978) investigated mutants of Pedio-
coccus eerevisiae resistant to FdUrd. They defined two types: one with
reduced or absent thymidylate kinase activity, which is thought to be in-
volved in thymidine uptake by bacterial cells; and the other with impaired
permeability to the fluoronucleotide but with normal kinase activity.
5-Trifluoromethyl-2f-deoxyuridine (F3Thd) at 1 vM irreversibly inhib-
ited replication of vaccinia virus (the W.R. neurotropic strain) in HeLaS3
cell cultures (mycoplasma-free) with selective toxicity to the virus (Umeda
and Heidelberger, 1969). FdUrd (1 vM) did not selectively inhibit the
virus. Its inhibition was transient, occurring primarily on the first day.
Umeda and Heidelberger concluded that the major antiviral activity of F3Thd
was probably due to its incorporation into viral DNA.
-------
86
The incorporation of p-FPhe into microbial protein can cause many
diverse effects. When incorporated into E. coli B ISj- it blocked cell
division; it also blocked ribonucleic acid polymerase synthesis when thy-
mine was added at the same time to thymine-starved cultures (Hardy and
Binkley, 1967). In E. ooli the interference with cell division seemed to
be with the initiation of DNA replication. Other consequences of p-FPhe
incorporation into microbial protein were discussed by Fowden (1972).
These include alterations in shape and size of cells, interference with
cell differentiation, and alterations of eukaryotic chromosomes.
The fluorinated base 5-fluorocytosine, usually in combination with
amphotericin B, has been used for many years for treatment of infections
caused by yeasts of the genera Candida, Torulcpeie, and Ciyptoeoeeus. The
mode of action in Candida appears (Polak and Scholer, 1975) to involve met-
abolic conversion to 5-fluorouridylate, which is then incorporated into RNA
with up to 502 replacement of uracil. The replacement then leads to dis-
turbances in protein synthesis. There was no indication of conversion to
5-fluorodeoxyuridylate in Candida or for inhibition of thymidylate
synthetase.
An uncoupler of photophosphorylation, carbonylcyanide-p-trifluoro-
methoxyphenylhydrazone (FCCP) at 1.5 * 10~7 M inhibited replication of the
virulent bacteriophage RC1 in the nonsulfur purple photosynthetic bacterium
RhodopBeudomonas oapeulata strain Z-l (Figure 3.8) (Schmidt, Ten, and Gest,
1974). The growth rate of the uninfected control plus 1.5 * 10~7 M FCCP
was substantial, but the infected cells in the presence of FCPP did not
ORNL-OW6 76-4656O
UO
0.5
- 10*
O.I
I
2468
INCUBATION TIME (hr)
Figure 3.8. Effect of the phosphorylation uncoupler carbonylcyanide-
p-trifluoromethoxy-phenylhydrazone (FCCP) on replication of RC1 phage in
photosynthetically grown cells of Rhodopeeudomonas eapeulata Z-l incubated
under photosynthetic conditions. Source: Adapted from Schmidt, Ten, and
Gest, 1974, Figure 4, p. 235. Reprinted by permission of the publisher.
-------
87
show production of progeny phage. The phage requirement for energy was
more stringent than that of the bacterial host cell.
Inorganic fluoride can inhibit several reactions involving nucleic
acids. Effects of sodium fluoride (50 off) on //. c??O33c (protein, RNA, and
DNA synthesis reduction) are illustrated in Figure 3.9 (Timberlake and
Turian, 1975). The cultures used were submerged pregerminated conidia.
Leucine incorporation into protein was the most rapidly reduced. Fluoride
inhibits DNA polymerase activity in the presence of Mg2+ (Hellung-Larsen
and Klenow, 1969; Lehman et al., 1958). Hellung-Larsen and Klenow reported
that 0.16 M potassium fluoride caused 90% inhibition of DNA polymerase of
E. coli B. They correlated inhibition with the formation of precipitable
complexes containing Mg2*, substrate phosphatases, and fluoride.
ORNL-DWG 76-16559R
123 <*
NoF TREATMENT (hr)
Figure 3.9. Effect of NaF treatment on protein, RNA, and DNA
synthesis of Senroapora crassa. Source: Adapted from Timberlake and
Turian, 1975, Figure 4, p. 153. Reprinted by permission of the publisher.
Fluoride may have important effects on nucleotide metabolism. For
example, Khandelwal and Hamilton (1971) found that fluoride stimulated the
adenyl cyclase enzyme of S. saHvariuB, and it is possible that this action
may have important effects on the regulatory circuits of microorganisms.
Marquis (1977) found that fluoride inhibited the membrane ATPase of S.
faeealia and suggested that this action could be partly responsible for
the potassium deficiency of cells treated with fluoride.
-------
88
3.3.2.4 Enzyme Activities Inhibition of enzymes responsible for acid
production may be especially important in the study of cariogenesis
(Jenkins, 1970). The enzyme of the Embden-Meyerhof pathway most sensi-
tive to fluoride is enolase (Jenkins, 1970; Warburg and Christian, 1942),
although the actual site of enzyme inhibition in saliva seems to be one
involving glucose uptake by the cell (Jenkins, 1970) and ionic transport
(Luoma and Tuompo, 1975).
Effects of fluorides on a variety of microbial enzyme systems are
given in Tables 3.12 and 3.13. In general, varying degrees of inhibition
are indicated, although the respiration and rate of multiplication of
certain yeasts are enhanced. Table 3.14 indicates no inhibitory effects
of fluoride (up to 9.6 nrtf) on the activity of several enzymes involved in
the synthesis and degradation of glycogen in crude extracts of Strepto-
coccus salivarius (Kanapka, Khandelwal, and Hamilton, 1971). Additional
information concerning fluoride effects on carbohydrate metabolism is in
Section 3.3.2.2. Table 3.15 lists some effects of 5-fluorouracil (FU) on
various microbial enzymes (Mandel, 1969). The inhibitory action of FU
seems to involve the fidelity of protein synthesis on FU-substituted mRNA.
TABLE 3.12. ENZYME INHIBITION BY SOLUBLE FLUORIDES
Organism Enzyme system Effect*2
Bacidiomycetes Acid phosphononoesterase +-H-
Yeast Adaptive fermentation of -H-
galactose
Cell permeability +
Fermentation -H-
Glycogen storage -H-
Multiplication
Respiration -H-
Yeast top Respiration
Acetycholinesterase ?
Apozymase + cozymase +
Cytochrome oxidase 0
Glucosulphatase ++
Invertase 0
Phosphatase (in vitro) +
Phosphatase (in vitro)
reactivation
Succinodehydrogenase
Takadiastase on
glycerophosphates
Takasulphatase
0 indicates no effect; + to +-H- indicates vary-
ing degrees of inhibition; - to indicates promotion.
Source: Adapted from Eagers, 1969, Table 16,
pp. 107-108. Data collected from several sources.
Reprinted by permission of the publisher.
-------
TABLE 3.13. EFFECTS OF FLUORIDE ON HICROBIAL ENZYMATIC ACTIVITY
Enzyae
Inorganic pyrophosphatase
B-Galactoaldase
Fungal lactaae A and B
p-Nltrophenylphosphataae
Phytase
Source Compound
Farrobaoillua fgrro- KF
oxidona (ThiobocilluB
ftnooxtdona)
Beoheriohia ooli p-Toluenesulfonyl
fluoride
Phenylatethane sul-
fonyl fluoride
Polyporoue vereioolof F"
Streptococcus mitana NaF
Pseudanonae sp. F"
Concentration
10'1 H
Enough to inhibit
protein breakdown
300 ug/nl
1 equivalent
0.67-1.67 nV
1.0-8.0 vN
Effect
90X inhibition
Blocked Induction in
starving cells
Blocked induction in
starving cells;
slight inhibition In
cells growing on
glycerol
Almost conplete inhi-
bition when bound to
type 2 Cu1*; inhibi-
tion decreased in
presence of substrate
No repressive or
induclve effect
Inhibition varied as
Reference
Howard and Lundgren,
1970
Goldberg, 1971
Goldberg. 1971
Brandon. Malastroai,
and VHnngard, 1973
Knuuttlla and HHklnen,
1973
Irving and Cosgrove,
the cube of fluoride
ion concentration
1971
00
VO
-------
90
TABLE 3.1A. INFLUENCE OF SODIUM FLUORIDE ON THE ENZYMES INVOLVED
IN THE SYNTHESIS AND DEGRADATION OF GLYCOGEN IN CRUDE EXTRACTS OF
STREPTOCOCCUS SALIVARIUS
Enzyme
Activity of enzyme
at NaF (mtf) concentration
1.2
2.A
A.8
7.2
9.6
Phosphoglucomutase
Preincubation
No incubation
ADPG pyrophosphorylase
ADPG glucan transferase
Phosphorylase
lA7a 159
147, 159
8r 90
106j 107
235 363
171
1A7
97
111
A07
1A7
1A7
85
108
171
1A7
450
.Nanomoles glucose-6-P formed per milligram protein per minute.
Picomoles ADP-glucose formed per milligram protein per minute.
Nanomoles glycogen formed per milligram protein per minute.
T'icomoles glucose-1-P incorporated into glycogen per milligram
protein per minute.
Source: Adapted from Kanapka, Khandelwal, and Hamilton, 1971,
Table II, p. 600. Reprinted by permission of the publisher.
TABLE 3.15. EFFECTS OF 5-FLUOROURACIL INCORPORATION ON ENZYMATIC ACTIVITY
Enzyme
Source
Effect
Comments
8-Galactosidase
Succinate dehydrogenase
Catalase
D-Serine dehydrase
8-Glucuronidase
Serine deaminase
Glucose-6-phosphate
dehydrogenase
Alkaline phosphatase
Ribonuclease
Deoxyribonuclease
Ribonuclease
Alkaline phosphatase
a-Amylase
Aconitase
Malate dehydrogenase
Fumarase
Succinate dehydrogenase
NADH oxidase
Penicillinase
d-Aminolevulinate
synthetase
Succinate dehydrogenase
ct-Glucosidase
Galactosidase
Eeche-pichia aoli
E. aoli
E. aoli.
E. aoli
E. ooli
E. aoli
E. ooli
E. coli
Staphylococcue
aureus
S. aureus
Bacillus subtilie
B. Bubtilia
B. aubtilis
Bacillus cereuB
B. cereue
B. cereua
B. aereus
B. cereuB
B. cereus
Rhodopeeudomonae
apheroidee
P. spheroidea
Soodhoromycee
carlebergenaiB
S. carlebergenaie
Inhibition
Stimulation
None
Inhibition
Inhibition
None
None
None
Inhibition
None
Inhibition
Inhibition
None
Inhibition
Inhibition
Inhibition
None
None
None
Inhibition
None
None
None
Inducible and constitutive;
occasionally reversed by
uracil; decreased enzyme
specific activity
Constitutive
Constitutive
Inducible
Constitutive (?)
Decreased thermostabillty
Inconclusive
Inconclusive
Exoenzyme
Inducible
Exoenzyme; thermostability
unchanged
Constitutive
Constitutive
Constitutive
Constitutive
Constitutive
Inducible
Uracil reversed effect
Inducible; no qualitative
change
Inducible; no qualitative
change
Source: Adapted from Mandel, 1969, Table 6, p.
sources. Reprinted by permission of the publisher.
117. Data collected from several
-------
91
3.4 PROSPECTS FOR FUTURE RESEARCH
3.4.1 Inorganic Fluorides
3.4.1.1 Dental and Medical Uses It seems unquestionably clear that there
will be extensive future use of fluorides as anticaries agents, and since
they do have antiplaque properties, possible use of them against periodon-
tal disease. A study by Erickson (1978) of mortality rates in 24 cities
with fluoridated water and 22 with nonfluoridated water revealed no signif-
icant differences between the two. Therefore, the view that water fluorid-
ation has no harmful effects was supported. These findings are encouraging
for more extensive use of water fluoridation in the United States and other
industrialized countries. Of course, this increased use means greater
exposure of microorganisms, as well as humans, to fluorides.
There is currently an increasing incidence of dental caries, even in
developing countries, mainly because of changes in diet. This increase
has prompted study by the World Health Organization and others. The use
of fluoride seems to be the best way to curb this rise in caries. How-
ever, in Third World countries water fluoridation is not always feasible,
and fluoride may have to be provided in foods or in tablets. Again, the
future seems to hold increased fluoride exposure to people and flora.
Topical fluorides are likely to become more popular in the United
States. In fact, there are new fluoride-containing mouthwashes on the
market in the United States with approximately 23 millimoles of fluoride.
Of course, topical fluoride preparations used under supervision of a den-
tist are much more concentrated and cannot reasonably be used by the gen-
eral public because of the danger of accidental ingestion. However, the
preparations appear to be so highly effective that their use will become
more widespread. It is not now clear whether or not it is best to have a
prophylactic cleaning of the teeth prior to topical fluoride application.
The National Institute of Dental Research is currently funding work on
the question. There is some feeling that leaving bacteria in plaque on
teeth helps in fluoride retention.
Fluoride usage in medicine is not extensive; however, fluoride is
experimentally used to reduce osteoporosis. The maximum dosage is usually
about 50 mg/day given with calcium and vitamin D. If distributed evenly
throughout the body, this dosage would give a level of only about 0.03 mW.
One would not expect this concentration of fluoride to greatly affect the
normal flora. However, if fluoride is accumulated by the gut bacteria, it
is possible that microbiologically significant levels could be attained.
Some 10% of fluoride ingested is excreted in feces.
Microbiological aspects of fluoride ingestion by man have been
sketchily studied, and concerns about the safety of increased ingestion
require more thorough investigations. It has been clearly shown that
bacteria in dental plaque accumulate rather high levels of fluoride (mil-
limolar range). These levels are effective in upsetting microbial phys-
iology, even to the extreme response of lysis shown by certain species of
bacteria. The concentration of fluoride by plaque would be expected to
-------
92
have effects on the population, favoring the less sensitive types. In-
direct effects would also be expected. For example, fluoride reduces acid
production by plaque, and less acid conditions should favor growth and
metabolism of the less aciduric members of the flora. Reductions in acid
production due to fluoride ingestion could have effects in other parts of
the body, for example, in the vagina where the maintenance of acid condi-
tions through bacterial metabolism is thought to be partly responsible
for resistance to certain infections.
There is a possibility that the now long-term use of fluoride in
drinking water has contributed to a rise in resistant bacteria, much as
the use of antibiotics has led to a disasterous selection of resistant
bacteria. There is a need to find out if the use of fluoride does indeed
result in selection of resistant forms, and if the selection occurs in
the normal flora of man.
Another possible effect of fluoride on normal flora that is being
investigated deals with the natural immune systems in the mouth specif-
ically lysozyme, lactoperoxidase, and lactoferrin. It appears that bac-
teria grown in media with plaque levels of fluoride are more susceptible
to lysozyme killing or inactivation by the lactoperoxidase system than
are bacteria from nonfluoridated media. Fluoride may adversely affect
bacteria indirectly by rendering them more susceptible to normal host
defense mechanisms. An interest in this research comes from the desire
to formulate more effective anticaries regimens.
The National Institute of Dental Research has a number of contracts
to assess the interactions of fluoride with other ions and their effects
on dental caries. There is also a need for research on interactions of
fluoride with other agents used to reduce caries (e.g., chlorhexidine,
calcium phosphate rinses, and alkylamines).
3.4.1.2 Basic Studies of Microbial Responses to Fluoride The National
Institute of Dental Research has tried to obtain basic information on the
mechanism of the anticaries action of fluoride. A large component of the
needed information is microbial responses to fluoride. Recent research
has shown that bacteria have a complex array of responses to fluoride.
Enolase-action inhibition is the most widely accepted view of how
fluoride inhibits bacterial acid production. This inhibition results in
diminished supplies of phosphoenolypyruvate and secondary inhibition of
the phosphotransferase sytem for sugar uptake. However, it appears that
fluoride may also act as a transmembrane proton conductor to acidify
cytoplasm and render cells acid sensitive. The importance of the latter
action in the inhibition of the metabolism of oral bacteria remains to
be determined.
There are indications that fluoride is effective in either inhibiting
or changing the production of extracellular polysaccharides by oral bac-
teria. Since the polymers are thought to play important roles in coloniza-
tion of teeth by bacteria, this action may be involved in the anticaries
effects of fluoride.
-------
93
The uptake of fluoride by bacteria, especially in relation to fluoride
concentration by dental plaque, is not completely understood. It is not
known if specific transport systems bring fluoride into the cell or if
fluoride enters only by diffusion of the hydrogen fluoride form. Research-
ers do not know if the bacterial membrane has a low level of permeability
to the anionic form or what polymers are responsible for binding fluoride
in the cell. There is still a question of whether this tightly bound fluo-
ride is of any metabolic significance.
Fluoride has a number of other important actions that may be pertinent
to its effects on plaque bacteria. For example, it inhibits the membrane
ATPase of streptococci, and presumably other bacteria. Perhaps this inhi-
bition causes sufficient loss of potassium from cells so that processes
such as glycolysis and protein synthesis are inhibited. There may be other
metabolic actions of fluoride not currently known. Certainly, many iso-
lated enzymes are inhibited by fluoride, and a multiplicity of actions are
expected within the cell. Also, some enzymes (e.g., adenylate synthetase)
can be stimulated by fluoride. Again, important metabolic alterations
result.
Another area likely to receive a great deal of attention is related
to the anticaries action of topical fluorides. There is evidence to sug-
gest that the action may be different from the anticaries action of fluo-
ride in drinking water. It is clear that fluoride, especially in concen-
trated solutions, can kill certain bacteria. However, the mechanism of
this killing and how the killing alters plaque flora are not known.
Major research during the next decade on the biological actions of
fluoride will probably have a dental orientation. However, there are many
industrial and environmental problems that should receive attention, some
relating to the use of fluoride as an anticaries agent. For example, water
used for microbial processes (e.g., brewing or sewage treatment) is fluo-
ridated in many cases, and fluoride may be concentrated by the organisms
with resulting alterations in metabolism. The major industrial problem
probably comes from emission of fluorides from industrial plants with
resultant pollution of surrounding areas. The major sector of the biolog-
ical community interacting with these fluorides would be microorganisms.
These microorganisms would metabolize the compounds, and to date there is
little information on the specifics of this process.
3.4.2 Organic Fluorocompounds
3.4.2.1 New Compounds One major area of future research in the micro-
biological aspects of organic fluorides is the development of antimicrobial
agents. The most useful compounds should be selectively toxic to micro-
organisms. Microbial resistance to antibiotics is increasing at an alarm-
ing rate, and there is an imminent need for compounds that can be used in
place of, or in conjunction with, antibiotics. For example, fluorocytosine
is commonly used with amphotericin B in treating fungal infections caused
by organisms such as C-pyptoQooaus neoformans. Recently, a new fluoroderiv-
ative, flumequine, was introduced as a substitute for nalidixic acid in the
treatment of urinary tract infections.
-------
94
Because of its size, fluoride is a good substitute for hydrogen in
organic compounds, and fluoroanalogues are commonly active biologically.
For example, many fluoroamino acids are incorporated into proteins in
place of the natural compounds. It seems that a rational approach would
be to synthesize fluoroderivatives of metabolites peculiar, or nearly so,
to prokaryotes. For example, peptidoglycan is a compound that occurs only
in the bacterial cell wall. Many peptidoglycans contain the unusual amino
acid diaminopimelate. Perhaps a fluoroderivative of diaminopimelate would
have selective toxicity for prokaryotes. Nearly all peptidoglycans con-
tain D-amino acids; for example, fluorinated D-alanyl-D-alanine might be
selectively toxic. Certainly, it seems that imaginative research in this
area is likely to be profitable. Development of antiviral properties and
further testing of compounds is likely to yield positive results.
Much research is still to be done in developing fluoroderivatives for
use in basic biochemical studies. Again, fluoride tends to mimic hydrogen
as a substituent, and fluoroanalogues tend to be active biologically. Flu-
oride is currently a popular substituent because of the possibility of
analyzing 19F nmr signals. This field too seems to be one in which imag-
inative research is bound to be successful.
3.4.2.2 Microorganisms for Degradation of Fluoroorganics Microorganisms
are able to catabolize many fluoroorganic compounds, sometimes resulting
in cleavage of the carbon-fluoride bond. These organisms should be useful
in cases of dangerous pollution by organic fluoride compounds. Moreover,
organisms capable of degrading fluoroorganics would be of interest to bio-
chemists studying reaction mechanisms and to tnicrobiologists. Specific
microbes could be isolated for use in specific pollution problems involv-
ing organic fluorides.
3.4.2.3 Additional Uses for Fluorinated Anesthetics Recent evidence
suggests that anesthetics, including fluorinated ones, can inhibit the
growth of cells. The spectrum of inhibition spans all cell types, from
bacteria to mammalian cells. Microorganisms should prove to be useful
for basic studies of the mechanisms of growth inhibition, although it is
unlikely that fluorinated anesthetics will find use as antiseptics or
disinfectants.
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SECTION 3
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105
127. Williams, R.A.D. 1968. Permeability of Fluoride-Trained Strepto-
cocci to Fluoride. Arch. Oral Biol. 13:1031-1033.
128. Yost, K. G., and P. J. VanDemark. 1978. Growth Inhibition of
Streptococcus mutans and Leuconoetoc mee&ntevoides by Sodium Fluo-
ride and Ionic Tin. Appl. Environ. Microbiol. 35:920-924.
-------
SECTION 4
BIOLOGICAL ASPECTS IN PLANTS
Fluoride is a well-studied pollutant in the ecosystem, and consider-
able data exist on its effects on plant systems. For some of the earlier
work in the field, several good literature reviews may be consulted (Adams,
1956; Brewer, 1966; Chang, 1975; National Academy of Sciences, 1971; Thomas
and Alther, 1966; Treshow and Pack, 1970).
4.1 SUMMARY
The metabolism and effects of fluorides in plants have been well stud-
ied, but important information is still lacking. Although soils contain a
high fluoride content (10 to 1000 ppm) , most is in a form not absorbed by
plants. Acid soils tend to have a higher available fluoride content; lim-
ing decreases this availability. The levels of major nutrients in the soil
affect the amount of fluoride absorbed through the root. Fluoride is trans-
located from root to shoot, and fluoride in the leaf moves to the tips and
edges of the leaves but not out of the leaves.
In polluted areas, most fluoride is probably absorbed by leaves.
Leaves of plants found in the vicinity of known sources of atmospheric
fluoride pollution, such as aluminum and phosphate fertilizer industries,
have high fluoride concentrations. Fluoride fumigation at night, when
stomates are closed, produces less accumulation of fluoride in tissues
than fumigation during the day. Little downward translocation of fluoride
from shoots to roots has been found. Gaseous fluorides are more effec-
tively absorbed than particulate fluorides and lead to greater injury.
Cryolite, even when present at high levels, produces few injury symptoms
in plants.
Fluoride metabolism in plants is not well understood. Some plants
have the ability to synthesize relatively large quantities of carbon-
fluorine compounds. These plants are toxic to animals, and the toxic
principle is usually monofluoroacetate. Whether all plants can synthe-
size carbon-fluorine bonds is uncertain. There is some evidence that a
variety of plants can form small amounts of fluoroacetate and fluoroci-
trate. No information is available on the enzyme system(s) necessary to
synthesize or degrade the organofluorides. Why fluoroacetate is not
toxic to these plants is not known.
Fluoride is found in virtually all plants. In unpolluted areas,
fluoride concentrations range from about 2 to 20 ppm. Except for certain
species (e.g., Camellia), plants are not able to concentrate fluoride much
above these levels from the soil. There is no apparent relationship be-
tween soil concentration of fluoride and tissue concentration of fluoride.
However, exposure to even low concentrations of atmospheric fluoride can
lead to significant accumulation of foliage. Significant amounts of fluo-
ride can be removed from leaves by washing with distilled water or deter-
gents. Tissue fluorides increase as length of exposure and atmospheric
106
-------
107
concentrations increase. Data are inadequate to determine subcellular
sites of localization; however, some evidence suggests that chloroplasts
accumulate fluoride to a greater extent than mitochondria or cell walls.
Fluoride is eliminated from plants by loss of leaves, twigs, and
roots; by rain; and, although evidence for this is meager, perhaps
through volatilization of organofluorides.
Fluorides affect cells in an undefined manner. Eventually, the
altered metabolism of the cell is expressed as visible symptoms, which
ultimately can cause death of the plant or plant organ. The buildup of
fluorides in plant material increases the availability of fluoride to
other components of the ecosystem, which may, for example, increase the
incidence of fluorosis in animals.
Although fluorides are known to be in vitro inhibitors of a variety
of enzymes, it is difficult to establish whether inhibition of these
enzymes also occurs in vivo and which inhibition is directly responsible
for the altered metabolism. It is known, however, that fluorides alter
photosynthesis, carbohydrate metabolism, respiratory and oxidative proc-
esses, RNA metabolism, and calcium nutrition.
Fluoride injury to foliage usually involves tip or marginal necrosis,
sometimes preceded by chlorosis; however, other environmental stresses
can duplicate these symptoms. Wilting is observed with higher doses of
fluorides. Not all plants are equally sensitive to fluorides; gladiolus,
apricot, and Douglas fir are examples of sensitive plants, whereas cherry,
tomato, and wheat are resistant plants. Fruits can also be injured by
fluoride exposure. The most common example of injury is the soft suture
disease in peaches; fruit yield can be decreased by fluoride exposure.
High fluoride concentrations in solutions can inhibit germination of seeds
and restrict growth, although at low concentrations some enhancement of
linear growth may occur. Growth inhibition is usually accompanied by vis-
ible injury symptoms, but hidden injury (growth inhibition without visible
injury) has been reported when plants were exposed to relatively high
concentrations of fluoride.
From an agricultural point of view, permissible fluoride exposures
are difficult to determine. Interacting factors include the species
diversity of the community, the sensitivity of each species, and the
nature and pattern of fluoride exposure. Data are insufficient to rec-
ommend air quality concentrations at the present time. Few data also
exist on the effects of interactions of fluoride with other pollutants
or with parasitic organisms.
Fluorides apparently can be mutagenic; cytological abnormalities
have been observed in a variety of plants exposed to either hydrogen
fluoride or sodium fluoride.
-------
108
4.2 METABOLISM
Fluorine, a rather abundant element, occurs naturally in all soils.
It is released to the environment by a number of industrial processes.
Fluoride contamination of plants has been extensively investigated because
exposure to fluorides can induce disease. Although greater emphasis has
been placed on symptomatology, there is considerable information concern-
ing the metabolism of fluoride in plants. However, information gaps do
exist, particularly with respect to the fate and effect(s) of fluoride
at the cellular and molecular level.
Based on the generally accepted criteria of Arnon and Stout (1939),
fluoride is not considered essential for plant nutrition. Although some
reports show that in certain plants (Douglas fir, citrus, rose, alfalfa,
and beans) fluoride can stimulate growth, this increased growth rate does
not normally result in a better adapted plant (Thomas and Alther, 1966).
4.2.1 Uptake and Absorption
Because fluoride can be absorbed by most plant organs, the major
route of entry depends on the source of fluoride. For example, atmos-
pheric pollution from aluminum and phosphate industries is the major
source of fluoride for many plants, entry occurring through stems and
leaves. Soils, however, contain considerable amounts of fluoride, and
absorption from soil occurs if the fluoride is in an available state.
No information was found on the uptake mechanism for any cell type.
4.2.1.1 Exposure to Fluoride in Soil Most soils contain from 10 to
1000 ppm fluoride. In alkaline soils, much of this is bound in clays,
but in acid soils some fluoride is soluble and can be absorbed by the
plant.
Sand and water culture experiments with added sodium fluoride show
that plant roots will absorb fluoride, the amount absorbed depending on
external concentration and exposure time. For example, after addition
of isotopically labeled sodium fluoride to soil, fluorine-18 was detected
in roots, stems, and leaves of tomato plants (Lyoapereican eaaul&ntum),
indicating both absorption and translocation (Ledbetter, Mavrodineanu,
and Weiss, 1960). Furthermore, uptake of fluoride by whole grass seed-
lings grown in water containing 5.25 to 21.00 mM fluoride increased from
28 to 51 ppm (wet weight) after 1-hr exposure, from 30 to 62 ppm after
4-hr exposure, and from 58 to 282 ppm after 16-hr exposure (Peters and
Shorthouse, 1964). Plants grown in 1.05 mW fluoride contained only 3.4
ppm after a 4-hr exposure.
Acacia geovginae grown in water culture and then exposed for 18 hr
to an aqueous solution containing 10 ppm fluoride accumulated 3.6 ppm
inorganic fluoride (wet-weight basis) in the aerial parts and 10.3 ppm
in the roots (Peters, Murray, and Shorthouse, 1965). When exposed to
20 ppm fluoride for 120 hr, the Inorganic fluoride in the aerial parts
increased from 1.2 to 5.5 ppm, and the root content increased from 1.4
to 16.2 ppm. With higher concentrations of fluoride in the growth solu-
tion (200 to 300 ppm) , large amounts of fluoride were taken up (Figure
-------
109
4.1). Considerable variation among plants was observed in these experi-
ments. For example, four plants grown in water culture and exposed to 10
ppm fluoride for eight days contained from 10 to 25.2 ppm fluoride. In
pot experiments where fluoride was supplied as a saturated solution of
calcium fluoride for 54 days, the aerial portions contained from 0 to 82
ppm inorganic fluoride.
ORNL-DWG 77-2427)
PH
6.6
T
A AERIAL PARTS
R ROOTS
INORGANIC FLUORIDE
O ORGANIC FLUORIDE
4.0
A
J_
_L
_L
J_
I
800
4600 2400
FLUORIDE
3200 4000 4BOO
Figure 4.1. Comparison of the amounts of fluoride taken up by Acacia
geovginae from solutions of sodium fluoride, 300 pg/ml (15.75 mW) at pH 6.6
and pH 4.0 (acidification with nitric acid). Experiment 3 was also exposed
to dipotassium hydrogen phosphate. Source: Adapted from Peters, Murray,
and Shorthouse, 1965, Figure 2, p. 727. Reprinted by permission of the
publisher.
Liming soil decreases the available fluoride content. Studies by
Maclntire et al. (1949) showed that tops of plants do not accumulate fluo-
ride from soils amended with calcium fluoride, rock phosphate, or hydro-
gen fluoride when the soils were adequately limed. In further studies,
Maclntire et al. (1951) increased the fluoride content of clover by adding
hydrofluoric acid to Hartsells-fine sandy loam and Clarksville silt loam.
Treating the soil with lime reduced the fluoride content of clover to con-
trol values (about 20 ppm). Similarly, Hansen, Wiebe, and Thome (1958)
reported that sodium fluoride additions to soil increased the plant-
fluoride content of turnips and alfalfa grown in Orem loamy soil (low
lime, low clay, and low organic content) to a much greater extent than
those grown in soils higher in lime or clay. Additions of sodium fluoro-
silicate produced similar results, although less fluoride was absorbed
-------
110
than with sodium fluoride additions. In other studies, increasing the
pH of loam and sandy loam soils supplemented with fluoride from 4.5 to
6.5 decreased the amount of fluoride in the leaves of tomato and buck-
wheat (Prince et al., 1949). Similar percentage decreases in leaf fluo-
ride concentration were observed with either hydrogen fluoride or sodium
fluoride added to Sassafrass loam or to sandy loam soils. Hurd-Karrer
(1950) found that liming decreased the uptake of fluoride in collards,
buckwheat, and barley. In unlimed plots with added sodium fluoride,
uptake was greater from loamy sand soils than from sandy loam soils.
Because soil fluoride may be unavailable to plants, a direct relation-
ship between soil fluoride content and plant fluoride content does not
necessarily exist. However, Israel (1974a) found a positive statistical
correlation between soil fluoride content and alfalfa fluoride content.
Under his experimental conditions, a soil concentration of 120 ppm fluo-
ride was necessary to produce the same tissue level of fluoride (1 ppm)
as is produced by exposure to only 0.007 yg/m3 of hydrogen fluoride. These
data illustrate the difficulty of trying to correlate tissue fluoride con-
tent with soil fluoride content in field studies where small, but measur-
able, atmospheric concentrations of fluoride may be present. These data
also support the argument that airborne fluorides do not add enough fluo-
ride to soils to increase plant uptake from the soil.
In a German industrial area, yearly additions to soil by fallout
from the atmosphere were approximately 2.1 kg of fluoride per hectare,
and additions by fertilization were between 8 and 20 kg of fluoride per
hectare (Oelschlager, 1972). Of this amount, only about 0.1% to 0.4% is
removed by harvesting crops.
Levels of nutrients in the soil can also affect the amount of fluo-
ride taken up by plants. The data of Brennan, Leone, and Daines (1950)
(Table 4.1) suggest that levels of nitrogen, calcium, and phosphorus
affect the concentration of fluoride in tomato roots and leaves when flu-
oride is supplied to soil as sodium fluoride. However, the fluoride con-
centrations in roots and leaves are not greatly affected when fluoride is
supplied in gaseous form (hydrogen fluoride) to the plant. On the other
hand, MacLean et al. (1969) found an effect of mineral nutrition on the
response of tomato plants to gaseous hydrogen fluoride. Exposure to hydro-
gen fluoride increased the extent of foliar injury in plants grown in
either a calcium-deficient or magnesium-deficient medium. Fluoride uptake
was greater in plants grown on potassium-deficient medium and was less in
plants grown on calcium- or magnesium-deficient media. McCune, Hitchcock,
and Weinstein (1966) found that nutrient levels did not affect fluoride
accumulation in gladiolus, but the extent of necrosis was affected. Low
levels of nitrogen or calcium reduced necrosis, whereas low levels of
potassium, phosphorus, or magnesium increased necrosis. Necrosis was not
affected by either iron or magnesium deficiencies. Pea plants grown in
low-calcium solution showed more injury (reductions in number and weight
of seeds) from fluoride fumigation than when grown in standard solution
(Pack and Sulzbach, 1976). Pepper, however, showed the opposite response.
Several types of mineral-deficient bean plants were tested, and only the
nitrogen-deficient plants developed necrosis upon exposure to gaseous
hydrogen fluoride (Adams and Sulzbach, 1961).
-------
TABLE A.I. EFFECT Of 50 ppa FLUORINE (AS NaP) IN NUTRIENT SOLUTIONS (SERIES A AND B) AND OF HP FUMIGATION (SERIES C AND D) ON THE DEGREE OF INJURY
AND FLUORIDE LEVELS IN TISSUES OF TOMATO PLANTS GROWN WITH DIFFERENT l.KVFI.S OF NITROGEN, CALCIUM, AND PHOSPHORUS
Serlea A
(13 day* treatment)
Nu*n«,t Concentration
Nuttltnt (PP.) Degree
of
Nitrogen
Calclim
Phoaphoru*
1A
56
112
AA8
10
AO
80
2AO
0
0.8
IS. 5
62
injury
None
None
Moderate
None
None
Moderate
None
None
Trace
Slight
Slight
Moderate
Fluoride
in tlaaue
(PP»)
Leave*
7A
96
SAO
160
170
950
116
62
27A
A 80
A6A
1010
Root*
280
3010
2000
1800
A60
1290
3610
A 360
2739
2305
1050
970
Series
,eo Day* of
injury <"««<
None
Moderate
Moderate
None
None
Moderate
Moderate
None
Trace
Slight
Moderate
Severe
11
2A
11
31
31
6
fl
11
31
31
13
13
B
Fluoride
in tlaau*
(PP«)
Leave*
250
1000
500
430
A35
1000
850
161
A21
620
890
672
Roots
1310
3AAO
1185
1220
A80
750
1300
39AS
6585
2305
2080
1340
(A8
Series C
ppb HF. A
Fluoride
in leave*11
(pp.)
1 day
AO
A3
35
A7
AS
55
AO
45
43
AO
23
AO
7 day*
51
AO
32
30
SO
30
AO
30
AO
40
28
35
.5 hr)
(A70
""root0 Flw
7-day (l
average .
18
13
23
IS
14
22
18
14
30
11
10
1A
375
655
500
SAO
460
435
550
A05
385
375
A 70
57 S
Series D
ppb HF, 3.
5 hr)
>rtde """"I
>>»>" l;4S
7 days
i,
415"
360'.
465^
360
355^
405;
255
K
4201
365
A 20',
280''
average
(PP»)
19
13
22
16
15
32
25
27
13
32
17
16
?No leaf Injury In Series C.
^Slight leaf Injury.
^Moderate leaf Injury.
Severe leaf Injury.
Source: Adapted from Brannan, Leone, and Dalnei, 1950, Tables III, IV, and V, pp. 739-7A2. Reprinted bv permission of the publisher.
-------
112
Bovay (1969) observed that certain fertilizers containing boron
produced symptoms of fluoride damage in crops. Field and pot studies
demonstrated that apricot trees, grapevines, and forage plants took up
more fluoride from boron-enriched fertilizers than from fertilizers with-
out boron, even though the fluoride content in the two types of fertiliz-
ers was similar. About 57% of the fluoride in the boron fertilizer was
fluoroborate. Apparently boron can increase plant uptake of fluoride.
4.2.1.2 Exposure of Plants to Fluoride in Air It has long been recog-
nized that exposure of plants to gaseous and particulate fluorides in the
atmosphere results in fluoride accumulation and eventual injury (National
Academy of Sciences, 1971; Thomas and Alther, 1966; Treshow, 1971).
The data of Hill (1969) illustrate the rate and extent of uptake of
hydrogen fluoride by gladiolus leaves (Table 4.2). This general trend
is observed by most researchers. Additional data on the relationships
among length of exposure, air concentration, and tissue concentration of
fluoride are presented in Section 4.2.4.
TABLE 4.2. CHANGES IN FLUORIDE CONCENTRATIONS IN
DIFFERENT SECTIONS OF SNOW PRINCESS GLADIOLUS LEAVES
FOLLOWING FUMIGATION WITH HYDROGEN FLUORIDE
Fluoride
treatment
890 ug/m*
for 1 hr
40 ug/m*
for 24 hr
Time after
beginning
treatment
2 hr
5 hr
45 hr
1 day
2 days
10 days
Tip
4 in.
71
94
159
132
188
224
Fluoride
(ppm dry
Next
4 in
87
115
104
97
83
71
content
weight)
Remainder
of leaf
92
68
45
34
26
27
Source: Adapted from Hill, 1969, Table 1, p. 332.
Reprinted by permission of the publisher.
A significant portion of the fluoride associated with plants is not
absorbed but is merely bound to the leaf or stem surface. The amount
bound is highly variable and can be as high as 75% (Thomas and Alther,
1966). Exposure of plants to airborne cryolite increases the tissue flu-
oride concentration; however, a considerable portion of this can be removed
by washing the tissue (up to 70% in tomato and gladiolus) (Ledbetter,
Mavrodineanu, and Weiss, 1960; McCune et al., 1965). As usual, tissue
content depends on the fluoride concentration and exposure time, but few
fluoride symptoms occur with cryolite, even at relatively high tissue
fluoride concentrations.
As might be expected, soybean plants accumulate considerably less
fluoride when exposed to nighttime fumigation with hydrogen fluoride as
compared with daytime fumigations, presumably because of stomatal closure
(Poovaiah and Wiebe, 1973). Plants exposed to nighttime fumigations were
-------
113
only slightly injured. On the other hand, Adams, Hendrix, and Applegate
(1957) found that with the same extent of injury the foliar fluoride con-
centration was less in nighttime-fumigated plants than in daytime-fumigated
plants. However, with nighttime fumigations, longer exposures at equiva-
lent fumigant concentrations were required to produce injury.
4.2.2 Translocation
The amount of fluoride translocation occurring in plants depends on
the site of absorption. For example, root absorption of fluoride by mature
navel orange trees led to large increases in the fluoride content of roots
and a small but significant increase in leaf fluoride content (Brewer et
al., 1959) (Table 4.3). Growth was depressed when trees were grown in
solutions containing 25 ppm fluoride. The large amount of fluoride found
in small roots was perhaps due to the formation of insoluble calcium fluo-
ride in the soil and its adherence to the root surface.
Peach seedlings exposed to 10 and 25 ppm fluoride in nutrient solu-
tion accumulated fluoride in leaf tissue to 220 and 261 ppm, respectively,
whereas control leaf tissue contained only 6 ppm fluoride (Leone et al.,
1948). Exposure of Rutgers tomatoes to nutrient solutions containing 10
and 25 ppm fluoride resulted in the accumulation of 82 and 277 ppm fluo-
ride, respectively, in leaf tissue. Thus fluoride supplied to the root
can be translocated (presumably by the transpiration stream) to aerial
portions of the plant.
However, exposure of the aerial portion of the plant to fluoride does
not lead to increases in the fluoride content of roots. Fumigation of
tomato plants with 0.048 and 0.47 ppm fluoride (4.5- and 3.5-hr exposures
respectively), which elevated fluoride levels in leaves, did not increase
the root fluoride content above control values (Brennan, Leone, and Daines,
1950). Thus no significant fluoride translocation from shoots to roots
occurred. Continuous fumigation with about 1 pg/m3 of fluoride did not
produce injury symptoms in alfalfa, orchard grass, chard, and romain let-
tuce, and most of the fluoride was found in the leaves, again indicating
little translocation to roots (Benedict, Ross, and Wade, 1964).
Leaf margins and tips often have higher fluoride concentrations than
the rest of the leaf blade (Benedict, Ross, and Wade, 1964; Garrec, Plebin,
and Lhoste, 1975; Hitchcock, Zimmerman, and Coe, 1962). Movement within
the leaf probably occurs through the transpiration stream (Zimmerman and
Hitchcock, 1956). Fluoride is taken up and distributed mainly to the tip
when cut leaves are placed in aqueous fluoride solutions (Davison, Marsland,
and Betts, 1974). When the plant is exposed to particulate fluorides, lit-
tle translocation is observed.- McCune et al. (1965) found that gladiolus
leaves exposed to cryolite contained the same tissue concentration in all
portions of the leaf; exposure to gaseous hydrogen fluoride resulted in
accumulation of considerably more fluoride in the tip region. New leaves
of potted elm and black locust that had been exposed to atmospheric flu-
orides during the winter contained higher fluoride levels than control
leaves, suggesting mobilization and translocation of fluoride from bark
and buds to the new leaves (Keller, 1974).
-------
114
TABLE 4. 1. FLUORIDE CONTENT AND FRESH WEIGHTS OF MATURE NAVEL ORANGE TREES
GROWN FOR 18 MONTHS IN SOLUTION CULTURES WITH AND WITHOUT FLUORIDE
PRESENT IN THE NUTRIENT SOLUTIONS
Tissue analyzed
Fluoride content
(pp«n)a
25 ppm
fluoride
added"
No
fluoride
added0
Fresh weight (kg)
25 ppm
fluoride
added
No
fluoride
added
Spring flush leaves, 1-year-old
Branches, whole cross sections
Large (over 1 in.)
Intermediate (*j-l in.)
Twigs
Trunk
Old xylem
New xylem
Phloem and bark
Whole cross section
Roots
Large roots, whole
Center wood, old xylem
Intermediate wood, new xylem
Epidermis
Small roots
Fruit
Rind
Pulp, Juice
34
5.5
6.0
10.0
3.0
3.5
8.3
7.0
67
9
13
641
20,000
1.70
6.14*
5.5
2.0
2.5
5.0
1.0
2.0
4.0
3.0
6
13
4
3
46
0.271;
0.09
3.49
3.58
2.98
8.13
6.18
4.49
5.06
6.31
^On an 80°C dry weight.
Average of two trees.
.Average of four trees.
^Fresh weight.
Source: Adapted from Brewer et al., 1959, Table 2, p. 185, and Table 4,
187. Reprinted by permission of the publisher.
4.2.3 Cellular Metabolism of Fluoride
Fluoride ions are very reactive and can be expected to combine with
various molecular species within cells. Fluoride Is an Inhibitor of var-
ious metalloenzymes (Hewitt and Nicholas, 1963); the mechanisms of Inhibi-
tion are discussed more fully in Section 4.3.1.6.
The observation In the 1940s that fluoroacetate Is the toxic Ingre-
dient In the South African plant Didhapetalum aymoew demonstrated that
certain plants have the ability to synthesize covalently bonded carbon-
fluorine compounds (Peters, 1972a). Approximately 36 species and varie-
ties, found mainly in Africa, Australia, and Brazil, are now known to
-------
115
synthesize fluoroacetate. Oxylobiwn pawiflorwn and Gaetvoldbiwn bilobum
have been reported to have fluoroacetate concentrations as high as 12,500
ppm. Monofluoroacetate has been shown to be the toxic principle In GaBtvo-
lobiw gpandiflovum (McEwan, 1964), Aaaoia georginae (Oelrichs and McEwan,
1961), and Palioourea rrwogvavii (de Ollveira, 1963), three plants
extremely poisonous to livestock.
Analysis of many other species, however, has failed to detect fluo-
roacetate or other organofluorldes. The presence of specific organoflu-
orides In plant tissues can be established by the use of extraction and
analytical techniques that can cope with interfering substances. Vickery,
Vickery, and Ashu (1973) discussed the interference of iron and pigments
with the detection of monofluoroacetate in Diahapetalum heudelotti, a spe-
cies in which organofluorldes had not previously been detected. Peters
and Shorthouse (1964) expressed the opinion that synthesis of the carbon-
fluorine bond is not a general property of all plants. Kakabadse et al.
(1971) supported this statement with the observation that Darjeeling tea,
which has a high fluorine content, contains only inorganic fluoride.
Peters (19722?), however, later acknowledged that many plants possess trace
amounts of fluoroacetate and fluorocltrate and commented that they had
detected fluorocltrate in commercial tea (about 30 yg per gram tea) by
gas chromatography. Cheng et al. (1968) observed that soybeans grown in
nutrient solution with sodium fluoride or with hydrogen fluoride fumiga-
tion also synthesized fluoroacetate and fluorocitrate. These compounds
were identified by paper chromatography. Lovelace, Miller, and Welkle
(1968) found both fluoroacetate (179 ug per gram leaf dry weight) and
fluorocltrate (896 ug per gram leaf dry weight) in forage crops (pasture
mix of Medioago eativa and Agvapyvon orietatum) grown near a phosphate
plant. Control area crops contained no detectable fluoroacetate or flu-
orocltrate. In the above studies, additional support for the occurrence
of fluorocltrate was established by experiments demonstrating the .inhibi-
tion of purified aconltase. Later work by Yu and Miller (1970) produced
gas chromatographic evidence for fluoroacetate and fluorocltrate in A.
ovietatum, although these compounds were not detected in all samples.
Miller (1972) could not detect any fluoroorganic acids in grass samples
from several locations. Ward and Huskisson (1969) reported that lettuce
could convert fluoroacetate to fluorocltrate, but later work (Ward, 1972)
showed the amount converted to be quite small (about 2%). There are not
enough data to conclude that all plants have the ability to synthesize
fluoroorganic acids, but the results with soybean and forage plants
suggest this possibility.
Organofluorides have been extensively studied in species of Diahape-
talum and A. georginae. No organic or inorganic fluorides were detected
in D, aymoewn seeds, but the leaves contained fluoroacetic acid. However,
Diohapetalum toxiaavium seeds, which are toxic, contained iD-fluoroolelc
acid and another long chain fatty acid, but the leaves contained no fluo-
rides (Peters and Hall, 1960). Ward et al. (1964) later found a number
of fatty acids (e.g., u-fluoropalmitic acid) in D. toaeioarium seeds and
suggested that longer chain u-fluoro acids were produced by additions of
malonyl coenzyme A to shorter chain u-fluoro acids. Vickery and Vickery
-------
116
(1972), however, reported that D. toxiaarium plants contain both fluoro-
acetate (450 ppm in young leaves, 60 ppm in mature leaves, and 1100 ppm
in leaves adnate to flowers) and inorganic fluoride (65 ppm in young
leaves, 14 ppm in mature leaves, and 85 ppm in leaves adnate to flowers).
Tap and lateral roots contained 23 and <1 ppm fluoroacetate and 30 and
38 ppm inorganic fluoride respectively. The high fluoride content prob-
ably was not related to fluoride pollution because fluoride concentrations
in the soil and water were low, and other plants in the vicinity did not
contain more than 2 ppm fluoride.
Hall (1974) exposed cultured A. geovginae (in either quartz or soil)
to solutions of sodium monofluoroacetate or ammonium fluoride. In all
cases, most of the fluoride found in the roots and leaves was inorganic
(Table 4.4). No biosynthesis of fluoroacetate was detected in the plants.
Indeed, the plants apparently metabolized the added monofluoroacetate to
inorganic fluoride, although the existence of microbial degradation prior
to uptake was not experimentally tested. Thus while the toxic principle
of A. georginae is fluoroacetate (Oelrichs and McEwan, 1961), in vivo for-
mation of fluoroacetate is not easily induced in cultured plants. Preuss,
Birkhahn, and Bergmann (1970), however, did detect fluoroacetate in tissue
cultures from A. georginae stem sections.
Metabolism of 1*C-labeled fluoroacetate in A. georginae, peanut, cas-
tor bean, and pinto bean produced labeled carbon dioxide (indicating cleav-
age of the carbon-fluorine bond) and radioactivity in neutral lipids and
water-soluble fractions (Preuss, Lemmens, and Weinstein, 1968). Preuss and
Weinstein (1969) later showed that germinating peanut seeds could cleave
the carbon-fluorine bond in fluoroacetate. No fluorine was detected in
fatty acids, and only inorganic fluoride was detected in the seedlings.
No information was found concerning enzyme systems in plants which cleave
the carbon-fluorine bond.
Hall (1972) and Hall and Cain (1972) collected and studied a variety
of toxic plants and the soils in which they grew. Organofluorides were
detected in soils, perhaps mainly as fluoroacetate, but no relation to
organic fluoride content in the plant could be demonstrated. Hall (1972)
reported data on total and organic fluoride content in portions of toxic
plants (Table 4.4) and concluded that there were wide variations in leaf
fluoride content in all species, that high total fluoride content does
not necessarily mean a high organic fluoride content, and that differences
in distribution within the plant existed in members of the same species
growing in Africa and Australia.
In plants that contain fluoroacetate as the toxic ingredient, lit-
tle is known about the specific environmental or physiological conditions
that determine the amounts or distribution of organofluorides formed.
Similarly, there is little information on why fluoroacetate is not toxic
to those plants possessing measurable amounts of it. Fluoroacetate and
fluoroacetamide have also been used as systemic insecticides for plants.
Injury to plants occurred at doses 50 to 100 times that required to kill
Aphis fdbae (David and Gardiner, as cited in Treble, Lamport, and Peters,
-------
117
TABLE 4.4. DISTRIBUTION OF FLUORINE IN TROPICAL PLANTS
Fluorine (ppm in
Species
Aoaoia georginae
(toxic)
A. georginae (experi-
mentally cultivated)
Diohapetalum aymoeum
D, gieinaenae
D. moeaambicerwe
D. etuhlmannii
D. toxiaanum
GaBtrolobium bilobum
G. aalliataahye
G. aalycinum
G, grondiflontn
G. miarooarpion
G. apinoeum
G. villoeun
Tissue
Seed
Leaf
Root
Leaf
Root
Leaf
Stem
Small root
Large root
Seed
Leaf
Stem
Root
Leaf
Stem
Seed (1)
Seed (2)
Seed shell
(endocarp)
Leaf
Thin stem
Thick stem
Root (without
bark)
Root bark
Seed
Leaf
Stem
Root
Seed shell
(endocarp)
Seed
Seed pod
Leaf
Stem
Root
Seed
Leaf
Stem
Root
Seed
Leaf
Stem
Root
Seed
Leaf
Stem
Leaf
Root
Seed
Leaf
Total
4
42
11
33
36
111
341
162
196
19
9
13
38
11
72
870
1470
223
142
321
265
1916
385
1980
145
75
127
19
1292
163
175
34
15
473
35
27
12
760
8
77
19
488
11
15
27
35
65
26
Acid-
labile
4
19
5
15
29
6
23
48
139
12
7
4
16
6
70
622
1360
218
55
164
73
1440
337
192
55
59
33
9
38
10
9
10
2
21
4
1
2
35
4
6
4
10
6
4
8
35
1
8
air-dried
tissue)
Organic
soluble
Total
<1
14
6
<1
<1
99
242
92
17
10
2
2
2
4
2
292
93
8
50
126
144
22
19
1800
32
16
66
8
1230
128
160
7
9
443
30
18
9
669
4
51
16
256
2
4
3
7
18
Acid-
labile
<1
2
1
<1
<1
2
2
4
2
3
2
1
2
2
1
42
13
3
3
3
1
4
16
169
3
1
12
1
42
4
4
<1
3
6
2
1
1
7
1
3
3
2
1
1
<1
3
1
-------
118
TABLE 4.4 (continued)
Fluorine (ppm in air-dried tissue)
Organic^
Species
Oxylobium parviflorum
Palicourea maragnwii
Tissue
Seed
Calyx (flower
head)
Corolla
(petals)
Mature leaf
Young leaves
and steins
Thin stem
Small root
Seed
Fruit stalk
Leaf
Stem
Root
Total
1400
877
206
116
465
67
10
1228
1216
455
118
41
Acid-
labile
44
34
6
9
23
2
2
30
52
146
11
10
soluble"
Total
1090
744
119
110
440
59
7
1136
1010
278
117
31
Acid-
labile
3
6
1
3
20
1
3
15
6
8
1
4
'^Defined as extractable in alkaline 902 propanol.
Source: Adapted from Hall, 1972, Table 5, p. 861.
permission of the publisher.
Reprinted by
1962). Trebel, Lamport, and Peters (1962) found that fluoroacetate in-
hibited the aconitate hydratase (aconitase) of Acer pseudoplatanus tissue
culture cells to a much lesser extent than pig heart aconitate hydratase.
Inhibition by fluoroacetate was largely reversible by the addition of
isocitrate. Louw, de Villiers, and Grobbelaar (1970) also observed that
the aconitase of D. oymosum and of Pcari-nariton capense was less sensitive
than pig heart aconitase to fluoroacetate. Since 50 mW fluoroacetate did
not cause citrate to accumulate in leaf discs of D. cymosum but did cause
accumulation in the disc of P. oapense, they suggested that D. cymosum
did not convert fluoroacetate to fluorocitrate while P. oapenee did.
4.2.4 Distribution
4.2.4.1 Concentration in Tissues For plants growing in unpolluted areas,
the concentration of fluoride in tissues is usually between 2 and 20 ppm
(National Academy of Sciences, 1971). The exact concentration depends on
many factors such as species, organ examined, age, and physiological con-
dition. Table 4.5 is a compilation of fluoride concentrations found in
selected crop plants and a few noncrop plants grown in unpolluted areas
or used as controls in fumigation experiments. The concentration of
fluoride in most of these plants is between 0.4 and 30 ppm.
There are few data on the fluoride content of noncrop plants growing
in unpolluted areas. Most plants do not accumulate fluoride from soil;
however, some members of the Theaceae family are accumulator species.
Thus leaves of camellia and tea contain extremely high concentrations of
fluoride (Brewer, 1966; Thomas and Alther, 1966).
-------
119
TABLE 4.5. FLUORIDE CONCENTRATIONS IN SELECTED PLANTS*
Plant
Alfalfa
Orchard grass
Red clover, timothy
Clover
Grass, hay
Lucerne
Beet
Corn
Rutabaga
Wheat
Rye
Barley
Oats
Corn
Rice
Potato
Sugar beet
Endive
Lettuce
Spinach
Cabbage
Cauliflower
Cress
Parsley
Celery
Part
Tops
Tops
Roots
Leaves
Cobs
Stalk and
leaves
Grain
Straw
Grain
Straw
Grain
Straw
Grain
Straw
Grain
Grain
Tuber
Leaves
Peel
Root
Leaves
Leaves
Leaves
Outer leaves
Edible part
Flowers
Leaves
Leaves
Leaflets
Stalks
Heart
Fluoride
concentration
(pp. dry CoamentB
weight)
Forage and feed plants
0.8-36.5 (3.6 Area free of Indus-
mean) trial pollution
7-15 Controls
10 Controls
10 Controls
10 Mixed planting
6-13 Controls
1-6
2-4
2.9
7
1.6
2.2-6.3
4-7
Grains
1
2.3-6.4
1.5
1.2
1.7
9.0
0.5
6.8
0.15-0.38
0.76
Root crops
1.5-3.0
9-30
5.0-22.5
3.3-6.0
12
Vegetables
51 Controls
23 Controls
4.4-11.3
35 Controls
1.3-28.3
9.5
1.5
0'.9
0.8
4.4
9.0
5.7
10
2
4
Reference
Suttie, cited In
Israel, 19742?
Zimmerman and
Hitchcock, 1956
Benedict, Ross,
and Wade, 1964
Benedict, Ross,
and Wade, 1964
MacLean and
Schneider, 1973
Gislger, cited in
Groth, 1975
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Benedict , Ross ,
and Wade, 1964
Benedict, Ross,
and Wade, 1964
Garber, 1967
Benedict , Ross ,
and Wade, 1964
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Zimmerman and
Hitchcock, 1956
Zimmerman and
Hitchcock, 1956
Garber, 1967
-------
120
TABLE 4.5 (continued)
Plant
Carrots
Radishes
Onions
Beans
Tomato
Red beets
Part
Roots
Tops
Roots
Tops
Tendergreen
leaves
Pinto leaves
Leaves
Leaves
Stem
Fruit
Fluoride
concentration .
(ppm dry Comments
weight)
0.4-8.4
40
1
2
3.0
3.2
13.2 Controls
13.1 Controls
8.0 Controls
8-13
2
2
2.8
Reference
Carter, 1967
Garber, 1967
Garter, 1967
Garber, 1967
Garber, 1967
Garber, 1967
McCune, Weinsteln,
and Mancinl,
1970
McCune, Welnstein,
and Mancinl,
1970
McCune, Weinsteln,
and Mancinl,
1970
Zimmerman and
Hitchcock, 1956
Zimmerman and
Hitchcock, 1956
Zimmerman and
Hitchcock, 1956
Garter, 1967
Noncrop plants
Peach
Aeaoulus hippoaaetanea
SambuouB nigra
Acer sp.
Trig germmiaa
Taxue baoaata
Pinue eilvestria
Water hyacinth
Leaves
Leaves
Leaves
Leaf
Petiole
28
3.4
2.5
2.0
2.1
0.4
0.7
25
60
Unpolluted area
Growing naturally
in water contain-
ing 1 ppm fluoride
Drovley, Rayner,
and Jephcott,
1963
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Garber, 1967
Ras et al. , cited
In Groth, 1975
^Plants either growing wild not near obvious fluoride pollution sources or plants used as
controls in fumigation experiments.
Table 4.4 lists the fluoride content of some toxic tropical plants.
The indicated fluoride concentrations are relatively high. Since these
plants were grown in soils low in fluoride, accumulation in these species
is significant. No comments were made on the possibilities of fluoride
air pollution in the areas of collection.
The National Academy of Sciences (1971) listed several conclusions
about the relationship between environmental fluoride concentrations and
plant fluoride concentrations: (1) Soil is the main source of fluoride
in vegetation which is not exposed to air pollution. (2) There is not
necessarily a direct relationship between soil fluoride concentration and
plant fluoride concentration, but plants in acid soils generally have
higher fluoride concentrations than plants in alkaline soils. (3) Indus-
trial air pollution exposes plants to both particulate and gaseous fluo-
rides which are taken up (or surface bound) by aerial portions of the
-------
121
plant. The amount of fluoride deposited on soil does not increase the
soil content enough to significantly increase root absorption of fluoride
(and thus concentration in the plant) .
If it is assumed that plants are passive accumulators of fluoride,
a useful relationship may be expressed by the equation AF = KCT , where
AF is the change in tissue fluoride content due to atmospheric fluoride
exposure, K is the apparent accumulation coefficient, C is the concentra-
tion of fluoride in air, and T is the time of exposure (National Academy
of Sciences, 1971). Complicating circumstances arise, however, in apply-
ing this equation. K is not constant and is usually reported only for
gaseous hydrogen fluoride exposures. Moreover, particulate fluorides
are common in the atmosphere and could affect the determination of K in
field studies. In fact, there is a lack of field data relating plant
fluoride levels to atmospheric fluoride levels (Israel, 1974a; National
Academy of Sciences, 1971). Such information is needed, however, to
assess fluoride movement via feeds to animals. With the use of limed
filter papers to measure airborne fluorides, Israel (1974a) found an
average K value of 3.8 for field crops of alfalfa and orchard grass.
This is about two times the value found by other researchers for gaseous
hydrogen fluoride exposures. Israel's overall conclusion was that "fac-
tors governing the accumulation of gaseous and particulate fluorides are
not well enough understood at this time to allow a rational interpreta-
tion of the field results."
Only limited data exist on deposition velocities (vg) for gaseous
fluorides. Israel (1974a) reported values of 16 and 31 ppm/sec for gas-
eous fumigation experiments with alfalfa and field exposures with alfalfa
and orchard grass. The corresponding velocities related to the leaf
surface area (v^ were 3.2 and 6.2 ppm/sec.
In general, plants exposed to high levels of atmospheric fluorides
have elevated fluoride levels. Table 4.6 gives the range of fluoride con-
centrations found in organs of different species exposed to varying concen-
trations of fluorides and the range of concentrations in those tissues
which show toxicity symptoms. Fluoride accumulates primarily in leaves
of fumigated plants, while fruits and seeds generally accumulate little
fluoride (Pack and Sulzbach, 1976). Oat seeds may be an exception. There
are many other examples of increased fluoride contents in plants sprayed
or fumigated with fluorides. Additional data presented in greater detail
are given in Figures 4.2 and 4.3 and Table 4.7.
The experiments cited used relatively high fluoride concentrations,
but the data of Pack (1971i) showed that even with lower fumigation con-
centrations, bean leaves accumulated fluoride in amounts roughly propor-
tional to the concentration of fumigating gas. For instance, tendergreen
beans accumulated 260, 700, and 1200 ppm fluoride when exposed to fumiga-
tion concentrations of 2.2, 6.6, and 13.9 yg of fluoride per cubic meter
respectively. Stem, petioles, and fruit also showed proportional increases
with increased fumigant concentration; the absolute amounts were consider-
ably smaller, however. In controlled exposures, the fluorine content of
grass was found to be proportional to the fluoride concentration in air
-------
TABLE 4.6. FLUORIDE VALUES IN TISSUES OF VARIOUS PLANTS
Plant
Alfalfa (Medicago eativa)
Apple (Mains spp.)
Apricot (Primus armeniaaa)
Avocado (Peraea amerieana)
Bean (Phaseolue spp.)
Blueberry (Vacainium spp.)
Type of culture
Exposed to 1.5 ppb F°
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Field
Field
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Before and after
exposure to HF gas
Orchard, near Al
reduction plant
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Field
Field
Field near steel
plant
Field near steel
plant
Exposed to 5.0 ppb F
aa HF, 5 to 17
weeks
Grown In soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Tissue
sampled
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fruit
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppm)a
Sample description Internedlate
range* Hlgh range
Not specified 25.00-149.00
Not specified 132.00-203.00
Not specified 182.00
From industrial and 3.00-9.00 13.00-52.00
nonlndus trial
areas (washed)
From industrial and 5.00-15.00 19.00-65.00
nonlndustrlal
areas (unwashed)
Not specified 35.00-18.00
Not specified 37.00
Not specified
Not specified 24.00 56.00
Not specified
Not specified
Not specified
Not specified
From industrial and 1.00-6.00 15.00-30.00
nonindustrial
areas (washed)
From industrial and 0.04-0.25
nonindustrial
areas (washed)
Mature (washed)
Mature (unwashed)
Washed 5.00-17.00
Not specified 19.00
Not specified
Not specified
Not specified
Showing toxlclty
symptoms
72.00-234.00
79.00-259.00
142.00-194.00
247.00-403.00
58.00-130.00
83.00-84.00
107.00
32.00-640.00
1.35
168.00
336.00
195.00-1027.00
<310.00
34.00-53.00
72.00-103.00
64.00
-------
TABLE 4.6 (continued)
Plant
Buckwheat (Fagopyrum spp.)
Carrot (Dauaus aarota
eativa)
Cherry (Primus oeraeue)
Grapefruit (Citrue
paradiei)
Lemon (Citrus limon)
Mandarin (Citrue
retioulatd)
Orange (Citrue eineneie)
Type of culture
Soil with and without
F added (limed)
Soil with and without
F added (unllmed)
Grown In soil to
which NaF was added
Grown In acid soil;
exposed to HF gas
Grown In limed soil
to which HF was
added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Before and after
exposure to HF gas
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 2.0 to 5.0
ppb F as HF for 6
months
Exposed to 2.0 to 5.0
ppb F as HF for 6
months
Exposed to 2.0 to 5.0
ppb F as HF for 6
months
Exposed to 2.0 to 5.0
ppb F as HF for 6
months
Field
Cultures with about
Tissue
sampled
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppm)a
Sample description
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Washed
Washed
Washed
Washed
From industrial and
nonindustrial
areas (washed)
Washed
Intermediate ... .
range* Hlgh range
10.00 87.00-900.00
59.00
16.00-62.00 101.00
37.00-98.00
10.00 900.00
20.00
2.00-8.00 24.00-48.00
5.00-9.00 16.00-24.00
3.00-6.00 40.00-59.00
8.00-11.00 20.00-116.00
1.00-6.00 7.00-211.00
2.00-5.50 34.00-60.00
Showing toxiclty
symptoms
2450.00-9900.00
533.00-1910.00
594.00-1388.00
250.00-323.00
309.00-723.00
307.00
112.00
51.00-62.00
51.00-53.00
126.00
163.00-365.00
72.00-146.00
85.00-345.00
158.00-334.00
to
to
1.0 and 25.0 ppm F
-------
TABLE 4.6 (continued)
Plant
Corn (Zea may a)
Sweet corn
Cotton (Goaaypivm spp.)
Douglas fir (Pseudotauga
taxifoUa)
Elm, English (tfZmua
prooara)
Fig (Fiaue spp.)
Type of culture
Cultures with about
1.0 and 25.0 ppm F
Cultures with about
1.0 and 25.0 ppm F
Before and after
exposure to HF gas
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 0.0 and
2.0 to 3.0 ppb F as
HF in atmosphere
Exposed to 0.0 and
2.0 to 3.0 ppb F as
HF in atmosphere
Exposed to 0.0 and
2.0 to 3.0 ppb F as
HF in atmosphere
Exposed to 0.0 and
2.0 to 3.0 ppb F as
HF in atmosphere
Exposed to 0.0 and
2.0 to 3.0 ppb F as
HF in atmosphere
Grown in neutral
soil; exposed to
HF gas
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Orchard near Al
reduction plant
Tissue
sampled
Hood
Feeder roots
Leaves
Leaves
Leaves
Leaves
Leaves
Husks
Kernels
Cobs
Stalks
Leaves
Needles
Needles
Needles
Leaves
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppm)a
Sample description
Hashed
Hashed
Not specified
Not specified
Not specified
Not specified
Nature (washed)
Hashed
Unwashed
Unwashed
Hashed
Unwashed
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Intermediate
range0 6 6
1.00-5.00 3.00-10.00
3.00-46.00 9.00-20,000.00
8.00
151.00
99.00-133.00
85.00
5.00-14.00 29.00-67.00
9.00 12.00
2.00 10.00
3.00 3.00
6.00 15.00
5000.00
102.00-238.00
103.00-200.00
212.00
Showing toxicity
symptoms
302.00
178.00
147.00
48.00-491.00
18.00-265.00
72.00
160.00
247.00-403.00
ro
-------
TABLE 4.6 (continued)
Plant
Fir (Abiea grmckia)
Gladiolus (Gladiolus spp.)
'
Grape (Vitie spp.)
Wine grapea
Hemlock (Teuga aanadeneie)
Kale or collard (Braaeiaa
oleraaea aoephala)
Larch (Larix spp.)
Type of culture
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Near fluoride-
emitting factory
Near fluoride-
emitting factory
Exposed to HF gas
Grown in soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 0.0 and
5.0 ppb F as HF for
several months
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Field
Field near steel
plant
Field near steel
plant
Exposed to 5.0 ppb F
Soil (limed) with and
without F added
Soil (unllmed) with
and without F added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Tissue
sampled
Needles
Needles
Needles
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Whole leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Needles
Leaves
Leaves
Needles
Needles
Needles
Fluoride concentration in dry matter (ppm)a
Sample description _
intermediate
Not specified
Not specified
Not specified
Mature (washed)
Mature (unwashed)
Not specified 7.00-10.00
Not specified 7.00-10.00
Not specified
Not specified
Not specified
Washed 2.00-28.00
Not specified
Not specified
Not specified
From industrial and 2.00-8.00
nonlndustrial
areas (washed)
Unwashed
Washed
Not specified
Not specified 3.00-3.20
Not specified 3.70-37.00
Not specified
Not specified
Not specified
_. . Showing toxicity
nigh range
symptoms
43.00-71.00
41.00-155.00
140.00
149.00-275.00
279.00-284.00
30.00-50.00
20.00-141.00
37.00-59.00
44.00-46.00
57.00
129.00-733.00
51.00-117.00
84.00-138.00
122.00
12.00-27.00 22.00-462.00
336.00
168.00
133.00
18.00-45.00
20.60-96.00 96.00-262.00
53.00-62.00
73.00-147.00
106.00
K
Ul
-------
TABLE 4.6 (continued)
Plant
Lilac (Syringa vulgarie)
Locust, black (ftcbinia
paeudoaaaoia)
Haple (Acer spp.)
Marigold (Tagatea spp.)
Mountain laurel (Kalmia
latifolid)
Mulberry (Home spp.)
Nasturtium (Tropaeolum
spp.)
Parsnip (Paatinaaa gatira)
Peach (Prumca persied)
Type of culture
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Grown in soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Grown in soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Before and after
exposure to RF gas
Exposed to HF gas
Grown in soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Near Al reduction
plant
Near Al reduction
Tissue
sampled
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fruit peel
Fluoride concentration In dry matter (ppm)a
Sample description
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
intermediate Hlgh ^
123.00
113.00
153.00
80.00
80.00
209.00
129.00
200.00-600.00
34.00-35.00
21.00-42.00
58.00
129.00
128.00-144.00
42.00-60.00
177.00-218.00
146.00-470.00
208.00
6.00-16.00 30.00
6.00-15.00
6.00
2.00-8.00
2.00-5.00
Showing toxicity
symptoms
123.00
216.00
122.00-273.00
213.00
172.00
77.00-390.00
30.00-50.00
220.00-1442.00
54.00-92.00
89.00-101.00
94.00
44.00-112.00
(fruit was
damaged but
leaves were
not)
19.00-34.00
I-1
N>
plant
-------
TABLE 4.6 (continued)
Plant
Pepper (Capsicum spp.)
Petunia (Petunia spp.)
Pine (Pinua ponderoea and
other species)
Pine, eastern white (Pinua
etfobus)
Potato (Solomon tvberoaum)
Prune (Pmana domeetiaa)
Type of culture
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Grown in soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Field
Field
Field
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Near Al reduction
plant
Near Al reduction
plant
Near Al reduction
plant
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 0.0 and
and 3.0 ppb as HF
Exposed to 0.0 and
and 3.0 ppb as HF
Near fluoride-
emitting factory
Near Al plants and
90 miles away
Near Al plants and
90 miles away
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Tissue
sampled
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Needles
Leaves
Tubers
Leaves
Leaves
Twigs
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppm)a
Sample description
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Young
1 year old
2 years old
Not specified
Not specified
Not specified
Partially expanded
Newly expanded
Expanded 3 months
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Washed
Washed
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
intermediate Hlgh range
154.00
200.00-600.00
66.00-84.00
273.00-362.00
148.00
2.00-3.00
2.00-3.00
3.00-4.00
26.00
32.00
106.00
19.00-46.00
70.00-136.00
138.00
67.00
19.00-27.00 163.00-267.00
4.00-17.00 10.00-34.00
9.00-20.00 43.00
6.00-15.00 25.00
0.70-1.00
Showing toxiclty
symptoms
136.00-449.00
203.00
244.0
129.00
229.00-330.00
462.00
39.00
55.00-73.00
70.00
15.00-20.00
30.00-35.00
80.00
83.00
54.00-72.00
80.00
73.00
41.00
121.00-496.00
30.00-1400.00
2.20-17.00
42.00-64.00
60.00-90.00
107.00
to
-------
TABLE 4.6 (continued)
Plant
Raspberry (Rubua spp.)
Rhododendron (Rhododendron
spp.)
Rose (Rosa spp.)
Spanish moss (Tillandela
luneoidge)
Spinach (Spinaoia aleraoea)
Spruce, Engelnann (Pieoa
6ngBUficovti)
Squash (Cuaufbita spp.)
Sweet pea (LattyruB
odoKttua)
Sweet potato (Tpomoea
batatas)
Type of culture
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1 , 5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 0.0 and
3.0 ppb F for 6
months
Exposed to 0.0 and
3.0 ppb F for 6
months
Exposed to 0.0 and
3.0 ppb F for 6
months
Exposed In areas
where air was
contaminated with F
Grown In soil to
which MaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 0.0 and
3.0 ppb F as HF in
atmosphere
Tissue
sampled
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Branches
Flowers
Whole plant
Leaves
Needles
Needles
Needles
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppm)a
Sample description
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Mature (washed)
Mixed, young and
old (washed)
Mature (rinsed)
Unwashed
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
Washed
intermediate Hlgh rjmge
104.00-176.00
44.00-55.00
30.00
80.00-120.00
64.00-244.00
175.00
4.00-8.00
3.00-5.00 24.00
4.00 13.00
22.00-27.00 32.00-2418.00
49.00 200.00-600.00
80.00
31.00
149.00
114.00
85.00
99.00
118.00-144.00
8.00-25.00
Showing toxicity
symptoms
88.00-243.00
216.00
162.00
85.00
118.00-323.00
803.00-857.00
57.00
210.00-245.00
134.00
179.00
327.00
148.00
141.00
00
-------
TABLE 4.6 (continued)
Plant
Tomato (Lyaopevaiaon
eeaul«ntvm)
Willow (Salix spp.)
Type of culture
Exposed to 0.0 and
3.0 ppb F as HF In
atmosphere
Before and after
exposure to HF gas
Before and after
exposure to HF gas
Grown In soil to
which NaF was added
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Exposed to 10.0 ppb F
as HF In greenhouse
Exposed to 10.0 ppb F
as HF In greenhouse
Exposed to 1.5 ppb F
Exposed to 5.0 ppb F
Exposed to 10.0 ppb F
Tissue
sampled
Tubers
Leaves
Fruit
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Leaves
Fluoride concentration in dry matter (ppa)a
Sample description
Washed
Not specified
Not specified
Not specified
Not specified
Not specified
Not specified
New (washed)
Old (washed)
Not specified
Not specified
Not specified
Intermediate
range6
3.10
28.00-54.00
6.00
10.00-14.00
3.00-25.00
5.00-36.00
High range Showln* «=°^clty
** symptoms
91.00-146.00 220.00-319.00
289.00-780.00
26.00-82.00 277.00-2179.00
231.00-247.00
123.00-291.00 278.00
171.00 207.00
241.00 294.00-1365.00
65.00-144.00
98.00-271.00
270.00
?There were no values showing deficiency symptoms or low ranges.
Data derived from fumigation experiments are values found when no fluorine was present In the air. Otherwise, data in this column are
from culture controls or nonindustrial areas.
"Refers to concentration of fluorine as hydrogen fluoride Introduced into greenhouse fumigation chambers.
Source: Adapted from Brewer, 1966, Table 1, pp. 184-194. Data collected from several sources. Reprinted by permission of the publisher.
I-*
10
vo
-------
130
600
400
200
a °
ORNL- DWG 79-20891
400
O
200
OC
O
3 °
"" 600
400
200
VALENCIA
HAMLIN
MARSH SEEDLESS
PINEAPPLE
TEMPLE
Ml,,
JUk
TANGELO
844281 4218.52.51.5
4844181 24.5 81422
3232 168884 444 4222 1
844281 424 8.5 2.51.5
48441 81 24.5 81422
3232168 88444442221 ppm hr
ppm
hr
Figure 4.2. Fluorine content of washed (solid) and unwashed
(shaded) leaves of six citrus varieties as affected by gaseous hydrogen
fluoride exposure. Source: Adapted from Maclean et al., 1968, Figure
2, p. 448. Reprinted by permission of the publisher.
-------
131
ORNL-DWG 79-20890
600
400
200
a.
a.
1200
UJ
8
800
E 400
o
1500
1000
500
0
IXORA
MELALEUCA
HIBISCUS
1
MUlJki
CARISSA
CROTON
Illlhl,
AZALEA
I
J
tfiJiJi-
IIIIIIIIIIIIHIIIJIIIrfldlJlJi I IIIIIIIIIIIIHIIIIIIItfui j
844281 421 8.5 2.51.5 844281421 8.5 2.5 1.~
484418 124.5 81422 48441 8124.5 81422
I 321 88844444222 1 |32|888444442221
32 16 32 16
E
Q.
Q.
600
UJ
400 §
o
LJ
200 1
o
ppm
hr
ppm hr
Figure 4.3. Fluorine content of washed (solid) and unwashed
(shaded) leaves of six ornamental species as affected by gaseous hydrogen
fluoride exposure. Source: Adapted from MacLean et al., 1968, Figure
3, p. 448. Reprinted by permission of the publisher.
-------
TABLE 4.7. TREATMENTS AND TISSUE FLUORIDE CONCENTRATIONS FOR BEAN EXPERIMENTS
Bean
variety
RK
RK
RK
PPW
TC
FCL
TG
RK
TG
TG
PPW
RK
TG
TC
PPW
RK
TG
TG
TG
TG
TG
TG
Nutrient.
solution
S
S
S
S
S
L
L
L
L
L
L
L
L
L
L
L
L
S
L
S
S
S
Day
length
(hr)
12
12
12
12
12
12
12
11
11
11
11
11
11
11
11
11
11
13
14
16
10
16
Days
exposed
to HF
7
7
7
9
14
7
69
70
70
70
70
70
70
70
70
70
70
82
92
84
92
74
Average HF
concentration
Pg F/m8
4.8
5.3
8.0
8.0
7.8
4.5
5.4
2.2
2.2
2.2
2.2
6.6
6.6
6.6
6.6
13.9
13.9
10.5
9.1
2.1
0.60
0.58
F content of plant tissue
When
exposed
A
E
B
BE
BE
BE
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Leaflets
Control
3.2
1.1
2.7
1.2
2.5
3.0
3.5
1.0
1.5
1.0
0.3
0.3
0.3
0
1.0
3.6
2.4
4.5
4.5
3.0
4.0
3.5
HF
160d
120*
270
180
330j
52
880
260
260
340
220
710
700
710
540
1670
1220
690
775
140
54
49
Stems,
Control
0.3
0
0.2
0.6
0.7
2.0
1.7
0
0
0
0
0
0
0
0
1.4
1.8
1.5
0.8
0.5
1.5
0.9
petioles
HF
2.4*
2.0*
26
12
20 d
3.3d
39
8.3
10
24
19
25
29
26
31
59
49 ,
28*
30
14
3.0
2.5
(ppm)
Fruit
Control
0.1
0.2
0
0.3
0.2
2.1
0.9
0.7
0.3
0.5
0.3
0
0
0
0
2.4
2.2
0
0.5e
0
0
Qe
HF
4 Ud
o'.7d
/J
0.6*
0.3*
3.1*
33
4.2
13
21
21
29
46
47
34
66
80,
13 '
20e
14e
4.0e
3.6e
rRK red kidney; PPW pencil pod wax; TC tendercrop; TG tendergreen; FCL fordhook concentrated lima.
S standard nutrient solution containing 200 ppm Ca; L low Ca nutrient solution containing 40 ppm Ca.
A directly after flowering; E during early flowering; B directly before flowering; BE beginning before flowering and
extending into early flowering; C continuously, from seeding to harvest.
"Samples for F analysis collected some time after HF treatment, when plants were harvested. All other F analyses of fumigated
plants apply to samples collected at end of HF treatment.
^Mature seed only.
Source: Adapted from Pack, 1971b, Table I, p. 1129. Reprinted by permission of the publisher.
to
-------
133
(Less et al., 1975). Gaseous hydrogen fluoride was more easily absorbed
than particulate matter, and absorption was greater during wet cool
weather (Figure 4.4).
ORNL-DWG 79-20889
I I
HF (WINTER)
I
HF (SUMMER, RAIN)
HF (SUMMER)
SUBMICRON PARTICULATE
FLUORIDE (SUMMER)
10
20
25
30
MEAN CONCENTRATION OF FLUORIDE IN AIR (pg/md)
Figure 4.4. Comparison of uptake by grass of fluoride from hydrogen
fluoride and from submicron particulate fluoride. Source: Adapted from
Less et al., 1975, Figure 8, p. 159. Reprinted by permission of the
publisher.
Continuous exposure to fluoride is more harmful to plants than inter-
mittent exposure. For example, the intermittent spraying of citrus with
either sodium fluoride or hydrogen fluoride was less injurious than con-
tinuous exposure to gaseous hydrogen fluoride. With intermittent exposure
there is a chance for the absorbed fluoride to be "chemically fixed" be-
tween exposures, whereas there is no "rest period" with continuous exposure
(Brewer, Sutherland, and Guillemet, 1969; Chang, 1975). Toxicity symptoms
were the same with either treatment. Fluoride accumulation in foliage of
timothy (Fhleum pvatense L.) and red clover (.Trifolium pratense L.) was
greater with continuous exposure (10 days, 2.3 and 5.0 yg of fluoride per
cubic meter) than with intermittent exposures (same concentrations, 2-day
exposure to fluoride alternated with a 2-day exposure to filtered ambient
air; total fluoride exposure time was 10 days) (Figure 4.5) (MacLean and
Schneider, 1973). However, intermittent exposure yielded larger fluoride
accumulation when total time was held constant and fumigant concentration
was increased (MacLean, Schneider, and Weinstein, 1969). In all cases,
plants were exposed to the same dose (defined as the product of fumigation
concentration and the days of fumigation). The data illustrate the diffi-
culty in predicting fluoride accumulation in field crops when only the
-------
134
60
ORNL-DWG 79-20888
o>
5 40
IU
to
O
o
u.
u
> 20
o
0
200
I
Q.
0.
u
o
10 15
TIME (days)
20
Figure 4.5. Fluoride accumulation in mixed planting of timothy and
red clover with intermittent (solid symbols) and continuous (open symbols)
fumigations. Source: Adapted from MacLean and Schneider, 1973, JOURNAL
OF ENVIRONMENTAL QUALITY, Volume 2, page 501, by permission of the American
Society of Agronomy, Crop Science Society of America and Soil Science
Society of America.
average air concentration is known. In field situations, airborne fluoride
concentrations and duration of exposure vary. Moreover, rain leaches flu-
oride from vegetation. Volatilization of organofluorides may also occur
(Section 4.2.5). Exposure times and concentrations required to produce
injury symptoms for several species are presented in Section 4.3.2.
4.2.4.2 Concentration in Plants Near ...Pollution Sources Proximity to a
fluoride pollution source usually increases the plant fluoride content.
-------
135
Plants growing in the vicinity of a phosphorus extraction facility at
Silverbow, Montana, contained much higher fluoride contents than control
area plants (van Hook, 1974). Bluebunch wheatgrass contained average
concentrations of 200 to 350 ppm fluoride in areas adjacent to the indus-
try, while concentrations decreased to less than 50 ppm 1 to 2 miles away.
Similarly, concentrations in juniper decreased from about 400 to 20 ppm
fluoride. The rate of change in tissue fluoride concentrations with dis-
tance from the pollution source depended on the prevailing air currents.
Table 4.8 shows fluoride content of grasses, herbs, shrubs, and
conifers found on plots surrounding the Anaconda Aluminum Company smelter
in northwestern Montana (Carlson, 1973). Correlation of fluoride content
with an index of injury implicated fluoride as the cause of injury. Fluo-
ride concentrations in the lichen Parmelia eulaata decreased with distance
from an aluminum factory; concentrations were about 900 ppm at 1 km, 870
ppm at 4 km, 500 ppm at 8 km, 340 ppm at 9 km, and 120 ppm at 15 km
(LeBlanc, Rao, and Comeau, 1972). Fluoride levels increased significantly
in Spanish moss placed in areas of known fluoride air pollution. Fluoride
concentrations increased with exposure time and were indicative of the
proximity of fluoride sources. The highest concentration detected was
2418 ppm, an increase from an initial concentration of 27 ppm. However,
fluoride levels in the moss fluctuated with rainfall. A collection from
the site that contained 2418 ppm was decreased to 1760 ppm after a rain-
fall of 2.89 in. (Maclntire, Hardin, and Hester, 1952). Ivos et al. (1970)
reported high fluoride concentrations in plants near aluminum factories
in Lozovac and Razine, Yugoslavia. Pine needles contained as much as
1806 ppm fluoride and "dusty" oleander leaves, 2747 ppm fluoride.
4.2.4.3 Subcellular Distribution The subcellular distribution of
fluorine-18 and fluorine-19 in tomato leaves after long and short fumiga-
tion exposures is presented in Table 4.9. Cell walls, chloroplasts, and
soluble proteins contained the largest quantities of label. Chang and
Thompson (1965) obtained similar results in cellular fractions from fumi-
gated citrus leaves; however, because of cross contamination in organelle
separation and preparation, they reasoned that accumulation was greatest
in the chloroplasts, less in the cell-wall-nuclei fraction, and least in
the mitochondria fraction. Some 60% of the fluoride was in the supernat-
ant, rather than the organelle, fraction.
4.2.5 Bioelimination
There are few data on fluoride elimination from plant materials.
Evidence for volatile organofluorides in homogenates of several plant
species has been presented, but whether any loss of volatile fluorides
occurs in vivo is unknown (Peters and Shorthouse, 1967). Monofluoroace-
tone was identified as the volatile fluoride lost from homogenates of A.
georginae, but since it accounted for only about 13% of the total fluo-
ride lost, other volatile compounds must exist (Peters and Shorthouse,
1971). Washing leaves of plants with distilled water can remove signif-
icant amounts of fluoride from plants previously exposed to either atmos-
pheric fluoride or soil fluoride (Section 4.2.1.2) (Jacobsen et al., 1966).
In the former case, the water probably removes airborne pollutants that
-------
TABLE 4.8. CONCENTRATIONS OF FLUORIDE IN PLANTS NEAR THE ANACONDA ALUMINUM COMPANY
SMELTER IN NORTHWEST MONTANA
Average fluoride content (ppm dry wt)
Plot No.a
Control No. 1-6
R1-P1-7
R2-P1-7
R3-P1-7
R4-P1-10
R5-P1-10
R6-P1-10
R7-P1-7
R8-P1-7
R9-P1-7
R10-P1-7
Shrubs
4. 77-11. 4&
3-108.5
3.6-112.7
10-1166.6
8-778
11.05-1719
7.5-1125.3
4.8-1073
11.8-399.8
5.6-108.7
6.8-76.5
Conifers
1969
3.5-10
5.8-300
5.5-143.5
7-637
8.93-681.5
10.1-341
13.5-1950
10-168
14.2-119.8
7.8-110
9.2-133
1970
3-11
9-40.8
2.3-20
8-229
4-116.5
4.1-68.6
6-33
4.5-22.3
9.2-175
10-39.5
3.5-42.5
Herbs
5-12
12.5-188
5.5-93.8
3.3-875.5
5.7-628
8.28-1038
11-431
7-600
13.3-235
6.5-51.5
10-45
Grasses
1.3-16
2.5-70
2.5-83.3
2.1-775
5.8-234
5.5-600
24.5-581
20.5-338
8-110
5-41
6.5-38.5
Grand
average
4.79-10.36
6.8-122.36
3.7-91.21
8.2-1004.3
6.88-604.14
7.46-1181.5
11.75-877.6
10.87-871.7
12.6-409.8
7.72-70.97
7.54-66.3
?R radius; P plot.
Samples were on transects radiating from the smelter. These values represent the range of
fluoride concentrations found in all plots on the radius. Lower values were associated with plots
distal from the fluoride source.
Source: Adapted from Carlson, 1973, Table la, p. 131. Reprinted by permission of the publisher.
-------
137
TABLE 4.9. DISTRIBUTION OF '*F AND "F IN VARIOUS
CELLULAR CONSTITUENTS OF TOMATO LEAVES TREATED
THROUGH THE AERIAL PORTIONS OF THE PLANT
"F after 2-hr
Cellular
constituent
"F at the
end of 10-day
fumigation
(ppn dry wt)
fumigation
(counts rain'1
dry wt)
»g"
Nonvashed Washed
Cell walls
Chloroplasts
Mitochondria
Microaomes
Soluble proteins
Supernatant
168S
693
99
21
371
142
176
78
592
82*
155
145
34
662
37°
the concentration of "F is expressed for this
fraction in counts mln"1 mg~* of fresh leaf tissue.
Source: Adapted from Ledbetter, Mavrodineanu, and
Weiss, 1960, Table V, p. 346. Reprinted by permission
of the publisher.
have settled on the leaves and any surface-extruded fluorides. The latter
case implies that some of the fluoride that has been translocated to the
leaf may eventually be deposited on the surface of the leaf and, thus,
easily removed by brief water washings. Therefore, rainfall may be ex-
pected to remove a portion of the fluoride from the crown portion of the
plant.
Loss of fluoride in plants also occurs through the seasonal loss of
leaves, twigs, and roots. Hitchcock et al. (1971) suggested that the post-
fumigation loss of fluoride from alfalfa plants was due mainly to leaf
abscission and "weathering." Growth dilution (biomass added after fumiga-
tion) also leads to a decrease in tissue concentration of fluoride, but
it is not an elimination mechanism. Weinstein (1961) observed a signifi-
cant decrease in fluoride content of stem and leaf tissue from bean and
tomato during a postfumigation period. The reason for this decrease could
not be explained, but it was not due to growth dilution.
4.3 EFFECTS
Fluorides affect plants through chemical interactions that occur once
the plant has taken up a quantity of fluoride. These effects can occur at
various levels of organization, and ultimately all effects should be expli-
cable in molecular terms. Table 4.10 summarizes some of the effects of
fluoride observed at different levels of organization.
Fluorinated analogues of a variety of natural constituents have been
used as inhibitors in numerous biological and biochemical studies. For
example, fluorophenylalanine is an analogue of the amino acid phenylala-
nine; incorporation of this analogue into enzymes often results in reduced
enzymatic activity. Since few data exist on the natural occurrence of
formation of these analogues when plants are exposed to fluorides, their
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138
TABLE 4.10. NATURE OF FLUORIDE-INDUCED EFFECTS IN PLANTS
AT DIFFERENT LEVELS OF BIOLOGICAL ORGANIZATION
Cell
Tissue or organ
Organism
Ecosystem
Altered cell milieu?
Effects on enzymes
and metabolites
Modification of cell
organelles and
metabolism
Pathway disruption
Cellular modification
Disruption and death
of cell
Decreased
assimilation
Altered respiration
Altered growth and
development
Chlorotic lesions
Necrotic lesions
Death or abscission
of leaf
Modified growth
Reduced
reproduction
Decreased fitness
for environment
Death of plant
Increased fluoride
in ecosystem
Increase in fluoride
burden of animals
Fluorosis in animals
Change in plant
community
Desolation
Source: Adapted from Weinstein and McCune, 1971, Table 1, p. 411. Reprinted by
permission of the publisher.
effects are not discussed in this section. An exception is fluorocitrate,
which can be formed from fluoroacetate. Production of fluorocitrate and
fluoroacetate is discussed in Section 4.2.3.
4.3.1 Metabolic Effects
4.3.1.1 Photosynthesis Although inhibition of photosynthesis by fluo-
ride is well documented (Bennett and Hill, 1974; Chang, 1975; Thomas and
Alther, 1966), the mechanisms by which it occurs have not been unequivo-
cally determined. Suggested mechanisms include enzymatic inhibitions,
loss of subcellular organization, and granulation of chloroplasts. Photo-
synthesis in sensitive plants (e.g., gladiolus and apricot) can be inhib-
ited by a few parts-per-billion fluoride, whereas more resistant plants
may require several hundred parts-per-billion fluoride to attain similar
results.
Chlorosis is a common effect of exposure to fluorides (Chang, 1975).
Newman (as cited in Wallis et al., 1974) found that fluoride decreased the
chlorophyll content of bush bean leaves and suggested that fluoride inhib-
its photosynthesis by affecting chlorophyll synthesis. Both fluoride and
chloride at 0.1 vM to 10 mW inhibited the in vivo production of chlorophyll
and pheophytin a from 1*C-6-aminolevulinic acid (ALA) in tobacco leaf discs
(Wallis et al., 1974). Fumigation with 12.4 ppb hydrogen fluoride for
nine days slightly decreased chlorophyll a and chlorophyll b contents of
tomato and bean leaves, although recovery occurred in the postfumigation
period (Weinstein, 1961).
Potassium fluoride (35 mftf) inhibited oxygen evolution (Hill reaction)
at pH 4.8 to 5.7 in isolated chloroplasts from bush beans (Ballantyne,
-------
139
1972). Inhibition was overcome by increasing the pH above 5.6 and inject-
ing magnesium and potassium salts into a chloroplast preparation. Inhibi-
tion did not occur with monofluoroacetate. The threshold for inhibition
was 2 mV fluoride. Other examples of the fluoride inhibition of the Hill
reaction are given in Chang (1975).
Apparent photosynthesis in barley and alfalfa was inhibited about 5%
with 2-hr hydrogen fluoride exposures at 40 ppb fluoride and about 40% at
200 ppb fluoride (Bennett and Hill, 1973). Below about 150 ppb no detect-
able tissue necrosis occurred. At 40 and 100 ppb fluoride, carbon dioxide
uptake decreased over the 2-hr fumigation period; recovery occurred after
the end of the fumigation period, and near normal rates were observed the
next day. At equivalent concentrations, inhibition of photosynthesis by
hydrogen fluoride was 2 times as effective as ozone or chlorine, 4 times as
effective as sulfur dioxide, 25 times as effective as nitrogen dioxide, and
40 times as effective as nitric oxide. Photosynthesis in detached leaves
of three pine and six hardwood species was inhibited significantly when
placed in 1 mW to 10 mW sodium fluoride solutions for 24 hr (Mclaughlin and
Barnes, 1975). Table 4.11 shows the decrease in apparent photosynthesis
observed after exposure of samples collected on the given dates. In gen-
eral, pines were more sensitive than hardwoods, and new needles more sen-
sitive than old. Inglis and Hill (1974) observed that a 24-hr exposure to
50 mW fluoride almost completely inhibited carbon dioxide fixation (photo-
synthesis) in three moss species. At 25 mAf fluoride, inhibition was 1% in
Tovtula muralie, 72% in Hypnum cupressiforme, and 90% in Brywn argenteum.
TABLE 4.11. SEASONAL EFFECTS OF FLUORIDE (1 mtf NaP) ON PHOTOSYNTHESIS AND RESPIRATION OF FOLIAGE FROM
THREE SPECIES OF PINES AND SIX SPECIES OF HARDWOOD
Species
Change from control (!)
Apparent photosynthesis*
Dark respiration"
Pines
Loblolly pine
New needles
One-year needles
White pine
New needlea
One-year needles
Shortleaf pine
One-year needles
28
May
ND
-44
-86
-100
-80
9
June
-67
-40
-100
-89
-90
23
June
-79
-30
-85
-55
-33
7
July
-85
-75
-79
-59
-94
21
July
-69
-50
-71
-52
-57
7
Aug.
-45
-54
-74
-46
-60
28
May
+8
+20
-27
+21
+41
9
June
+8
+10
-36
+40
+13
23 7
June July
-9 -9
0 +38
+30 +33
+43 +67
+75 +15
21
July
0
+20
+100
+109
+67
7
Aug.
+18
+55
+50
+136
+23
Hardwoods
Red maple
Sycamore
Yellow poplar
Red gun
Dogwood
Sourwood
3
June
+22
-17
-81
0
-27
-83
17
June
-85
-18
-30
ND°
-16
+29
1
July
-66
-48
-30
-12
-35
-50
15
July
-47
+1
-38
-31
-7
-3
29
July
-57
-11
-80
-22
-9
-55
3
June
+14
+19
+21
+5
+5
-6
17
June
-13
+22
+71
ND°
+22
+48
1
July
+43
+2
+49
+28
+15
-34
IS
July
+51
+29
+47
+52
+22
+5
29
July
+44
+16
+110
+53
+5
+10
Samples were collected at the dates listed and lanersed In fluoride solutions for 24 hr. Measurements were
performed after this exposure.
Source: Adapted from McLaughlln and Barnes, 1975, Table 2, p. 95. Reprinted by permission of the publisher.
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140
A summary of the study by Bennett and Hill (1974) of the inhibition
of photosynthesis by several air pollutants is shown in Figure 4.6. The
relative order of inhibition of equal concentrations of these pollutants
for barley and oats is HF > C12 ^ 03 > S0a > N02 > NO. Although hydrogen
fluoride can also induce stomatal closure and thus restrict carbon dioxide
entry, inhibition of biochemical processes within the leaf is thought to
be the major inhibitory mode. Recovery from hydrogen fluoride exposure
occurs but is slower than that from other pollutants. Hill (1969) reported
that a 24-hr average concentration of 48 ppb caused a 50% reduction of
photosynthesis in strawberries; complete recovery required three weeks.
ORNL-DWG 79-20899
100
£ 75
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80
4
100
80
60
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"FUMIGATION
^ I
^^^O% .»***
f V* ,fl%**** ^^
RECOVERY
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TIME (hr)
100 200
CONCENTRATION (pphm)
300
Figure 4.6. Inhibition of apparent photosynthetic rates of barley
and oat canopies by 2-hr air pollution fumigations. Source: Adapted from
Bennett and Hill, 1974, Figure 1, p. 118, in Air Pollution Effects on
Plant Growth. Reprinted by permission of the publisher.
Although fluoride can inhibit photosynthesis in the field, it is
difficult to determine if ambient fluoride levels are responsible for the
observed damage. Ambient air pollution in the Los Angeles Basin reduced
transpiration and apparent photosynthesis of lemon and navel orange trees.
However, atmospheric levels of fluoride (averages of about 0.32 to 0.77
Vg/ta3) were apparently not responsible, since controlled experiments
designed to simulate ambient conditions failed to detect significant
decreases in transpiration and photosynthesis (Thompson et al., 1967).
-------
141
Inhibition of photosynthesis leading to yield depression without the
formation of chlorosis or necrosis has been termed hidden injury and is
discussed in Section 4.3.3.3.
4.3.1.2 Respiration and Oxidative Processes Many reports provide evi-
dence that exposure of plants to fluoride alters respiration (Chang, 1975).
Generally, low concentrations stimulate respiration while higher concentra-
tions inhibit respiration. The exact concentrations causing these effects
depend on the species, exposure period, age of the plant material, and con-
centration of fluoride in the sensitive part of the cell (Weinstein, 1961).
For example, exposure of detached leaves of three pine species and six
hardwood species to 1 roM sodium fluoride increased respiration in most
cases (Mclaughlin and Barnes, 1975). However, the extent of stimulation
varied considerably with species and with the age of the leaf (Table
4.11). Exposure of tomato and bean plants to fumigation with 1.6 ppb
hydrogen fluoride increased respiration 67% and 72%, respectively, over
control values (Weinstein, 1961). The data of Applegate, Adams, and
Carriker (1960) (Table 4.12) showed that distinct inhibition of 02 uptake
by bush bean seedlings infiltrated with fluoride solutions occurred at
sodium fluoride concentrations of 10 wM or greater. At the oldest devel-
opmental stage examined (five days "of germination"), 0.1 wM sodium flu-
oride stimulated respiration. Growing conditions (light or dark) and C02
concentration in the atmosphere in which 02 uptake was measured affected
the respiration rate. In the fluoride-sensitive plant Chenopodium morale
24- and 48-hr exposures of detached leaves to 1 tsM KF decreased respira-
tion, whereas in soybean, a fluoride-resistant species, similar exposure
TABLE 4.12. THE Q0a RATIO (WATER INFILTRATED TO FLUORIDE INFILTRATED)
OF BEAN SEEDLINGS AT THREE GROWTH STAGES
Fluoride
concentration
in Infiltration
solution
(mW)
100
10
1
0.1
Light
or dark
germinated
Light
Dark
Light
Dark
Light
Dark
Light
Dark
C0a In
Warburg
flask
«)
0
0.6
0
0.6
0
0.6
0
0.6
0
0.6
0
0.6
0
0.6
0
0.6
Stage 1
1.539
1.784
1.625
2.420
1.049
1.254
1.118
1.287
1.048
1.168
1.116
1.199
1.047
1.164
1.146
1.196
QOj ratio**
Stage 2
2.089
3.188
2.779
3.428
1.209
1.921
1.454
1.910
0.941
1.327
1.111
1.469
0.903
0.918
1.015
1.122
Stage 3
1.459
3.406
1.769
2.214
1.085
1.912
1.253
1.299
0.920
0.994
0.944
1.007
0.703
0.789
0.829
0.818
aQOs microliters of Oa uptake per milligram dry weight.
Source: Adapted from Applegate, Adams, and Carriker, 1960, Table 2,
341. Reprinted by permission of the publisher.
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142
slightly increased respiration (Yu and Miller, 1967). Except at one-day
exposures, younger leaves showed more fluoride-induced respiration than
older leaves. They also showed the greatest inhibition after four to
five days of exposure. In general, respiration was not inhibited until
visible necrotic injury was severe. In Cetvaria islandicd (lichen), expo-
sure to 5 mM sodium fluoride increased respiration over a 5-hr exposure
period, but respiration decreased after a 24-hr exposure to 70% of control
(Vainshtein, 1973). Higher concentrations were inhibitory over the whole
24-hr exposure period.
Although the reason for fluoride-stimulated respiration is not known,
observations in Chlorella pyrenoidosa indicated that stimulation may be
related to the amount of undissociated hydrogen fluoride in the medium
(McNulty and Lords, 1960). Higher concentrations of phosphorylated nucle-
otides occurred in fluoride-treated cells, and since respiration rate is
thought to be governed by the ADP levels (or the ATP/ADP ratio), high ADP
levels might stimulate respiration.
Dinitrophenol, an uncoupler of mitochondrial phosphorylation from
electron transport, increased the rate of respiration in fluoride-treated
soybean leaves to a lesser extent than in untreated tissues (Yu and
Miller, 1967). This suggests that fluoride-induced respiration results
from increased utilization of ATP, providing higher ADP pools in the cell.
Heatherbell, Howard, and Wicken (1966) found that sodium fluoride slightly
decreased oxygen consumption and phosphorylation in mitochondria isolated
from etiolated pea seedlings.
Leaf tissue isolated from soybean plants fumigated for 48 hr with
9 to 12 yg/m3 hydrogen fluoride showed increased respiration, mitochondrial
succinate oxidation with ATPase activity, and decreased mitochondrial phos-
phorylation (Miller and Miller, 1974). After a 96-hr exposure, all the
above activities were less than control values. Tightly coupled mitochon-
dria, isolated from etiolated soybean hypocotyl and then exposed to con-
centrations of from 0 to 67 wM potassium fluoride, showed no increase in
respiration when succinate, malate, or NADH was used as the substrate.
Exposure of hypocotyl tissue itself to 10 wM potassium fluoride produced
no stimulation in respiration. The osmotic properties of corn shoot mito-
chondria treated with potassium fluoride suggested that fluoride altered
the permeability of the mitochondrial membranes. The authors concluded
that fluoride may be acting at the membrane level, leading to an altered
mitochondrial metabolism. The higher ATPase activity in fluoride-treated
green tissues would increase ADP concentration, thus stimulating respira-
tion. At longer periods of exposure to fluoride, higher internal concen-
trations of fluoride would occur and could, therefore, inhibit respiratory
enzymes.
Miller and Miller (1974) discussed evidence that fluoride inhibits a
variety of respiratory enzymes: succinic, malic, and NADH dehydrogenases;
enolase; phosphoglucomutase; hexokinase; and ascorbic acid oxidase (Section
4.3.1.3). Levels of several enzymes were examined in soybeans fumigated
with hydrogen fluoride. Glucose-6-phosphate dehydrogenase, cytochrome
oxidase, peroxidase, and catalase activities increased in the fumigated
-------
143
leaves (Lee, Miller, and Welkie, 1966). Exposure of isolated enzymes to
fluoride, however, showed glucose-6-phosphate dehydrogenase, cytochrome
oxidase, and catalase to be unaffected while peroxidase was inhibited.
There are no data on the turnover of these enzymes in fluoride-treated
tissues. Peroxidase and cytochrome oxidase activities determined by histo-
chemical procedures were highest in the phloem near the necrotic areas of
Pelargonium zonale leaves fumigated with hydrogen fluoride (Poovaiah and
Wiebe, 1971). This study provides in vivo evidence to support the above
in vitro findings of Lee, Miller, and Welkie (1966). However, observed
increased respiration is apparently not due to direct stimulation of enz-
ymatic activity. The manner and site in which fluoride initiates injury
are unknown.
4.3.1.3 Carbohydrate Metabolism Fluoride is known to inhibit glucose
catabolism in isolated plant tissues (National Academy of Sciences, 1971).
The manner in which this occurs in vivo is unknown. In vitro, fluoride
can inhibit enolase, the enzyme in the glycolysis pathway that converts
D-2-phosphoglyceric acid to phosphoenolpyruvic acid (Lehniger, 1975;
Miller, 1958). Inhibition occurs through the formation of a magnesium
fluorophosphate complex.
The use of the pentose phosphate pathway would bypass inhibition of
enolase and thus confer a selective advantage (increased fluoride resist-
ance) to varieties using this pathway to a larger extent. Ross et al.
(1968) examined this possibility by studying the release of labeled carbon
dioxide from glucose containing 1AC in the 6 position (6-C02) and in the
1 position (1-C02). These studies were made on leaf discs from varieties
of gladiolus that differed in their susceptibility to fluorides. Although
there were considerable differences, varieties with increased resistance
to fluoride generally had lower 6-C02/l-COa ratios, suggesting that there
might be a correlation between resistance and the increased use of the
pentose phosphate pathway. Multiple correlation analysis showed that the
6-C02/l-C02 ratio accounted for 16% of the variation in leaf injury, flower
color accounted for 32%, and leaf area for 15%.
While fluoride does inhibit growth, there is little proof that the
growth inhibitory mechanism is through enolase, because other enzymes are
also inhibited by fluoride. Ordin and co-workers demonstrated fluoride
inhibition of the incorporation of X*C glucose into cellulose and other
components of the aqueous and acid-soluble cell wall fraction of oat cole-
optile (Ordin and Skoe, 1963). From studies using glucose labeled with
1I§C in several positions, they concluded that enolase was not inhibited
in vivo.
In vitro, fluoride also inhibits phosphoglucomutase, the enzyme
converting glucose-6-phosphate to glucose-1-phosphate (Yang and Miller,
1963Z>). Ordin and Alt man (1965) demonstrated that oat coleoptile phospho-
glucomutase was inhibited by fluoride in vitro and suggested that this was
"the major cause of fluoride-induced inhibition of cellulose biosyntheses."
Later, however, glucose-6-phosphate and glucose-1-phosphate pools were
observed not to change with fluoride treatment (Gordon and Ordin, 1972).
UDP-glucose pools did decrease after fluoride treatment. Thus inhibition
-------
144
in this system appears not to be related to phosphoglucomutase inhibition
but to some other process that reduces incorporation of glucose into wall
materials. Other researchers report that phosphoglucomutase is not inhib-
ited by fluoride. De Moura, Le Tourneau, and Wiese (1973) found that
potato tuber phosphoglucomutase was relatively insensitive to fluoride
in vitro, and their preliminary data suggested that it also was not sus-
ceptible in vivo. Fluoride at 0.5 wM and 1.25 mW does not inhibit corn
phosphoglucomutase in vitro, but at 0.5 mW and 1 mW it does inhibit corn
seedling root growth 20% and 40% respectively (Chang, 1968). These stud-
ies provide further evidence that growth inhibition is not due to the in
vivo inhibition of phosphoglucomutase.
Yang and Miller (1963a, 19632?) examined the metabolic effects of
fluoride fumigation on soybean plants. After three- to five-day expo-
sures to 0.03 ppm hydrogen fluoride, the fluoride content in the leaves
was about 200 yg/g (on a fresh-weight basis). Fumigated leaves contained
less sucrose and increased levels of reducing sugars and organic acids.
Respiration increased 30% and 100% above controls (Yang and Miller, 1963a).
Pipecolic acid accumulated in necrotic regions of the leaf. These data
suggest that sucrose synthesis is inhibited by fluoride. The four known
enzymes that convert glucose-6-phosphate to sucrose (phosphoglucomutase,
UDP-glucose pyrophosphorylase, UDP-glucose-fructose transglucosylase, and
UDP-glucose-fructose 6-phosphate transglucosylase) differ in vitro in their
sensitivity to fluoride (Yang and Miller, 1963i). Soybean phosphoglucomu-
tase is very sensitive to fluoride, while UDP-glucose-fructose transglu-
cosylase is only slightly sensitive. UDP-glucose pyrophosphorylase is
completely insensitive to fluoride. Increased dark carbon dioxide fixa-
tion occurs in fluoride-treated leaves and may explain the elevated levels
of organic and amino acids found in necrotic leaves (Yang and Miller,
1963c).
The metabolism of phosphorus compounds is intimately related to carbo-
hydrate metabolism. Pack and Wilson (1967) cited references showing that
the enzymes enolase, phosphoglucomutase, phosphatases, and phosphorylases
(all concerned with phosphorus metabolism) are inhibited by fluorides.
They also showed, however, that levels of some 20 phosphorus metabolites
in bean seedlings are not altered by exposure to 14 yg of hydrogen fluoride
per cubic meter exposure that produced no injury but produced 275 ppm
fluoride in tissue. Thus, inhibition of enzymes concerned with acid-
soluble phosphorus compounds did not occur in vivo.
McCune, Weinstein, and Mancini (1970) reported that there was "no
consistent effect on the levels or composition of acid-soluble nucleotides"
in fluoride-fumigated leaves of beans, tomatoes, and corn (4.8 to 10.7 yg
of fluoride per cubic meter, 4 to 12 days). However, fumigated leaves did
show reduced incorporation of phosphorus-32 into nucleotides, possibly
because of decreased uptake of translocation of phosphorus.
Phytase from germinating pea seeds was inhibited 80% with 1 wM fluo-
ride (Hauskrecht, 1972). Phytase activity in seeds increased with germi-
nation, presumably supplying phosphate for activation of various processes.
Although conclusive experimental evidence is lacking, this may provide an
-------
145
alternative explanation for inhibition of germination by fluoride. Chang
(1973) also observed that fluoride (0.1 vM to 10 mW) inhibited phytase
activity in vitro (13% to 54% inhibition respectively).
4.3.1.4 Effects of Fluoride on Ribosomes with RNA Metabolism The growth
rate of corn seedlirig roots was decreased by treatment before germination
with 0.01 M sodium fluoride for 1.5 to 7 hr. After exposure, the seeds
were washed with deionized distilled water, treated lightly with a fungi-
cide, then allowed to germinate and grow to a standard size of 12 ± 3 mm
in a moist chamber containing deionized distilled water. Control seedling
roots grew 0.36 mm/hr, whereas treated seedling roots grew only 0.28 mm/hr
after 1.5-hr exposure, 0.24 mm/hr after 3-hr exposure, 0.20 mm/hr after
5-hr exposure, and 0.17 mm/hr after 7-hr exposure (Chang and Thompson,
1966). The RNA content of the 3 mm root tips was directly correlated with
growth rates, but the DNA content was not. Since the RNA content per cell
was correlated with the growth rate for different fluoride exposures, an
effect of fluoride on RNA metabolism was postulated. Inhibition of both
cell elongation and cell division occurred.
Fluoride-induced changes in acid-soluble nucleotides were observed
in roots produced from fluoride-treated corn seeds (Chang, 1968). The
triphosphate nucleotides increased the most. The base composition of RNA
was also altered by fluoride treatment. Further studies showed that fluo-
ride reduced the amounts of both free and bound ribosomes (Chang, 1970a,
1970Z>)» and ribonuclease activity increased in plastids, mitochondria,
the soluble fraction, and to the greatest extent in microsomes. A review
of some of the biochemical changes in ribosomal metabolism and changes
in cellular RNA content that occur during fluoride inhibition of root
growth can be found in Chang (1973, 1975).
4.3.1.5 Fluorides and Calcium Nutrition Some data suggest that fluoride
injury is due to a calcium deficiency caused by precipitation of calcium
as calcium fluoride. Since the calcium content of the cell is usually
much larger than the fluoride concentration observed after exposure to
fluoride pollutants, it is necessary to postulate that much of the calcium
is present as chelates or as insoluble complexes and that the actual free
ionic calcium content is quite small. Thus buildup of fluoride could
precipitate the small concentration of ionic calcium required for normal
metabolism.
Ramagopal, Welkie, and Miller (1969) observed that 5-min fluoride
treatments of wheat seedling roots produced the same response as calcium
deficiency and that potassium oxalate, sodium ethylenediaminetetraacetate,
and sodium monofluoroacetate additions all elicited a similar response.
Garrec et al. (1974) found that both fluoride and calcium accumulated in
the injured tips of fir needles, presumably as calcium fluoride. However,
although fluoride increased the total calcium level and the amount of cal-
cium oxalate in these needles, other insoluble calcium salts (e.g., carbo-
nates and phosphates) were only slightly increased. Brennan, Leone, and
Daines (1950) reported that increased calcium in nutrient solutions led
to increased fluoride content "in and about" tomato roots, apparently
due to calcium fluoride precipitation.
-------
146
In support of the idea that the mechanism of fluoride injury occurs
through interference with calcium metabolism, Pack (1966) observed that
injury to foliage from hydrogen fluoride fumigation was greatest when
tomatoes were grown at the lowest calcium level (40 ppm calcium). At
calcium levels of 40, 80, 120, and 200 ppm, hydrogen fluoride treatment
caused significant decreases in total fruit weight per plant and in average
fruit weight. A seedless condition of fruit was also more prevalent for
hydrogen fluoride treatments at the 40 ppm calcium level. These effects
were observed at the "high" hydrogen fluoride level of fumigation (6 yg
of fluoride per cubic meter, 21 weeks), but not at the "low" level (2.9
yg of fluoride per cubic meter, 21 weeks); both levels are considerably
higher than expected for outdoor areas. In other studies, the decreased
sensitivity of mandarin leaves to atmospheric fluoride compared with glad-
iolus leaves, was attributed to the increased calcium and decreased sili-
con contents of mandarin leaves (Suketa and Yamamoto, 1975).
4.3.1.6 Mechanisms of Enzyme Inhibition Fluoride inhibition of most
enzymes probably occurs by complex formation with the polyvalent cations
(iron, calcium, and magnesium) of metalloenzymes, making the ions unavail-
able for their role as cofactors. A discussion of the effects of fluoride
on enzyme activity is given by Hewitt and Nicholas (1963). Enolase inhi-
bition by fluoride occurs by the formation of a magnesium fluorophosphate
complex that is inactive as a cofactor. A complex of fluoride, magnesium,
and glucose-1-phosphate inhibits phosphoglucomutase activity. Several
other enzymes requiring magnesium are also inhibited, to a varying extent,
by fluoride. Similar examples exist for enzymes containing iron. The
observed inhibition kinetics are often complex, and the extent of inhibi-
tion for different divalent metalloenzymes varies considerably. Most of
these studies involve enzymes isolated from animal or microbial systems.
A variety of enzymes are inhibited in vitro by fluorides, but the
relationship between the inhibition of specific enzymes and the physio-
logical disorders and symptoms that occur is poorly understood (Section
4.3.1.3). For example, adenosine diphosphate sulfurylase, isolated from
yeast or spinach leaves, is inhibited by fluorides (Burnell and Anderson,
1973). However, data are not available to determine if such inhibition
occurs in vivo, and no information on aberrant sulfur metabolism in
fluoride-treated plants was found.
4.3.2 Symptoms of Fluoride Accumulation
4.3.2.1 Foliar Symptoms The best described symptoms of fluoride expo-
sure relate to foliage. On monocotyledonous plants, marginal chlorosis
and subsequent marginal necrosis often occur (Weinstein and McCune, 1971).
On dicotyledonous plants, fluoride exposure results in leaf tip chlorosis,
which develops downward along the margins with subsequent necrosis. In
both types of plants, necrosis usually occurs without prior chlorosis and
is prevalent in the tip and margin regions, areas where tissue fluoride
concentrations are the highest (Treshow and Pack, 1970). Depending on
the species, the necrotic zone may become yellow, brown, violet, or red.
Interveinal chlorosis also occurs in some species, (maize, some citrus,
and rose) exposed to low fluoride concentrations for a short period of
time (Brewer, 1966).
-------
147
There is wide variation in the susceptibility of different plant
species (Table 4.13). Some ornamental and forest conifers are highly
susceptible, while many broadleaf forest and ornamental deciduous plants
are intermediate to resistant. Most important fruits and berries are at
least moderately susceptible, and some (e.g., peaches and blueberries)
are very susceptible to fluoride injury. There is disagreement on the
degree of susceptibility of some species or varieties (National Academy
of Sciences, 1971).
Common agricultural species used as indicators of fluoride pollution
include gladiolus, wine grapes, apricots, and ponderosa pines (Brewer,
1966). Nettle-leaf goosefoot (Chenopodium murale), chickweed (Stellaria
media), pigweed (Amaranthus retroflexus), and annual bluegrass (Poo. annua)
are weed species useful as indicators.
The concentration of fluoride in tissues showing toxic symptoms
varies with species (Table 4.6) (Brewer, 1966). With some exceptions,
little injury is expected in plants containing less than 20 ppm fluoride
or plants exposed to less than 0.2 ppb fluoride in air (Hill, 1969). In-
jury is shown in many species containing tissue levels of 20 to 200 ppm
fluoride and in species exposed to fumigation concentrations of 0.2 to 4
ppb fluoride. Some plants are not damaged at tissue fluoride concentra-
tions greater than 500 ppm (National Academy of Sciences, 1971). Various
factors determine the exact response occurring under field conditions;
these include environmental factors (light, water, and temperature), pol-
lutant form, and biological factors (species, developmental stage, and
age).
Severity of injury is not necessarily related to the fluoride content
of the tissue, although a certain minimum level of fluoride is required
before visible injury occurs. Examination of many species shows that there
is no relationship between the number of stomata per leaf and the suscept-
ibility of the species to hydrogen fluoride (Zimmerman and Hitchcock, 1956).
The leaf-fluoride content of different rose varieties exposed to 1 to 3
ppb hydrogen fluoride is not related to the severity of chlorosis or necro-
sis that develops (Brewer, Sutherland, and Guillemet, 1967). Extensive
work on the effects of fluorides on gladiolus showed that more resistant
varieties accumulate more fluoride in the leaves than susceptible varie-
ties (Hitchcock et al., 1971; Hitchcock, Zimmerman, and Coe, 1962). For
a given variety, a significant linear relationship exists between the
extent of tip burn and the concentration of fluoride. In mixed plantings
of the forage crops timothy (Phleum pratense L.) and red clover (TrifoHum
pvatense L.), high continuous hydrogen fluoride treatment produces severe
tip burn, marginal necrosis, chlorosis, and high tissue content of fluo-
ride. Intermittent exposure to hydrogen fluoride results in high tissue
levels of fluoride; however, tissue damage is not as extensive as with
continuous exposure to the same concentration. This suggests that detox-
ification might occur during the nonfumigation period. Injury, therefore,
is related to the manner of exposure and the concentrations experienced
during the life cycle.
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148
TABLE 4.13. SENSITIVITY OF SELECTED PLANTS TO FLUORIDE
Apricot, Chinese and Royal
Prunue armeniaca L.
Box elder
Acer negundo L.
Blueberry
Vaecinium sp.
Corn, sweet
Zea may a L.
Fir, Douglas
Paeudotauga taxi folia Brit.
Gladiolus
Gladiolus sp.
Apple, Delicious
Malue eylveetria Mill.
Apricot, Moorpark and Tilton
Prunua armeniaca L.
Arborvitae
Thuia sp.
Ash, green
FraxinuB penneylvanica var.
lanceolata Borkh.
Aspen, quaking
Populus tremuloidee Michx.
Aster
Aster sp.
Barley (young plants)
Hordewn vulgare L.
Cherry, Bing, Royal Ann
Prunua avium L.
Cherry, choke
Prunua virginiana L.
Chickweed
Ceraetium sp.
Clover, yellow
Melilotiia oflieinalia Lam.
Citrus (lemon, tangerine)
Citrus sp.
Geranium
Geranium sp.
Goldenrod
Solidago ap.
Ash, European mountain
Sorbue causuparia L.
Ash, Modesto
Fraxinue velutina Torr.
Asparagus
Aeparague sp.
Birch, cutleaf
Betula pendula var.
graoilie Roth.
Bridal wreath
Spiraea prunifolia Sieb.
and Zucc.
Burdock
Arctium sp.
Cherry, flowering
Prunua aerrata L.
Cotton
Goeaypium hirautum L.
Sensitive
Grape, European
Vitie vinifera L.
Grape, Oregon
Mahonia repene Don.
Larch, western
Larix occidantalie Nutt.
Peach (fruit)
Prunue peraioa Sieb. and
Zucc.
Pine, Eastern white, lodgepole.
Scotch, Mugho
Pinna atrobua L.,
Pinua contorta Dougl.,
Intermediate
Grape, Concord
Vitie lobrueca L.
Grapefruit (fruit)
Citrus paradiai Mact.
Grass, crab
Digitoria eanguinalia L. Scop.
Lamb's-quarters
Chenopodium album L.
Lilac
Syringa vulgarie L.
Linden, European
Filia cordata Mill.
Maple, hedge
Acer oampeetre L.
Maple, silver
Acer aaoaharinum L.
Mulberry, red
Mofua mbra L.
Narcissus
Narcioeue sp.
Nettle-leaf goosefoot
Chenopodium sp.
Orange
Citrus eineneia Oabeck
Peony
Poeonia sp.
Resistant
Current
Ptibee sp.
Elderberry
SambucuB sp.
Elm, American
UlmuB ameriaana L.
Juniper, most species
Juniperue sp.
Linden, American
Tilia americana L.
Pear
Pyrue aormunie L.
Pigweed
Amaranthua retroflexua L.
Plane tree
Platonua sp.
Plum, flowering
Prunue oeroeifera Enrh.
Pinua aylveatria L.,
Pinue mugho Turra.
Pine, ponderosa
Pinus ponderoaa Laws.
Plum, Bradshaw
Prunua domeatioa L.
Prune, Italian
Prunua domeatiea L.
Spruce, blue
Picca pungene Englm.
Tulip
Tulipa geeneriana L.
Poplar, Lombardy and Carolina
Populua nigra L. and Populua
eugenei Simon-Louis
Raspberry
Rubua idaaue t.
Rhododendron
Rhododendron sp.
Rose
Rosa odorata Sweet
Serviceberry
Amlanohier alnifolia Nutt
Sorghum
Sorghum vulgare Pera.
Spruce, white (young needles)
Picea glanca Moench, Voss.
Sumac, smooth
Rhua glabra L.
Sunflower
tielianthuB sp.
Violet
Viola sp.
Walnut, black
Juglans nigra L.
Walnut, English
Juglane regia L.
Yew
Taxue auepidata Sieb. and
Zucc.
Pyracantha
Pyraaantha sp.
Squash, summer
Curourbita pepo L.
Strawberry
Fragaria sp.
Tomato
Lycopersiaon eseulentum Mill.
Tree of heaven
Ailanthue altiseima L.
Virginia creeper
Parthenooieeue quinquefolia
Planch.
Willow, several species
Salix sp.
Wheat
Triticum sp.
Source: Adapted from Treshow and Pack, 1970, Table D-l, p.
the publisher.
D-3. Reprinted by permission of
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149
Atmospheric fluorides and root-absorbed fluorides can produce the
same symptoms (Brennan, Leone, and Daines, 1950). Brewer, Sutherland,
and Guillemet (1969) reported that sprays of sodium fluoride and hydrogen
fluoride produced toxic symptoms in citrus trees indistinguishable from
those produced by fumigations with hydrogen fluoride gas. Detached leaves
placed in fluoride solutions developed symptoms similar to those developed
through exposure to gaseous fluorides (Davison, Marsland, and Betts, 1974).
The percent of the leaf area injured was proportional to the fluoride con-
centration in the aqueous solution. The authors are currently evaluating
this method at the University of Newcastle (England) as a technique to
determine relative susceptibility among various species.
While specific symptoms produced by excessive fluoride exposure are
quite similar in many species, they are not unique and can be induced in
some species by disease or environmental stress (National Academy of Sci-
ences, 1971). For example, moisture stress can cause necrosis in leaf
margins, and manganese deficiency in peach, cherry, and citrus can cause
marginal chlorosis and necrosis. Treshow and Pack (1970) listed other
examples that mimic fluoride injury. It is difficult to prove that a
particular injury is due to fluoride exposure, especially in the field.
Adams (1963) discussed the problem of relating injury symptoms to causal
agents and presented modifications of Koch's postulates (originally used
to relate disease to a causal agent) as a guide for experiments designed
to determine causes of injuries.
Fluorides affect the water balance of plants. Tomato, buckwheat,
and peach wilt when treated with high concentrations of fluoride (50 to
400 ppm) in nutrient solutions (Leone et al., 1948; Prince et al., 1949).
At moderate fluoride levels (10 to 50 ppm), tip and marginal scorching
(necrosis) occurs. Citrus trees wilt when exposed to 100 ppm fluoride
in nutrient solution (Brewer et al., 1959). High fumigation concentra-
tions produce extensive abscission of leaves and young fruits of citrus
plants (MacLean et al., 1968). Wilting of the succulent portions of new
growth also occurs.
Poovaiah and Wiebe (1973) found that hydrogen fluoride fumigation
greatly reduces transpiration in soybean, producing partial stomatal
closure in 1 hr and complete closure within 4 hr. The transpiration rate
was greatly reduced by fumigation, whereas leaf temperature increased.
Halbwachs (1970) found that trees injured by fluoride exhibit a decrease
in suction tension with increasing leaf or needle injury. The suction
tension in trees with an uneven water balance declines abruptly in the
upper regions of the crown. Garrec, Plebin, and Lhoste (1975) demon-
strated that increased transpiration occurs in the region of corn leaves
undergoing necrosis. This effect is not unexpected, however, since
necrosis results in tissue disruption, including plasmolysis, leading to
decreased ability of tissues to regulate water loss.
Water status can affect the response of the plant to hydrogen fluo-
ride (Zimmerman and Hitchcock, 1956). Exposure to periodic wilting con-
ditions allowed tomato and sweet potato plants to be more resistant to
fluoride injury even though there was an ample water supply during the
-------
150
fumigation period. This result was not due to the amount of fluoride
absorbed, since tomato and corn plants exposed to periodic wilting con-
tained higher fluoride concentrations than the watered controls.
Fluoride-induced injury symptoms in plants are discussed further in
a report on injury symptoms observed in ten common crop species (Pack and
Sulzbach, 1976). Injury symptoms caused by other agents resembling fluo-
ride injury are discussed in Treshow and Pack (1970).
4.3.2.2 Histological Observations Microscopic observations of fluoride
injury are rare, and of the few observations made, most are of tissue
with extreme damage rather than tissue just beginning to show toxicity
symptoms. Treshow, Anderson, and Harner (1967) summarized Solberg's data
on the histological changes that occur in pine needles showing fluoride
injury. Phloem and xylem parenchyma become enlarged and distorted, fol-
lowed by granulation, vacuolation, and eventual collapse of the protoplasm.
The advancing region of collapsing mesophyll next to the necrotic zone is
only a few cells in thickness. Carlson (1973) observed that fluoride in-
jury in pine needles caused hypertrophy in phloem and transfusion paren-
chyma which led to collapse of xylem and phloem. Nuclear enlargement and
chlorophyll destruction also occurred. Pine needles from trees growing
near fluoride pollution sources or from low-dose fumigation experiments
showed hyperplasia and hypertrophy of phloem cells and resin duct occlu-
sion (Stewart, Treshow, and Harner, 1973). However, several other envi-
ronmental stresses can also produce similar histological responses.
In cotton (Gossypium hirsutum), fewer chloroplasts occur in mesophyll
cells of fluoride-treated leaves; the effect is more pronounced in spongy
than in palisade mesophyll cells (Timmermann, Applegate, and Engleman,
1970). Electron microscopy of Rubus hispidus explants cultured in the
presence of fluoride showed elongation of mitochondrial cristae and in-
creased density of the stroma (Pilet and Roland, 1972). The number of
free ribosomes diminished, and the endoplasmic reticulum dilated causing
formation of vesicles.
4.3.2.3 Fruit Disorders Fluoride exposure affects fruit production in
a number of species. Peaches exposed to atmospheric fluoride concentra-
tions too low to produce foliar symptoms developed a soft "suture red spot"
syndrome (Facteau and Wang, 1972; Treshow and Pack, 1970). The extent of
fruit injury is influenced by calcium and boron nutrition. Lime sprays
are effective in reducing the occurrence of soft suture (Thomas and Alther,
1966).
Exposure of strawberry plants to 0.55 to 10.4 yg of fluoride per
cubic meter produced deformed fruit, decreased the average fruit weight,
and reduced the proportion of flowers that set fruit (Pack, 1972). No
effect was found on the number of flowers formed. The data support the
author's contention that hydrogen fluoride affects fruiting in plants by
interfering with fertilization or seed development.
Tendergreen beans showed no foliar injury or consistent effects on
fruiting with continuous exposures (60 to 92 days) of 2.2 yg of hydrogen
-------
151
fluoride per cubic meter (Pack, 197l£>) . Chlorosis was observed with con-
tinuous exposures of 6.6 and 13.9 yg of fluoride per cubic meter. At 13.9
pg of fluoride per cubic meter, dry and wet weights of bean tops were not
affected; however, the number of fruits per plant, number of seeds per
fruit, and dry weight of fruit were all significantly decreased. Contin-
uous exposure to 2.1 yg of fluoride per cubic meter did not produce foli-
age symptoms but did increase the amount of starch found in a seed. Beans
grown in an atmosphere containing 2.1, 9.1, and 10.5 yg of fluoride per
cubic meter produced Fj. progeny that were less vigorous than controls
and had increased abnormalities of early trifoliate leaves (Pack, 1971a).
These effects appear related to the decreased starch content per seed or
decreased seed size. Fewer F3 generation plants had abnormalities; con-
sequently, the inheritability of such characteristics is in doubt.
Tomato plants exposed to high concentrations of hydrogen fluoride
produce small partially or completely seedless fruit. Plants on low cal-
cium budgets respond similarly. The combined effects of hydrogen fluoride
and low calcium appear additive; thus, fluoride apparently functions by
interfering with calcium metabolism. Supporting evidence is found in
experiments concerning the effects of hydrogen fluoride and low calcium
on germination of tomato and cucumber pollen (Sulzbach and Pack, 1972).
With low calcium (.15 mA/), 2.6 and 10.5 raM sodium fluoride inhibits tomato
pollen germination, but no fluoride inhibition is observed with higher
calcium concentrations. Similar observations occur with pollen from fumi-
gated plants. However, cucumber pollen germination is not inhibited at
concentrations of fluoride lower than 10.2 yg/m3, regardless of calcium
nutrition.
Fruit production decreased in citrus trees sprayed with aqueous
sodium fluoride, but no significant effects on fruit quality occurred
at doses designed to yield foliar fluoride concentrations of 75 and 150
ppm (Brewer, Sutherland, and Guillemet, 1969). Fluoride exposure also
caused necrosis, decreased tree growth, and smaller fruit yield. Most
reduction in yield probably resulted from fluoride exposure during spring
bloom and growth flush (Leonard and Graves, 1970, 1972). Extensive injury
decreased the fruit yield the next year even though the tree was not
exposed to additional atmospheric fluorides.
Examination of the fruiting response of ten important crop species
exposed to hydrogen fluoride in growth chambers showed that soybean was
the most sensitive (no seeds produced with continuous exposure of 0.64 yg
of fluoride per cubic meter) and cotton the least sensitive (no effects
at 8.0 yg of fluoride per cubic meter) (Pack and Sulzbach, 1976). The
order of decreasing sensitivity was soybean, bell pepper, sweet corn,
cucumber, pea, grain, sorghum, oat, wheat, barley, and cotton. Common
responses included fewer seeds per plant and smaller seed size. The
authors suggested that reduced seed production was due to the inhibition
of pollen germination or pollen tube growth.
Fewer data are available on fluoride injury to flowers (National
Academy of Sciences, 1971). Fluoride may reduce the number of flower buds
and size of the flower, change the flower color, and produce necrotic zones
-------
152
(lonescu, Serbanescu, and Pal, 1972). Treshow and Pack (1970) stated that
"flower petals are rarely injured in the field." However, petunia and
cyclamen flowers were cited as exceptions. Gladiolus flowers are resist-
ant to fluoride, even though their leaves are extremely sensitive. Cut
gladiolus flowers developed injury symptoms when exposed to about 1 ppm
fluoride in reservoir water (Marousky and Woltz, 1971). Flower develop-
ment was inhibited by hydrogen fluoride in pepper (4.5 yg/m3) and corn
(8.7 yg/m3) (Pack and Sulzbach, 1976).
4.3.2.4 Germination The effects of fluoride on seed germination are
reviewed by Thomas and Alther (1966). Germination is inhibited at higher
fluoride concentrations, although the extent of inhibition depends on
species and exposure time. For example, a 72-hr exposure of lentil seeds
to 1 mW and 10 wM sodium fluoride reduced germination to 75% and 5% of
control respectively. In some field experiments, increased germination
was observed after application of fluorides to the soil.
4.3.3 Effects of Fluoride on Growth and Productivity
4.3.3.1 Implications of Agriculture Weinstein and McCune (1971) dis-
cussed the effects of fluoride on agriculture (Figure 4.7). They noted
that effects on the quality of agricultural produce are easier to establish
than effects on quantity and that fluoride damage not only affects the
product directly but affects production costs as well. Even if product
quality or quantity is not affected, increased fluoride content in plants
ORNL-DWG 79-20900
EFFECT ON AGRICULTURE
I
DECREASED VALUE
OF PRODUCT
INCREASED COST ,
OF PRODUCTION
I
I
t
I
JL
EFFECTS ON QUANTITY
OF PRODUCT
EFFECTS ON QUALITY
OF PRODUCT
EFFECTS ON MARKETING
OF PRODUCT
INCREASED UNIT COST
INDIRECT EFFECTS OF
POLLUTANT
COST OF AMELIORATION
OR PREVENTION
DECREASED VALUE OF FACILITIES
AND EQUIPMENT
Figure 4.7. Possible effects of fluoride on agriculture. Source:
Adapted from Weinstein and McCune, 1971, Figure 1, p. 412. Reprinted by
permission of the publisher.
-------
153
may lead to fluorosis in animals consuming these plants. These concerns
are the impetus for studies relating atmospheric fluoride concentrations
to tissue fluoride concentrations, growth inhibition, and visible damage
symptoms symptoms that might decrease the quality of the plant product
or decrease plant productivity. Ultimately, such data could be used to
recommend air quality criteria.
In establishing air quality standards for fluoride, three different
criteria can be used: (1) the fluoride content of vegetation, (2) the
fluoride content of the atmosphere, and (3) vegetation markings (necrosis,
chlorosis, and other symptoms) (Hill, 1969). One should also consider that
(1) fluoride is an accumulative toxicant, and injury is usually associated
with long-term exposure; (2) gaseous and particulate fluorides differ in
their phytotoxicity; (3) plant species and varieties differ greatly in
susceptibility to fluoride; and (4) extremely low concentrations can cause
damage to sensitive species (Hill, 1969). Hill discussed the advantages
and problems of each approach and concluded that analysis for necrosis or
chlorosis (damage assessment) is the best approach because this reflects
the fluoride content in air. For a given area, species diversity, sensi-
tivity, and air-concentration-time relationships are all manifest in such
an assessment. However, Weinstein (1969) pointed out that examining the
extent of fluoride damage is a useful procedure for evaluating and recti-
fying the proposed standard, not implementing it. He believes that more
constant vigilance is necessary and that this could best be accomplished
through "use of a series of provisional time concentration values for
atmospheric fluorides which reasonably reflect the state of our present
knowledge, in conjunction with appropriate atmospheric sampling stations,
vegetation analysis, and periodic vegetation surveys." Obviously, air
standards cannot be determined without adequate information relating air
concentrations of fluoride to markings and fluoride accumulation in plants.
By considering the factors listed by Hill (1969) and accumulating data
concerning the relation of fluoride time-concentration exposure to injury
(growth reduction and visible symptoms), a set of air quality criteria
could be established for a given area with known species diversity. There
is consensus that such data are lacking at the present time. Treshow and
Pack (1970) noted the inability of investigators quantitatively to relate
the degree of injury in plants to fluoride concentrations in plant tissue
or in the air. Thus crop loss and injury can only be observed in the field
(i.e., after the fact). They concluded that knowledge of vegetation fluo-
ride levels is only useful to determine the effectiveness of air pollution
control programs. Considerable disagreement thus exists concerning what
criteria should be used to establish air quality standards. Furthermore,
the adopted concepts should not be restricted to agricultural systems but
should be extended to natural ecosystems as well.
Fluoride is an accumulative toxicant and injury in the field is
usually caused by the accumulation of fluoride over a period of several
weeks to several months. Unfortunately few long-term fumigation studies
have been conducted to determine the relationship between long-term expo-
sure and injury. Hill (1969) summarized his long-term exposure studies
as follows: "In the greenhouse, continuous exposure to hydrogen fluoride
-------
154
in the concentration range 0.4 to 0.6 ppb for several months will cause
severe injury to sensitive varieties of gladiolus, apricots, peaches,
and corn."
To summarize relationships between atmospheric fluoride concentrations
and injury, McCune (1969) presented log-log plots of the data from many
literature reports. For each species, mean concentrations of fluoride in
air are plotted on the ordinate and the duration of exposure is plotted on
the abscissa; in addition, an indication is made at each point whether
visible injury occurred, whether growth or yield was affected, and what
tissue fluoride concentrations were found. Figures 4.8-4.11 give results
for tomato, alfalfa, gladiolus, and sorghum respectively. Since the data
were gathered from diverse literature sources, a number of factors contrib-
ute to the uncertainty of establishing permissible air concentrations of
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-------
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by permission of the publisher.
-------
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from McCune, 1969, Figure 4, p. 17. Reprinted by permission of the
publisher.
-------
158
fluoride below which no effects are observed (McCune, 1969; National Acad-
emy of Sciences, 1971). In Figures 4.8-4.11, the dashed lines represent
maximum air concentrations of fluoride that cannot be exceeded during spe-
cified time intervals without causing plant injury. For tomato (Figure
4.8), line a represents limits above which foliar markings occur, whereas
line b represents limits above which reduction in quality or quantity of
tomato fruits occurs. For alfalfa (Figure 4.9), line a represents fluo-
ride concentrations in air above which leaf markings occur; line b repre-
sents concentrations which, if exceeded, would lead to the accumulation
of tissue fluoride greater than 35 ppm. (At the time of publication, 35
ppm was used as an air quality standard in Montana and New York.) For
gladiolus (Figure 4.10), a plant very susceptible to fluoride injury, the
line represents concentrations in air which, if exceeded, damage more than
5% of the leaf area. If damage greater than 10% occurs, there is a sig-
nificant reduction in flower and corn yields. The data plotted for sorghum
(Figure 4.11) illustrate the difficulty in establishing criteria. Lines
a and c represent levels in air that define vegetative markings and reduc-
tions in yield, respectively, in a fluoride-susceptible variety. Lines
b and d are similarly defined for a resistant variety.
* > '
One problem with the graphs presented by McCune is that the duration
of the exposure periods used for intermittent exposures is the sum of the
periods in which treatment took place, not the length of the entire expo-
sure period. It is difficult to use these curves for establishing stand-
dards or determining the relationship between ambient concentrations and
injury because the relationship in the field has to be based on average
concentrations (not just when the pollutant is blowing from the source)
over the total duration of the exposure period.
Modern studies of the effects of fluoride on growth and productivity
of agricultural plants are usually extrapolations of the results of exper-
imental fumigations to field situations. Large-scale field studies are
seldom made because of the difficulties of controlling variables, the un-
certainties of applying the results to other sites and crops, and the exces-
sive cost (Weinstein and McCune, 1971). However, field studies are still
occasionally performed to evaluate special environmental circumstances,
such as the presence of a fluoride-emitting factory. In one such study
made near Dresden, DMssler (1971) measured the yield of winter wheat as a
function of distance from a hydrofluoric acid factory. He observed reduc-
tions in yield of 12.5%, 21.6%, and 25.5% at distances of 2000 m, 1700 m,
and 1100 m, respectively, from the factory, compared with the yield at
2700 m. Emissions from the factory varied during the test but frequently
exceeded 10 ug of fluoride per cubic meter and occasionally exceeded 50 yg
of fluoride per cubic meter. Decreased yields or damaged fruit were also
observed at distances up to 6 km for fruit trees (particularly pear, sweet
cherry, apple, and plum) and tomatoes.
4.3.3.2 Fluorides and Pollution Fluoride content is increased in plants
growing in the vicinity of fluoride pollution sources, and as a result,
growth and productivity of these plants are inhibited. Because of the
extensive mining of large phosphate deposits in Florida (over 30 years)
and the subsequent release of fluoride to the atmosphere, vast citrus and
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159
gladiolus crops, as well as the truck crops in the area, have been damaged
(Thomas and Alther, 1966). The expansion of the aluminum industry in the
western United States and Canada has, likewise, produced significant fluo-
ride pollution in the surrounding area. Thomas and Alther (1966) cited
cases in California of industrial fluoride pollution damage to citrus
fruits and wine grapes. Pines and gladiolus in the northwestern United
States also have been damaged by fluorides produced from aluminum factor-
ies. Fluoride pollution from a phosphate reduction plant in Georgetown
Canyon, Idaho, killed about 200 acres of Douglas fir trees (Treshow,
Anderson, and Haraer, 1967). Needles from trees that eventually died
contained an average of 274 ppm fluoride, while needles from trees with
no visible symptoms of injury contained 150 ppm fluoride. Needles from
control area trees contained only 24 ppm fluoride.
Fluoride injury can occur over an extensive area. Conifers in an
area of about 69,000 acres in northwestern Montana showed fluoride damage
and contained greater than control levels of fluoride (Carlson, 1973).
Emissions from the Anaconda Aluminum Company smelter were determined to
be the source of the fluoride.
-
Gilbert (1973) reviewed the sensitivity of lichens to fluoride pol-
lution and documented several instances where industrial point squrces of
fluoride pollution resulted in the loss of lichen flora. Fluoride contents
of lichens may vary considerably, and the content can be decreased by wash-
ing or by rains. Toxicity symptoms include chlorosis and necrosis.
Only a few literature comments are available concerning the recovery
of woody plants after field exposure to high fluoride concentrations.
After a spill-related release of fluoride in New Jersey in May, peach trees
(completely defoliated) and Douglas firs recovered and appeared near normal
by August. Norway and blue spruce showed necrosis and abscission and did
not show regrowth; the buds did not emerge from their already dormant con-
dition. Needles of Austrian and Scotch pine did not abscise, but new
growth did not appear (Rhoads and Brennan, 1975) .
4.3.3.3 Growth Effects Concentrations of fluoride producing high tissue
fluoride concentrations and extensive leaf damage will also reduce the
growth of the plant (Thomas and Alther, 1966; Treshow, 1971). Numerous
examples of this behavior are reported. Linear growth enhancement occurs
in some plants at low fluoride concentrations. Fumigation of Koethen sweet
orange trees increased linear growth with no increase in leaf number, in-
dicating spindly growth (Matsushima and Brewer, 1972). Stimulation of
shoot growth with hydrogen fluoride fumigation (2 ppb) occurs in some rose
varieties; however, the stems were weak and therefore the plants were more
fragile (Brewer, Sutherland, and Guillemet, 1967). Hitchcock et al. (1971)
found that both the wet and dry weight of alfalfa and orchard grass in-
creased with fluoride exposure (six to eight days at the relatively high
levels of 16 to 17 yg of fluoride per cubic meter). Benedict, Ross, and
Wade (1964), however, found that alfalfa, orchard grass, chard, and romaine
lettuce showed no injury symptoms, no significant growth reduction, and no
enhancement when continuously fumigated at <1 yg/m3 for 80 to 120 days.
Treshow and Harner (1968) found significant increases in bean weight with
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160
fumigations of 2.3 yg of fluoride per cubic meter for 21 days. The prob-
lems of intermittent versus continuous exposure, exposure duration, and
species variability are discussed in Sections 4.2.4.1 and 4.3.3.1.
Another somewhat controversial type of injury discussed in the lit-
erature is hidden injury. Hidden or invisible injury to a plant caused
by a pollutant is defined as interference with growth and normal function-
ing without the appearance of visible lesions or symptoms (Thomas, 1958,
1961). This concept is of direct concern to agriculturalists interested
in optimizing plant yield because data must be obtained to determine if
such injury occurs with the levels of fluoride found in the environment.
Data supporting the hidden injury concept for fluorides are rare, however.
Hill (1969) summarized long-term studies as follows: in a ten-year-
greenhouse study, orchard grass, brome grass, alta fescue, alfalfa, red
clover, barley, onions, gladioli, celery, and other species were grown to
the normal harvest stage in filtered air, the ambient air near an indus-
trial plant, and hydrogen fluoride at concentrations well above those of
the ambient air. No growth reductions were measured except for gladiolus
where leaf destruction was severe. In similar studies with raspberries,
strawberries, corn, tomatoes, prunes, apricots, and peaches, insufficient
fruit was produced for reliable yield measurements, but determinations
were made of the overall plant growth, dry weight, terminal growth, girth,
number of runners, and other growth indices. The ambient atmosphere had
no effect on growth of these crops and hydrogen fluoride caused an effect
only when visible injury was produced.
Exposure of gladiolus, a sensitive plant, to low levels of fluoride
caused visible injury at the same rate as photosynthesis decreased (Table
4.14) (Thomas, 1958). Fumigation with higher concentrations of fluoride
produced a larger decrease in photosynthesis, but recovery occurred after
exposure, and the final decrease in photosynthesis was proportional to the
damaged leaf area. Fluorides that accumulated in the uninjured portions
of the leaf during exposure were translocated to the margins of the leaf
during the recovery period. Estimates of the extent of decrease in photo-
synthesis during high-exposure periods, not accountable by leaf area dam-
age, were only a few percent of the total photosynthesis of the crop.
Thus it appears that hidden injury does not occur in gladiolus. Hill
(1969) presented similar data for gladioli, strawberries, tomatoes, apri-
cots, and corn. He concluded that the treatment either did not have any
significant effect on apparent photosynthesis or the effect could be
accounted for by an equal amount of leaf necrosis. With corn, chlorotic
mottling developed rather than necrosis, and the measured reduction in
photosynthesis was attributed to reduced photosynthesis in the chlorotic
tissue. Hill et al. (1958) exposed tomatoes, a crop relatively resistant
to fluoride, to rather high airborne fluoride concentrations (1.8 to 6.5
yg/m9 for the Moscow variety and 3.4 to 73 yg/m9 for the Loran Blood vari-
ety) . This exposure caused high tissue levels of fluoride. No leaf symp-
toms were observed in Moscow tomatoes and only a trace to 2% leaf area
damage in the Loran Blood variety. No difference in respiration or in
average carbon dioxide assimilated per hour per plot was detected between
treatment and control plots. Consequently, the authors concluded that no
hidden injury occurred even with the high fluoride concentrations used.
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161
TABLE 4.14. EFFECT OF FUMIGATION WITH RELATIVELY LOW CONCENTRATIONS
OF HYDROGEN FLUORIDE ON THE PHOTOSYNTHESIS OF PLANTS
HF fumigation
Plane
Fruit trees
Gladiolus
Surfside
Alladin
Algonquin
Commander Koehl
Mixed grain
Cotton
Duration0
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162
Few data were found on the effects on plants exposed to combinations
of fluorides and other pollutants. Effects of hydrogen fluoride and sul-
fur dioxide were additive with respect to reduction of linear growth and
leaf area of Koethen orange and Satsuma mandarin (Matsushlma and Brewer,
1972). With the concentration of hydrogen fluoride and sulfur dioxide
used, necrosis did not occur on Koethen orange. Effects of sulfur diox-
ide and hydrogen fluoride on chlorosis in Satsuma mandarin were less than
additive. Bennett and Hill (1974) observed that the inhibition of photo-
synthesis in alfalfa by nitrogen dioxide plus hydrogen fluoride was addi-
tive; Inhibition with sulfur dioxide plus hydrogen fluoride was slightly
greater than additive. Both barley and sweet corn showed Increased foliar
damage when fumigated with hydrogen fluoride (approximately 0.00075 ppm)
plus low concentrations of sulfur dioxide (0.08 ppm) as compared with
either sulfur dioxide or hydrogen fluoride alone (Mandl, Weinsteln, and
Keveny, 1975). Beans were not injured at any of the concentrations used.
Fluoride accumulation by leaves of barley and corn was less for hydrogen
fluoride plus sulfur dioxide than for hydrogen fluoride alone, the result
possibly relating to the effectiveness of sulfur dioxide in producing
stomatal closure. Zimmerman and Hitchcock (1956) observed that some
species most susceptible to sulfur dioxide (chicory, eggplant, geranium,
pigweed, tobacco, dandelion, and celery) are resistant to hydrogen fluoride,
There are few data on the relationship between susceptibility of a
species to parasitic invasion and fluoride Injury of the species. Wentzel
(as cited in ten Houten, 1972) observed that fluoride-injured spruce con-
tained many more galls of the spruce-gall aphid than uninjured spruce.
Although an Injured plant is often thought to be more susceptible to Injury
from another agent, this Is not always the case. Examples with other
pollutants Illustrate that increased pollutant levels may decrease para-
sitic injury and that parasitic attack may decrease pollutant injury. Few
reports detail the Interactions between fluorides and parasites. Exposure
of bean plants to 7 to 10 ug of hydrogen fluoride per cubic meter reduced
the extent of infection with powdery mildew (McCune et al., 1973, as cited
in Treshow, 1975). Fluoride reduced the number of rust uredia found on
bean and reduced early blight of tomato caused by Alternaria eolani when
hydrogen fluoride fumigation occurred prior to inoculation with the fungus.
Fluorides did not affect the severity of halo blight caused by Peeudomonae
phaeeoUooluB or of late blight caused by Phytophthora infeetena.
Exposure of young pinto beans to fluorides increased viral activity
as tissue fluoride concentrations of cut leaves and intact plants increased
to about 300 ppm and 500 ppm respectively (Treshow, 1975). Above these
concentrations, virus activity decreased below control values. The extreme
variation observed in such lesion assays and the influence of environmental
factors make it unlikely that variations in virus infectlvity due to field
exposure of plants to fluorides could be detected.
4.3.4 Cytogenetic Effects
There is evidence that fluorides can be mutagenlc. Fumigation of
tomato plants with hydrogen fluoride at 3 ug/m3, a concentration that did
not produce visible injury until 11 days of exposure, induced chromosomal
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163
aberrations during mitosis and melosis (Mohamed, Smith, and Applegate,
1966). The aberrations observed were chromosomal bridges and fragments.
Solutions of 10 vcM sodium fluoride caused chromosomal breakage and stick-
iness In mltotlc cells of onion root tips (Mohamed, Applegate, and Smith,
1966). Fumigation of mlcrosporocytes from maize plants with 3 wg/m3 hydro-
gen fluoride produced no visible Injury, but the treated mlcrosporocytes
contained a higher frequency of asynaptic regions and total aberrations
than mlcrosporocytes from control plants (Mohamed, 1970). An increase In
aberrations occurred with Increased exposure to hydrogen fluoride (four-
to ten-day exposures). Contrary to experiments with onion and tomato,
hydrogen fluoride partially Inhibited cytokinesis In maize.
Root tip cells of germinating barley treated with sodium fluoride and
hydrogen fluoride at 10 mM, 0.1 mM, and 1 \iM showed several anomalies
chromosomal bridges with and without fragments, polyploid cells, binucleate
cells, ball metaphases, micronuclel, tripolar and multipolar anaphases,
and fusion of telophasic groups of chromosomes (Bale and Hart, 1973a).
Treatment of barley coleoptiles with 1%, 4%, or 6% sodium fluoride alone
or with dimethyl sulfoxide (DMSO) did not produce Injury symptoms or In-
hibit subsequent growth of the barley seedlings (Bale and Hart, 1973£>).
However, the incidence of chromosomal aberrations in the pollen mother
cells and percentage of pollen aborted from treated plants Increased with
fluoride concentration and was significantly greater than that from un-
treated plants. At low fluoride concentrations, DMSO increased the number
of abnormalities. No chlorophyll mutations were observed in the progeny,
suggesting that fluoride does not induce specific mutations. No chloro-
phyll mutations were observed in the M2 generation of barley obtained from
seed that had been soaked in 10 mW sodium fluoride (Jagannath and Bhatia,
1974). Fluoride did, however, significantly increase the mutagenic effects
of gamma radiation under aerobic conditions.
Increased exposure time (1 to 24 hr) and concentration of fluoride
(1 to 1000 ppm) produced increased mitotic and meiotic aberrations in
Vioia faba (Hakeem and Shehab, 1970). The abnormalities were similar to
those observed by Bale and Hart (1973
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164
SECTION 4
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77. McCune, D. C., A. E. Hitchcock, and L. H. Weinstein. 1966. Effect
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78. McCune, D. C., L. H. Weinstein, and J. F. Mancini. 1970. Effects
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-------
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80. Maclntire, W. H., and associates. 1949. Effects of Fluorine in
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83. McLaughlin, S. B., Jr., and R. L. Barnes. 1975. Effects of Fluo-
ride on Photosynthesis and Respiration of Some South-East American
Forest Trees. Environ. Pollut. 8:91-96.
84. MacLean, D. C., D. C. McCune, L. H. Weinstein, R. H. Mandl, and
G. N. Woodruff. 1968. Effects of Acute Hydrogen Fluoride and
Nitrogen Dioxide Exposures on Citrus and Ornamental Plants of
Central Florida. Environ. Sci. Technol. 2(6):444-449.
85. MacLean, D. C., 0. F. Roark, G. Folkerts, and R. E. Schneider.
1969. Influence of Mineral Nutrition on the Sensitivity of Tomato
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by Forage: Continuous vs. Intermittent Exposures to Hydrogen Fluo-
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87. MacLean, D. C., R. E. Schneider, and L. H. Weinstein. 1969. Accu-
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24:165-166.
88. McNulty, I. B., and J. L. Lords. 1960. Possible Explanation of
Fluoride-Induced Respiration in ChloveVla pyrenoidosa. Science
132:1553-1554.
89. Mandl, R. H., L. H. Weinstein, and M. Keveny. 1975. Effects of
Hydrogen Fluoride and Sulphur Dioxide Alone and in Combination on
Several Species of Plants. Environ. Pollut. 9:133-143.
90. Marousky, F. J., and S. S. Woltz. 1971. Effect of Fluoride and a
Floral Preservative on Quality of Cut Gladiolus. Proc. Fl. State
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91. Matsushima, J., and R. F. Brewer. 1972. Influence of Sulfur
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92. Miller, G. W. 1958. Properties of Enolase in Extracts from Pea
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-------
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93. Miller, G. W. 1972. General Discussion I: Fluoride Effects in
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London, and New York. pp. 118-121.
94. Miller, J. E., and G. W. Miller. 1974. Effects of Fluoride on
Mitochondrial Activity in Higher Plants. Physiol. Plant. 32:115-121.
95. Mohamed, A. H. 1970. Chromosomal Changes in Maize Induced by
Hydrogen Fluoride Gas. Can. J. Genet. Cytol. 12:614-620.
96. Mohamed, A. H., H. G. Applegate, and J. D. Smith. 1966. Cytolog-
ical Reactions Induced by Sodium Fluoride in Allium cepa Root Tip
Chromosomes. Can. J. Genet. Cytol. 8:241-244.
97. Mohamed, A. H., J. D. Smith, and H. G. Applegate. 1966. Cytolog-
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99. Oelrichs, P. B., and T. McEwan. 1961. Isolation of the Toxic
Principle in Acacia georginae. Nature (London) 190:808-809.
100. Oelschlager, W. 1972. Fluoride Uptake in Soil and Its Depletion.
Fluoride 4(2):80-84.
101. Ordin, L., and A. Altman. 1965. Inhibition of Phosphoglucomutase
Activity in Oat Coleoptiles by Air Pollutants. Physiol. Plant.
18:790-797.
102. Ordin, L., and B. P. Skoe. 1963. Inhibition of Metabolism in
Avena Coleoptile Tissue by Fluoride. Plant Physiol. 38:416-421.
103. Pack, M. R. 1966. Response of Tomato Fruiting to Hydrogen Fluoride
as Influenced by Calcium Nutrition. J. Air Pollut. Control Assoc.
16 (10):541-544.
104. Pack, M. R. 1971a. Effects of Hydrogen Fluoride on Bean Reproduc-
tion. J. Air Pollut. Control Assoc. 21(3):133-137.
105. Pack, M. R. 197lZ>. Effects of Hydrogen Fluoride on Production and
Organic Reserves of Bean Seed. Environ. Sci. Techno1. 5(11):1128-
1132.
106. Pack, M. R. 1972. Response of Strawberry Fruiting to Hydrogen
Fluoride Fumigation. J. Air Pollut. Control Assoc. 22(9):714-717.
107. Pack, M. R., and C. W. Sulzbach. 1976. Response of Plant Fruiting
to Hydrogen Fluoride Fumigation. Atmos. Environ. 10:73-81.
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172
108. Pack, M. R., and A. M. Wilson. 1967. Influence of Hydrogen Fluo-
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109. Peters, R. 1972a. Introduction. In: Carbon-Fluorine Compounds:
Chemistry, Biochemistry and Biological Activities. Elsevier,
Excerpta Medica, and North-Holland, Associated Scientific Publishers,
Amsterdam, London, and New York. pp. 1-7.
110. Peters, R. 19722?. Some Metabolic Aspects of Fluoroacetate Espe-
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Chemistry, Biochemistry and Biological Activities. Elsevier,
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112. Peters, R., and M. Shorthouse. 1964. Fluoride Metabolism in Plants.
Nature (London) 202:21-22.
113. Peters, R., and M. Shorthouse. 1967. Observations on the Metabolism
of Fluoride in Acacia geovginae and Some Other Plants. Nature
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114. Peters, R., and M. Shorthouse. 1971. Identification of a Volatile
Constituent Formed by Homogenates of Acacia georginae Exposed to
Fluoride. Nature (London) 231:123-124.
115. Pilet, P., and J. Roland. 1972. Effets Physiologiques et Ultra-
structuraux du fluor sur des tissus de Ronce cultives in vitro
(Ultrastructural and Physiological Effects of Fluoride on Bramble
Tissues Cultivated In Vitro). Ber. Schweiz. Bot. Ges. 82(3):
269-283.
116. Poovaiah, B. W., and H. H. Wiebe. 1971. Effects of Gaseous Hydro-
gen Fluoride on Oxidative Enzymes of Pelargonium zonale Leaves.
Phytopathology 61:1277-1279.
117. Poovaiah, B. W., and H. H. Wiebe. 1973. Influence of Hydrogen
Fluoride Fumigation on the Water Economy of Soybean Plants. Plant
Physiol. 51:396-399.
118. Preuss, P., R. Birkhahn, and E. D. Bergmann. 1970. The Effect of
Sodium Fluoride on the Growth and Metabolism of Tissue Cultures of
Acacia geovginae and Tomato. Isr. J. Bot. 19:609-619.
119. Preuss, P. W., A. G. Lemmens, and L. H. Weinsteln. 1968. Studies
on Fluoro-organic Compounds in Plants: I. Metabolism of 2-1AC-
Fluoroacetate. Contrib. Boyce Thompson Inst. 24:25-32.
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173
120. Preuss, P. W., and L. H. Weinstein. 1969. Studies on Fluoro-
organic Compounds in Plants: II. Defluorination of Fluoroacetate.
Contrib. Boyce Thompson Inst. 24:151-156.
121. Prince, A. L., F. E. Bear, E. G. Brennan, I. A. Leone, and R. H.
Daines. 1949. Fluorine: Its Toxicity to Plants and Its Control
in Soils. Soil Sci. 67:269-277.
121. Ramagopal, S., G. W. Welkie, and G. W. Miller. 1969. Fluoride
Injury of Wheat Roots and Calcium Nutrition. Plant Cell Physiol.
10:675-685.
122. Rhoads, A. F., and E. Brennan. 1975. Fluoride Damage to Woody
Vegetation in New Jersey in 1974. Plant Dis. Rep. 59:427-429.
123. Ross, C. W., H. H. Wiebe, G. W. Miller, and R. L. Hurst. 1968.
Respiratory Pathway, Flower Color, and Leaf Area of Gladiolus as
Factors in the Resistance to Fluoride Injury. Bot. Gaz. (Chicago)
129(l):49-52.
124. Stewart, D., M. Treshow, and F. M. Harner. 1973. Pathological
Anatomy of Conifer Needle Necrosis. Can. J. Bot. 51:983-988.
125. Suketa, Y., and T. Yamamoto. 1975. Effect of Atmospheric Fluoride
on Plants. Nippon Nogei Kagaku Kaishi 49:341-346.
126. Sulzbach, C. W., and M. R. Pack. 1972. Effects of Fluoride on
Pollen Germination, Pollen Tube Growth, and Fruit Development in
Tomato and Cucumber. Phytopathology 62:1247-1253.
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by Citrus Trees. Environ. Sci. Techno1. 1(8):644-650.
132. Timmermann, D., Jr., H. G. Applegate, and E. M. Engleman. 1970.
Macroscopic and Microscopic Response of Goaaypium hireutum L. to
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174
133. Treble, D. H., D.T.A. Lamport, and R. A. Peters. 1962. The Inhi-
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Biochem. J. 85:113-115.
134. Treshow, M. 1971. Fluorides as Air Pollutants Affecting Plants.
Annu. Rev. Phytopathol. 9:21-44.
135. Treshow, M. 1975. Air Pollutants and Plant Diseases. In: Re-
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136. Treshow, M., F. K. Anderson, and F. Harner. 1967. Responses of
Douglas-Fir to Elevated Atmospheric Fluorides. For. Sci. 13:114-120.
137. Treshow, M., and F. M. Harner. 1968. Growth Responses of Pinto
Bean and Alfalfa to Sublethal Fluoride Concentrations. Can. J.
Bot. 46:1207-1210.
138. Treshow, M., and M. R. Pack. 1970. Fluoride. In: Recognition
of Air Pollution Injury to Vegetation: A Pictorial Atlas, J. S.
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Pittsburgh, pp. D1-D17.
139. Vainshtein, E. A. 1973. Effect of Inhibitors on Respiration of
the Lichen Cetrcaria islandioa (L.) Ach. Sov. Plant Physiol. 19(4):
598-601.
140. van Hook, C. 1974. Fluoride Distribution in the Silverbow, Montana,
Area. Fluoride 7(4):181-199.
141. Vickery, B., and M. L. Vickery. 1972. Fluoride Metabolism in
Dichapetalum toxicarium. Phytochemistry 11:1905-1909.
142. Vickery, B., M. L. Vickery, and J. T. Ashu. 1973. Analysis of
Plants for Fluoroacetic Acids. Phytochemistry 12:145-147.
143. Wallis, W. J., G. W. Miller, M. Psenak, and J. Shieh. 1974. Fluo-
ride Effects on Chlorophyll Biosynthesis in Niaotiana tabaaum.
Fluoride 7(2):69-77.
144. Ward, P.F.V. 1972. General Discussion I: Fluoride Effects in
Higher Plants. In: Carbon-Fluorine Compounds: Chemistry, Bio-
chemistry and Biological Activities. Elsevier, Excerpta Medica,
and North-Holland, Associated Scientific Publishers, Amsterdam,
London, and New York. pp. 118-121.
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acetate by Plants. Biochem. J. 113:9P.
146. Weinstein, L. H. 1961. Effects of Atmospheric Fluoride on Meta-
bolic Constituents of Tomato and Bean Leaves. Contrib. Boyce
Thompson Inst. 21:215-231.
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175
147. Weinstein, L. H. 1969. Discussion of A. C. Hill's Paper on Air
Quality Standards for Fluoride Vegetation Effects. J. Air Pollut.
Control Assoc. 19:336.
148. Weinstein, L. H., and D. C. McCune. 1971. Effects of Fluoride on
Agriculture. J. Air Pollut. Control Assoc. 21(7) : 410-413.
149. Yang, S. F., and G. W. Miller. 1963a. Biochemical Studies on the
Effect of Fluoride on Higher Plants: 1. Metabolism of Carbo-
hydrates, Organic Acids, and Amino Acids. Biochem. J. 88:505-509.
150. Yang, S. F. , and G. W. Miller. 1963i. Biochemical Studies on the
Effect of Fluoride on Higher Plants: 2. The Effect of Fluoride
on Sucrose-Synthesizing Enzymes from Higher Plants. Biochim. J.
88:509-516.
151. Yang, S. F., and G. W. Miller. 1963e. Biochemical Studies on the
Effect of Fluoride on Higher Plants: 3. The Effect of Fluoride
on Dark Carbon Dioxide Fixation. Biochem. J. 88:517-522.
152. Yu, M. , and G. W. Miller. 1967. Effect of Fluoride on the Respir-
ation of Leaves from Higher Plants. Plant Cell Physiol. 8:483-493.
153. Yu, M. , and G. W. Miller. 1970. Gas Chromato graphic Identification
of Fluoroorganic Acids. Environ. Sci. Technol. 4(6) : 492-495.
154. Zimmerman, P. W. , and A. E. Hitchcock. 1956. Susceptibility of
Plants to Hydrofluoric Acid and Sulfur Dioxide Gases. Contrib.
Boyce Thompson Inst. 18:263-279.
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SECTION 5
BIOLOGICAL ASPECTS IN DOMESTIC AND WILD ANIMALS
5.1 SUMMARY
Animals are exposed to fluorides in various forms and concentrations
by ingestion of food and water, receiving only minimal amounts from the
atmosphere. Ingestion is the principal form of uptake by most animals.
Normally, inhalation and skin absorption contribute negligible amounts to
the total fluoride intake. In animals, fluorides accumulate in mineral-
ized tissues such as bones and teeth.
Mammals usually excrete fluorides rapidly from the body, with urinary
excretion accounting for the major portion of elimination. Small amounts
are excreted in feces, saliva, and perspiration. Both rapid elimination
and deposition of fluorides in mineralizing tissues provide methods of
reducing fluoride toxicosis.
Fluoride-induced effects in animals generally result from the inges-
tion of excessive amounts. Some specific enzymatic activity is inhibited
by excessive fluoride body levels. Impaired ability to metabolize fat
(suggesting fatty acid oxidase inhibition) may occur in animals with fluo-
ride toxicosis, and carbohydrate metabolism may also be altered. During
periods of excessive fluoride intake, bone alkaline phosphatase activity
increases.
Both inorganic and organic fluorides produce toxic effects in some
insects. General effects include lethal and sublethal toxicosis, decreased
reproduction, and changes in mutation frequencies.
Some aquatic organisms are sensitive to fluorides. This sensitivity
is related to environmental acclimatization and species. For example,
crustaceans are tolerant of high fluoride levels in seawater, while the
most sensitive aquatic organisms appear to be filter-feeding molluscs.
Environmental concentrations of less than 1.5 ppm do not seem to have
harmful effects on aquatic species.
Ingestion of excessive fluoride by birds induces a reduced growth
rate and inhibits specific enzymes such as neurotoxic esterase; however,
it enhances the activity of other enzymes such as plasma alkaline phos-
phatase. Both acute and chronic toxicity occur as a result of exposure
to excessive fluoride levels. Dental and bone lesions are the primary
clinical signs of chronic fluoride toxicosis. Loss of appetite and hem-
orrhages of the gastrointestinal tract are associated with acute fluoride
toxicosis.
In mammals, developing teeth are sensitive to fluoride. During the
formative stage, dental fluorosie is a major symptom of excessive fluoride
exposure. Bone lesions, lameness, and reduced feed intake are induced by
prolonged periods of high fluoride ingestion. Dairy cattle are the domes-
tic animals most sensitive to fluoride toxicosis. Therefore, fluoride
176
-------
177
levels that are safe for dairy cattle are considered safe for other spe-
cies of domestic livestock.
5.2 INSECTS
5.2.1 Metabolism
Data concerning the metabolism of fluoride-containing compounds by
insects are limited; most are found primarily in fluoride toxicology
studies.
5.2.1.1 Uptake Insects usually take up fluorides by ingestion. By
feeding on substances on which fluoride-containing compounds are depos-
ited or by cleaning itself of adhering fluoride compounds, an insect will
ingest varying quantities of these compounds. Some fluoride-containing
insecticides, such as sodium fluoride, are thought to be directly absorbed
by some insects through the membranous areas of the cuticle, at the junc-
tion of the head and thorax, and the coxa (Griffiths and Tauber, as cited
in Metcalf, 1966).
In tests designed to study fluoride uptake, eggs of Schistooerca
gvegapia and Ten&brio molitov were exposed at 30 °C to 11 ppm 33S-labeled
sulfuryl fluoride for 4, 8, 16, 24, 32, or 62 hr (Outram, 1967). Penetra-
tion was mainly through the micropylar complex in S. gvegapia eggs and
through the general surface of the chorion in T. tnolitor eggs. Both the
total uptake and irrecoverable fraction of the fumigant varied with the
stage of embryonic development (Figure 5.1). The rapid uptake pattern
for T. molitov eggs indicated that uptake was governed by the rate of
fixation of the fumigant in tissues, whereas the slower uptake of S.
gvegcaria eggs may have represented a toxicosis process of the embryonic
tissues.
240
§
180
tf
5 120
60
A ORNL-OWG 77- 21272
\ * 1
E?% S02F2 TAKEN UP
f~~| SOjF2 UNRECOVERED
_
~ S. GREGARIA
~ Y~
L!
M
1 ra-i ,
I
fy
{
r*
1 V^
T.MOLITOR 1
I
-
pv«
]:
S 12 2
AGE (days)
33(
Figure 5.1. The amount of 33SOaF2 present in the eggs of Schietocerca
gregaria and Tenebvio molitor at different stages of embryonic development.
Source: Adapted from Outram, 1967, Figure 2, p. 258. Reprinted by
permission of the publisher.
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178
5.2.1.2 Accumulation Dewey (1973) found fluoride accumulation in in-
sects collected near an aluminum reduction operation. Fluoride levels in
insects collected near the operation ranged from 2 to 20 times (pollina-
tors) as high as fluoride levels in control insects collected 50 miles
from the aluminum operation. Four groups of insects were collected: pol-
linators, predators, foliage feeders, and cambial-region feeders. Table
5.1 lists the fluoride levels found in control insects, and Table 5.2
lists the fluoride levels in test insects. High fluoride levels in the
predatory insects indicated that fluorides could be accumulated not only
from foliage feeding and by respiratory processes but through the food
chain.
No data were found concerning the distribution, half-life, or elimi-
nation of fluoride in insects.
TABLE 5.1. FLUORIDE LEVELS IN CONTROL INSECTS
Insect
Fluoride level
(ppm dry wt)a
Larch casebearer (Coleophora laricella) 16.5
Engraver beetle (Ipe sp.) 11.5
Honeybee (Apis mellifera L.) 10.5
Danselfly (Apgia sp.) 9.2
Grasshopper (Helanoplus sp.) 7.5
Bumblebee (BombuB sp.) 7.5
Red turpentine beetle (Dendroctcmue
valene LeConce) 4.8
Flatheaded borers (mixed Buprestldae) 3.5
Extract of whole Insect.
Source: Adapted from Dewey, 1973, Table 1, p. 180.
Reprinted by permission of the publisher.
5.2.2 Effects
5.2.2.1 Toxicity Fluoride compounds, such as sodium fluoride and iron
fluorides, have been used for insect control for the last 100 years
(Metcalf, 1966). Inorganic fluorides replaced arsenical insecticides for
agricultural uses; however, the use of inorganic fluorides has diminished
in recent years. Many organic fluoride-containing compounds, such as
fluoroacetic acid, fluoroethyl acetate, and methylsulfonyl fluoride, have
also proven to be effective insecticides (National Academy of Sciences,
1971). The effects of fluoride compounds on insects are general lethal
and sublethal toxicity, decreased reproduction, and changes in mutation
frequencies.
-------
179
TABLE 5.2. FLUORIDE LEVELS IN TEST INSECTS
T .. Fluoride level
Insect (ppm dry wt)a
Pollinators
Bumblebee (Bombus sp.) 194.0
406.0
Honeybee (Apis mellifera) 221.0
Mixed Hymenoptera 585.0
Sphinx moth (Hemarie sp.) 394.0
Wood nymph butterfly (Cercyanis sp.) 58.0
144.0
Skipper butterfly (Erynnie sp.) 146.0
81.3
Mixed Syrphidae 140.0
Predators
Ants (mixed Formicidae) 170.0
Robberfly (mixed Asilidae) 82.9
Ostomids (Temnochila sp.) 53.4
Dragonfly (mixed Anisoptera) 24.8
Damselfly (Argia sp.) 21.7
Long-legged fly (Medetema sp., larvae) 10.2
Ostomidae (larvae) 6.1
Foliage feeders
Arctiidae (larvae) 255.0
Notodontidae (larvae) 168.0
Weevil (mixed Curculionidae) 48.6
Grasshopper (Melonoplua sp.) 31.0
29.0
Larch casebearer (Coleophora laricella) 25.5
Cicada (Cicadidae) 21.3
Cambial region feeders
Engraver beetle (Ipa sp.) 52.5
Flatheaded borer (mixed Buprestidae) 20.0
Red turpentine beetle (Dendroctonue Valeria) 11.5
Douglas fir beetle (Dendroctonus
paeudotaugoe Hopkins) 9.4
Flatheaded borer (mixed Buprestidae, larvae) 8.5
Miscellaneous Insects
Long-horned beetle (mixed Cerambycidae) 47.5
Click beetle (mixed Elateridae) 36.0
Extract of whole insect.
Source: Adapted from Dewey, 1973, Table 2, p. 180.
Reprinted by permission of the publisher.
-------
180
5.2.2.1.1 General toxicity Sodium fluoride administered by Ingestlon
was toxic to Mcaneetva braeeicae caterpillars, Sootia segetum caterpillars,
larvae of Leptinotaraa deaemlineata, Lymantria dtepar caterpillars, and
Hyphantria ounea caterpillars (Weismann and SvataraTcova", 1974). The LD90
for each species, based on the milligrams of sodium fluoride administered
and the kilograms of living weight of the Insect, Is given in Table 5.3.
The most resistant insect was L. deoemlineata. The differences in sus-
ceptibility were attributed to the bonding of fluoride ions to calcium
to form insoluble calcium salts. In this manner, fluoride may have re-
stricted the function of calcium in the insect and Induced death. The
LTso for each insect Is given in Table 5.4.
TABLE 5.3. SODIUM FLUORIDE TOXICITY TO
SELECTED INSECT SPECIES
Ineact epeciii
Sootia ifffftun
Mamtitra
brattiaae
litptinotarta
Inater
V
IV
V
III
IV
Averege
weight
0.416
0.269
0.502
0.118
0.198
LD..
(g MeP)
0.078
0.027
0,0)2
0.031
0.0)0
LD../kg
living
weight
(g Ker)
187.)
102.7
103.6
262.7
2)2.)
TABLE 5.4.
Source! Adapted tram Uelemenn end Sveterlkovi, 1974,
Teble 1, p. 848.
LT,o VALUES COMPUTED FOR VARIOUS DOSES OF SODIUM FLUORIDE AND DEVELOPMENT
STAGES OF SELECTED INSECT SPECIES
ttmV
dose
consumed
("g)
0,25
0.1
0.05
0.025
LT*o value (daya)
Sootia
tegttum,
Inacar V
1.8
2.5
5.5
12.3
Mameetra broBtiaat
Inatar IV Inatar V
1.5
1.8 2.45
2.6 3.2
3,4 11.0
Ltptinotarta
dgoemlintata
Inatar III
1,75
2.45
2.15
3.1
Inetar TV
2.55
2.7
3.15
4.6
aicnea,
Inatar V
1.7
4.6
9.2
Lymantrta
tHepar,
Inatar V
1.8
5.6
10.3
Source: Adapted from Weienann and Svatarfkovf, 1974, Table 2, p. 849.
The uptake of 0.1 mg of sodium fluoride by 8. eegetwn caused a
decrease in food uptake, movement reduction, shrinking, body blackening,
and finally death (Weismann and Svatara'kova', 1973). The average life
span of the caterpillar decreased in proportion to the sodium fluoride
level administered. Sodium fluoride was shown to be an effective stomach
poison as well as contact poison for the American roach (Periplaneta
amevioand) (Sweetman, 1941).
-------
181
Sulfuryl fluoride was an effective Insecticide for drywood termites
(Cvyptotermee brevie); temperature Influenced the toxlclty level causing
a higher mortality rate at 80°P than at 70°F (Table 5.5) (Bess, 1971).
Minnick, Kerr, and Wilkinson (1972) also reported that sulfuryl fluoride
was an effective control for C. brevie.
TABtE 5.5. MORTALITY OP CmfPTOTERMES BREVIS EXPOSED TO SULPURYL FLUORIDE FOR 3 hr
IN TEMPERATURE-CONTROLLED FUMIGATION CHAMBERS
7.5
9.0
10.5
11.5
12.0
14.0
8.0-10.0
11.5-12.0
13.0-13.5
15.5-16.0
17.5-19.0
0 (control*)
Exposed In microscope did* cage*
Exposed in sealed block cages
Dosage
(or/1000 ft')
Number of
termites
In tests
Number of
termites
dead after
5 dsys
Mortality
00
Number of
termites
In testa
Number of
termites
dead after
5 days
Mortality
(2)
247
348
248
100
247
98
198
198
199
299
200
348
Exposure data at 80*F
7
79
191
89
238
97
3
23
77
89
96
99
20
49
80
30
80
30
Exposure data at 70*F
4
37
102
178
197
2
19
51
60
98
206
1
11
16
6
37
18
5
22
20
20
46
60
Source;
publisher.
Adapted from Bess. 1971, Table 1, p. 12. Reprinted by permission of the
The toxlcity of various fluorine compounds to Borribyx mori and Apia
mellifeva is presented In Table 5.6. The Insectlcldal properties of these
compounds apparently depend on their fluorine content (Metcalf, 1966).
These and other inorganic fluorine compounds act principally as stomach
poisons, owing their activity to inhibition of magnesium-containing
enzymes by fluoride Ions.
Many organofluorlne compounds are effective insecticides. According
to Metcalf (1966), these organic compounds act in one of three ways: (1)
as a blocking atom that mimics hydrogen but does not take part in enzymatic
reaction, (2) as a reactive,atom that permits the compound to react with
a vital enzyme, and (3) as a halogen providing a stable llpophillc group
with an aliphatic or aromatic nucleus. Various organofluorine compounds
containing phosphorus (Josh! and Tholia, 1973) and a,a,a-trlfluoroaceto-
phenone oxlme carbamates (Rosenfeld and Kilshelmer, 1974) have insectlcldal
activity. Under experimental conditions, fluoroacetamlde was more toxic
against Aphis fdboe, Breviooryne broeeicae, Myzue pereicae, and the eggs
and larvae of Pierte braee-tcae than sodium fluoroacetate (David and
-------
182
TABLE 5.6. TOXICITY OF INORGANIC FLUORINE
COMPOUNDS TO BOMBYX MOEJ AND
APIS MELLIFERA
Oral LDSO (vg/g)
Compound
NaF
CaF2
MgF2
MnFa
PbF2
NaaSiFg
KaSiF6
BaSiF6
Na3AlF6
K3A1F«
(NH<.),A1F6
Bonibyx mori,
4th instar
110-150
>570
200-400
250-400
100-130
70-100
90-120
50-70
80-100
110-140
Apis
mellifera
60-70
>540
240
50
60-70
60-70
Source: Adapted from Metcalf, 1966,
Table 1, p. 356. Reprinted by permission
of the publisher.
Gardiner, 1958). A 0.001% solution of fluoroacetamide produced a 100%
kill of A. fabae and B. bvaseiaae. As a systemic insecticide, fluoro-
acetamide was as effective as or slightly superior to sodium fluoroacetate;
the LDjtoo in milligrams per kilogram of fresh plant weight for A. fdbae
was 0.09 to 0.9 for fluoroacetamide and 0.7 for sodium fluoroacetate.
5.2.2.1.2 Reproduction When insects are exposed to poisons there may be,
depending on the concentration of the poison and the length of exposure,
an inhibition or a stimulation in egg production. A seven-day exposure
of Tribolium confusion to flour containing 0.01% sodium fluoride produced
stimulation of egg production (Johansson and Johansson, 1972). However,
egg production was adversely affected by prolonged exposure to flour con-
taining 0.1% sodium fluoride (Table 5.7). Total egg production per female
exposed to flour containing 1% sodium fluoride for two and four days was
significantly greater than that of the nonexposed controls. However, egg
production was decreased in female insects exposed for six days.
Gerdes, Smith, and Applegate (1971) exposed two strains of Drosaphila
melanogastev to 1.3 and 2.9 ppm hydrogen fluoride. Fecundity, hatchabil-
ity, and male fertility were evaluated in adults raised from these eggs.
All three of these parameters were reduced in the flies (Table 5.8), but
there was no reduction in female fertility. Reduction of these parameters
in D. melanogaster exposed to sublethal levels of hydrogen fluoride may
be a result of genetic damage caused by the fluoride.
5.2.2.1.3 Mutagenicity Various fluoride compounds are mutagenic to
Drosophila, causing recessive sex-linked mutations. Garret and Fuerst
-------
183
TABLE 5.7. EGG PRODUCTION BY TRIBOLIUM CONFUSUM PER FIVE-DAY
INTERVAL AFTER EXPOSURE TO SODIUM FLUORIDE LEVELS VARYING
FROM 0 TO 0.1Z
NaF level (Z)
Mean number of eggs per female
Days
1-7
Days
7-27
Days
7-12
Days
13-17
Days
18-22
Days
23-27
Mean total
22.2
25.2
24.0
22.0
93.4 ab
Treatment A
0.0001
0.001
0.01
0.1
0.0001
0.001
0.01
0.1
23.7
18.9
19.6
13.9
24.3
23.8
24.4
20.9
27.
25,
26,
24.7
25.8
26.3
30.6
25.3
101.5 be
94.4 abc
101.3 be
84.8 a
Treatment B
0
0
0
0
0.0001
0.001
0.01
0.1
22.2
20.2
22.3
9.1
22.3
23.0
25.6
12.4
21.
24.
26.
15.4
22.3
25.2
26.1
17.7
87.9 a
93.1 ab
100.4 be
54.6
Treatment C
0.0001
0.001
0.01
0.1
0
0
0
0
27.7
26.0
27.0
10.7
29.1
29.5
28.0
28.0
24.5
25.5
31.5
28.5
25.9
26.7
30.4
28.3
107.2 c
107.7 c
116.9
95.5 abc
followed by one or more of the same letters are not
significantly different from one another.
Source: Adapted from Johansson and Johansson, 1972, Table 1,
p. 357. Reprinted by permission of the publisher.
TABLE 5.8. MEAN VALUES OF BIOLOGICAL PARAMETER RESPONSE IN DROSOPHILA MELANOGASTER
TO ATMOSPHERIC CONTAMINATION BY HYDROGEN FLUORIDE
Treatment
duration
(weeks)
0
3
6
HF
level
(ppm)
0
1.3
2.9
0
1.3
2.9
0
1.3
2.9
Fecundity"
Oregon-r
280
280
293
286
242
222
289
196
192
Yellow
white
262
271
268
261
241
225
270
212
198
Hatchability*
Oregon-r
82
79
78
79.5
71
73
79
74
65.5
Yellow
white
79.5
79
75.5
76
70.5
71
78
71
61
Male fertility"
Oregon-r
100
100
99
100
98.5
97
100
99
92
Yellow
white
100
99
99
99
97
93
100
96
91
14).
Tlean number of eggs from seven egg collections (days 2, 3, 6, 7, 10, 11, and
Mean percentage from four egg collections (days 2, 6, 10, and 14).
Mean percentage.
Source: Adapted from Gerdes, Smith, and Applegate, 1971, Table 1, p. 118.
Reprinted by permission of the publisher.
-------
184
(1974) reported a significant increase in sex-linked recessive lethal
mutations in D. melanogastev when exposed to perfluorobutene-2; fluoroform;
1,1-difluoroethane; and sulfurchloridopentafluoride. Perfluorobutene-2
produced a recessive mutation rate of 1.78%, compared to a rate of 0.25%
for the control. The mutagenic effects of perfluorobutene-2 in combina-
tion with oxygen, carbon dioxide, nitrogen, and compressed air were also
tested. These results are given in Table 5.9.
TABLE 5.9. RECESSIVE MUTATION RATE IN DROSOPHTLA MELANOGASTER EXPOSED TO PERFLUOROBUTENE-2
AND PERFLUOROBUTENE-2 IN COMBINATION WITH OXYGEN, CARBON DIOXIDE,
NITROGEN, AND COMPRESSED AIR
Gas introduced
Gas atmosphere
Recessive mutation
rate CO
None (atmospheric air control)
Compressed air
Perfluorobutene-2
50% perfluorobutene-2
Oxygen
50% perfluorobutene-2, 50% oxygen
Nitrogen
50% perfluorobutene-2, 50% nitrogen
Carbon dioxide
50% perfluorobutene-2, 50% carbon dioxide
100% air 0.21 ± 0
100% air 0.25 ± 0.05
10% perfluorobutene-2, 1.78 ± 0.02
90% air
5% perfluorobutene-2, 1.01 ± 0.04
95% air
10% oxygen, 90% air 0.72+0.04
5% perfluorobutene-2, 5% 1.23 ± 0.05
oxygen, 90% air
10% nitrogen, 90% air 0.31 ± 0.04
5% perfluorobutene-2, 5% 1.03 ± 0.04
nitrogen, 90% air
10% carbon dioxide, 90% air 0.29+0.05
5% perfluorobutene-2, 5% 0.91 ± 0.02
carbon dioxide, 90% air
aThe gases were introduced into 100-ml Turner bulbs containing the flies in air at a
flow rate of 13 ml/mln, which was monitored by Matheson flowmeters. The Droeophila males
were gassed for 1 min and then kept in the gas atmosphere for 6 rain.
Source: Adapted from Garrett and Fuerst, 1974, Table 2, p. 291. Reprinted by permis-
sion of the publisher.
Repair of radiation damage in Droaophila is influenced by sodium
fluoride. Valentin (1971) injected Droscphila. with 5-wM and 10-mA/ solu-
tions of sodium fluoride. A complex response pattern resulted in which
both increases and decreases of recombination occurred. Ivashchenko,
Grozdova, and Kholikova (1971) also found that sodium fluoride changed
the frequency of lethal and sublethal mutations in Droeaphila when they
were irradiated. In the cases where irradiation occurred in air, the
change in mutation frequency took place at the stage of mature germ cells.
Injection of 0.15 mg of sodium fluoride per fly lowered the frequency of
lethal mutations and increased the frequency of sublethal mutations.
-------
185
5.3 AQUATIC ORGANISMS
5.3.1 Metabolism
5.3.1.1 Uptake Aquatic organisms can obtain fluoride by ingestion of
high-fluoridecontaining foods (Wright and Davison, 1975). However, fluo-
ride ions can also enter fish through fluoride-permeable gills (Bielawski,
1971). Hemens and Warwick (1972) stated that the mullet Mugil cephalus,
the crab Tylodiplax bZephariskios, and the shrimp Palaeman pacificus take
up fluoride mainly from water, not from foods.
5.3.1.2 Accumulation and Distribution Mullet, crab, and shrimp exposed
for 72 days to 52 ppm fluoride, added as sodium fluoride to the water, had
a higher fluoride tissue concentration than the control organisms exposed
to 1.05 ppm fluoride (Hemens and Warwick, 1972). Mullet accumulated the
highest concentration at 7743 ppm fluoride; the control mullet had 141.8
ppm fluoride. Shrimp accumulated 3116 ppm fluoride, and the mud crab
accumulated 1414 ppm fluoride. The control groups accumulated 106 ppm
and 169.6 ppm respectively.
Fluoride concentration in muscle tissues of carp (Cypinnus earpio)
and rainbow trout (Salmo gaivdneri) varied with the fluoride concentra-
tion (0.1 to 25 ppm) in the water in which the fish were placed (Neuhold
and Sigler, I960). High fluoride levels in water produced fluoride tis-
sue levels of 20.83 ppm, whereas low fluoride water levels gave fluoride
tissue concentrations of 2.95 ppm. Fluoride levels in the osseous tis-
sues were related to the fluoride water concentrations and the length of
exposure. Fluoride accumulation by bone was assumed to result from an
enzymatic process. Fluorides tend to occur in fish blood in both an un-
associated ionic form and associated with another ion or molecule. Because
of its high electronegativity the fluoride ion is more likely to be asso-
ciated with the electropositive elements.
Blue crabs (Cal'l'in&cteB sapidus) from relatively unpolluted water
(0.5 to 1.5 ppm fluoride) contained fluoride levels that varied for the
different kinds of tissues sampled (Table 5.10) (Moore, 1971). Gills
were the only tissue that showed a significant difference in the amount
of fluoride accumulated between large and small crabs; a possible accumu-
lation mechanism associated with the gills may be responsible for this
difference. The exoskeleton, gills, hepatopancreas, and muscle tissues
all accumulated significant amounts of fluoride in crabs exposed to water
containing 20 and 100 ppm fluoride for 90 days, 200 ppm for 22 days, and
400 ppm for 70 days. Crab muscle tissue accumulated 50 ppm fluoride (dry
weight) when exposed to water containing 20 ppm fluoride. This behavior
indicates that crab muscle can accumulate sufficient fluoride from pol-
luted water to be a potential health problem for humans if ingested at
a higher rate. Over a 20-day period in fluoride-free water following a
30-day exposure time, tissues readily released accumulated fluoride and
most returned to near normal tissue levels (Figure 5.2).
-------
186
TABLE 5.10. FLUORIDE CONCENTRATIONS IN DRIED
TISSUES OF CRABS FROM NATURAL, UNPOLLUTED WATERS
Fluoride concentration (ppm)
Tissue
Exoskeleton
Average
Gills
Average
Hepatopancreas
Average
Muscle
Average
Small crabs
(53-81 mm)
267
272
319
295
290
288.6
158
180
145
174
165
164.4
20
15
21
18
23
19.4
13
8
10
10
12
10.6
Large crabs
(100-117 mm)
300
325
300
310
256
298.2
210
225
280
190
360
253.0
28
20
20
24
18
22.0
10
16
7
9
8
10.0
Source: Adapted from Moore, 1971, Table 1,
p. 5. Reprinted by permission of the publisher.
In other studies, fluoride accumulated in the skeleton and skin of
fish and the exoskeleton of aquatic invertebrates (Wright and Davison,
1974). Tissue and seawater samples were taken from the inflow filter at
a power station in England and from offshore points several kilometers
away from the plant. In fish bone, fluoride deposition was thought to
occur by fluoride-anion exchange in the hydroxyapatite complex. In exo-
skeletons, the process of fluoride accumulation was by calcium fluoride
precipitation. A comparison of fluoride levels in fish taken from the
inflow filter and off shore indicated that there were no differences in
fluoride concentrations; however, variability of the data was too large
to make the comparison significant (Wright and Davison, 1975). Tissue
fluoride concentrations for the species sampled are presented in Table
5.11. Fluoride accumulated rapidly in tissues of the mollusc Mytilus
eduHs, probably because of the large turnover of seawater and suspended
particles containing fluoride. Shore crabs (CarainuB maenas') exposed to
various fluoride concentrations accumulated fluoride in proportion to
the fluoride level of the seawater (Figure 5.3).
5.3.1.3 Excretion Very little information is available concerning
excretion of fluoride by aquatic organisms. Neuhold and Sigler (1960)
-------
187
ORM.-OWG 7V-Z090Z
3500
0 10 20 30 10 20
DAYS IN DAYS OUT
FLUORIDE OF FLUORIDE
40 20
DAYS IN
FLUORIDE
30 10 20
DAYS OUT
OF FLUORIDE
Figure 5.2. Uptake and removal of fluoride from the (a) exoskeleton,
(2?) gills, (c) hepatopancreas, and (d) muscle tissue of crabs exposed to
0.5, 2.0, 8.0, 32.0, and 128.0 ppm fluoride. Source: Adapted from Moore,
1971, Figures 3-6, pp. 6-8. Reprinted by permission of the publisher.
reported that fluoride excretion is accomplished through the kidneys or
the respiratory epithelium in carp and rainbow trout. Such elimination
is probably the main defense mechanism of these species against fluoride
toxicosis. The mucous cells of carp and rainbow trout are morphologically
similar to chloride-secreting cells found in other fish and may function
as fluoride-secreting cells.
-------
188
TABLE 5.11.
FLUORIDE ANALYSIS OF TISSUES FROM AQUATIC SPECIES COLLECTED FROM LYNEMOUTH POWER
STATION (ENGLAND) INFLOW FILTER AND FROM OFFSHORE SITES
Species Location Tissue
Cod (Gadua morhua) Inflow filter Axial skeleton
Skin
Liver
Kidney
Stomach wall
Muscle
Blyth Bay Gill
Axial skeleton
Skin
Gonad
Liver
Kidney
Stomach wall
Muscle
Fat body
Blood
Haddock (.Gadue Inflow filter Axial skeleton
aeglefinue)
Gill bar
Skin
Liver
Stomach wall
Muscle
Blyth Bay Gill
Axial skeleton
Skin
Gonad
Liver
Kidney
Stomach wall
Muscle
Fat body
Blood
Sprat (Clupea eprattua) Inflow filter Axial skeleton
Skin
Month of
collection
December, 1972
January, 1973
February, 1973
March, 1973
December, 1972
January, 1973
February, 1973
March, 1973
December, 1972
January, 1973
February, 1973
March, 1973
January, 1973
December, 1972
January, 1973
February, 1973
March, 1973
December, 1972
January, 1973
February, 1973
March, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
November, 1972
January, 1973
November, 1972
November, 1972
January, 1973
November, 1972
January, 1973
November, 1972
January, 1973
November, 1972
January, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
October, 1972
November, 1972
December, 1972
January, 1973
March. 1973
October, 1972
November, 1972
December, 1972
January, 1973
March, 1973
Fluoride
concentration
(ppm wet wt i
std deviation)0
42.8 ± 17.1 (3)
69.3 ± 67.1 (4)
20.0 (1)
37.1 (2)
13.3 ± 7.2 (3)
21.6 ± 5.8 (4)
35.6 (1)
27.4 (2)
2.2 ± 0.1 (3)
4.6 ± 4.3 (4)
0.9 (1)
2.9 (2)
2.2 (2)
2.5 ± 1.5 (3)
3.6 ± 2.1 (4)
3.6 (1)
3.1 (2)
1.0 ± 0.6 (3)
3.4 ± 1.6 (4)
0.5 (1)
2.5 (2)
2.1 ± 1.5 (5)
23.9 ± 4.9 (5)
29.6 i 19.2 (5)
2.8 ± 1.9 (5)
1.2 ± 1.9 (5)
2.1 ± 2.3 (5)
19.2 ± 35.2 (5)
1.7 ± 1.0 (5)
0.9 ± 0.6 (5)
<0.2
18.2 (1)
60.4 (1)
100.4 (1)
74.3 (1)
15.5 (1)
4.0 (1)
1.9 (1)
2.0 (1)
2.0 (1)
3.7 (1)
2.2 (1)
5.7 ± 2.9 (3)
49.3 ± 24.4 (3)
37.0 ± 13.12 (3)
1.5 ± 0.8 (3)
0.2 ± 0.1 (3)
0.6 ± 0.7 (3)
3.6 ± 1.6 (3)
1.8 ± 0.7 (3)
0.5 (2)
55.1 ± 20.0 (4)
52.8 4 35.5 (3)
52.5 ± 37.1 (3)
52.2 ± 27.4 (3)
48.5 ± 19.1 (4)
22.8 t 12.9 (4)
21.3 ± 12.1 (3)
10.8 ±1.1 (3)
18.7 i 12.2 (3)
14.2 ± 6.9 (4)
-------
189
TABLE 5.11 (continued)
Species
Flounder (Pleuronectee
fleaue)
Lumpsucker (Cyclopterue
lumpua)
Dab (Pleuronectee
Umonetd)
Shore crabs (Corcinua
noenoa')
Location Tissue
Muscle
Inflow filter Axial skeleton
Skin
Liver
Stomach wall
Muscle
Inflow filter Axial skeleton
Skin
Liver
Kidney
Stomach wall
Muscle
Inflow filter Axial skeleton
Skin
Liver
Stomach wall
Muscle
Blyth Bay Gill
Axial skeleton
Skin
Gonad
Liver
Kidney
Stomach wall
Muscle
Fat body
Blood
Cresswell Skeleton (carapace)
Skeleton (leg)
Month of
collection
October, 1972
November, 1972
December, 1972
January. 1973
March, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
December, 1972
January, 1973
March, 1973
December, 1972
January, 1973
March, 1973
December, 1972
January, 1973
March, 1973
December, 1972
January, 1973
March, 1973
December. 1972
January, 1973
March, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
December, 1972
January, 1973
May. 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
May, 1973
October, 1972
November, 1972
December, 1972
January, 1973
February, 1973
March, 1973
April, 1973
October, 1972
December, 1972
January, 1973
Fluoride
concentration
(ppm wet wt ±
std deviation)
5.2 ± 0.9 (A)
4.9 ± 3.4 (3)
2.7 ± 1.7 (3)
3.6 t 2.2 (3)
4.7 ± 1.9 (4)
19.9 (1)
48.7 (1)
11.6 (1)
10.6 (1)
1.3 (1)
4.2 (1)
1.1 (1)
16.0 (1)
1.7 (1)
1.8 (1)
30.7 (1)
34.3 (1)
34.0 (1)
12.0 (1)
6.2 (1)
2.2 (1)
3.2 (1)
1.5 (1)
3.1 (1)
3.2 (1)
2.3 (1)
4.5 (1)
5.6 (1)
6.0 (1)
15.1 (1)
4.7 (1)
51.2 (1)
60.6 (1)
17.8 (1)
21.2 (1)
1.6 (1)
0.9 (1)
2.8 (1)
2.2 (1)
1.0 (1)
2.4 (1)
1.9 ± 1.5 (3)
99.7 ± 112.3 (3)
52.2 ± 10.2 (3)
1.4 ± 0.6 (3)
2.5 (2)
4.1 i 2.2 (3)
1.0 i 0.2 (3)
14.2 ± 6.0
15.4 ± 8.3
14.4 ± 4.7
16.3 ± 9.7
4.6 ± 1.8
7.4 ± 1.5
6.6 ± 7.2
11.4 ± 3.7
15.0 ± 3.9
15.0 ± 3.9
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190
TABLE 5.11 (continued)
Species
Swimming crab (Portunua
depurator)
Shrimp (.Crangan
vulgaria)
Pravm (Leander
eerratue)
Location Tissue
Gill
Gonad
Hepatopancreas
Muscle
Whole animal
Inflow filter Exoskeleton (carapace
and leg)
Muscle
Whole animal
Inflow filter Exoskeleton (carapace
and leg)
Muscle
Whole animal
Inflow filter Exoskeleton (carapace
and leg)
Muscle
Whole animal
Month, of
collection
October, 1972
November, 1972
December, 1972
January, 1973
February, 1973
March, 1973
April, 1973
October, 1972
November, 1972
December, 1972
January, 1973
March, 1973
April, 1973
October, 1972
November, 1972
December, 1972
January, 1973
March, 1973
April, 1973
October, 1972
November, 1972
December. 1972
January, 1973
February, 1973
March, 1973
April, 1973
October. 1972
November, 1972
December, 1972
January, 1973
February, 1973
March, 1973
April, 1973
June, 1973
June, 1973
October, 1972
June, 1973
October, 1972
June, 1973
October, 1972
June, 1973
October, 1972
June, 1973
June, 1973
June, 1973
October, 1972
June, 1973
Fluoride
concentration
(ppm wet wt ±
std deviation)0
3.2 2.5
1.2
2.0
3.3
1.1
1.1
0.8
1.6
2.5
2.0
1.0
0.8
1.7
2.2
2.1
1.7
1.6
0.8
1.5
1.5
3.5
1.0
2.1
2.0
1.6
2.7
5.0
2.3
0.9
0.9
0.5
0.7
0.6
1.3
1.4
0.8
1.0
0.2
0.6
1.4
2.1
0.8
1.51
0.1
0.7
0.7
3.0
0.3
1.5
0.9
0.6
0.9
3.0
4.9 t 2.4
7.2 ± 2.2
8.3 ± 4.1
3.2 ± 0.8
3.5 ± 1.0
5.4 ± 2.4
11.6 i 5.6
1.6 i 0.6
3.9 ± 1.3
3.5 ± 0.4
9.7 ± 1.6
11.5 ± 5.3
1.1 ± 0.5
1.8 ± 1.9
3.8 ± 2.8
4.7 ± 2.4
11.3 ± 6.8
2.1 ± 1.2
4.1 i 2.0
4.8 ± 1.9
lumber of analyses shown in parentheses.
Source: Adapted from Wright and Davlson, 1975, Tables 4 and 5, pp. 5-6. Reprinted by permission
of the publisher.
5.3.2 Effects
5.3.2.1 Physiological Effects - Sodium fluoride (0.01 mW) did not affect
respiratory activity during cleavage and gastrulation of Bufo ccp&ncanm
eggs. However, the pools of pyruvate and ot-ketoglutarate were decreased
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191
ORNL-OWG 79-20903
300
E
Q.
O.
200 -
(£
O
O
U
O
CC
O
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192
5.3.2.2 Toxicity Fluoride concentrations above certain levels in
aquatic systems have profound toxic effects. The response of aquatic
organisms is related to environmental acclimatization and species of
organism. The concentrations of fluoride in otherwise unpolluted water
have no detrimental effects (Becker and Thatcher, 1973). Concentrations
of 1.5 ppm appear not to have harmful effects on aquatic organisms. Table
5.12 presents a list of toxic levels of fluoride for various aquatic
species.
TABLE 5.12. TOXICITY OF FLUORIDES TO AQUATIC
Chemical compound
Sodium fluoride
Sodium fluoride (F)
Fluoride (F)
Fluoride
Test organism
Caraaaius auratua
Polyoelie nigra
(planaria)
Daphnia magna
(cladocera)
Gambuoia af finis
Salmo gairdneri
HomaruB ameriaanue
(lobster)
Salmo gairdneri
Cyprinua corpio
Oombuaia affinia
Caraeeiua oweatua
Tinea vulgarie
Eeaheriahia ooli
(bacteria)
Daphnia magna
(cladocera)
Salmo gairdneri
Hiaroregma hateroetema
(protozoa)
Salmo gairdneri
Minnows
Caraeeiua ouratue
Test Concentration
conditions (ppo)
SB, FW, LS 1000
1000
100
SB, FW, LS 0.0011 M
SB, FW, LS 504
SB, FW, LS 1240
925
SB, FW, LS 5.9-7.5
2.6-6.0
SB, FW, LS 0.9-4.5
CB, FW, LS 2.7-4.7
222-273
242-261
237-281
61-85.3
75-91
500
500
SB, FW. LS 120
FW, LS 678
180
45
270
SB, PW, LS 5.9-7.5
2.6-6.0
2.3-7.3
SB, FW, LS 226
SB, FW, LS 250
150
100
113
75
FW 7.7
100
1000
1000
SPECIES
Remarks
Killed in 60-102 hr, hard water
Killed in 12-29 hr. soft water
No kill in 4 days, hard water
Toxic threshold, survives 48
hr; pH 6.6, 14-18'C
"Toxicity threshold" or dose to
Just Immobilize in 48 hr;
Lake Erie water, 25'C
24-hr Tim, acute
48- and 96-hr TLm, acute; all
data at pH 7.1-8.1. 21-24*C.
turbid water
48-hr TLm, acute; 7.2'C
48-hr TLm, acute; 12.8'C
Nontoxlc in 10 days; 2°C
20-day TLm; 12.8'C; flngerllngs
424-hr TLn,; 7.8'C; eggs
214-hr TLm; 12.8'C; eggs
167-hr TLm; 15.6'C; eggs
825-hr TLm; 12.8'C; fry
20-day TLm; 18.3-23.9'C
50X kill in 14 hr and 100Z kill
in 19 hr; anlon normality
0.026
SOX kill in 30 min and 100Z
kill in 1 hr; anlon normal-
ity Increased to 0.26
Killed in 4 days
Lethal dose
Toxic threshold, 4 days; 27*C
Toxic threshold, 4 days; 24*C
Toxic threshold, 48 days; 23'C
10-day Tin,; 7.2'C
10-day TLm; 12.8'C
10-day TLm; 18.3'C; Ca and Mg
ions held at low values
Toxic threshold, 28 hr; 27*C
Total kill in 21 days, hard
water
90* kill in 21 days, hard water
No toxic effect in 21 days,
hard water
Total kill in 21 days, soft
water
No toxic effect in 21 days,
soft water
Not harmed in 1 hr
Survived over 4 days
Killed In 12-29 hr, soft water
Killed in 60-102 hr, hard water
aSB - static bloassay; CB - constant-flow bioassay; FW - freshwater; SW - sea (salt) water; LS - lab
study.
Source: Adapted from Becker and Thatcher, 1973, Table R, p. R2. Data collected from several sources.
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193
Crustaceans are able to tolerate high levels of fluoride in seawater
(Wright and Davison, 1975). The effects of various fluoride levels on
three species of crab, CaxoinuB maenas, Canoer pagurus, and Portunus depu-
rator, are shown in Table 5.13. The mussel Mytilus edulis also showed
toxic effects when exposed to water containing 30 ppm fluoride for two
or three weeks. Mussels exposed to 10 ppm fluoride died after five-week
exposures. Evidence from this study shows that the aquatic animals most
sensitive to fluoride appear to be filter-feeding molluscs.
Frogs (Rana pipiens) exposed to sodium fluoride in water at concentra-
tions ranging from 5 to 50 ppm showed few external signs of toxicosis but
had a definite decrease in total red and white cell counts (Kaplan, Yee,
and Glaczenski, 1964). Changes in the internal organs, engorgement of
blood vessels, and local hemorrhages in the stomach and intestines occurred
at 50 ppm fluoride. Death occurred at 28 days in 50 ppm fluoride, and as
the fluoride concentrations increased, the survival time shortened and the
percentage of deaths increased. Death followed after a 2-hr immersion in
3.5 parts-per-thousand (ppt) fluoride, after 15 hr in 2.8 ppt, 18 hr in
2.5 ppt, 50 hr in 2.2 ppt, 72 hr in 1.5 ppt, and 72 hr in 1 ppt. Fluoride
entered the frogs by ingestion and by penetration through the skin. Kaplan,
Yee, and Glaczenski (1964) also discussed experiments in which injection
of sodium fluoride in concentrations as high as 1000 ppm (no data given
on total amount of solution injected) into the dorsal lymph sacs produced
only a slight drop in red and white cell counts. Blood clotting time was
not changed by injection of sodium fluoride, whereas clotting time was
delayed when frogs were immersed in solutions containing concentrations
of fluoride as low as 30 ppm. This difference in buildup of blood levels
may partially explain the differences in fluoride toxicosis following
different means of exposure.
Fish exposed to sodium fluoride become apathetic, lose weight, have
periods of violent movement, and wander aimlessly. Finally, there is a
loss of equilibrium accompanied by tetany and death. Mucus secretion
increases, accompanied by proliferation of mucus-producing cells in the
respiratory and integumentary epithelium (Neuhold and Sigler, 1960). Alger
(as cited in Sigler and Neuhold, 1972) reported a decrease in total serum
protein in trout and carp during fluoride intoxication. Serum alkaline
phosphatase activity and plasma magnesium levels increased and calcium
decreased with exposure to solutions containing increasing fluoride con-
centrations. Fish size also affected toxicity; the larger the fish, the
more resistant they were to a given level of fluoride.
Symptoms of acute fluoride intoxication in rainbow trout and carp
were lethargy, erratic movement, and death when partial or complete muscle
contraction occurred (Neuhold and Sigler, 1960). Rainbow trout embryos
died within the egg and displayed symptoms similar to those of adults.
Hatching time of eggs decreased with exposure to increasing fluoride con-
centrations; however, the earlier hatching embryos were not as developed
as those hatching later. Variables such as size of fish, temperature of
the medium, and calcium and chloride concentration of the medium affected
the lethal doses and sensitivity of the fish. As the fish size increased,
the length of time before mortality increased at a given fluoride level;
-------
TABLE 5.13. THE EFFECT OF INCREASED FLUORIDE (AS SODIUM FLUORIDE) IN ARTIFICIAL SEAWATER ON VARIOUS
MARINE, INTERTIDAL ANIMALS OF THE NORTHUMBRIAN COAST
Number of
Species animals used at Fluoride-
each fluoride free
concentration
Swimming crab
(Portunus depurator)
Edible crab (Cancer
pagurue)
Shore crab (Cafoinus
maenaa)
Edible mussel0
(Mytilus odulia)
2 Alive after 90
days
1 Alive after 90
days
4 Alive after 90
days
4 Alive at 42
days
1 ppm
fluoride
One dead after 60
days, other alive
at 90 days
Alive after 90 days
Alive after 90 days
Two dead after 10
days (lack of Oa
probable cause as
aerator stopped)
Two still alive
after 42 days
2-4 ppm
fluoride
Alive after 90
days
Alive after 90
days
Alive after 90
days
Alive at 42
days
10 ppm
fluoride
Alive but unhealthy
after 90 days
Alive after 90 days
Alive after 90 days
Three dead after 30
days, fourth dead
after 36 days
30 ppm
fluoride
Alive after 90 days
Alive after 90 days
Alive after 90 days
Three dead after 14
days, fourth dead
at 21 days
In a preliminary experiment at room temperature (groups of four animals), all animals survived 0, 1, and 2.44 ppm for two weeks; in 10 ppm
fluoride, two dead at two weeks; in 30 ppm fluoride, all dead in ten days.
Source: Adapted from Wright and Davison, 1975, Table 9, p. 10. Reprinted by permission of the publisher.
\o
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195
however, the LDSo did not change. An increase in temperature altered the
sensitivity from 2.02 ppm fluoride at 7°C to 10.81 ppm at 16°C. The LD3o
increased from 246 ppm fluoride at 7°C to 251 ppm at 16°C. Higher than
normal concentrations of calcium in the medium increased resistance of fish
to fluoride. The toxicity of fluoride to mosquitofish (Garribuaia affinis)
increased when the total anion normality was increased by adding sodium
chloride to the medium. Mortality time for 50% of the fish at 500 ppm
fluoride was 14 hr; increasing anion normality from 0.026 to 0.26 by adding
chloride decreased the mortality time for 50% of the fish to 30 min. Cal-
cium deficiency induced by high fluoride levels seemed to cause hypertrophy
of the ultimobranchial gland. Fluoride forms a stable mineral complex
with calcium, making calcium less available for mobilization from the bone.
The uptake of fluoride by the bone is a defense mechanism against fluoride
toxicosis. This mechanism works by eliminating fluoride from body
circulation.
5.4 BIRDS
5.4.1 Metabolism
5.4.1.1 Uptake Fluoride in poultry is primarily derived from ingestion
of food and water containing fluorides (Cass, 1961). Minimal quantities
can enter the body through the respiratory tract. These fluorides are in
either a gaseous or particulate form. Systemic absorption of inorganic
fluorides through the skin is negligible.
5.4.1.2 Distribution and Accumulation Kay, Tourangeau, and Gordon
(1975a) determined the fluoride levels in indigenous animals collected
from ecosystems uncontaminated by industrial fluoride. Femur fluoride
levels found in birds are given in Table 5.14. Table 5.15 presents the
natural or "background" fluoride levels found in birds in a nonindustri-
alized area in New Zealand (Stewart et al., 1974).
TABLE 5.14. FEMUR FLUORIDE LEVELS IN BIRDS COLLECTED
FROM UNCONTAMINATED ECOSYSTEMS
Species
Blackbilled magpie
(Pica pica)
Blue grouse
(Dendragapua obeourua)
Ruffed grouse
(Bonoaa unbellua)
Sage grouse
(Centroaeroua tovphoeiomia)
Sharptall grouse
(Pedioaaatoe phaeionallua)
Spruce grouse
(Conoahitee oanadtraia)
Sample
size
4
3
5
1
1
2
Mean
fluoride level
(ppm dry wt)
535.8
321.3
127.6
216.0
97.0
176.5
Source: Adapted from Kay, Tourangeau, and Gordon,
1975a, Table 1, p. 127. Reprinted by permission of the
publisher.
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TABLE 5.15. BONE AND GIZZARD FLUORIDE CONCENTRATIONS IN BIRDS IN AN UNCONTAMINATED AREA OF NEW ZEALAND
Number
Species of Diet
samples
Fluoride concentration (ppm)
Bonea Gizzard contents*
Mean Range Mean Individual values
Red-billed gull (Larua 16
novaehoIlandiae
saopulinua)
White-faced heron (Ardea 3
novaehoIlandiae)
Mallard duck (Anas 11
platyrhynchos)
Black-backed gull (Lams 16
dominiccm.ua)
Harrier hawk (CirauB 14
approximans)
Pied oyster-catcher 14
(Haematopue oetralegue
finaohi)
Hedge sparrow (Prunella 1
modularis)
Starling (Sturnue imlgans) 14
Pukeko (Porphyvio 16
melanotue)
Mainly macroplankton (predominantly
euphausid Crustacea), small for-
age fish, some beach scavenging,
some insects and worms from agri-
cultural land
Small fish, tadpoles, frogs, soft-
shelled crabs, freshwater cray-
fish, and aquatic insects
Aquatic plants, freshwater molluscs,
soft-bodied invertebrates (e.g.,
worms and slugs)
Mollusks, offal, and garbage
Large Insects (e.g., grasshoppers),
young fish, mice, lizards, frogs,
and carrion (hares, opossums, and
hedgehogs)
Shellfish, marine worms, grass
grubs, and insect larvae
Insects, buds, and seeds
Grass grubs, birds' eggs, nectar,
and scavenges in seaweed
Main diet consists of stems, leaves,
seedheads of plants, birds' eggs,
and Insects
4003 1058-8050 28 9.4, 24, 50
2208 1006-3264 35 13, 30, 62
1902 430-5440 13 4, 9.2, 28
1907 754-3140 144 2.9, 24, 405
1445 379-4775 3.5 1.9, 5.2
1243 393-1965 6 1.9, 4.1, 12
1021
703 157-1390 3.1 2.0, 3.6, 3.7
489 143-1400 1.7 1.0, 1.7, 2.6
\O
vAsh-welght basis.
Fresh-weight basis.
Source: Adapted from Stewart et al., 1974, Table 2, p. 108. Reprinted by permission of the publisher.
-------
197
Fluoride levels in seabirds from the coast of Great Britain indicate
that higher fluoride levels occur in the skeletal tissue than in the soft
tissues (Table 5.16). The apparently high bone fluoride levels are well
within the range found in other terrestrial vertebrates (Wright and
Davison, 1974).
TABLE 5.16. TISSUE FLUORIDE LEVELS OF SEABIRDS FROM THE COAST OF GREAT BRITAIN
(ppm wet wt)
Guillemots
Tissue
Liver
Heart
Crop
Kidney
Muscle (pec tor alls
major)
Tibia
Skull bone
Skin
Feathers
Lung
Newblggin,
November 1972
<0.2
0.25
0.2
1.12
1.67
40
Newblggin,
August 1972
<0.2
12.0
0.3
1.5
1.5
Whitley Bay,
January 1972
1.61
0.43
1.99
750
1.18
Mousehole,
Cornwall ,
January 1972
0.95
0.88
1.00
Greater black-
backed gulls,
Newbiggin,
October 1972
0.42
0.61
0.20
0.26
0.72
0.81
0.60
Source: Adapted from Wright and Davison, 1974, Table 3, p. 120.
the publisher.
Reprinted by permission of
Roosters receiving a 200-mg/kg dose of sodium fluoride twice a day
for 24 hr showed the highest percent of nonskeletal fluoride ion accumu-
lation in the liver, heart, and feathers (Slesinger and Tusl, 1966). How-
ever, in both the control and experimental roosters the highest fluoride
levels occurred in bones.
Cass (1961) reported that from 0 to 0.02% of a fluoride dose injected
into the bloodstream of laying hens was recovered from developing eggs.
The less mature egg yolks had the highest fluoride concentration, while
in mature eggs, the fluoride level in the albumin was higher than in the
yolk.
Anderson et al. (1955) fed turkeys various levels of sodium fluoride
and found that the fluoride concentration in bones increased as the fluo-
ride level in the feed increased. The concentration of fluoride in bones
also increased as the length of time the feed was administered increased
(Table 5.17). Fluoride levels in soft tissues increased with the fluoride
level in the feed, but did ndt increase with time.
5.4.2 Effects
5.4.2.1 Physiological Effects Interaction between fluoride and magnesium
in chicks affects both skeletal and body growth. A fluoride supplemental
level of 0.08% (added as sodium fluoride to diets) reduced growth rate but
-------
198
TABLE 5.17. FLUORIDE LEVELS IN TISSUES OF TURKEYS FED VARIOUS AMOUNTS OF SODIUM FLUORIDE
Tissue
Sternum
Femur
Breast
flesh
Thigh
flesh
Liver
Kidney
Initial
fluoride
concentration
(ppn)a
b
b
1.2
1.5
1.9
2.6
Treatment
time
(weeks)
8
16
8
16
8
16
8
16
8
16
8
16
Fluoride level In tissues at various
amounts of fluoride in ration (ppm)
43 ppm
450
383
390
360
1.3
2.2
1.9
1.9
2.7
1.6
5.6
6.5
100 ppm
740
1,268
770
1,210
2.2
1.5
2.3
1.6
2.4
1.8
10.7
8.2
200 ppm
1,500
1,975
1.660
1,775
2.7
2.3
3.9
1.5
4.7
6.3
5.9
9.0
400 ppm
4,050
5,650
4,050
5,400
8.2
2.7
2.8
2.0
5.6
2.5
9.3
9.7
800 ppm
8,000
12,500
8,550
14,875
5.6
7.5
7.8
6.1
9.1
3.8
13.5
16.2
1,600 ppm
12,300
14,700
12,000
14,900
30.9
24.6
11.8
9.4
15.6
11.3
39.0
36.1
.All values are on a dry basis except those from bones, which are on a dry, fat-free basis.
Samples lost.
Source: Adapted from Anderson et al., 1955, Table 4, p. 1151. Reprinted by permission of the
publisher.
did not affect bone ash, bone calcium or phosphorus, or plasma magnesium or
inorganic phosphorus (Gardiner, Rogler, and Parker, 1961). A combination
of 0.08% supplemental fluoride and 0.25% supplemental magnesium caused a
greater reduction in growth than fluoride alone. The combination of fluo-
ride and magnesium also produced leg weakness, reduced bone ash, and caused
a smaller calcium and phosphorus bone content. Along with reduced growth
rate and leg weakness, Griffith, Parker, and Rogler (1964) found that the
addition of supplemental fluoride and magnesium to diets of chicks reduced
the citric acid content of bones by 64% when compared with bones of chicks
maintained on a basal diet. Fluoride supplementation alone reduced bone
citrate by an average of 32%. Later, Rogler and Parker (1972) reported
that excess amounts of calcium improved the growth rate of chicks fed flu-
oride alone or fluoride plus magnesium; however, the growth rate was infe-
rior to that of the controls. In chicks fed high fluoride diets, bone ash
was increased and the fluoride content of plasma and bone was reduced when
excess calcium was added to the diets. These alleviating effects of cal-
cium result from reduced absorption of fluoride and magnesium.
Some fluoride compounds inhibit specific enzymes in hens. Sulfonyl
fluoride progressively inhibited "neurotoxic esterase" by attaching a sub-
stituent covalently at the active site (Johnson, 1970). Inhibition of the
enzyme by phenylmethanesulfonyl fluoride did not induce neurotoxic effects;
prior inhibition by sulfonyl fluorides in vivo prevented neurotoxic effects
of organophosphorus compounds. Dietary fluoride had little or no effect on
several enzyme systems of chicks (Weber, Doberenz, and Reid, 1969). Cyto-
chrome oxidase activity in heart muscle was elevated at 500 ppm fluoride
but not at 1000 ppm fluoride. Increasing dietary fluoride levels increased
plasma alkaline phosphatase activity (Table 5.18).
-------
199
TABLE 5.18. THE EFFECT OF DIETARY FLUORIDE ON
ENZYME SYSTEMS OF CHICKS
Enzyme activity
Enzyme system
Lactic dehydrogenase
Cytochrome oxidase
Succinic dehydrogenase
Isocitric dehydrogenase
Alkaline phosphatase^
Tissue
Liver
Kidney
Liver
Kidney
Heart
Liver
Kidney
Liver
Plasma
0 ppm
fluoride
669 a
271 a
42.7 a
31.5 a
36.2 a
16.6 a
19.0 a
20.0 a
27.8 a
500 ppm
fluoride
40.0 a
32.6 a
48.8 b
17.4 a
19.0 a
15.6 a
34.1 ab
1000 ppm
fluoride
734 a
272 a
47.9 a
29.6 a
42.9 ab
18.4 a
18.8 a
15.8 a
40.1 b
Means not having common letters are significantly different at
the 0,05 level of probability.
^Enzyme activity is given as delta oxygen demand per milligram
per minute.
cEnzyme activity is given as delta oxygen demand per milligram
per hour.
^Enzyme activity is given as sigma units per milliliter.
Source: Adapted from Weber, Doberenz, and Reid, 1969, Table 4,
p. 233. Reprinted by permission of the publisher.
High levels of fluoride affected the tibia bone development in chick-
ens (Hicks and Ramp, 1975; Smith et al., 1970). Tibia bone ash was signifi-
cantly reduced, whereas fluoride content of fat-free dried bones increased.
Hicks and Ramp (1975) reported that in vitro fluoride either increased or
decreased bone mineralization in embryonic chick tibia at low calcium and
phosphorus concentrations, respectively, indicating that the effects are
dependent on cellular control of calcium and phosphorus compounds in bone
extracellular fluid. From these data, it was suggested that fluoride plays
a role in the rate of mineralization in growing bones.
5.4.2.2 Toxic Effects High fluoride ingestion by birds can result in
reduced growth rate, leg weakness, and bone lesions. Tolerance to fluo-
rides varies among bird species and among individuals of the same species.
Birds are usually more resistant than mammals to toxic effects of fluoride
ingestion (Shupe, 1969).
5.4.2.2.1 Acute toxicity Typical symptoms of acute toxicity are a reduc-
tion or loss of appetite, local or general congestion, and submucosal hem-
orrhages of the gastrointestinal tract (Cass, 1961). Feeding chickens for
ten days on a diet containing 6786 ppm fluoride produced acute responses;
a one-time dose of 27.1 ppm BaSiF« on grain was lethal. Roosters receiving
a 200-mg/kg dose of sodium fluoride twice a day for 24 hr developed gastro-
enteritis with edema of the mucosa of the stomach and upper bowels, subcu-
taneous edema, hepatomegaly, and atrophy of the pancreas (Slesinger and
Tusl, 1966).
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200
5.A.2.2.2 Chronic toxiclty Chronic fluorosis In birds can be difficult
to diagnose and is dependent on several factors. It is necessary to estab-
lish the presence of characteristic lesions, a history of exposure at the
proper time to high levels of fluoride, and analytical evidence that bone
contains fluoride concentrations consistently associated with lesions of
chronic fluorosis before a definite diagnosis can be made (Cass, 1961).
In birds, chronic fluoride toxicosis develops slowly and primarily
involves gross and microscopic changes in bone (Cass, 1961). If elevated
fluoride intake persists, the bird's general health progressively deteri-
orates. Lameness may develop, and there commonly is a loss of appetite.
High levels of fluoride Ingestion often Induce a reduced growth rate
In poultry. Weight gains by male turkeys were decreased by the addition
of 200 ppm fluoride in the ration (Anderson et al., 1955). A critical flu-
oride level between 200 and 400 ppm exists for growing turkeys. Between
these levels there were (1) decreases in weight gain for male and female
turkeys, (2) decreases In food consumption, (3) decreases In feed effi-
ciency, and (A) gross changes in the intestinal tract.
Fluoride added to feed at a rate of 1000 ppm reduced the weight gain
of chicks, while a combination of 1000 ppm fluoride and 10,000 ppm bromide
caused further weight reductions (Doberenz et al., 1965). A diet contain-
ing 2000 ppm fluoride plus 10,000 ppm bromide caused 100% mortality within
three weeks. Fluoride alone produced 25% mortality by four weeks of age.
Weber, Doberenz, and Reid (1969) also reported a growth reduction in chicks
fed 500 ppm fluoride; a 21% reduction occurred at 1000 ppm fluoride. Along
with a reduction In body-weight gain, Gardiner, Winchell, and Hironaka
(1968) found that an 0.08% fluoride diet supplement caused a decrease in
feed consumption and metabollzable energy from the feed. The total energy
needed per unit weight gain was Increased. The difference In growth rate
between control and experimental chicks was due to a 51.4% decrease in
feed consumption, a 13.3% decrease in metabolizable energy from the feed,
and a 33.3% lower efficiency of energy metabolism.
Possibly one reason for the decrease In feed consumption of chickens
fed high levels of fluoride Is the changes that take place in the proven-
trlculus. Dietary fluoride at 0.08% and 0.10% increased the size and
weight of the proventriculus (Gardiner et al., 1959). Cellular changes
were most pronounced on the gland surface and included hypertrophy and
hyperplasia of the columnar epithelium and a thickening of the tunica
propria.
5.4.2.2.3 Teratogenicltv - Injection of 5-fluorouracll, S-fluoro-21-
deoxyurldine, or 5-fluoroorotic acid into the yolk sac during the first
four days of development of the chicken embryo produced specific develop-
mental anomalies that varied with the stage of development at the time
of injection and the compound Injected (Kury and Craig, 1966). Skeletal
malformations included the absence, shortening, curvature, and/or fusion
of bones. Microphthalmia, defective eyelids, retardation of growth of
extremities, and abnormal bill development were common malformations
induced by the three fluorinated pyrimidine compounds used.
-------
201
5.4.2.2.4 Tolerance to fluoride Poultry are more resistant to fluoride
toxlcity than most other animals. They also usually ingest smaller amounts
of fluoride than most animals because of the low fluoride content of grains
(National Academy of Sciences, 1971). Resistance to fluorides in the young
chick is due to the lack of adverse effects from a high serum fluoride con-
tent (Suttie, Phillips, and Faltln, 1964). Growing chicks can tolerate up
to 300 ppm fluoride in their diet (National Academy of Sciences, 1974).
Laying hens have a higher tolerance to fluoride than chicks. Feeding
chickens 5000 ppm fluoride (based on body weight) one time failed to pro-
duce any symptoms of fluoride toxlcity (Cass, 1961). Turkeys have a toler-
ance level of 200 ppm dietary fluoride, above which significant decreases
in growth rate occur (Anderson et al., 1955). Vohra (1973) reported that
50 ppm fluoride, as sodium fluoride, in the drinking water of Japanese
quail did not affect body weight, tibia weight, bone ash, or eggshell
thickness. Fluoride concentrations up to 200 ppm were tolerated by the
quail.
5.5 DOMESTIC AND WILD MAMMALS
5.5.1 Metabolism
The metabolism of fluorine-containing compounds by domestic and wild
mammals is similar to that of humans, and much of the data presented In
Section 6 are applicable to mammals discussed in this section. However,
metabolism data dealing directly with these mammals, particularly live-
stock, are presented in this section.
5.5.1.1 Uptake and Absorption
5.5.1.1.1 Routes of entry Fluoride in the body of mammals is derived
mainly from the ingestion of fluoride-containing food and water (Cass,
1961). Usually only small quantities of fluoride in gaseous or particu-
late form enter the body through the respiratory tract. Absorption of
Inorganic fluorides through the skin is insignificant.
The principal sources of excessive fluoride to livestock are ingestion
of high-fluoride vegetation in areas with a fluoride pollution problem
(National Academy of Sciences, 1971) and the Inclusion of raw rock phos-
phate in the diet (Dale and Crampton, 1955). Other sources of fluoride
for mammals are waters containing high concentrations of fluoride and the
Ingestion of soils high in fluorides.
5.5.1.1.2 Absorption The absorption of soluble fluorides from the gas-
trointestinal tract is rapid and almost complete (Underwood, 1971). This
absorption appears to be passive and does not involve active transport
(National Academy of Sciences, 1974). Parkinson et al. (1955) reported
that in sheep and cattle, absorption took place rapidly from the rumen.
Approximately 1% of an Ingested dose of fluoride represented the peak
blood value, which occurred at 2- and 5-hr postingestlon in sheep and
cows respectively.
-------
202
The gastrointestinal absorption of fluorides is greatly influenced by
the chemical form of the fluoride and the dietary consumption. Generally,
the less soluble a fluoride compound is, the slower the rate of absorption
(Largent, 1961; National Academy of Sciences, 1974). tiowever, small amounts
of relatively insoluble fluorides ingested in solution can be absorbed al-
most as well as the more soluble forms (Underwood, 1971). Large amounts
(1% to 2%) of certain ions in the diet (e.g., aluminum, calcium, and mag-
nesium) form less soluble complexes with fluoride, decreasing the amount
of absorbable fluoride (National Academy of Sciences, 1974; Shupe, Olson,
and Sharma, 1972).
5.5.1.2 Accumulation and Distribution
5.5.1.2.1 Accumulation Natural fluoride levels in the skeletons of
small mammals, cattle, and sheep in the Bluff area of New Zealand were
determined before the operation of an aluminum smelter (Stewart et al.,
1974). Bone fluoride levels ranged from 20 to 1500 ppm, bone-ash basis
(Table 5.19). Variation of fluoride levels within species was mainly due
to age differences, since specimens were collected randomly without regard
to age. Fluoride levels in lambs and calves were lower than in adults.
Bone fluoride levels in wildlife seemed to be a function of amount and
duration of exposure. Differences in fluoride-tissue concentrations be-
tween species were probably due to differences in dietary exposure.
TABLE 5.19. FLUORIDE CONCENTRATIONS IN BONES
OF WILD AND DOMESTIC ANIMALS
Sample
Opossum (TrichoatawB
vulpecula)
Rabbit (Oryctolague
cwriculue)
Cattle
Jawbone
Tail
Adult
Calf
Sheep
Jawbone
Tail
Adult
Lamb
Number
of
samples
2
1
1
105
32
17
11
36
Bone fluorine
concentrations
(PPm)fl
Mean Range
247 216-278
184
1207
643 229-1469
245 19-944
735 352-1178
327 91-990
202 42-669
aBone-aeh basis.
Source: Adapted from Stewart et al., 1974,
Table 4, p. 110. Reprinted by permission of the
publisher.
-------
203
The results of a study to determine fluoride levels in animals from
an uncontaminated ecosystem are given in Table 5.20. Animals collected
from areas near human habitation or those maintained on a commercial lab-
oratory ration had higher fluoride levels than the animals collected from
a natural ecosystem (Kay, Tourangeau, and Gordon, 1975a). Redtail chip-
munks caught wild and fed a laboratory ration for three months had over
1000 ppm fluoride (dry, fat-free basis) in the femurs, whereas chipmunks
not fed the ration had only 77 ppm fluoride. Predatory mammals appeared
to have higher levels of femur fluoride than herbivorous animals. The
higher fluoride concentrations in predatory animals were thought to result
from consumption of prey skeletons.
TABLE 5.20. FLUORIDE LEVELS IN FEMURS OF WILD ANIMALS
Species
Beaver (Castor canadeneia)
Black-tailed jackrabbit (Lepue californicus)
Black-tailed prairie dog (Cynomye
ludoviciantte)
Chipmunk (Eutamiae sp.)
Columbian ground squirrel (Citellus
aolvmbianue')
Coyote (Canla latrons)
Mandible
Deer mouse (Peromyeaus maniculatus)
Golden mantled squirrel (Citellus lateralie)
Long-tailed weasel (Muetela frenatd)
Lynx (Lynx oanadensie)
Masked shrew (Sorex cinereus)
Meadow vole
MiarotuB permsylvanicuB
MiarotuB montanus
Mink (Mustela vieori)
Moose (Alaee alaee) (mandible 5.5 years old)
Mountain cottontail (Sylvilagua nuttalli)
Muskrat (Ondatra aibetkicus)
Northern flying squirrel (Glauaomye
eabrima)
Northern water shrew (Sorex paluetris)
Ord kangaroo rat (Dipodomya ordi)
Porcupine (Erethizon doraatum)
Red squirrel (TamiasciuruB hudeaniaue)
Red-backed vole (Clethrionomys gapperi)
Red-tailed chipmunk (Eutamiaa mfioaudus')
Richardson ground squirrel (Citellue
ridhardaoni)
Short-tailed weasel (Mustela erminea)
Snowshoe hare (Lepus amencanus)
Stone sheep (Ovia dalli Btcnei) (mandible
8.5 years old)
Vagrant shrew (Sorex vagrana)
Western big-eared bat (PlecotuB touneendi)
White-tailed jackrabbit (Lepuo townsendi)
Yellow pine chipmunk (Eutamias amoenuB)
Sample
size
3
1
1
19
23
1
1
70
2
2
1
1
3
2
2
1
4
11
6
1
2
6
9
5
2
1
5
4
1
5
1
14
1
Mean
fluoride level
in femur
(ppm)a
148.7
122.0
120.0
103.1
112.5
321.0
257.0
143.8
67.0
279.0
176.0
589.0
139.0
133.0
499.5
248.0
167.5
266 .'4
141.8
340.0
440.5
161.0
151.9
258.0
77.5
64.0
363.6
138.2
380.0
474.8
78.0
258.6
67.0
ury, defatted weight.
Source: Adapted from Kay, Tourangeau, and Gordon, 1975a, Table 1,
127. Reprinted by permission of the publisher.
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204
5.5.1.2.2 Transport Absorbed fluoride is transported rapidly by the
blood throughout the body as the fluoride ion (Underwood, 1971). Fluorine
ions easily cross cell membranes, including the red blood cell. Plasma
fluoride concentration is usually twice the level in red blood cells and
is approximately 75% of the total blood fluoride concentration (National
Academy of Sciences, 1974). Fluoride leaves the blood rapidly and is
distributed to various body tissues.
5.5.1.2.3 Distribution Fluorides are distributed throughout the body
and are selectively accumulated in skeletal and mineralizing dental tis-
sues (Shupe, Olson, and Sharma, 1972). Throughout the life of the animal,
fluorides are deposited in bones; approximately 98% of the total fluoride
body burden accumulates in mineralized tissues. Fluoride deposition, being
related to tissue metabolism, occurs more readily in forming and mineral-
izing teeth and bones. The concentration of fluoride ions in soft tissues
approximates that of the plasma.
5.5.1.2.3.1 Blood Fluorides occur in intracellular fluid (National
Academy of Sciences, 1974). Erythrocytes contain a fluoride level that
is 40% to 50% of that in plasma. Five percent of the plasma fluoride is
bound to protein; the compounds that bind fluoride have a lower molecular
weight than albumin. Fluoride concentrations in plasma are controlled by
regulatory mechanisms involving skeletal and renal tissues. The concentra-
tion of plasma fluoride in animals not exposed to higher than background
fluoride levels is very low, usually 0.1 to 0.2 ppm (Underwood, 1971).
Elevated plasma fluoride concentrations occur in mammals during per-
iods of high fluoride intake. Plasma fluoride levels change rapidly in
response to changes in fluoride intake levels. Suttie, Carlson, and Faltin
(1972) alternated six-month periods of high- and low-fluoride intake levels
in dairy cattle and found that the plasma levels rose or fell accordingly
within a week. Also affecting plasma fluoride concentration is the method
of fluoride administration. Perkinson et al. (1955) administered 10F to
lambs and cows. Figures 5.4 and 5.5 illustrate the 18F levels in the blood
of lambs over time. Fluorine-18 given intravenously produced a higher
initial blood fluorine level than a dose given orally, and the rate of
removal from the blood was more rapid for the intravenous dose.
A regular fluctuation in plasma fluoride has been reported to occur
following oral administration of a single dose per day or during continu-
ous intrarumenal infusion (Simon and Suttie, 1968). When sheep were given
2 ppm fluoride (based on body weight), a rapid increase in plasma fluoride
occurred, peaking 3 hr after the dose and then decreasing to preingestion
levels by 12 hr after the dose (Figure 5.6).
Cows fed 1.2, 1.4, or 2.0 ppm fluoride (based on body weight) for
four years followed by two years without added fluoride had 0.12 ppm, 0.36
and 0.53 ppm, and 0.48 and 1.12 ppm fluoride plasma levels respectively
(Phillips, Suttie, and Zebrowski, 1963). Bell, Merriman, and Greenwood
(1961) reported high levels of 18F in blood and rapid removal rate fol-
lowing intravenous injection of tracer levels in cattle. Two minutes
following injection, 53% of the dose remained in the blood; after 240
-------
205
ORNL-DWG 76-18334
100
0.1
100
200 300
TIME (min)
400
500
Figure 5.4. Fluorine-18 concentration in blood of lambs following
intravenous administration. Source: Adapted from Perkinson et al., 1955,
Figure 1, p. 384. Reprinted by permission of the publisher.
minutes, 4% of the dose was in the blood (Figure 5.7). Bogdanov and
Vlasova (1973) reported 0.7 ppm fluoride in plasma of cows fed phosphates
containing 0.2% to 0.4% fluoride.
5.5.1.2.3.2 Bones and teeth Fluoride accumulates in bone and is incor-
porated into hydroxyapatite, forming fluorapatite (National Academy of
Sciences, 1974). Following incorporation of fluoride ions into the apa-
tite of bone, the ions cannot be removed without resorption of the unit
crystalline structure of the mineral phase. Fluoride levels normally
increase with the age of the animal and in proportion to duration, rate,
amount, and form of the fluoride intake (Underwood, 1971). The rate of
-------
206
10.0-1
§
o
ffl
_l
<
1.0-
o
a
o:
O
01-
ORNL-DWG 76-»8320
200 400
TIME (mini
600
Figure 5.5. Fluorine-18 concentration in blood of lambs following
oral administration. Source: Adapted from Perkinson et al., 1955, Figure
2, p. 384. Reprinted by permission of the publisher.
OMNL-OWC ?-18322
1.6
< 1.4
tn
z 1.0
g 0.8
IT
§ 0.6
u.
0.4
01235 8 12
TIME AFTER FLUORIDE (hr)
24
Figure 5.6. Diurnal variation in plasma fluoride in sheep. Each
curve represents a single animal. Source: Adapted from Simon and Suttie,
1968, Figure 1, p. 512. Reprinted by permission of the publisher.
-------
207
ORNL- DWG 76- 18321R
OUJ100
1°
TOTAL BLOOD
10
en
o
o -
o
cc
PROTEIN-FREE
FILTRATE :
PLASMA"
WHOLE BLOOD'
10 1OO 24O
TIME AFTER DOSING (min)
1000
Figure 5.7. Fluorine-18 levels in blood from mature cows after in-
travenous dosing. Source: Adapted from Bell, Merriman, and Greenwood,
1961, Figure 1, p. 380. Reprinted by permission of the publisher.
accumulation decreases with increased fluoride bone content and age of
animal.
Fluoride deposition in bone varies with the kind of bone and with the
area of bone involved. Some bones tend to have greater fluoride-induced
exostosis formation than others, such as the mandibles and shaft bones
(Underwood, 1971). Active areas of bone growth have a high rate of fluo-
ride incorporation, cancellous areas incorporate fluoride faster than cor-
tical areas, and surface areas faster than middle regions. Kay (1975)
reported that in mule deer the cancellous portions of bones and the bone
sections with the largest surface-area-to-weight ratio had the highest
fluoride concentrations.
Fluoride is incorporated into teeth as fluorapatite during calcifica-
tion; once calcified, the tooth does not respond to fluoride as the bone
does (National Academy of Sciences, 1974). Dentin fluoride concentrations
normally increase with time.
Dairy cows fed a basal ration containing 3 to 5 ppm fluoride for 5.5
years had less than 1000 ppm fluoride (dry, fat-free weight) in the meta-
carpal, metatarsal, mandible; maxilla, and frontal bones (Suttie, Phillips,
and Miller, 1958). When 20 and 50 ppm fluoride were added to the diet,
fluoride bone content increased 4.5 to 10 times, respectively, over the
basal diet controls.
The form of fluoride ingested influences the amount of fluoride
deposited in the bones (Ammerman et al., 1964). Calves and steers fed for
91 days on different sources of fluoride had higher fluoride deposition
-------
208
from consuming soft phosphate (134 ppm fluoride) than those consuming half
the equivalent level of supplemental fluorine as sodium fluoride (67 ppm).
More fluoride was deposited from 67 ppm fluoride as sodium fluoride than
from 134 ppm as calcium fluoride (Figure 5.8). Mule deer inhabiting areas
with vegetation containing high fluoride levels had 5- to 50-fold increases
in bone fluoride content as compared with deer from an uncontaminated area
(Kay, Tourangeau, and Gordon, 1975Z?).
0.8
0.7
0.6
0.5
ORNL-DWG 79-20898
0.3
0.2
0.1
SOFT PHOSPHATE
(134 ppm F)
CALCIUM FLUORIDE
(134 ppm F)
SODIUM FLUORIDE
(67 ppm F)
PROXIMAL ty CENTER /2
SECTION OF METACARPAL
DISTAL
Figure 5.8. Effect of fluoride source on fluoride deposition
(expressed as percentage of bone ash) in three sections of the metacarpal
bones of cattle. Source: Adapted from Ammerman et al. , 1964, Figure 1,
p. 412. Reprinted by permission of the publisher.
Examination of incisor teeth of cattle in fluorosis and nonfluorosis
areas showed that a relationship existed between dental changes and fluo-
ride content of teeth (Mortenson et al., 1964). Fluoride levels were
higher in the dentin than in the enamel; average fluoride content of enamel
was 37% to 43% of that in dentin. The enamel acquired its fluoride before
-------
209
the incisors erupted from the gums. The dentin continued metabolic activ-
ity and accumulated fluoride much like bones. As the fluoride concentration
and tooth injury increased, the amount of enamel in the tooth decreased.
5.5.1.2.3.3 Soft tissues Fluoride concentrations in soft tissues are
low and do not increase significantly with age (Underwood, 1971) . Soft
tissues begin to increase in fluoride content when the bone reaches a flu-
oride saturation point (Lillie, 1970). Kidneys have the highest fluoride
concentration of soft tissues because of urine retained in the tubules and
collecting ducts. The placenta, aorta, and tendon have higher fluoride
levels than most other soft tissues, probably as a result of pathologic
calcification, which binds fluoride to the tissue (National Academy of
Sciences, 1974).
The fluoride concentration in soft tissues of control cows fed a basal
ration containing 3 to 5 ppm fluoride for 5.5 years was 2 to 3 ppm (Suttie,
Phillips, and Miller, 1958). When 50 ppm dietary fluoride was added, tis-
sue fluoride content increased (Table 5.21). The increase in tissue fluo-
ride concentration was not significant enough to use soft-tissue analyses
as a criterion of fluorosis. Bell, Merriman, and Greenwood (1961) reported
that stable fluoride concentrations in soft tissues varied with the level
of fluoride ingested by cows; however, the increase in tissue-fluoride
levels with increased fluoride intake was small.
5.5.1.2.4 Placental transfer Some transfer of fluoride across the pla-
centa appears to take place, although there may be species variation in
the amount (National Academy of Sciences, 1974). Shupe, Harris, Greenwood,
Butcher, and Nielsen (1963) found that in the fetus, fluoride was deposited
in teeth and bones. Newell and Schmidt (1958) showed a selective deposit
of fluoride in the metacarpal bones of newborn calves from cows fed in-
creased levels of fluoride. As the fluoride intake of the cow increased,
the fluoride concentration of the fetal metacarpal bones increased (Table
5.22), indicating transfer of fluoride from cow to fetus. Greenwood et
al. (1964) reported a correlation between fluoride bone content of calves
and the amount of fluoride ingested by the dam. However, calf bone-
fluoride content did not increase in succeeding gestations.
The distribution of intravenously administered 1BF to pregnant cows
indicated that part of the iaF passed into the fetus, but there was a
barrier for the free passage of fluoride (Bell, Merriman, and Greenwood,
1961). The maternal placenta contained 0.60% of the dose, compared with
0.25% in the fetal placenta.
Bawden, Wolkoff, and Flowers (1964) injected sheep with 18F to study
maternal-fetal fluoride metabolism. Maternal plasma clearance of 18F was
rapid, and fetal plasma concentrations were low when compared with maternal-
plasma levels. This suggested that the placenta may limit the transfer of
fluoride to the fetus. Fluorine-18 injected into the fetus of a pregnant
sheep was found in the maternal plasma; this result demonstrated that
fluoride can be transferred from the fetus to the mother.
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210
TABLE 5.21. THE EFFECT OF ADDED DIETARY INCREMENTS OF FLUORIDE (AS SODIUM FLUORIDE)
ON SOFT TISSUE FLUORIDE CONCENTRATIONS IN DAIRY COWS
Lot
I
II
III
IV
V
VI
U., , Cow
added
(ppm)
0 2
3
4
Av
20 5
6
7
8
Av
30 10
11
12
Av
40 13
14
15
16
Av
50 17
19
20
Av
50 + CaCOs 22
23
24
Av
Fluoride concentration (ppm)
Heart0
1.8
3.3
1.7
2.3
2.7
4.4
2.5
4.0
3.4
2.7
4.7
3.0
3.5
3.3
5.5
4.5
2.9
4.0
5.0
3.2
6.3
4.6
3.8
4.6
5.6
4.6
Livera
3.1
1.9
1.9
2.3
2.4
2.1
2.3
3.9
2.7
2.5
4.6
5.1
4.1
5.6
3.3
3.4
3.0
3.8
2.3
2.1
4.8
3.6
3.5
2.7
2.8
3.0
Kidneya
3.1
2.9
4.4
3.5
7.3
6.0
8.3
12.8
8.6
12.5
9.1
10.5
10.7
19.7
20.4
7.8
16.0
16.0
13.7
15.4
28.9
19.3
11.1
7.7
8.4
9.0
b
Pancreas
1.7
4.0
2.0
2.8
1.4
2.6
3.2
1.7
2.2
2.0
5.0
3.5
3.5
3.0
5.1
3.4
3.8
4.5
4.1
4.0
4.2
3.6
3.5
3.0
3.4
Thyroid
0.6
2.7
2.9
2.1
2.9
7.0
6.6
11.2
6.9
2.4
4.1
4.1
3.5
4.9
5.0
7.6
5.8
5.2
12.2
4.4
7.3
4.2
4.9
9.0
6.0
Adrenal6
2.0
11.9
2.2
5.3
3.8
3.3
3.5
3.3
3.3
3.3
2.5
3.5
8.8
4.7
8.7
4.1
6.4
4.2
4.1
4.1
TDry weight.
Dry, fat-free weight.
Source: Adapted from Suttie, Phillips, and Miller, 1958, Table 2, p.
by permission of the publisher.
299. Reprinted
TABLE 5.22. FLUORIDE CONCENTRATION IN
METACARPAL BONES OF NEWBORN CALVES
Total daily
fluoride fed cows
(ppm body wt)
Average
fluoride in fetal
metacaroal bones'2
(ppm)
0.15-0.3
1.0
1.5
2.0
2.5
43
99
113
152
165
aDry, fat-free basis.
Source: Adapted from Newell and
Schmidt, 1958, Table 8, p. 369. Reprinted
by permission of the publisher.
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211
5.5.1.3 Elimination Fluoride is excreted in urine, feces, and sweat.
Traces of fluoride are also found in hair, saliva, and milk. The major
route of excretion, urine, is influenced by total fluoride intake, form
of fluoride taken in, frequency and duration of exposure, fluoride con-
tent of the bone, general health, and other factors. Except during
excessive sweating, only very small amounts of fluoride are eliminated
in perspiration.
In the urine and feces, the relative proportions of excreted fluoride
are dependent on the type of fluoride compound ingested, its solubility,
the initial amount ingested, and the method of ingestion (Underwood, 1971).
Soluble fluorides are excreted in the urine. Smaller amounts of the less
soluble fluorides, such as calcium fluoride, appear in urine as a result
of lower absorption. Sheep and cows usually excrete 50% to 90% of dietary
fluoride in the urine. Bell, Merriman, and Greenwood (1961) reported that
most of the 18F added to the basal ration of beef cattle was excreted in
the urine (Figure 5.9). The average urinary 18F level reached a peak of
40.4 x 10~* percent of dose per milliliter 15 min after dosing. Saliva
peaked at 1.3 x 10"* percent per milliliter after 5 min, and 18F in feces
was 4.1 x lO'* percent per milliliter at 180 min.
ORNL-OWG 76-18325
45
-------
212
ORNL-OWG T6-18SZ6R
> a
a: a
20 30 40
FLUORIDE IN URINE
-------
213
5.5.2.1 Physiological Effects Exposure to excessive fluoride levels
inhibits specific enzymes involved in vital processes (National Academy
of Sciences, 1971). Fluoride inhibits cholinesterase, which may be par-
tially responsible for effects on the nervous system. Fatty acid oxidase
activity is also inhibited, causing a blockage of fatty acid utilization
(Underwood, 1971). Carbohydrate metabolism is altered and the level of
glucose-6-phosphate dehydrogenase decreased in some fluorotic animals.
Bone alkaline phosphatase activity is related to fluoride intake
and degree of fluoride-induced bone changes. In cattle, Greenwood et al.
(1964) reported a correlation among bone alkaline phosphatase activity,
level of fluoride intake, fluoride content of bone, and degree of osteo-
fluorosis. Phosphatase activity increased with increasing amounts of
ingested fluoride. There were no effects on lipase and amylase in the
pancreas, succinic dehydrogenase in heart muscle, enolase and pyruvate
kinase in the skeletal muscle, and pepsin in abomasal mucosa.
Faccini and Care (1965) reported changes in the ultrastructure of
parathyroid glands in sheep given 200 ppm sodium fluoride in drinking
water for one week and four weeks. An immunoassay showed that there was
a fivefold increase in the amount of blood parathyroid hormone after one
week of ingesting the fluoride. These results indicate that the para-
thyroid glands are hyperactive in severe skeletal fluorosis.
5.5.2.2 Acute Toxicity Acute fluoride toxicosis is relatively rare
and has not been intensely investigated. Acute fluoride toxicosis usu-
ally is the result of accidental ingestion of compounds such as sodium
fluorosilicate, sodium fluoride (National Academy of Sciences, 1974),
sodium fluoroacetate ("1080"), and fluoroacetamide (Shupe, 1969).
Various types of toxic responses occur, depending on several factors.
The rapidity of symptom appearance is dependent on the amount of fluoride
ingested. Symptoms may appear within 30 min for excessively high amounts
(Shupe, 1969). Symptoms usually present are: high fluoride levels in
blood and urine, stiffness, restlessness, anorexia, reduced milk produc-
tion, nausea and vomiting, excessive salivation, chronic convulsions,
necrosis of mucosa of digestive tract, weakness, depression, and cardiac
failure (National Academy of Sciences, 1974). In 1927, Krug (as cited in
Shupe and Alther, 1966) reported cows dying 18 to 24 hr after ingestion
of sodium fluorosilicate added mistakenly to the diet. Convulsions,
exaggerated chewing motions, and hyperemia were observed.
Cass (1961) reviewed cases of acute fluorosis in livestock. Responses
to various levels of fluorides inducing acute effects are given in Tables
5.23-5.25.
Egyed and Shlosberg (1975) reported 27 field cases of acute sodium
fluorosilicate poisoning in domestic animals. The affected cattle dis-
played drowsiness, loss of appetite, constipation, paresis of the rumen,
and severe abdominal pain. Sheep showed grinding of the teeth and frothing
at the mouth, and bradycardia occurred in horses. Under experimental con-
ditions, mild symptoms of acute sodium fluorosilicate poisoning appeared
-------
214
TABLE 5.23. RESPONSE OF DOMESTIC ANIMALS TO VARIOUS LEVELS OF FLUORIDE DOSAGE: MINIMAL RESPONSE
Compound
NaF
NaaSiF.
Ca phosphate
(2-3Z NaF)
3NaF«AlF,
(synthetic
cryolite)
A1F,
Al,(SiF4)j
BaF2
3NaF«AlF,
Species
of
animal
Cattle
Swine
Sheep
Horse
Horse
Cattle
Sheep
Horse
Cattle
Sheep
Swine
Fluoride
concentration
(ppm)
Acute
300 and less
\-7.0-90.5
M.96-982
24,249
10,860 and 27,150
20,361
14,246
4,334
27,145
Daily fluoride dose
signs not induced
"1-4.12 mg/kg and less
1.83 and 2.35 mg/kg
13.8-41.4 mg/kg
11 mg/kg
196-982 rag per animal
12 g per animal
1.14-1.9 g per animal or
2.54-4.22 mg/kg
25.3, 38.8, and 51.2 mg/kg
599 mg/kg
469 and 1730 mg/kg
1210 mg/kg
178 mg/kg
919 and 1196 mg/kg
Schedule
In diet, several months
In feed, ad lib 75 days
In capsule orally, 1 time
In capsule, every other day.
3 doses
In molasses and bran, 1 time
In bran (refused feed) force
fed, 1 time
In the diet for 11 days
Daily in water, orally 28, 30,
and 15 days respectively
In capsule, 1 time (1 sheep)
In feed, 1 day (2 pigs)
In feed, 1 day (1 pig)
In feed, 1 day (1 pig)
In feed, 1 day (3 pigs)
Marginally acute signs Induced
NaF
Na,SiF»
Cattle
Horse
Cattle
302-<453
2,262 and 6,786
403-<909
0.9-1.36 g per animal
5.27 and 12.8 mg/kg
10.3 mg/kg
19.9 mg/kg
7.9 mg/kg
1.2 to <1.82 g per animal
Dally In water, stomach tube,
several days
In water, orally, once daily
28 and 15 days respectively
In feed, daily during 12 days
omitting days 6 and 11
In capsule, dally for 2 days
In feed, dally for 12 days
In water by stomach tube for
2 to 3 months
Source: Adapted from Cass, 1961, Table I, p. 474. Data collected from several sources. Reprinted by
permission of the publisher.
in 1- to 3-year-old female sheep given oral doses of 25 to 50 mg/kg body
weight. With a 200-mg/kg dose severe symptoms occurred, followed by
death on the sixth day after poisoning. Death occurred 3.0 and 2.5 hr
after administration of 1.5 and 2.0 g of fluorosilicate per kilogram re-
spectively. In fatal poisoning, hypocalcemia; hypomagnesemia; increased
blood sugar; and increased blood phosphorus, glutamate oxaloacetate trans-
aminase, isocitric dehydrogenase, and lactate dehydrogenase were found.
These findings indicated an effect on calcium and magnesium metabolism
and cellular malfunction.
5.5.2.3 Chronic Toxicity Chronic fluorosis results from long-term
excessive fluoride ingestion in livestock and wildlife. Industrialization
(e.g., factories that manufacture aluminum, steel, or phosphate or factor-
ies that heat ores to high temperatures) has made fluoride toxicosis in
livestock an important problem in the United States as well as other coun-
tries (Grunder, 1972; Milhaud and Godfrain, 1975; Shupe, 1970; Suttie,
1969). The onset of fluoride toxicosis is usually insidious, and symptoms
may be confused with other element toxicoses or deficiencies. Fluoride
toxicosis is influenced by the amount of fluoride ingested, duration of
-------
215
TABLE 5.24. RESPONSE OF DOMESTIC ANIMALS TO VARIOUS LEVELS OF FLUORIDE DOSAGE: ACUTE RESPONSE
Species Fluoride
Compound of concentration
animal (ppm)
Daily fluoride dose
Schedule
NaF
NajSiF.
Ca phoaphate
(2-3Z NaF)
CaSiF.
3NaF*AlF,
(synthetic
cryolite)
BaFa
Cattle
Swine
Sheep
Goat
Horse
Cattle
Swine
Goat
Swine
Horse
Swine
600 and more
453-903
13,572
4,524 and more
18,096
>90.5
4,524
909-1,212
606
225.8 and 248.8
Cattle 1,250 and 2,500
Cattle 43,400 and 54,300
6,501
t6.13 mg/kg or more
1.36-2.71 g per animal
37.5 mg/kg
23.6 mg/kg
153 mg/kg
136 mg per animal
136 mg per animal
11.9 and 12.6 mg/kg
73.7 mg/kg
166 mg/kg
46.0 and 55.2 mg/kg
22.6 g per animal
1.82-3.64 g per animal
1.22-2.43 g per animal
121-668 mg/kg
69 mg/kg
190-304 mg per animal
3.4 g per animal increased
to 3.8 g
1.25 and 2.5 g per animal
(intended)
46.4, 63.9, and 94.4 mg/kg
267 mg/kg
In feed for 2 to 3 days
Dally in water, stomach tube,
a few days
In grain feed, 1 time
In water, orally, once daily
for 27 days
In feed for 1 to 3 days
In feed, for 1 meal
Reduced Intake of feed, 75
days
In mixture of milk and water,
orally, 1 time
In mixture of milk and water,
orally, 1 time
In water, stomach tube, dally
6 days
In capsule, 1 time
In grain feed, 1 time
(refused feed)
In feed for 1 day
In grain feed, 1 time
(refused feed)
In feed for a few days
In distilled water for a few
days
In feed for 1 meal
In feed for 4 days
In feed for a few days
In feed for 22 days
In feed for a few days
Lower dose (7.57 mg/kg) in-
creased after 2 days to
higher dose (8.44 mg/kg)
for 2 days
In feed (most of feed refused)
In water, orally, once dally,
16, 72, and 27 days
respectively
In feed for 1 day (1 pig)
Source: Adapted from Cass, 1961, Table
by permission of the publisher.
II, p. 474. Data collected from several sources. Reprinted
ingestion period, fluctuations of fluoride-ingestion level with time, flu-
oride solubility, species of animal, age during fluoride ingestion, level
of nutrition, stress factors, and individual response (National Academy
of Sciences, 1974). Chronic fluorosis may be difficult to diagnose, and
evaluation should be based on clinical, histopathological, radiographical,
and necropsy findings (including chemical analyses). In particular, the
following combination of factors is of prime importance in diagnosing
chronic effects: (1) the extent of dental fluorosis, (2) the extent of
osteofluorosis, (3) the levels of fluoride in the soft tissues, body
fluids, mineralized tissues, and dietary rations, and (4) the occurrence
and degree of intermittent lameness (Shupe, Olson, and Sharma, 1979).
5.5.2.3.1 Dental fluorosis One of the most sensitive reactions to fluo-
ride toxicosis occurs in teeth (Shupe and Alther, 1966). When evaluated
fluoride levels are ingested during tooth formation, both enamel and dentin
-------
TABLE 5.25.
216
RESPONSE OF DOMESTIC ANIMALS TO VARIOUS LEVELS OF FLUORIDE DOSAGE:
LETHAL DOSES
Compound
NaF
NaaSiF»
Species
of
animal
Cattle
(calf)
Swine
Sheep
Goat
Horse
Sheep
Fluoride
concentration
(ppm)
22,620
24,248
Daily fluoride dose
45.2 mg/kg
293 and 554 mg/kg
86.6 and 129.8 mg/kg
15 mg/kg
99.5-199 mg/kg
285 mg/kg
>45 g/kg
24.1 g per animal
Schedule
Orally, 1 time
In feed for 1 day
In capsule, 1 time
In feed for 51 days
In capsule, 1 time
In feed for 1 day
Orally, 1 time
In bran (refused feed,
Goat
Ca phosphate Swine
(2-3* NaF)
3NaF»AlF. Sheep
(synthetic
cryolite)
334 mg/kg
1.82 g per animal
82-90 mg/kg
304 mg increased to
380 mg per animal
so force fed), 1
time
In capsule, 1 time
In feed for 1 meal
In feed for a few days
(calculated)
In feed (low dose 24.4
mg/kg for 4 days in-
creased to 30.4 mg/
kg for 5 days)
Orally, 1 time
Source: Adapted from Cass, 1961, Table III, p. 475. Data collected from several
sources. Reprinted by permission of the publisher.
are adversely affected. Schmidt, Newell, and Rand (1954) found that the
maximum effect of fluoride on incisor enamel of cattle fed 1.0 to 2.5 mg/kg
fluoride daily, occurred approximately 9 to 12 months prior to tooth erup-
tion. Affected teeth show characteristic fluorotic lesions such as mot-
tling, staining, hypoplasia, hypocalcification, and excessive abrasion
(Shupe, 1969). Specific damage varies in degree as influenced by the
fluoride level intake. For the purpose of classification, the following
standards are used in determining the severity of dental fluorosis: (0)
normal smooth, translucent, glossy white appearance, normal shape; (1)
questionable effect slight change from normal, cause may or may not be
determined, enamel flecks but no mottling; (2) slight effect slight
mottling as horizontal striations, normal wear rate; (3) moderate effect
definite mottling and staining, large areas of chalky enamel, slightly
increased wear rate; (4) marked effect definite mottling, staining,
hypoplasia, hypocalcification, enamel may be pitted, increased wear rate;
and (5) severe effect definite mottling, hypoplasia, hypocalcification,
excessive wear rate, and erosion or pitting of enamel.
Histological changes in the dental fluorosis are: the ameloblasts
are prematurely reduced in size and filled with basophilic-staining glob-
ules; epithelial papillae are abnormal; enamel epithelium has series of
interruptions in its smooth surface; and the abnormal enamel matrix does
not calcify normally (National Academy of Sciences, 1971). Affected teeth
-------
217
are subject to more rapid wear and erosion of enamel away from the dentin.
The pattern of excessive or accelerated teeth erosion is important in
determining the relative loss in effective use and length of service of
the teeth (Garlick, 1955). A level of 2 ppm fluoride in livestock drinking
water may cause tooth mottling; however, this is the upper limit of fluo-
ride in drinking water recommended for livestock (National Academy of
Sciences and National Academy of Engineers, 1972).
Dental fluorosis caused by ingestion of mineral supplements containing
high fluoride levels has been reported. Cattle ingesting a daily total of
5976 ppm fluoride from mineral supplements during tooth development showed
badly affected incisors (Dale and Crampton, 1955). Neeley and Harbaugh
(1954) detected distinct evidence of dental effects (mottling, staining,
and abnormal wear) in cattle exposed to fluoride in their diet for six
years at levels of 0.52 to 1.69 mg/kg body weight. Adding 20 to 50 ppm
fluorine as sodium fluoride to the basal ration of cattle caused slight
to severe mottling and wear of teeth respectively (Suttie, Miller, and
Phillips, 1957). The addition of 200 g of calcium carbonate had a slight
alleviating effect. Suttie and Faltin (1971) later exposed dairy heifers
(by ingestion) to 2.5 mg of fluoride per kilogram body weight during their
13th to 15th or 16th to 18th month of age. Dental fluorosis in at least
one pair of incisors was evident, especially in the heifers exposed during
their 16th to 18th month of age. The most severe dental effects were
observed when exposure coincided with the initiation of crown formation
and calcification for a particular incisor.
Greenwood et al. (1964) reported that dental effects or lesions were
indicative of exposure of cattle to fluorine during the time of tooth for-
mation and calcification. They found that positive correlations existed
between dental lesions of certain incisor teeth and degree of abrasion of
certain molar teeth. The first incisor correlated with the second molar,
the second incisor with the third molar, and the third incisor with the
second premolar.
Shupe, Miner, Greenwood, Harris, and Stoddard (1963) found that cattle
fed a diet containing 49 ppm fluoride had moderate to marked dental effects,
whereas a diet containing 93 ppm fluoride resulted in severe dental fluo-
rosis. Calcium fluoride fed at a level to constitute 69 ppm of the total
diet plus low-fluoridecontaining hay (10 ppm fluoride) caused less severe
effects on incisor teeth of dairy heifers than did sodium fluoride fed at
the same level plus low-fluoridecontaining hay (Shupe et al., 1962). This
result indicated that calcium fluoride is less toxic than sodium fluoride.
Horses grazing in areas where cattle and sheep had developed severe fluo-
rosis showed characteristic dental lesions. However, the horses had to
ingest larger amounts of fluoride than cattle or sheep before these symp-
toms became evident (Shupe and Olson, 1971).
Chronic fluorosis was found in a herd of sheep in the Vredenburg
district, Cape Province, South Africa (Zumpt, 1975). The sheep had pro-
truding hipbones, sharp vertebral columns, and poor muscular development.
Incisors were pitted and showed irregular severe wear. Pasture samples
contained 232 ppm fluoride, the source of which was rock phosphate dust
from a fertilizer factory.
-------
218
In cattle grazing in fluorotic and nonfluorotic areas, a close rela-
tionship was found among lesions of incisors, fluorine content of teeth,
and amount of enamel (Mortenson et al., 1964). As the effect of incisors
increased in severity, fluoride levels increased and the percentage of
enamel decreased. The enamel acquired its fluoride before the incisors
erupted from the gums. Table 5.26 illustrates the dental effects of
various fluoride concentrations on several species of livestock.
Examining cattle from areas receiving various fluoride levels from
industrial sources, Wohlers and Newell (1964) found a correlation between
severity of teeth effects and distance from the fluoride source. Almost
50% of incisor pairs within a distance of 2 miles from the source were
classified 4 and 5, whereas at a distance greater than 2 miles, only 5%
were classified 4 and 5 (Figure 5.11).
5.5.2.3.2 Osteofluorosis Prolonged ingestion of low fluoride levels
does not produce adverse effects on bone structure (Shupe and Alther,
1966); however, the intake of excessive levels of fluoride for long time
periods will induce characteristic lesions (National Academy of Sciences,
1974). Bones with fluoride-induced periosteal hyperostosis are chalky
white, rough, and porous. Mineralization of the tendons at the point of
attachment to the leg bones can occur. The severity of the lesions is
partially related to the stress and strain imposed on the bones (National
Academy of Sciences, 1974).
Three mechanisms are involved in the production of osteofluorosis;
(1) impairment of the mechanical properties of normal bone, (2) decompen-
sation of bone function by remodeling, and (3) direct inhibition of normal
osteoblastic activity by excessive fluoride levels (Hodge and Smith, 1965).
Table 5.27 describes the bone lesions associated with exposure of live-
stock to various levels of fluoride.
Shupe, Miner, Greenwood, Harris, and Stoddard (1963) reported marked
bone changes in cows fed 49 to 93 ppm fluoride. Lesions occurred after
1.5 to 2 years in cows fed 93 ppm and 3.5 to 4 years in cows fed 49 ppm.
The first lesions appeared on the medial surface of the proximal third of
the metatarsal bones and were bilateral. The authors suggested that abnor-
mal osteoblastic activity results in formation of abnormally poor organic
matrix with faulty and irregular calcification. Table 5.28 presents data
showing the relationship between fluoride concentration in the diet and
severity of osteofluorosis and ankylosis of the metacarpus and metatarsus
bones. Jones (1972) reported lesions of the bones and arthritis in the
hips of cows, attributing these effects to mineral supplements high in
fluorine. Analysis of feed showed that the intake of fluorine was 50 to
70 ppm of the total dry matter. However, other researchers have not
incriminated elevated fluoride intake with uncomplicated degenerative
osteoarthritis (Shupe, Olson, and Sharma, 1972). Fluoride-induced bone
lesions do not initially or primarily affect articular surfaces, but sec-
ondary changes and overgrowth may affect joint movement in severe cases.
Belanger et al. (1958) found defective growth and mineralization of
bones, costochondral beading, softened and deformed epiphyseal plates,
-------
TABLE S.26. DENTAL LESIONS ASSOCIATED WITH EXPOSURE OF LIVESTOCK TO ELEVATED FLUORIDE LEVELS
Animal
Cattle
Source
Soluble fluoride in feed
Natural fluoride in drinking
Fluoride
concentration
in source
(ppm)
£15 to 25
5
Dally exposure
Av 0.4-0.6 mg/kg
Av £0.95 mg/kg
Age at start of
exposure
Nil to slightly moderate markings
and stain; no abnormal wear
Changes comparable with those
water
Sheep
Soluble fluoride in feed
Natural fluoride in drinking
water
Soluble fluoride in feed
Natural fluoride in drinking
water
Raw rock phosphate In feed
Pasturage contaminated with
fluoride-containing atmos-
pheric waste from industry
Pasturage contaminated with
fluoride-containing atmos-
pheric waste from phosphate-
producing Industry
Na.AlF, In feed
NaF in feed
144
40
SO
16
Estd 77 or
more
Estd 18 or
more
>200
12-14
27-44
40-60
Av £0.88-1.26 mg/kg
Av £1.2-1.64 mg/kg
(peak 1.91)
Av £1.7-2.5 mg/kg
Av £1.7-2.5 mg/kg
1.2 and 2.0 mg/kg
£3.5-4 mg/kg
5 mg/kg
5 mg/kg
60 mg per animal per
day for 195 days
15 mg per animal per
day for 71 days
1 calf
1 lamb
associated with 15 to 25 ppm in
feed, above
Changes comparable with those
associated with 15 to 25 ppm in
feed, above; 60Z of 35 cattle
showed these lesions
Medium to well marked; no abnor-
mal wear
More marked than at 40 ppm; no
particularly abnormal wear
Changes comparable with 50 ppm In
feed above
Severe dental changes marked mot-
tling, staining and abnormal
wear on some animals
Severe dental changes marked mot-
tling, staining and abnormal
wear on some animals
Slight to moderate
Severely marked
Nil
Slight to moderate
Marked to severely marked
Severely marked (exposure Included
tooth-forming period)
Nil (exposed after tooth-forming
period)
Moderate
Moderate
N)
M
VO
-------
TABLE 5.26 (continued)
Animal
Source
Fluoride
concentration
In source
(ppm)
Daily exposure
Age at start of
exposure
Dental lesions
CaF, In feed
Raw rock phosphate in feed
NaF added to drinking water
£7
10
20
0.3
10.0
20.0
10.0
340 mg per animal
7 mg per animal for
3 years
60 mg per animal for
3 years
120 mg or more per
animal for 3 years
1.5
6.0
Winter: av 9 mg per
animal, M3.29 mg/kg;
summer: av 13 mg
per animal, £0.37
mg/kg for 3.5 years
Winter: av 18 mg per
animal, ^p.57 mg/kg;
summer: av 27 mg
per animal, ^3.71
mg/kg for 3.5 years
Winter: av 37 mg per
animal, ^JLIO mg/kg;
summer: av 53 mg
per animal, ^..45
mg/kg for 3.5 years
After 1 year old
After 1 year old
After 1 year old
Feeder yearlings
After 1 year old
3 to 6 months for
2 years
At 13 to 14 months
(animals penned)
At 13 to 14 months
(animals penned)
From birth, on pas-
ture almost 7
years
From birth, on pas-
ture almost 7
years
From birth, on pas-
ture almost 7
years
At 2.5 to 3.5 years
of age on pasture
for 2 years
Well marked
Nil
Mild to moderate
Severe
Slight discoloration
Fracturing and erosion
Nil to very slight mottling; no
abrasion (molar teeth fluoride
content 1300 ppm)
Nil
Moderately severe, selective
abrasion (molar teeth fluoride
content 1900 ppm)
Severe (molar teeth fluoride con-
tent 5100 ppm)
Nil (molar teeth fluoride con-
tent 300 ppm)
Slight mottling and selective
abrasion (molar teeth fluoride
content - 2100 ppm)
Severe (molar teeth fluoride
content - 2700 ppm)
Nil (molar teeth fluoride con-
tent <1000 ppm)
to
to
O
-------
TABLE 5.26 (continued)
Animal
Source
Fluoride
concentration
In source
(ppm)
Daily exposure
Age at start of
exposure
Dental lesions
Swine
Natural fluoride in ground-
water 'for drinking purposes
Pasturage contaminated with
fluoride-containing atmos-
pheric waste from industry
NaF added to feed
20.0
10.0
10.0
10.0
vS.O
&2.0
12.0 (at time
of survey)
2£1.0
^4.0
£16.0
290
580
Calcd: 43 to 73 mg
per animal
NaF or NaaSiF« added to feed
Raw rock phosphate added to 330
feed
15 mg per animal,
for 117 days
At 2.5 to 3.5 years
of age on pasture
for 2 years
At 3 months; alter-
nating 3 months
exposed, 3 not
6 months exposed,
6 not
6 months exposed,
3 not
From birth irregu-
larly for 1 year
From birth for 6
years
From birth
From birth
From birth
From weaning for 2
or more years as
reproducing
females
From weaning for 2
or more years as
reproducing
females
8 weeks old
From weaning for 2
or more years as
reproducing
females
Nil (molar teeth fluoride con-
tent <1000 ppm)
Slightly moderate, some weakening
of cutting surfaces
Moderately severe, some fractures
Hoderate, some wear
Chipping and mottling
Severe, marked wear on central
incisors
20Z of flock with badly worn and
broken teeth
100Z of flock severely affected
~60Z severely affected
High percentage of flock with
much less effect than at 44 ppm
above
Moderate to severe
Moderate to severe
Moderate
Moderate to severe
N)
-------
TABLE 5.26 (continued)
Fluoride
Animal Source concentration exposure Age at start of Dental lesions
In source exposure
(ppm)
650 From weaning for 2 Moderate to severe
or more years as
reproducing
females
569 ^19-26 mg/kg Young pigs for 2 Severe
years
140 Young pigs for 2 Moderate
years
Source: Adapted from Cass, 1961, Table V, pp. 530-531. Data collected from several sources. Reprinted by permission of the publisher.
NJ
-------
223
OPNL-OWG 76-18323
50
0-1 1-2 2-3 3-4
DISTANCE FROM PLANTS IN ANNULAR SEGMENTS (miles)
Figure 5.11. Variation of incisor classification of 4 or 5 with
distance from industrial plants in annular segments. Source: Adapted
from Wohlers and Newell, 1964, Figure 11, p. 148. Reprinted by permission
of the publisher.
-------
TABLE 5.27. SKELETAL LESIONS ASSOCIATED WITH EXPOSURE OF LIVESTOCK TO ELEVATED FLUORIDE LEVELS
Fluoride
Animal Source concentration
in source
(ppm)
Cattle NaF added to the feed 30
30
40
"""" * "
50
20
14-94
7
107
NaF in a capsule, orally ^907 in feed
^1207 in feed
Daily exposure
Av 0.63-0.91 mg/kg
Av 0.63-0.91 mg/kg
Av 0.88-1.26 mg/kg
Av 1.20-1.60 mg/kg
Av 0.40-0.61 mg/kg
0.32-2.12 mg/kg
v-2.0 mg/kg
^2.5 mg/kg
^3.0-4.0 mg/kg
i,2.2 mg/kg
;w&.25 mg/kg
^9.0 mg/kg
Pasturage contaminated with Exposure uncalculated but elevated;
fluoride-containing atmos- hay: 20-80;
dust on hay: 260-
Age at start of
exposure
2 years old for 5
lactations, dairy
4 to 6 years old (2
to 4 lactations)
for an additional 3
lactations, dairy
4 to 6 years old (2
to 4 lactations)
for an additional 3
lactations, dairy
Calves, 3 months old
2 years old, dairy
2 years old, dairy
20 to 24 months old,
beef
3 to 5 years old,
hill cattle
20 to 24 months old,
beef
20 to 24 months old,
beef
20 to 24 months old,
beef
Various ages
Duration of
exposure before
appearance
of lesion
5.5 years
3 years (no
pasture)
3 years (no
pasture)
3 years (no
pasture)
3 years (no
pasture)
372 days
2 years
2 years
422 days
Within 8 to 10
months
422 days
71 and 104 days
respectively
40 and 81 days
respectively
After 2 to 3
months
Type of lesion
Thin mantle of periosteal
overgrowth on bones care-
fully cleaned at slaughter
Thin mantle of periosteal
overgrowth on bones care-
fully cleaned at slaughter
Increasing roughness and
thickening, some minerali-
zation of periarticular
structures and ligamentous
attachments on bones care-
fully cleaned at slaughter
Increasing roughness and
thickening, some minerali-
zation and periarticular
structures and ligamentous
attachments on bones care-
fully cleaned at slaughter
Nil
Rib biopsies gross and
microscopic, nil
Nil
Slight osteofluorosis
Nil
Osteofluorosis
Osteofluorosis
Osteofluorosis
Osteofluorosis
Palpable osteofluorosis on
ribs
pheric waste from industry 480
Rock phosphate in feed >200 400 ppm estd as 6
mg/kg
Experimentally at 6
months old, clin-
ically at various
ages
to 6 years
Osteofluorosis
-------
TABLE 5.27 (continued)
Animal Source
Natural fluoride in drink-
Ing water
NaF added to drinking water
Sheep NaF in feed
Raw rock phosphate in feed
NaF added to drinking water
Swine NaF in feed
Raw rock phosphate in feed
NaF, NaaSiF., Na.AlF.
(mineral cryolite), or
Na.AlF. (synthetic
cryolite)
Fluoride
concentration
in source
(ppm)
25-32
14.4-18.6
206
111
112
10 and 20
10 and 20
10 and 20
±290
>330
>293
140
Daily exposure
Calcd as 1.2-2.0
mg/kg
V4.91 and 5.35 mg
per animal
15.0 mg/kg
i30 mg/kg
^3.9 mg/kg
120 mg or less per
animal
160-170 mg per
animal
Up to 6.0 mg/kg
Up to 6.0 mg/kg
2£1 to 14 mg/kg or
more
15.0 mg/kg
Age at start of
exposure
As calves, and as
lactating cows
2 calves, starting
with 50 and 86 kg
One 2.5 years old,
one 6 months old
1 year old
1 year old
Weanlings
1 year old
1 year old
Growing lambs
Ewes
13-14 months old, fed
in pens
2.5-3.5 years old,
grazing on pasture
13-14 months old,
grazing on pasture
Weanlings
Weanlings
Young pigs
Young pigs
Young pigs
Duration of
exposure before
appearance
of lesion
Up to 5 3/4
years
Host of lifetime
Most of lifetime
10 months
1 month
140 days
3 years
98 days
3 years
3 years
136 to 235 days
2.5 to 3 years
3.5 years
2.6 months
6 years
Within 144 days
Within 144 days
5 years
5 years
168 days
Type of lesion
Nil
Osteofluorosls
Nil
Osteofluorosis
Osteof luoroais
Nil
Nil
Nil
Nil
Osteofluorosls
No osteofluorosis mentioned
No osteofluorosis mentioned
No osteofluorosis mentioned
No osteofluorosis mentioned
No osteofluorosis mentioned
Osteofluorosis
Osteofluorosls
Size, smoothness, texture and
color of bones changes; no
osteofluorosis mentioned
No gross changes of bones
Palpable osteofluorosis of
mandible, and lesser degree
of diaphyses
N3
10
Ul
Source: Adapted from Cass, 1961, Table VI, p. 533. Data collected from several sources. Reprinted by permission of the publisher.
-------
226
TABLE 5.28. THE EFFECTS OF ADDED DIETARY INCREMENTS OF FLUORIDE (AS SODIUM
FLUORIDE) ON THE CALCIFICATION OF BONES AND JOINTS OF DAIRY COWS
Lot
I
II
III
IV
V
VI
Fluoride _
, , , Cow
added
/ \ No-
(ppm)
0 2
3
4
20 5
6
7
8
30 10
11
12
40 13
14
15
16
50 17
19
20
50 + CaCOs 22
23
24
Degree of
osteof luorosis
a
Metacarpus Metatarsus
0
0
0
0
0
0
0
1
0
1
1
1
1
2
4
3
4
4
4
3
0
0
0
0
0
0
0
1
0
2
2
2
1
2
5
3
4
4
4
4
Degree of cartilage
calcification0
Metacarpus
0
0
0
1
0
0
0
1
1
2
2
1
0
0
2
2
2
1
2
1
Metatarsus
0
0
0
1
0
0
0
3
1
3
2
2
1
1
5
4
3
4
4
2
aBased on a rating of 0 for normal bone and 5 for the most severely affected.
Source: Adapted from Suttie, Phillips, and Miller, 1958, Table 3, p. 300.
Reprinted by permission of the publisher.
and enlarged and malformed bone trabeculae in young pigs fed 30, 60, and
90 days on a diet containing 1000 ppm sodium fluoride. Shorter and thicker
bones were found in young pigs from sows fed a diet containing 450 ppm
fluoride (Forsyth, Pond, and Krook, 1972). Decreased length, width, vol-
ume, and fresh weight of the humeri of baby pigs from sows fed additional
fluoride indicated impaired skeletal growth of fetuses due to fluoride.
At high fluoride levels, increased dietary calcium and phosphorus levels
decreased fluoride accumulation in the offspring.
5.5.2.3.3 Lameness Lameness associated with fluorosis is usually a
nonspecific stiffness and is intermittent in nature (National Academy of
Sciences, 1974). In advanced cases of fluorosis, lameness may be associ-
ated with bone lesions and calcification of ligaments. Lameness has been
correlated with the degree of fluoride exposure (Table 5.29), but varia-
tion in other possible inducing factors makes a causal relationship dif-
ficult to confirm. In some severe cases, animals may eventually refuse
to walk and stand, and intermittently move around on their knees (Shupe,
1972).
-------
TABLE 5.29. LAMENESS ASSOCIATED WITH EXPOSURE OF LIVESTOCK TO ELEVATED FLUORIDE LEVELS
Animal Source
Cattle NaF in feed
*
Raw rock phosphate in feed
Natural fluoride in
drinking water
Pasturage contaminated with
fluoride-containing atmos-
pheric waste from industry
Swine Raw rock phosphate in feed
NaF in feed
Fluoride
concentration Daily exposure
in source (mg/kg body wt)
(pptn)
SO Av VL4 (peaks 2.0)
100-200 Av 3.0-4.0
Eat. t.6. 0
18 ^2.0
25-32 or more
20-80
98
650
580
1000
Age at start of
exposure
2 years of age, after
first calving
Yearling cattle
Birth
Young adults and
adults
Adult dairy cattle
Weanlings
Weanlings
120-150 days old
Duration of
exposure before
appearance
of lesion
At 5th
lactation
Within 8 to 16
months
Common occur-
rence by 4th
year
During lifetime
During lifetime
1-2 years
About 1 month
5-7 months
144 days
40-75 days
Effect on locomotion
Lameness and stiffness
appeared for the first time
Lameness and stiffness
Lameness
Lameness
t<20X of herd lame
Lameness
Lameness
Reluctance to move and
stiffness
Reluctance to move and
stiffness
Leg stiffness
NJ
N>
Source: Adapted from Cass, 1961, Table VIII, p. 534. Data collected from several sources. Reprinted by permission of the publisher.
-------
228
Cows fed a 93 ppm sodium fluoride diet showed signs of lameness at
2.5 years; after 3.5 years, two out of eight cows went down on their knees
(Greenwood et al. 1964). After three weeks they partially recovered and
apparently walked normally. However, intermittent lameness occurred again
during the remainder of the trial period. Cows on 49 ppm sodium fluoride
showed lameness after 4.5 years. It should be noted, however, that lame-
ness in the absence of other signs of excessive fluoride ingestion cannot
be considered an indication of fluorosis. Stiffness and lameness occur
in livestock for reasons other than high fluoride ingestion.
5.5.2.3.4 Reproduction There is some discrepancy in the literature
concerning effects of excessive fluoride ingestion on reproduction. Most
researchers agree that there is no direct effect on reproduction. However,
because of fluoride's impairment of general body health, reproduction could
be indirectly affected (National Academy of Sciences, 1974). Neeley and
Harbaugh (1954) found that daily food and water levels of 0.52 to 1.69 mg
of fluoride per kilogram body weight did not affect reproductive efficiency
in cattle exposed for six years. Shupe (1972) and Shupe, Miner, Greenwood,
Harris, and Stoddard (1963) also reported that reproductive efficiency in
cattle was not affected when up to 93 ppm sodium fluoride (total dry-weight
basis) was added to the diets. In contrast to these findings, cattle re-
ceiving 8 and 12 ppm fluoride in drinking water showed an increase in post-
calving anestrus in the second season of reproduction (van Rensburg and
de Vos, 1966). The third season revealed an appreciable decline in fertil-
ity in animals receiving over 5 ppm fluoride, and in the fourth season,
cattle on 8 and 12 ppm also showed a reduced reproduction efficiency (Fig-
ure 5.12). This effect on reproduction was manifested prior to evidence
of general health impairment. The authors suggested that the fluorine
content of water should be under 5 ppm for normal reproduction since flu-
oride levels in water are more toxic than similar levels in dry matter.
5.5.2.3.5 General conditions and systemic effects Excessive fluoride
intake can result in appetite impairment, causing general unthriftiness
and loss of condition (Shupe, 1972). Dry hair and thick nonpliable skin
have been observed in animals with fluorosis. Fluoride effects can also
be more severe on undernourished animals (Suttie and Faltin, 1973).
Stoddard, Harris, Bateman, Shupe, and Greenwood (1963) reported that
cattle receiving 93 ppm sodium fluoride in their diet consumed less hay
and total dry matter than those on lower sodium fluoride levels. However,
no significant loss in body weight gain was detected during the twenty-
three 112-day periods of the trial. No effects were found on increases
in height. Hobbs and Merriman (1962) and Hobbs et al. (1954) reported
that cattle receiving rations containing 200 to 1200 ppm fluoride showed
a decrease in body weight directly related to the level of fluoride inges-
tion. Table 5.30 presents the nutritional symptoms found with excessive
fluoride exposure.
Sheep given water containing 10 ppm fluoride showed no adverse effects
but did have a decrease in wool production (Peirce, 1959). Water contain-
ing 20 ppm fluoride adversely affected not only wool production but also
the health of the sheep. Earlier, Peirce (1954) reported that intake of
-------
229
ORNL-DWG 79-20904
\ 2
BREEDING SEASONS
Figure 5.12. Calving rate of cows on three levels of fluorine intake.
Source: Adapted from van Rensburg and de Vos, 1966, Figure 1, p. 189.
Reprinted by permission of the publisher.
water containing up to 20 ppm fluoride had no effect on general health or
body weight.
In evaluating fluoride effects on the hematopoietic system, liver,
and thyroid gland in cattle, Hoogstratten et al. (1965) fed heifers 10,
25, 50, and 100 ppm sodium fluoride for 7.5 years. They found that con-
centrations up to 100 ppm did not induce gross, histological, or functional
effects on the thyroid gland or liver. There were no significant changes
in the serum calcium or phosphorus. In cattle fed 100 ppm sodium fluoride,
a slightly higher total eosinophil count and a lower level of serum folic
acid activity was induced. No anemia or abnormalities of the bone marrow
were detected.
5.5.2.3.6 Milk production -Milk production is not directly affected by
ingestion of low levels of fluoride. Effects on milk production are prob-
ably secondary to major symptoms and lesions and result from interference
with lactogenesis and alteration of metabolic functions. Lactating cows
were fed dietary fluoride (sodium fluoride) over a 5.5-year period. Under
adequate nutritional conditions, 50 ppm fluoride had no effect on milk pro-
duction. However, at 1.5 mg of fluoride per kilogram body weight, certain
cows had reduced milk and butterfat production as a result of anorexia.
-------
TABLE 5.30. NUTRITIONAL SIGNS ASSOCIATED WITH EXPOSURE OF LIVESTOCK TO ELEVATED FLUORIDE LEVELS
Animal
Cattle
Beef
Dairy
Hill bulls
Dairy
Sheep
Feeder lambs
Lambs
Ewes
Swine
Self feeder
In dry lot
Self feeder
in pasture
Self feeder
in dry lot
Self feeder
in pasture
Source
NaF in feed
NaF in feed
NaF in feed
Rock phosphate
in feed
NaF in feed
Raw rock phos-
phate in feed
Raw rock phos-
phate in feed
Raw rock phos-
phate in feed
Raw rock phos-
phate in feed
Raw rock phos-
phate in feed
Raw rock phos-
phate in feed
Fluoride
concentration
in source
(ppm)
>40
40
50
50
100
440 and 880
206
106
111
217
140
293
293
569
569
Daily
exposure
(mg/kg
body wt)
Av -\-1.4
1.4
1.7
1.9
i2.12
3.0
1.5
3.0
6.0
1.5-3.0
6.0
$.1 to 14
^11 to 14
£L9 to 26
2iL9 to 26
Age at start
of exposure
1-2 years
Freshening 2
years old
Freshening 2
years old
2nd and 4th
lactation
3 months
Adult
117-193 days
8-12 months
8-12 months
8-12 months
Growing
Growing
Growing
Yearling
Yearling
Young pig
Young pig
Young pig
Young pig
Young pig
Young pig
Duration of
exposure before
appearance
of lesion
2 years or longer
5th lactation
3rd lactation
3 additional
lactations
16 months
7 months or longer
During 1st lactation
140 days
140 days
3 years
136-235 days
136-235 days
136-235 days
2 years and more
2 years and more
2 years
2 years
2 years
2 years
2 years
2 years
Depressed
feed
intake
Yes
Yes
Yes
No
No
a
Yes
Yes
No
No
No
No
Yes
No
Yes
a
a b
Yes*
Yes0
a
a
Depressed
weight gains
or growth
Yes
No
Yes
No
No
Yes
Yes
Yes
No
No
No
c
Yes
0
Yes
Yes
No
Yes
No
Yes
Yes
?Not mentioned.
Sows during suckling.
°Slight.
Source: Adapted from Case,
publisher.
1961, Table VII,
p. 534. Data
collected from
several sources. Reprinted by permission of the
ro
u>
o
-------
231
Cows tolerated 30 ppm fluoride, 40 ppm fluoride was marginal, but 50 ppm
induced fluorosis. A latent period of two to five years elapsed between
initial dental effects and inhibition of milk production. Stoddard,
Bateman, Harris, Shupe, and Greenwood (1963) reported that 93 ppm fluoride
reduced milk production in the third and subsequent lactations of Holstein
cows maintained on diets with added fluoride from three months of age to
7.5 years of age. Milk production of some cows on 49 ppm sodium fluoride
was adversely affected in the fourth and subsequent lactations. The tol-
erance level of fluoride for lactation was less than 49 ppm on a total
dry-diet basis (Stoddard, Bateman, Harris, Shupe, and Greenwood, 1963).
5.5.2.4 Tolerance Tolerance to fluoride varies with the solubility of
the fluoride in the gastrointestinal tract (Phillips, 1956). At levels
of fluoride where fluorosis occurs, there is a difference in toxicity of
soluble and relatively insoluble fluorides. Therefore, tolerance levels
for soluble fluorides and fluorides exposed by water solutions are lower
than the tolerance levels for fluoride in dry matter (Underwood, 1971).
Fluoride tolerance differs among species, as shown in Table 5.31.
Horses are able to tolerate more fluoride than beef or dairy cattle but
less than feeder lambs. Even though Table 5.32 indicates cattle as being
the most sensitive of livestock, Peirce (1959) has shown that sheep have
adverse effects from fluoride concentrations in water as low as 20 ppm.
Swine appear to be the most resistant mammal to fluorosis. Breeding and
lactating animals seem to have a lower tolerance for fluorides than do
finishing animals (Table 5.32). This is partially due to both the eventual
human utilization of the animal and the exposure length dose response
patterns associated with these uses. For example, Harris et al. (1958)
demonstrated that total feed levels of 112 ppm fluoride (dry weight) had
no significant effect on the performance of feeder lambs over a fattening
period of 14 weeks.
Therefore, establishment of tolerance levels for livestock should
take into consideration the economic use and well-being of the animal.
Animals used for breeding purposes have a lower tolerance than those being
used for slaughter, since the long-term general health of the animal in-
fluences breeding success.
-------
232
TABLE 5.31. DIETARY FLUORIDE TOLERANCES
FOR DOMESTIC ANIMALS*2
Animal Performance*
(ppm)
Beef or dairy heifers ,
Mature beef or dairy cattle
Finishing cattle
Feeder lambs
Breeding ewes
Horses
Finishing pigs
Breeding sows
Growing or broiler chickens
Laying or breeding hens
Turkeys*?
Growing dogs
40
50
100
150
60
60
150
150
300
400
400
100
Pathology0
(ppm)
30
40
NA*
n/
ID
40
NA
100
ID
ID
ID
50
values are presented as ppm fluoride in dietary dry
matter and assume the ingestion of a soluble fluoride,
such as sodium fluoride. When the fluoride in the ration
is present as some form of defluorinated rock phosphate,
these tolerances may be increased by 50%.
^Levels fed without clinical interference with normal
performance.
°A.t this level of fluoride intake pathologic changes
occur.
"Cattle first exposed to this level at three years of
age or older.
eNA not applicable.
JID insufficient data.
^Level shown to be safe for growing female turkeys.
Source: Adapted from the National Academy of Sciences,
1974, Table 4, p. 55. Reprinted by permission of the
publisher.
-------
233
TABLE 5.32. TOLERANCE OF ANIMALS FOR FLUORIDE
^
Species
Fluoride concentration in ration (ppm)
Finishing animals to be
*°" «* *-*« yith
average feeding period
Dairy and beef
heifers
Dairy cows
Beef cows
Steers
Sheep
Horses
Swine
30
30
40*
NA*
50
60
70
100
100
100
100
160
NA
NDC
Tolerances based on sodium fluoride or other fluorides
of similar toxicity.
^NA not applicable.
CND not determined.
Source: Adapted from Shupe, Olson, and Sharma, 1972,
Table 1, p. 358. Reprinted by permission of the publisher.
-------
234
SECTION 5
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Am. J. Physiol. 182:383-389.
62. Phillips, P. H. 1956. The Effects of Air Pollution on Farm Ani-
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63. Phillips, P. H., J. W. Suttie, and E. J. Zebrowski. 1963. Effects
of Dietary Sodium Fluoride on Dairy Cows: VII. Recovery from
Fluoride Ingestion. J. Dairy Sci. 46:513-516.
64. Rogler, J. C., and H. E. Parker. 1972. Effects of Excess Calcium
on a Fluoride-Magnesium Interrelationship in Chicks. J. Nutr.
102:1699-1707.
65. Rosenfeld, D. D., and J. R. Kilsheimer. 1974. Insecticidal Activ-
ity of ct,a,a-Trifluoroacetophenone Oxime Carbamates and Thiophos-
phates. J. Agric. Food Chem. 22(6):926-930.
66. Sawada, N., and L. I. Rebhun. 1969. The Effect of Dinitrophenol
and Other Phosphorylation Uncouplers on the Birefringence of the
Mitotic Apparatus of Marine Eggs. Exp. Cell Res. 55:33-38.
67. Schmidt, H. J., G. W. Newell, and W. E. Rand. 1954. The Controlled
Feeding of Fluorine, as Sodium Fluoride, to Dairy Cattle. Am. J.
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68. Shupe, J. L. 1969. Fluorosis of Livestock. Air Quality Monograph
No. 69-4, American Petroleum Institute, New York. 29 pp.
69. Shupe, J. L. 1970. Fluorine Toxicosis and Industry. Am. Ind.
Hyg. Assoc. J. 31:240-247.
70. Shupe, J. L. 1972. Clinical and Pathological Effects of Fluoride
Toxicity in Animals. In: Carbon-Fluorine Compounds: Chemistry,
Biochemistry and Biological Activities. Elsevier, Excerpta Medica,
and North-Holland, Associated Scientific Publishers, Amsterdam,
London, and New York. pp. 357-388.
71. Shupe, J. L., and E. W. Alther. 1966. The Effects of Fluorides
on Livestock, with Particular Reference to Cattle. In: Handbook
of Experimental Pharmacology, Vol. 20, Part 1, Pharmacology of Fluo-
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72. Shupe, J. L., L. E. Harris, D. A. Greenwood, J. E. Butcher, and
H. M. Nielsen. 1963. The Effect of Fluorine on Dairy Cattle: V.
Fluorine in the Urine as an Estimator of Fluorine Intake. Am. J.
Vet. Res. 24:300-305.
73. Shupe, J. L., M. L. Miner, D. A. Greenwood, L. E. Harris, and G. E.
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74. Shupe, J. L., M. L. Miner, L. E. Harris, and D. A. Greenwood. 1962.
Relative Effects of Feeding Hay Atmospherically Contaminated by
Fluoride Residue, Normal Hay Plus Calcium Fluoride, and Normal Hay
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76. Shupe, J. L., A. E. Olson, and R. P. Sharma. 1972. Fluoride Tox-
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New York. pp. 517-540.
78. Sigler, W. F., and J. M. Neuhold. 1972. Fluoride Intoxication in
Fish: A Review. J. Wildl. Dis. 8(3):252-254.
79. Simon, G., and J. W. Suttie. 1968. Effect of Method of Fluoride
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80. Slesinger, L., and J. Tusl. 1966. Fluoride Content in Feed Com-
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81. Smith, S. B., N. S. Cowen, J. W. Dodge, L. S. Mix, G. L. Rumsey,
A. A. Warner, and D. F. Woodward. 1970. Effects of Added Levels
of Fluorine on Selected Characteristics of Egg Shells and Bones
from Caged Layers (abstract). Poult. Sci. 49(4):1438-1439.
82. Stewart, D. J., T. R. Manley, D. A. White, D. L. Harrison, and
E. A. Stringer. 1974. Natural Fluorine Levels in the Bluff Area,
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83. Stoddard, G. E., G. Q. Bateman, L. E. Harris, J. L. Shupe, and
D. A. Greenwood. 1963. Effects of Fluorine on Dairy Cattle: IV.
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84. Stoddard, G. E., L. E. Harris, G. Q. Bateman, J. L. Shupe, and
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239-242.
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Alternating Periods of High- and Low-Fluoride Ingestion on Dairy
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87. Suttie, J. W., and E. C. Faltin. 1971. Effect of a Short Period
of Fluoride Ingestion on Dental Fluorosis in Cattle. Am. J. Vet.
Res. 32(2):217-222.
88. Suttie, J. W., and E. C. Faltin. 1973. Effects of Sodium Fluoride
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34(4):479-483.
89. Suttie, J. W., R. F. Miller, and P. H. Phillips. 1957. Studies
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Effects and the Developmental Symptoms on Fluorosis. J. Nutr. 63:
211-224.
90. Suttie, J. W., P. H. Phillips, and E. C. Faltin. 1964. Serum
Fluoride in the Chick. Proc. Soc. Exp. Biol. Med. 115(3):575-577.
91. Suttie, J. W., P. H. Phillips, and R. F. Miller. 1958. Studies
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92. Sweetman, H. I. 1941. Tests for Toxicity of Arsenicals and Sodium
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and Animal Nutrition, 3rd ed. Academic Press, New York. pp. 369-
406.
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94. Valentin, J. 1971. Recombination in Droaophila After Fluoride
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95. van Rensburg, S.W.J., and W. H. de Vos. 1966. The Influence of
Excess Fluorine Intake in the Drinking Water on Reproductive Effi-
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96. Vohra, P. 1973. Fluoride Tolerance of Japanese Quail. Poult.
Sci. 52:391-393.
97. Weber, C. W., A. R. Doberenz, and B. L. Reid. 1969. Fluoride
Toxicity in the Chick. Poult. Sci. 48:230-235.
98. Weismann, L., and L. Svatarakova. 1973. Influence of Sodium Fluo-
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99. Weismann, L., and L. Svatarakova. 1974. Toxicity of Sodium Fluo-
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29(11):847-852.
100. Wohlers, H. C., and G. W. Newell. 1964. A Field Investigation of
Fluorosis in Cattle. J. Air Pollut. Control Assoc. 14(5):139-148.
101. Wright, D. A., and A. W. Davison. 1974. Fluoride in Marine Ani-
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102. Wright, D. A., and A. W. Davison. 1975. The Accumulation of Fluo-
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103. Zumpt, I. 1975. Chronic Fluoride Poisoning in Sheep. J. S. Afr.
Vet. Assoc. 46(2):161-163.
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SECTION 6
BIOLOGICAL ASPECTS IN HUMANS
6.1 SUMMARY
Fluoride at an intermediate concentration (biological verging to
pharmacological) is beneficial to humans, but high concentrations are
toxic. Fluoride may be essential for nucleation of bone crystalline
material, maintenance of reproduction, and other metabolic processes.
There is continuing controversy engineered by those opposing fluo-
ridation of water as a public health measure. Evidence is overwhelming
that fluoridation is beneficial and is the most cost-effective and safest
way of improving dental health in a population. An even higher level of
fluoride than the 1.0 ppm considered optimal for caries resistance may
be of benefit to older persons in preventing osteoporosis. Thus there
appears to be no reason to withhold the benefits of fluoridation from the
general population. Despite controversial aspects of the problem, it
appears the real obligation of a public health authority is maintaining
an optimal level of fluoride in the public water supply, adding fluoride
when it is lacking and removing it when there is excess.
Man's intake of fluoride is chiefly through the diet with drinking
water furnishing the largest amount. Absorption of fluoride is largely
passive; the amounts absorbed depend on solubility. Absorbed fluoride is
quickly distributed throughout the body, easily crossing membranes and
going into tissues. Bone is a sink for fluoride, and uptake is so effec-
tive that bone blood flow can be measured by the rate of scavenging of 18F
from blood. Excess fluoride is sequestered by bone and released slowly
when the intake level subsides. Bones primarily accumulate fluoride as
fluorapatite, and to a lesser extent as magnesium fluoride, throughout an
individual's lifetime. The pattern of fluoride accumulation versus the
age of an individual is not fully known. Long-term intake of fluoride at
levels above 8 ppm causes fluorosis. Fluorosis is chiefly manifested by
changes in the bony structure with some parts of the bone becoming hyper-
calcified and other parts showing deterioration. In radiographs, these
bones are more dense and less structured than normal bones. When fluorosis
is pronounced, exostoses and bony infiltrations may cause crippling and
pain. Once in the bone, fluoride does not cause fluorosis; damage occurs
when fluoride is present in excess and interferes with the metabolism of
the osteocytes and the osteoblasts.
Fluoride absorbed into blood is excreted largely through the kidneys,
by relative lack of reabsorption. Some fluoride is excreted in sweat,
and there is a slight secretion through the mucosa of the intestines into
the gut. Some of the fluoride in blood is organically bound, which may
represent uptake of commercially used fluorinated products. The amounts
are small, and there is no indication of a hazard.
242
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The fetus obtains the fluorine needed for calcification of bony tis-
sues from its mother. The placenta plays a largely passive role but may
sequester fluoride through calcifications in case of excess.
Fluoride (at concentrations greater than trace level) inhibits some
enzymes including oxidative enzymes, phosphate-transferring enzymes, and
some lipases. It often acts by interfering with the magnesium necessary
for the enzyme action. Although fluoride stimulates adenylate cyclase,
the significance of this behavior is not clear because the effect has
been demonstrated primarily in broken cell preparations. At levels nor-
mally found in blood, fluoride does not seem to have any deleterious ef-
fect on any particular organ, including the thyroid gland; however, it
can adversely affect a number of physiological processes such as nerve
action, protein synthesis, membrane permeability, and possibly hormonal
secretions.
Fluoride is an irritant poison and is lethal starting at oral doses
of about 3 g. Aspects of fluoride poisoning leading to death are: block-
age of respiratory enzymes; interference with necessary body functions
controlled by calcium, such as blood clotting, membrane permeability,
nerve transmission, and muscle action; specific organ damage, particularly
to the kidneys; shock; and general collapse. Except for organ damage, the
effects are reversible, and with prompt treatment not only can a person
survive but recovery can be complete. In the case of exposure to hydrogen
fluoride and F2, the extremely corrosive nature of the reacting compounds
adds further damaging effects to the general fluoride toxicity. Absorbed
as vapors, they cause extreme irritation to the lungs resulting in edema
and tissue damage, as well as the systemic toxic effects.
Although the public may be exposed to numerous inorganic- and organic-
containing products, concentrations of these products are generally low
and innocuous. Man's chief exposure to excessive fluoride occurs in indus-
trial situations, as in processing industries where fluoride is associated
with other substances (e.g., phosphate fertilizer processing) or where
fluorides are being used as part of some process (e.g., steel making or
in chemical industries). Threshold limit values for industrially encoun-
tered fluoride compounds have been established. Exposure levels may be
monitored by air sampling, and worker uptake may be monitored by urine
analysis.
Information presented in this chapter indicates that inorganic fluo-
ride is probably not carcinogenic, but that at high doses it may be muta-
genic and teratogenic in experimental animals. The results of one study,
however, indicate that fluoride is not mutagenic in mice or bacteria. It
is important to realize that the concentrations of inorganic fluoride nor-
mally encountered by the general public (e.g., in fluoridation of public
water supplies) are not teratogenic, mutagenic, or carcinogenic. There
is concern, however, about potential teratogenic and other reproductive
effects among persons chronically exposed to fluorinated anesthetics
(organic fluoride compounds).
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6.2 ESSENTIALITY OF FLUORIDE
Because of the ubiquitous occurrence of fluoride in its various
forms and the obviously long association of living things with fluoride-
containing compounds, researchers have repeatedly tried to test whether
fluoride is an essential element for life. A representative study was
done by Doberenz et al. (1964). The difficulty in these studies is in
eliminating fluorine from the diet. The researchers prepared a diet from
hydroponically grown sorghum and soybeans that contained only 0.005 ppm
fluoride. Amino acid analyses of the soybeans and sorghum after several
generations of growing with very low concentrations of fluoride were no
different from those of plants grown under field conditions. The diet,
with and without added fluoride, was fed to rats from weaning to 90 days
of age. Growth of the rats was not impaired, and of numerous serum and
liver enzyme activities tested the only significant differences noted were
an increase in serum isocitric dehydrogenase and a concomitant decrease
in activity of this enzyme in the liver. Levels of bone fluoride were
significantly lower, but no adverse physiological effects were noted.
Thus, essentiality was not demonstrated.
Messer, Armstrong, and Singer (1974) also reviewed the question of
essentiality. They established two criteria as minimum requirements that
must be met before fluorine, or any other trace element, was considered
essential: (1) a specific deficiency state should be produced by a diet
lacking the element in question, but which is otherwise adequate and sat-
isfactory; and (2) the deficiency should be prevented or cured by addition
to the diet of that element alone. They added to these requirements three
supporting criteria: (1) in general, the deficiency should be correlated
with subnormal tissue levels of the element; (2) the deficiency should be
accompanied by pertinent biochemical or physiological changes which will
be prevented or cured when the deficiency is prevented or cured; and (3)
a homeostatic control mechanism regulating tissue levels of the element
should be demonstrable.
On the basis of studies with mice and rats showing retarded growth,
infertility, or anemia on low-fluoride diets and subsequent recovery from
these states upon administration of fluoride, Messer, Armstrong, and Singer
(1974) felt that their first two criteria had been met and that fluorine
was an essential trace element; however, specific biochemical lesions were
not detected, nor were biochemical mechanisms underlying the conditions
defined.
Fertility and growth may be affected by lack of fluoride. Maurer
and Day (1957) maintained reproduction in rats over four generations with
a diet estimated to contain only 0.007 ppm fluoride. They found that the
viability of the offspring was impaired. In a study by Messer, Armstrong,
and Singer (1972), female mice maintained on a low-fluoride diet showed a
progressive decline in litter production over two generations. The de-
creased fertility may have been the result of an irregular estrous cycle
or a slowing of the onset of sexual maturity, implying that hormonal fac-
tors could have been involved. Fertility, however, was restored when the
diet was supplemented with fluoride. Bone-ash (humerus) fluoride content
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fell, but no adverse effects were noted. The authors concluded that the
infertility, which took several generations to manifest itself, constituted
a deficiency state produced by a diet apparently otherwise nutritionally
adequate. This conclusion must be examined more critically because fluo-
ride has been shown to have manifold effects on cells and cell systems.
In contrast to the studies of Messer, Armstrong, and Singer (1972,
1974) which suggested that fluoride was essential for reproduction in the
mouse, Tao and Suttie (1976) conducted reproduction studies in mice and
found that restriction of maternal fluoride intake did not significantly
influence reproduction rate, litter size, or litter weights. The repro-
duction of mice fed a basal diet of <0.5 ppm fluoride was the same as when
the basal diet of the mice was supplemented with 2 or 100 ppm fluoride.
Although the fluoride levels in the basal diets of the mice were essential-
ly the same in the experiments of Tao and Suttie and of Messer, Armstrong,
and Singer, the iron and copper levels were not the same. The diets of
the mice in the Messer, Armstrong, and Singer experiments were deficient
in iron and copper levels which Tao and Suttie suggested was the cause of
the impaired fertility; the addition of fluoride prevented this deficiency
through more efficient utilization of the dietary levels of iron and cop-
per. Thus, the role of fluoride on the reproduction of the mice was sec-
ondary. In support of this hypothesis, Tao and Suttie (1976) sited the
works of Ruliffson, Burns, and Hughes, where fluoride was shown to enhance
intestinal iron absorption in rats, and of Hamuro where fluoride prevented
magnesium deficiency in mice.
Schwarz and Milne (1972) considered the effects of other trace ele-
ments (particularly tin, vanadium, and silicon) and showed that fluorine,
supplied as potassium fluoride, was essential for the growth of rats that
were kept in isolators and fed highly purified amino acid diets. The
authors emphasized that the amounts of fluoride required for growth and
development were physiological. Fluoride levels in human diets not defi-
cient in fluoride are similar to those that maintained growth of the rats
in the study.
Mechanisms of fluoride action are elusive. Potentiating effects on
enzymes and possible involvement with the action of hormones have been
mentioned. In the studies of Messer, Armstrong, and Singer (1974) in
which anemia conditions were noted, it was suggested that fluoride may
have had something to do with either the uptake or utilization of iron
(see also Tao and Suttie, 1976, in this section). Fluoride is involved
in the metabolism of calcifying tissues and has been described by Hodge
and Smith (1972) as the "prototype bone-seeker." Conversely, bone reacts
with fluoride, displacing the hydroxyl and carbonate groups of the bone
material. It has been suggested that fluoride is essential for nucleating
the precipitation and crystallization of hydroxyapatite in the formation
of bone (Newesely, 1961; Perdok, 1962). The concentrations required may
be low. Brown (1966) calculated that fluoride concentrations in the range
of 0.0002 to 0.002 ppm should be sufficient for the process of promoting
the transformation of octacalcium phosphate to fluorohydroxyapatite with
subsequent crystallization. Although a requirement for fluoride in calci-
fication probably exists, the difficulty of achieving such low concentra-
tions in work with animals may prevent rigorous experimental demonstration
of the need.
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Fluoride is probably needed for the maintenance of bony structure.
Underwood (1971) suggested that the high incidence of osteoporosis in
elderly persons, especially women, could be regarded as a fluoride defi-
ciency. Fluoride concentrations required to prevent osteoporosis are
somewhat higher than those considered optimal for development of caries-
resistant teeth in children, thus complicating the public health manage-
ment of fluoride.
It is generally thought that of all the essential trace elements,
fluoride has the narrowest margin between beneficial and undesirable
concentrations. In a well-balanced review of criteria for the essential-
ity of trace elements, Mertz (1970) clearly showed the different levels
of response of biological systems to trace elments: a biological response
level (e.g., catalytic effects, enzyme element requirements, and synergis-
tic effects), a pharmacological level (resistance to caries, possible pre-
vention of osteoporosis, and possible inhibition of aortic calcification),
and a toxic level. These ranges are often distinguished by plateaus of
responses, before a new range is attained. Mertz pointed out that where
the plateaus between ranges are narrow, or where the ranges merge, is an
indication that homeostasis is inefficient or for some reason hindered.
This may be the case with fluoride. Beyond excretion, which is passive,
and uptake by bone, a real homeostatic mechanism for shutting out excess
fluoride does not seem to exist. Toxic effects result from acute and
chronic exposure to excessive fluoride concentrations. From a biological
standpoint, the problem of evolving control is difficult because the ranges
are so narrow.
In summary, some evidence indicates that fluorine may be essential
for man and other higher animals (Mertz, 1970; Schwarz, 1974); however,
exact mechanisms remain uncertain. More than most trace elements, fluo-
rine shows a closeness among physiological (essential), pharmacological
(beneficial and preventive), and toxic dose ranges.
6.3 METABOLISM
6.3.1 Uptake
6.3.1.1 Entry Except in polluted and occupational environments where
fluoride compounds are inhaled as vapors, fumes, or dusts, humans are
exposed to fluoride mainly through food and beverages. In modern socie-
ties where extensive food processing is the rule, any fluoride-containing
residues will generally have been washed off the food. Thus, intake is
mainly from fluoride in the food itself. Jones, Harries, and Martin (1971)
measured the amounts of fluoride found in or on leafy vegetables grown in
England near sources of atmospheric pollution by fluorides, both particu-
lates and gases. Their studies showed that even when vegetables were
poorly washed, increased intake of fluoride was not significant. Some
fluoride was supplied by vegetables, but fluoride intake from water was
more important.
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6.3.1.2 Absorption Fluorine in food and water is mainly in the form of
fluorides. In foods, fluoride may be complexed with a counterion such as
calcium or aluminum, rendering it insoluble. This complexing decreases,
but does not entirely prevent, the absorption of fluoride. The absorption
of soluble fluoride is very rapid, starting in the stomach. In a study
by Carlson, Armstrong, and Singer (1960a) a small dose of radiolabeled
fluoride was given orally to human volunteers. A rapid decline in radio-
activity was noted in the region of the stomach only a few minutes after
ingestion. Animal experiments using isolated sections of the gastrointes-
tinal tract have also shown rapid absorption of soluble fluorides; the
chief region of absorption in both man and animals is the upper part of
the small intestine.
Absorption of fluorides seems to be a passive process. Excretion
of fluoride into the mucosa of the intestines may, however, be an active
transport process. In studies with several species of rodents, Parkins
(1971) showed active transport of.fluoride in a secretory direction across
everted sacs of intestinal sections. A decrease in the rate of fluoride
transport was observed with increased age of the animals. The authors
correlated the reduced transport with the fairly low base levels of fecal
excretion of fluoride found by Spencer et al. (1969) in a study of the
effect of fluoride supplementation on absorption of calcium in middle-
aged patients.
The chemical form of fluorine and the presence of other factors in-
fluence its absorption. Thus, the absorption of fluoride from ingestion
of products containing bone is hindered: for instance, only about 50% of
the fluoride from fish protein concentrate is absorbed because most of the
fluoride is in the form of the highly insoluble fluorapatite. On high-
fat- and high-cereal-product diets, absorption of fluoride is slowed. The
presence of milk and milk products in the diet also slows absorption of
fluoride. Milk contains very little fluoride, and even high levels of
fluoride in the diet do not result in the appearance of much fluoride in
the milk of lactating animals. Since the need for supplementing the diet
with fluoride for caries prevention is greatest in children, it has been
suggested that fluoride be added to milk rather than drinking water. Fur-
ther, since many areas of the world are not served with fresh milk, it
would be convenient to add the fluoride to dried milk. Konikoff (1974)
studied the availability of fluoride as a function of time in reconstituted
dried milk (with and without additions of calcium) and found that almost
all of the fluorine remained available in the ionic state up to 4 or 5 hr.
After this time, about 20% of the initial fluoride occurred as CaF2 and
was therefore not readily available. There was then a slow decline in
fluoride availability over six to seven days. Absorption of fluoride from
milk was slower than from water, as shown by the fact that while 1 ppm
fluoride added to fresh milk could be detected in the urine in about 90
min, it was detected in 30 min when added to water.
6.3.1.3 Appearance in Body Fluids Absorption can be measured indirectly
by the appearance of fluoride in some easily accessible body fluids (e.g.,
blood, urine, or saliva). In the study by Carlson, Armstrong, and Singer
(1960a), human subjects were given 1 mg of stable fluoride labeled with
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248
radiofluoride in water, preceded and followed by water over the observa-
tion period. Blood, saliva, and urine samples were taken. Maximum plasma
radiofluoride concentration was reached in 60 min. At that time, the
concentration in the urine was increasing. It reached a maximum at about
240 min. The appearance and decline of radiofluoride in the saliva paral-
leled those in the blood, at a slightly lower concentration level; however,
because of the difference in volume, less than 1% of the ingested activity
was recovered in the saliva. Fluoride-urine clearance was at all times
manyfold greater than the chloride clearance. A large urinary clearance
of fluoride was maintained even when the urine volume decreased. Readings
with a crystal scintillator probe over various body areas easily followed
gastric emptying and dissemination of the fluoride in the soft tissues
and into bone. Skeletal tissues retained the isotope. For instance,
whereas counts over the biceps had declined to nearly zero at 250 min
after ingestion, counts over the femur had decreased by only 15% from the
maximum value.
Brudevold, Bakhos, and Gron (1973) studied the appearance of fluoride
in saliva after ingestion of sodium fluoride or sodium monofluorophosphate,
alone and with additions of varying amounts of aluminum chloride. Fasting
adults were given 5 mg of fluorine as sodium fluoride or Na2P03F in a gel-
atin capsule, washed down with 10 ml of water. The capsules contained
either no aluminum or 3.5, 7.11, or 14.2 mg aluminum as aluminum chloride.
After ingestion of fluoride without aluminum, the salivary fluoride in-
creased rapidly, peak levels of about 0.2 ppm being reached in about 50
min. With the aluminum additions, the rates of increase of fluoride in
the saliva were decreased, roughly in proportion to the amount of aluminum.
The peak levels were also lower. Since no aluminum was found in the saliva,
it was felt that fluoride uptake was hindered at the level of absorption
in the digestive tract by aluminum complexing with fluoride, and not by
an effect at some later stage such as passage of fluoride from the blood
to the saliva.
When fluorine was given covalently bound as sodium monofluorophos-
phate, Brudevold, Bakhos, and Gron (1973) found that the rise of salivary
fluoride was slower in all subjects and the peak levels lower in three
out of five than when ionic fluoride was given. Response to the aluminum
additions was similar to the case of ingestion of fluorine as fluoride.
Only ionic fluorine was detected in the saliva, indicating that the fluo-
rine of the monofluorophosphate was hydrolyzed and then absorbed as
fluoride.
An interesting result from the studies with the aluminum additions
is that while rates of increase of salivary fluoride were lowered and
peak levels were lower, rates of decline of fluoride concentration were
also lowered in some cases. Thus, Brudevold, Bakhos, and Gron (1974)
postulated that aluminum intake within a certain range might actually
increase rather than reduce fluoride utilization and play a quasi-
regulatory role, particularly with respect to the effect of fluoride
on teeth.
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Sodium monofluorophosphate is one of the fluorine compounds added
to toothpaste for prevention of caries. Aside from the expected topical
effect, some of the compound may be swallowed. Glass et al. (1975) stud-
ied fluoride ingestion resulting from the use of a monofluorophosphate
dentifrice by children. The amounts of fluoride absorbed were minor with
respect to the total fluoride intake and presented no danger of excess
fluoride even in areas of fluoridation. A similar conclusion was reached
by Duckworth (1964) studying the distribution and excretion of dentifrice
stannous fluoride. Amounts absorbed caused urinary excretion of fluoride
amounting to only 5% to 10% of the usual daily physiological variation.
6.3.1.4 Potential Absorption of Fluoride from Tobacco Smoke Along with
data on the fluoride content of a variety of environmental agents (e.g.,
detergents and other cleaning materials, dusts, pollen grains, and fer-
tilizers) , Waldbott and Oelschlager (1974) gave figures for the fluoride
content of several brands of cigarettes and one brand of cigar. These
ranged from 17.0 ppm for one German cigarette to 19.2 for a German cigar,
21.7 and 22.1 ppm for two Austrian cigarettes, 24.2 and 26.8 ppm for two
other German cigarettes, and an average of 25.0 ppm for several U.S. brands.
A heavy smoker (50 cigarettes a day) inhales approximately 0.8 mg of fluo-
ride (this number is not greater because about 80% of the cigarette is
consumed and not all the smoke is inhaled) which is not an inconsiderable
amount in view of the usual normal intake of 2 to 3 mg a day. Waldbott
and Oelschlager (1974) suggested that fluoride through its association
with such materials as asbestos and fiberglass could be a factor in the
irritating action of these agents. These aspects are considered in Section
6.4.3.3, along with a discussion on the effects of compounds of fluorine
other than simple fluorides.
6.3.2 Distribution and Balance
6.3.2.1 Excretion Fluoride from soluble fluoride compounds is rapidly
absorbed into the blood and appears with only slight lag in the urine
(approximately 90% of that absorbed) and saliva. Fecal fluoride is often
reported as 5% to 10% of total intake; however, the proportion varies
depending on circumstances. Table 6.1 shows balances between urine and
stool under controlled conditions, during supplementation with sodium
fluoride, and following supplementation (Spencer et al., 1970). The aver-
age intakes of 4.39 and 4.23 mg of fluoride per day from the institutional
diet, including drinking water given before and after supplementation, are
higher than the 2 mg/day which is the typical target concentration when
water is fluoridated. Noteworthy in the study was the relatively constant
urinary excretion of fluoride in successive study periods of the control
groups. On forcing with fluoride, the balance rose to an average of 5.4
mg/day, the excess fluoride presumably depositing in bone. Retention was
high, 42.9% of intake in the control period and 39.3% during supplementa-
tion, returning to 31.9% in the period after supplementation.
Figure 6.1 shows the great rise in urinary excretion of fluoride
following supplementation. Not all fluoride given was excreted, the bal-
ance going to bone. On discontinuation of supplementation, excretion fell
rapidly to only a few percent of the retained fluoride, then fell slowly
with time.
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250
TABLE 6.1. FLUORIDE BALANCES BEFORE, WRING. AND AFTER SODIUM FLUORIDE (NaF) SUPPLEMENTATION
Fluoride (rag/day)
P.i 1 1 en t
Control
Intake
1
2
3
4
5
6
7
8
9
10
Av
3
3
it
5
ii
4
4
4
4
4
4
.93
.57
.47
.37
.47
.56
.11
.50
.29
.54
.39
Urine
1.84
J.51
2.41
3.09
/.09
2.30
1.91
2.56
/.30
i.51
^.26
Stool
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
19
19
27
40
19
38
26
37
25
43
29
Balance
+1
+ 1
+1
+ 1
+2
+1
+1
+1
+1
+1
+ 1
.90
.87
.79
.85
.19
.88
.94
.57
.74
.60
.84
Intake
13.27
13.14
13.46
15.09
14.03
14.26
13.56
13.67
13.70
13.20
13.79
NaF
Urine
7.59
6.01
7.71
9.27
6.94
8.12
6.60
7.79
7.90
6.85
7.52
Stool
0.59
0.63
0.62
0.95
0.58
1.56
1.11
1.25
n.48
0.98
0.88
Balance
+5.09
+6.50
+5.13
+4.87
+6.61
+4.58
+1.85
+4.63
+5.32
+5.37
+5.39
Intake
3.59
3.65
5.00
5.31
4.31
4.46
3.87
After
Urine
2.43
1.92
3.45
3.39
2.45
2.78
2.15
NaF
Stool
0.26
0.21
0.60
0.37
0.21
0.47
0.33
Balance
+0.90
+ 1.52
+0.95
+1.55
+ 1.65
+ 1.21
+1.39
4.07
4.23
2.35
2.56
0.24
0.32
Source: Adapted from Spencer et al., 1970, Table VI, p. 811. Reprinted by permission of the publisher.
+1.48
+1.35
ORNL OWC 77-53K
30.
a
c
s«
PATIENT S
PATIENT 6
6 8 10
TIME
-------
251
ingested being found in the feces. One substance, fluoborate (6 mg), was
unique in that all of the fluoride that was absorbed into the blood was
excreted and recovered in the urine. For all the other materials tested
(6 mg each), slightly less than 50% of the absorbed fluoride was recovered
in the urine with the other 50% of that absorbed apparently stored in the
tissues; a small percentage of that assumed to be stored possibly was lost
through the skin. Largent (1961) conducted further observations of fluo-
ride ingestion at levels of 12, 18, 19, 25, and 36 mg/day and found the
results to be essentially the same slightly more than 50% of the fluo-
ride absorbed apparently was stored in the bone tissues.
In another series of experiments with an adult human subject, Largent
(1961) administered extra dietary fluoride (sodium fluoride) at a dose of
3 mg/day for 25 weeks, and sometime later 12 mg/day was administered for
130 weeks. The rates of storage were plotted and a calculated curve with
the equation of y = 800(l-e~0-043£) was used to make predictions of skel-
etal fluoride saturation. At a dose of 12 mg/day, the skeletal tissues
approached a 95% dose-level saturation in approximately 70 weeks, a 97%
level in about 100 weeks, and a 99.8% saturation level in approximately
200 weeks. A steady state of balance between intake and output of fluo-
ride would be reached sometime between 1.5 and 3.0 years after the start
of ingestion of 12 mg/day. If the amount of fluoride ingested was in-
creased above 12 mg/day then the rate of storage would abruptly increase
and then gradually decrease until a new state of equilibrium was reached.
Fluoride is excreted more efficiently than chloride by being less
efficiently reabsorbed. The process is one of glomerular filtration with
a variable amount of tubular reabsorption. At normal charges of chloride
and fluoride, renal resorption of chloride is above 99% compared with about
92% for fluoride (Deichmann and Gerarde, 1969). Urine flow rate and chlo-
ride clearance were considered the main determinants of fluoride clearance,
but in recent experiments with pentobarbital-anesthetized rats, Whitford,
Pashley, and Stringer (1976) were able to dissociate these factors from
fluoride clearance. Their results suggested a pH dependence of fluoride
renal clearance, tubular reabsorption of fluoride being inversely related
to tubular pH. The fluoride reabsorption seemed to occur by nonionic
diffusion, apparently as hydrogen fluoride. These findings also have
application to absorption of fluoride from the stomach.
Sweat contains some fluoride and can be a significant route of excre-
tion among highly active workers and in hot climates. To some extent it
may compensate for higher intake of fluoride from drinking water. As much
as one-third of a small dose of fluoride has been recovered in sweat (Hodge
and Smith, 1970), and McClure et al. (1945) noted figures of 13% to 38%
of ingested fluoride appearing in sweat under conditions of controlled
temperature and humidity. Usually only a few percent of the normal intake
of fluoride is excreted in sweat. The bulk appears in urine, but non-
absorbed and some secreted fluorides are found in the intestinal excretion.
6.3.2.2 Deposition and Distribution Along with urinary excretion, up-
take by bone effectively removes excess fluoride. On low and moderate
fluoride intakes, there is a slow accumulation of fluoride in the bone,
-------
252
ultimately with the renewal rate equal to the deposit rate, and a steady
state between intake and elimination at any one time (Hodge and Smith,
1970, p. 102). Figure 6.2 shows fluoride accumulation with age in bones
at different long-continued levels of intake. Although this figure shows
a plateau with respect to fluoride accumulation, other data do not show
this pattern. The results of a study (Weatherell, 1966) on the fluoride
content of femoral compacta from humans of different ages who lived In
areas supplied with drinking water containing less than 0.5 ppm fluoride
showed that accumulation was more or less linear regardless of age. There
is obviously a need for further study regarding the accumulation of fluo-
ride versus age.
OTNL MO rruir
Ml in*t\
Figure 6.2. Skeletal concentrations of fluoride in residents of
West Hartlepool, South Shields, and Leeds, England, and Rochester,
New York. Adapted from Hodge and Smith, 1970a, Figure 2, p. 10A. Reprinted
by permission of the publisher.
The deposition of fluoride in bone shows two main phases. The first
phase, which may be quite rapid and may result in a high concentration of
fluoride in surface bone layers, results from perfusion of extracellular
fluid containing fluoride into the osteocyte lacunae and the bone canalic-
uli (Gedalia and Zipkin, 1973). The fluoride ions displace hydroxyl groups
in the bone crystal to make a mixed fluorohydroxyapatite (Hodge and Smith,
1970). Florkin and Stotz (1971) estimated that 1% to 2% of the skeleton
is available for this exchange and that the rate and amount of uptake of
a given dose depends on previous exposure to fluoride.
The second phase of fluoride deposition is in the denser parts of the
bone. The interlacunar crystals of fully calcified bone are so closely
packed as to largely exclude fluid (Rich and Feist, 1970). Thus, the dif-
fusion of ions to this part of bone is impeded. Nonetheless, during min-
eralization and through turnover, fluoride is incorporated into these
-------
253
crystals at a rate paralleling the deposition of phosphorus as bone phos-
phate. The substitution of fluoride for ions in the crystal surface is
termed by Weidmann and Weatherell (1970, p. 109) as "exchange," and incor-
poration into the crystal lattice is termed "uptake by accretion." Both
processes are maximal during the phase of bone growth or tooth development
when crystallites are forming and are still small, thus offering greater
surface in proportion to their mass. In addition, young mineralized tis-
sue has a high degree of hydration, which ensures high permeability and
good access of tissue fluids to crystal surfaces.
Neither the fluoride deposited in surface layers nor that in the
deeper crystals of bone is irreversibly fixed, in spite of the low solu-
bility of fluoroapatite. Fluoride in the surface bone is in equilibrium
with fluoride in the extracellular fluid (Florkin and Stotz, 1971). On
deprivation, fluoride is mobilized, partly from back exchange of fluoride
from crystal surfaces and partly from dissolution of crystals in the
osteoclastic-osteoblastic cycle of bone remodeling (Hodge and Smith, 1970).
Mobilization of fluoride (i.e., excess of excretion over intake following
storage) is shown in Figure 6.3. The "removal half-life" of fluoride is
eight to ten years (Forbes et al., 1978).
OBNIOWC, /I ti
-0.1
If
S
-14
M n
TIMI (Mlkil
100
Figure 6.3. Mobilization of fluoride from the human skeleton. Adapted
from Hodge and Smith, 1965, Figure 64, p. 543. Reprinted by permission of
the publisher.
Bone is a sink for fluoride, and the ultimate capacity for storage
of fluoride as fluorapatite is great. Hodge (1964) calculated that the
theoretical limit is of the order of 35,000 ppm. Fluorosis, however,
would appear long before this level was reached (Section 6.4.2.1). Figure
6.2 shows that a level of 4000 ppm was reached on a long-term intake of
1 ppm fluoride. At an Intake level of 1.5 to 2.0 rag/day the long-term
-------
254
bone level reached 5000 ppm (American Academy of Pediatrics, 1972). Up
to an intake level of 5 mg/day, no adverse effects were noted, except for
tooth mottling and possible mild fluorosis of the bones. At levels of
10 to 15 mg/day or more, which may be reached under conditions of high
industrial contamination, cases of skeletal fluorosis were noted (Largent,
1961). Osteosclerosis, or hypercalcification, may be detected by increased
opacity of the bones to X rays at a deposition level of 6000 ppm (National
Academy of Sciences, 1971). It has been estimated that a continuous intake
of 8 ppm (the drinking water fluoride level that persisted for several
years in Bartlett, Texas) in the diet for 35 years would be necessary for
this level to be reached.
Fluoride uptake and concentration differ among bones and parts of
bones. In the long bones, concentration of fluorine is lowest in the shaft
and higher at each end as a result of growth and remodeling (Hodge and
Smith, 1970). Bones with a tendency to exostosis formation, such as the
shaft bones and mandibles, have a high affinity for fluoride. Fluoride
in the exostoses can be as much as 20 times as high as in other parts of
these bones under conditions of high fluoride intake (Underwood, 1971).
Fluoride is incorporated more rapidly into surface (periosteal and endos-
teal) regions of bones than in the middle regions (Weidmann and Weatherell,
1959), and more rapidly into cancellous (spongy) than into cortical (com-
pact) bones and parts of bones. Bones that have a high cancellous compon-
ent (e.g., ribs, vertebrae, and sternum) accumulate a higher level of
fluoride than cortical bones (Marier, Rose, and Boulet, 1963). Hefferren
et al. (1972) studied the fluoride distribution in wedge and needle biop-
sies of iliac crest samples taken at necropsy from control and uremic
patients and found that the average fluoride content of the control samples
was 800 ppm and of the uremic samples, 2000 ppm, reflecting the poor excre-
tion of the uremic state. In all samples, an increasing fluoride gradient
of about 25% was noted from the surface to a depth of 8 mm or more into
the bone; fluoride levels were directly proportional to bone porosity.
Deposition of fluoride also depends on the metabolic activity and
vascularization of the particular bone or part of bone being considered.
The effect of vascularization is immediate. Thus, the kinetics of dis-
appearance of radioactive fluoride from the blood and its uptake by bone
after a single intravenous injection have been used to measure bone blood
flow. In one case the measuring was monitoring the positron emission (Van
Dyke et al., 1965), and in another blood and urine activity were measured
(Parker, 1972). The efficiency of removal of fluoride by the bone from
blood on each pass is near 100%. The differential equations used by Parker
(1972) to calculate the bone and urinary clearances of 1BF are shown in
Figure 6.4. Bone blood flow can change in skeletal-associated disorders;
for instance, Van Dyke et al. (1971) showed increased bone blood flow in
myelofibrosis.
6.3.2.3 Fluoride in the Blood Due to the relative low reabsorption and
efficient uptake by bone, fluoride is cleared from blood rapidly. The
fluoride blood concentration, following an oral dose of soluble fluoride,
peaks in about an hour and then declines, so that in 4 to 5 hr the serum
concentration is virtually normal (Hodge and Smith, 1970). When fluoride
-------
255
ORNL-DWG 79-20905
SLOWLY EXCHANGEABLE INITIAL
F- POOL (IN SOFT TISSUE) MIXING VOLUME
BONE
q,IO) INJECTED DOSE
q2(0) Q3(0) - q4(0) - 0
URINE
- k,2q2 - Ik2,
df
ID
" knit - ki2q2
(2)
(3)
(4)
Figure 6.4. The compartment-system model and differential equations
for calculation of bone and urinary 18F clearance after a single intravenous
injection. Source: Parker, 1972, Figure 1, p. 4.
is given intravenously, a rapid fall in concentration due to mixing is
followed by a process with a half-time of 30 min (skeletal deposition)
and then a process with a half-time of 2 to 3 hr (renal excretion) . In
general, fluoride occupies the same clearance space as chloride (i.e.,
equilibrates with the same extracellular fluid, but its distribution proc-
esses are slower). For instance, cells, including red cells, are easily
permeable to fluoride (underwood, 1971). However, passage across the cell
membranes is slower for fluoride than for chloride. Thus in the experi-
ments of Tosteson (1959), outflow rate constants for fluoride from cells
labeled with radiofluorine were 0.3 per sec and for chloride, 3.1 per sec.
Fluxes were 2,300 pmole/cm2 per sec for 18F and 13,100 pmole/cm
for 38C1.
per sec
Hodge and Smith (1970) gave the typical total fluoride content of
normal blood as 0.10 to 0.15 ppm. Singer and Armstrong (1960) found that
in four communities in which the water contained 0.15 and 0.25 ppm fluo-
ride, the mean plasma fluoride values of the residents lay within the
range 0.14 to 0.19 ppm. In a fifth community, where the water contained
5.4 ppm fluoride, a slight increase to a mean value of 0.26 ppm was found.
The data of Guy, Taves, and Brey (1976) indicated more clearly that the
inorganic fluoride levels in plasma are directly related to the inorganic
fluoride levels in drinking water. Plasma samples analyzed for fluoride
-------
256
ion concentrations from residents of Albany, New York (fluoride ion in
drinking water less than 0.1 ppm), Corpus Christi, Texas (fluoride ion in
drinking water of 0.9 ppm), and Andrews, Texas (fluoride ion in drinking
water of 5.6 ppm), showed mean fluoride ion concentrations of 0.38 ± 0.21
yftf, 1.0 ± 0.35 uW, and 4.3 ± 1.8 uW respectively.
Given the roughly equal distribution of fluoride between cells and
plasma and the usual hematocrits, about 75% of the blood fluoride has
been found in the plasma. The rest is mainly in or on red cells. Using
dog blood, Carlson, Armstrong, and Singer (19602?) studied the changes in
plasma content of chloride and fluoride induced by changes in whole blood
carbon dioxide tension in vitro. A plasma fluoride shift qualitatively
similar but quantitatively different than for chloride was found (i.e.,
at an elevated pH the increase in plasma chloride content was greater than
for fluoride, and at a lower pH the decrease in chloride was less than
for fluoride). Again, the lesser mobility of fluoride is seen.
Discrepancies between the fluoride content of plasma found by methods
measuring total fluoride (Singer and Armstrong, 1960) and ionic fluoride
(Taves, 1966) led to the realization that only a small part of fluoride
in the plasma or serum, and possibly other body fluids, was exchangeable
(i.e., in the form of free fluoride ion). Singer and Armstrong (1969)
found free fluoride to be in the range of 0.004 to 0.008 ppm in the serum
of individuals drinking nonfluoridated water, while in the serum of indi-
viduals drinking water fluoridated at a level of 1 ppm it was 0.01 to 0.02
ppm. Thus, exchangeable fluorine was about 20% of the total fluorine.
Another indication of the ionic fluoride concentration is that about 15%
to 20% of the total fluorine of normal human plasma is absorbed by calcium
phosphate (Armstrong and Singer, 1970).
Taves and co-workers (Guy and Taves, 1972; Guy, Taves, and Brey,
1975; Taves, 1968) did extensive work on the nature of the nonexchangeable
fluorine. They found that nonexchangeable fluorine in human plasma is
mainly a derivative of perfluorinated octanoic acid and related substances.
Taves, Grey, and Brey (1976) pointed out that perfluorinated octanoic acid
derivatives are widely used commercially because of their surface-active
properties. They suggested that the organic fluorine in human plasma is
at least partly the result of contamination from industrial sources and
probably has no relationship to fluoridation of drinking water. This view
was confirmed by testing plasma from 106 persons living in five cities
that had between 0.1 and 5.6 ppm fluoride in the drinking water. While
the average inorganic fluoride concentrations ranged from 0.007 to 0.08
ppm and were directly related to the fluoride content of the water, the
organic fluorine concentrations averaged 0.03 ± 0.016 ppm and showed no
relationship to either the inorganic fluoride concentration or the total
fluoride concentration of the water.
6.3.2.4 Fluoride in Soft Tissues Soft tissues do not normally accumulate
fluoride, and the low levels do not increase with age (Underwood, 1971, p.
377). Even in chronic fluorosis, increases in soft tissue concentrations
of fluorine are small. Table 6.2 shows the fluoride levels in soft tissues
of animals. The extreme case of supplementation of the feed of dairy cows
-------
257
TABLE 6.2. FLUORIDE LEVELS IN SOFT TISSUES OF ANIMALS
Fluoride level (ppm dry wt)
Rats
Sheep
Cows
Tissue
Liver
Kidney
Thyroid
Heart
Pancreas
Muscle
Normal
0.21
0.62
2.6
0.53
2 rag
fluoride
per day
for 76 days
0.28
1.50
5.4
1.60
Normal
3.5
4.2
3.0
3.0
2.8
10 ppm
fluoride
in water
for 2 years
2.4
20.0
7.6
2.3
3.2
Normal
2.3
3.5
2.1
2.3
2.8
50 ppm
fluoride in
ration for
5.5 years
3.6
19.3
7.3
4.6
4.2
Source: Adapted from Underwood, 1971, Table 44, p. 378. Data collected from
several sources. Reprinted by permission of the publisher.
with 50 ppm fluoride for 5.5 years only increased the fluoride levels in
heart, liver, thyroid, and pancreas two- to threefold above control levels;
the high value for kidneys was probably due to retained urine. Following
a temporary high intake of fluoride, the levels in the soft tissues quickly
returned to normal. Carlson, Armstrong, and Singer (1960a) used radioflu-
oride to label 1 mg of fluoride given as a single dose to human volunteers.
By monitoring fluoride concentrations with a probe-type scintillation
counter, they found that the soft tissues lost nearly all their activity
within 4 hr after ingestion.
Table 6.3 shows the concentration of fluoride in human soft tissues
taken at autopsy following normal death, in relation to fluoride in the
water supply. Table 6.4 is a condensation of the same data, giving the
concentrations in parts of fluoride per million in the wet tissue rather
than with respect to dry weight as given in the previous table. Table 6.5
shows the high levels of fluoride found in human tissues following fluoride
poisoning fatalities and also shows the relatively small increase due to
long- and short-term exposure to high atmospheric fluoride concentrations.
It should be noted, however, that soft-tissue fluoride levels in fatally
poisoned subjects depend on such parameters as dose and time of sampling
after dose.
Some differences in the situation of fluorine in soft tissues may
be discerned. For instance, while fluorine in the liver seems to be fully
exchangeable with the ionic fluoride of the body fluids, about half the
fluoride in the muscle is in a nonexchangeable form (Armstrong, 1967;
Armstrong, Singer, and Vogel, 1966; Gedalia and Zipkin, 1973). There is
also some indication of the existence in the brain of either a fluoride-
passage barrier or a slow exchangeable fluoride pool (Armstrong and Singer,
-------
258
TABLE 6.3. THE CONCENTRATION OF FLUORIDE IN HUMAN SOFT TISSUES IN RELATION
TO THAT IN THE WATER SUPPLY
Age
(years)
65
62
50
47
32
40
32
85
83
82
64
83
62
54
53
47
50
49
36
36
71
53
26
Sex
M
M
M
F
M
F
M
M
F
M
F
F
F
F
F
F
M
M
M
M
M
M
M
Fluoride
in water
(ppm)
0
0
0
0
0
0.5
0.5
1.0
1.0
1.0
1.0
2.6
2.6
2.6
2.6
2.6
3.7
3.7
3.7
3.7
4.0
4.0
4.0
Fluoride in desiccated tissues
(ppm dry wt)
Heart
2.12
2.44
2.49
1.39
2.47
1.22
4.29
2.00
2.53a
23.3
1.95
2.33
2.42
1.19
1.86
3.18
3.60
2.31
1.71
1.84
6.81
2.65
3.46
Liver
2.48
3.26
2.79
1.45
1.68
0.92
3.49
2.53
1.05
3.79
2.84
2.22
1.48
1.51
1.24
2.92
1.98
2.06
1.01
1.96
2.59
5.41
Lung
1.79
4.21
4.06
10.5
2.68
9.20
3.43
6.17
12.4
5.27
4.04
4.07
3.31
11.17
4.70
4.46
Kidney
2.50
2.59
2.79
2.90
2.83
1.35
4.19
3.97
4.95
4.04
3.78
8.12
5.00
5.41
2.74
9.02
7.37
3.39
2.28
16.8
7.63
25.6
Spleen
1.83
3.23
3.63
4.24
2.84
2.17
7.31
7.19
16.7
1.90
3.02
4.22
5.66
3.91
2.63
2.77
4.51
1.34
Aorta
106.1
23.4
4.39
4.18
2.64
10.0
2.65
47.98
20.68
166.3
62.7
40.35
33.6
30.30
5.29
40.63
6.04
4.73
3.09
46.01
59.4
6.21
Heart aorta.
Source: Adapted from Smith et al., I960, p. 330.
the publisher.
Reprinted by permission of
TABLE 6.4. CONCENTRATIONS OF FLUORIDE IN HUMAN SOFT TISSUES, NORMAL DEATHS
Fluoride
in water
supply*2
(ppm)
0.0 (7)
1.0 (4)
2.6 (5)
3.7 (4)
4.0 (3)
Fluoride in tissues (ppm wet wt)
Heart
0.64
0.32-1.25
0.55
0.43-0.68
0.67
0.37-0.96
0.61
0.46-0.88
1.29
0.71-2.14
Liver
0.64
0.29-1.02
0.70
0.27-0.92
0.52
0.38-0.73
0.60
0.3-1.13
0.92
0.59-1.47
Lung
0.81
1.20
0.58-1.81
1.40
0.89-2.22
0.71
0.54-0.87
1.98
1.06-2.91
Kidney
0.63
0.30-1.02
0.75
0.63-0.93
1.32
0.54-2.17
0.80
0.44-1.48
2.55
0.63-5.45
Spleen
0.71
0.33-1.19
0.51
0.55-0.47
0.82
0.47-1.19
0.68
0.31-1.05
Aorta
8.97
0.79-43.0
37.9
11.6-65.7
14.2
2.26-21.5
2.13
1.41-3.01
16.3
3.57-22.9
Figures in parentheses indicate number of samples.
Source: Adapted from Hodge and Smith, 1965, Table IVB, p.
permission of the publisher.
16. Reprinted by
-------
259
TABLE 6.5.
FLUORIDE CONTENT OF HUMAN TISSUES FOLLOWING
FLUORIDE POISONING FATALITIES
Fluoride (ppm fresh we)
Tissue
Normal"
Fluoride
poisoning
fatalities"
Exposure to high
atmospheric fluoride
concentration
Long-term
Blood
Brain
Lung
Heart
Spleen
Liver
Kidney
Thyroid
Aorta
Pancreas
0.
0.
0.
0.
0.
0.
0.
27
53
27
45
28
54
68
(4)
(4)
(3)
(3)
(2)
(3)
(2)
9
2
14
10
11
9
9
.2
.5
.0
.6
.8
.3
.0
(5)
(2)
(2)
(1)
(1)
(5)
(3)
1
3
2
1
1
2
5
29
1
.8
.9
.5
.7
.6
.9
.2
.4
.8
Short-term
1
3
1
1
1
2
4
28
1
.5
.5
.9
.8
,tt
.9
.0
.2
.7
Figures In parentheses indicate the number of subjects.
Source: Adapted from Armstrong and Singer, 1970, Table 6,
p. 101. Data collected from several sources. Reprinted by
permission of the publisher.
1970). The concentrations tend to reflect those in the plasma (Carlson,
Singer, and Armstrong, 1960). Some tissues such as the aorta, tendons,
cartilage, and placenta, may have a high fluorine concentration because of
fluoride fixed by ectopic calcification loci (Hodge and Smith, 1970).
Besides fixation on other calcified tissues, fluoride fixes second-
arily on calcifications in the aorta (Waldbott, 1966). Some levels of
fluoride intake may actually reduce calcification. Bernstein et al. (1966)
reported on 300 subjects over age 45 living in an area (North Dakota) where
the fluoride content of water was 4.0 to 5.8 ppm and 715 subjects where
the fluoride content of the water was 0.15 to 0.3 ppm. They found the
frequency of calcification of the aorta, as determined radiologically, to
be significantly higher in the low-fluoride area, particularly in men;
however, the reason was unexplainable. The results are shown in Figure
6.5. Studies with rat aorta in vitro (Zipkin et al., 1970), showing inhi-
bition of calcium-45 uptake by incubated aorta (24-hr incubation) in the
presence of fluoride, supported the above finding that fluoride in physi-
ological doses may reduce calcification. When no fluoride was added, the
calcium count per min per milligram of aorta was 1049 ± 21. After addi-
tion of 1.12 ppm fluoride, only 172 ±4.1 calcium counts per min per mil-
ligram of aorta were measured.
6.3.2.4.1 Fluoride in the placenta Fluoride passes from the mother to
the fetus and is used in mineralization. Gedalia, Brzezinski, Zukerman,
and Mayersdorf (1964) studied the placental transfer of fluoride in the
human fetus at low and high fluoride intake. Samples of maternal blood,
cord blood, and whole placental tissue were obtained at normal deliveries
from 39 women in Israel where the water contained 0.5 to 0.6 ppm fluoride,
from 12 women where the fluoride levels in water ranged from 0.6 to 0.9
-------
260
90
60
70
60
50
40
30
20
10
0
ORNL-DWG 79-20886
_ FEMALES
45-54 55-64 65+
AGE
45-54 55-64 65+
AGE
Figure 6.5. Percentage of radiologically detectable calcification
of abdominal aorta in males and females residing in high- and low-fluoride
areas. Source: Adapted from Bernstein et al., 1966, Figure 3, p. 501.
Reprinted by permission of the publisher.
ppm, and from 18 women where water fluoride levels ranged from 0.5 to 0.6
ppm and who had also received a supplement of 0.5 mg of fluoride daily
during the second half of pregnancy. Mean-total fluorine (not fluoride
ion) concentrations for the first group and for groups two and three to-
gether, respectively, were: placenta, 0.121 and 0.228 ppm; cord blood,
0.165 and 0.175 ppm; and maternal blood, 0.150 and 0.234 ppm. These
results were interpreted as showing that fluoride passes freely through
the placenta when the fluoride intake is low (cord blood fluoride levels
were slightly greater than maternal blood fluoride levels for group one
women), but the placenta regulates fluoride transfer and protects the
fetus when the intake is high (groups two and three cord blood fluoride
levels were lower than placenta or maternal blood fluoride levels).
Ericsson and Malmnas (1962), however, in studies involving the
maternal-fetal transfer of radioactive fluoride in humans and rabbits,
showed that the protective function of the placenta may be only a passive
one. Figure 6.6 shows these results. The bulk of the maternal fluid
space of fluoride, quick clearance, and slowness of diffusion across the
placenta offers protection to the fetus from unusual doses of fluoride.
Ectopic calcifications in the placenta also offer protection by fixation
of excess fluoride.
Using methods developed to distinguish between organic and inorganic
fluoride discussed in Section 6.3.2.3.1, Shen and Taves (1974) studied
the distribution of fluorine in the placenta, cord blood, and maternal
blood. As shown in Figure 6.7, the fetal blood fluoride (16 deliveries)
was parallel to, but lower than, the level in the maternal blood. Figures
for the acid-labile (inorganic) fluoride and organically bound fluoride
of the placentas are shown in Table 6.6. The organic fluoride levels are
like those previously found in blood. The high levels of inorganic fluo-
ride are postulated by the authors as being due to fixation by ectopic
-------
261
ORNL-DWG 775319
0.020 -I
0.015
0.010 -
OC 0.005
(9
tt
ui
a.
K
UI
a.
0.10.
0.08-
0.06-
0.04-
0.02.
HUMAN
MATERNAL BLOOD
PLACENTA
0 FETAL BLOOD
10 15 20 25 30 35
RABBIT
MATERNAL
BLOOD
FETAL
BLOOD
10 15 20 26
TIME AFTER INJECTION (mini
30
Figure 6.6. Maternal-fetal transfer of 18F in the human and in the
rabbit. Source: Adapted from Ericsson and Malmnas, 1962, Figure 1, p.
110. Reprinted by permission of the publisher.
2.0
4 1.5
ORNL-OWG 79-2090$
§
IL.
i
1.0
g 0.5
o
o
I I
Y- 0.725X0.039
I
I
0.5 1.0 1.5 2.0
MATERNAL SERUM FLUORIDE
2.5
Figure 6.7. Scatter diagram of the maternal versus the cord serum
fluoride values taken at the time of delivery. Source: Adapted from Shen
and Taves, 1974, Figure 1, p. 206. Reprinted by permission of the pub-
lisher.
-------
262
TABLE 6.6. FLUORIDE COSCESTRATTOS IH PLACEKTA
Sample
So.
1
2
3
4
5
Mean
Std error
Acid-labile
(u'O
fluoride
Electrode *>rinchori«
reagent
10.2
40.6
80.2
103.6
92.4
67.4
19.6
23.6
6.6
19.6
46.40
11.48
12.0
33.5
101.2
142.5
100.0
53.0
14.0
16.5
14.8
17.5
50.50
14.94
Organic
-------
263
OftNL-CMG 79-309*6
g 1-0
_ _
u. "^
I"
10
2O 3O
WEEK OF PREGNANCY
5O
CORRELATION BETWEEN THE WEEK OF PREGNANCY (4 = -0.317). OR
LACTATION U - 0-210) AND INORGANIC PLASMA FLUORIDE CONCENTRATION.
THE MEAN PLASMA INORGANIC FLUORIDE CONCENTRATION OF THE
CONTROL GROUP OF THE SAME AGE.
WOMAN WITH NORMAL PREGNANCY.
x TOXEMIC PATIENT.
Figure 6.8. Inorganic plasma fluoride related to duration of pregnancy.
Source: Adapted fro* Hanhijarvi, Kanto, and Ruponen, 1974, Figure 1, p.
144. Reprinted by permission of the publisher.
TABLE <-.!. FLOORIDE COWTEHT OF ASHED
FETAL BOSES AHD TEETH
Fecal age
(oaths)
Suaber
of cases
Mean fluoride value (ppa)
Mandible
Teeth
Low fluoride area
21
26
13
27
39.7
40.7
4.2.3
43.8
-2.3
39.0
38.5
46.9
Mediua fluoride area"
31
20
7
34
59.0
71.6
79.-
92.5
47.0
53.5
66.0
78.8
Elevated fluoride area"
30.9
34.0
31.7
-0.3
32.6
43.0
57.9
69.7
6
7
8
9
20
6
13
. 25
55.2
63.0
79.9
85.2
57.2
65.7
70.3
85.0
44.0
47.0
52.0
53.8
?About 0.1 pp* fluoride. Tel-Aviv. 1961-63.
^About 0.55 pp» fluoride, Jerusalem, 1961-63.
About 1 ppm fluoride, Segev. southern Israel,
1961-64.
Source: Adapted froa Gedalla et al., 1964.
Table 3, p. 334. and Cedalia. Zuterman, and
Leventhal, 1975, Table 2. p. 1122. fteprinted by
permission of the publishers.
-------
264
TABLE 6.8. CONCENTRATIONS OF FLUORIDE
FOUND IN HUMAN MILK
Fluoride
concentration Comment
(ppm)
0-0.35, av 0.131 4-5 days postdelivery; 0.55 ppm
fluoride in drinking water
0-0.24, av 0.107 4-32 weeks postdelivery; 0.55 ppm
fluoride in drinking water
0.08-0.147 Maternal blood contained 0.23-0.36
ppm fluoride
0.115-0.168 Mothers given 5 mg fluoride daily
2-6 days
0.10-0.18 Drinking water contained 0.055 ppm
fluoride
0.25 Drinking water contained 1.13 ppm
fluoride
0.13-0.25 Control subjects
0.45-0.60 Nonworkers living near superphos-
phate factory
1.05-1.88 Workers in superphosphate factory
0-12 Dry basis
Not detected to 3-8 days postdelivery; 0.06 ppm
0.12 fluoride in water supply
Source: Adapted from Smith, 1966, Table 26, p.
104. Data collected from several sources. Reprinted
by permission of the publisher.
no fluoride supplement where the community water supply was fluoridated.
In communities where fluoride is low, the authors advised supplementation
to bring the intake of the mothers to 1 mg/day. Contrasting results were
presented by Backer Dirks et al. (1974). Milk samples were collected
during the fourth and fifth days post partum from 11 mothers who lived
in an area where fluoride concentrations in the drinking water were only
0.1 ppm and from 11 mothers who were living in an area where the drinking
water had been fluoridated (1.0 ppm F~) for the past 18 years. Their
analysis of the milk samples, in contrast to the work of Simpson and Tuba
(1968), indicated that the total fluorine values of the two groups of
mothers were not significantly different.
6.3.2.5 Total Body Fluoride Using data available for fluoride concen-
tration in different human tissues, Smith (1966) calculated the amount
and distribution of fluorine in man. The vital organs (kidneys, lungs,
spleen, thyroid, heart, brain, pancreas, and liver) of a standard 70-kg
man (International Commission on Radiological Protection, 1959) were
assumed to weigh 5.04 kg, and fluoride therein was calculated to be 2.5
mg. Muscles and skin of a standard man comprise 30 kg and 2 kg, respec-
tively, and the fluoride content was calculated to be 16 mg. For a blood
weight of 5.4 kg and average whole-blood concentration of 0.11 ppm, the
blood would contain 0.59 mg of fluoride, of which 0.48 mg would be in the
plasma and 0.11 mg in the cells. The extracellular fluid is assumed to
weigh 12.25 kg and to contain about 1.96 mg of fluoride. Bones and teeth
account for 15.31 kg, and the fluoride content is assumed to be 2.55 g.
Note that these fluoride calculations are derived from analyses of cadavers
of persons who had used water containing about 0.1 ppm fluoride. The data
are summarized in Table 6.9.
-------
265
TABLE 6.9. CALCULATED DISTRIBUTION OF TOTAL BODY
FLUORIDE IN HUMAN TISSUES
Tissue
Bones and teeth
Skin and muscle
Vital organs
Whole blood
Extracellular fluid
Total
Fluoride
(g)
2.547
0.016
0.003
0.0006
0.002
2.5686
Percentage
of total
fluoride
99.16
0.62
0.12
0.02
0.08
100.0
Percentage
of nonakeletal
fluoride
74.1
14.0
3.0
9.3
100.4
Source: Compiled from Smith, 1966, pp. 92-93.
6.4 EFFECTS
6.4.1 Effects on Enzymes and Cell Systems
6.4.1.1 Effects on Enzymes In excess, fluoride is considered to be a
poison, exerting its effects mainly through interference with cellular
respiration by inhibition of key enzymes in the glycolytic cycle and elec-
tron transport. This is the first of the four major functional derange-
ments distinguished by Hodge (1969) in fluoride poisoning. The other
derangements are: shock caused by fluid and electrolyte loss due to
changes in permeability, central vasomotor depression, and depression of
activity of vascular smooth muscle. Fluoride has an effect in vitro on
cholinesterase activity, but Hodge did not consider this important in
fluoride poisoning. In fact, fluoride was shown (Albanus, Heilbronn, and
Sundwall, 1965) to have an antidote effect in cases of cholinesterase
poisoning by organophosphorus compounds. Renal changes occur in poison-
ing but are not the cause of acute death. Fluoride binds calcium as CaF2,
and the diminution in free-ionized calcium may cause pertubation of calcium-
associated processes (e.g., blood-clotting, nerve action, parathyroid gland
activity, and maintenance of cardiac regularity). Such toxicological
effects are discussed in Section 6.4.3.2.
Some enzyme processes seem to be activated by fluoride at low phys-
iological concentrations. Caution must be exercised in interpreting the
results of tests done with cell systems, as inhibition of an enzyme in
one pathway could make it appear that an enzyme of another pathway was
being activated. Frajola (1959) stressed the usefulness of multiple
simultaneous enzyme activity studies to elucidate such interactions.
Polar graphing makes a dramatic display of the effects.
Paunio (1970) described the effect of fluoride (concentrations not
given) on a number of highly purified enzymes in vitro. Among these were
proteases, enzymes from dental plaque, dental pulp, gingiva, and phospho-
rylating enzymes from fetal mineralizing tissues. Some enzymes were in-
hibited; others were not affected; and in some, activation was observed
at low fluoride concentration followed by inhibition at higher levels.
-------
266
Fluoride combines with metals; for instance, calcium, cobalt, iron,
magnesium, and manganese. It may inhibit enzymes by interfering with the
metal when this is an essential part of an enzyme complex. An example of
this is phosphoglucomutase. This enzyme catalyzes the reaction glucose-
6 to glucose-1-phosphate. The reaction needs glucose-l,6-phosphate as a
cofactor and magnesium. In the presence of fluoride, a magnesium fluo-
ride complex with glucose-1-phosphate and the enzyme is formed, inhibiting
the reaction (Najjar, 1948). Najjar observed that with a glucose-1-
phosphate concentration of 2.2 x 10~3Af and a magnesium concentration of
5 x 10~*A/, the concentration of fluoride that gave half maximum inhibition
was 1 x 1Q- 3M.
Enolase is a key enzyme in glycolysis and is inhibited by fluoride.
Warburg and Christian (1941, 1942) postulated that fluoride formed fluoro-
phosphate, which combined with the activating magnesium of the enzyme to
form an inactive complex. However, Peters, Shorthouse, and Murray (1964)
found fluorophosphate per se to not be inhibitory, while fluoride and
phosphate were. Evidently there is some concerted action of the fluoride
and phosphate for inhibition. A similar situation prevails with respect
to inhibition of succinic dehydrogenase by fluoride and phosphate together
(Slater and Bonner, 1952). The presence of the fluoride and the phosphate
enhance each other's affinity for the enzyme, resulting in inhibition. It
may be noted that fluoride and arsenate also inhibit enolase (Warburg and
Christian, 1942).
Fluoride and complexes of fluoride, such as HFF", may react with
metals that are in prosthetic groups of enzymes and thus interfere with
binding and processing of the normal ligands. Examples of this are found
among the heme protein enzymes, for instance, catalase, peroxidase, and
cytochrome oxidase. These reactions are relatively easy to reverse
(Hewitt and Nicholas, 1963). Inhibition of cytochrome oxidase is impor-
tant because it is terminal in the cytochrome chain, reducing oxygen to
water.
Hewitt and Nicholas (1963, pp. 401-402) stated that it might be
expected that many enzymes dependent on magnesium would be inhibited by
fluoride (concentrations not given), especially in the presence of phos-
phate. The particular susceptibilities, however, vary greatly among dif-
ferent enzymes. Thus, while the polynucleotide phosphorylase enzymes that
depend specifically on magnesium are insensitive to fluoride, the 5-
nucleotidases are inhibited. Acid phosphatases are usually sensitive
while alkaline phosphatases generally are not. Some pyrophosphatases are
not inhibited, but erythrocyte pyrophosphatase was inhibited 50% by 2 x
10~SM fluoride ion (Naganna and Narayana menon, 1948).
Isoenzymes may be inhibited to different degrees by fluoride
(Venkateswarlu, 1970, p. 181), perhaps due to differences in order of
reaction and affinity and also to different activator requirements. Thus
while human liver esterase is inhibited by fluoride, pancreatic and intes-
tinal esterases are not. Magnesium-activated animal and plant glutamine
synthetases are inhibited by fluoride more than the corresponding cobalt-
activated ones.
-------
267
Besides inhibiting enzymes by combining with a necessary metal,
fluoride has been postulated (Venkateswarlu, 1970) to activate some
enzymes by removal of metal inhibition.
Table 6.10 summarizes the effect of fluoride on some enzyme systems.
Table 6.11 gives the responses of several enzymes to inorganic fluoride
and some compounds giving rise to fluoride. Wiseman (1970) presented
several tables documenting the effect of inorganic fluoride on enzymes.
Many studies of fluoride inhibition have been made to delineate mechanisms
of toxicity, to cause an intermediate to pile up in studies of dissimila-
tion processes, or to show that fluoride at levels optimal for dental
health is not deleterious to the organism. Concentrations producing
noticeable effects are often many times those that would prevail in the
body. For instance, a "50% inhibition" of cholinesterase at 0.1 M sodium
fluoride and even a "detectable inhibition" at 0.001 M are well above the
10~s Af fluoride which is a higher limit (about 0.2 ppm) for fluoride in
the blood.
6.4.1.2 Fluoride and Adenylate Cyclase Even though a fluoride effect
may be minor in itself, it may have some part in modulating a cell proc-
ess. For instance, activation or inhibition of an enzyme may be part of
control of permeability or of a transport process. Discussion of the
effects of fluoride on broken cell preparations as noted experimentally,
is given as an example of the type of involvement mentioned.
This system is important because adenosine 3',5'-cyclic phosphate
(cyclic AMP) is the "second messenger1' in a great number of hormone and
other receptor-initiated actions. Cyclic AMP is formed from magnesium-
ATP by the action of adenylate cyclase found in the plasma membrane of
many types of cells. The receptor part of the enzyme is apparently on
the outside of the cell and the catalytic part on the inside. The cyclic
AMP, formed on stimulation of the enzyme, modulates actions within the
cell, sometimes inhibiting but usually initiating a cascade of catalytic
TABLE 6.10. SUMMARY OF EFFECTS OF FLUORIDE ON ENZYME SYSTEMS
Concentration for
Enzyme effective Inhibition Effect
(M)
Enolase
Acid phosphatase
Alkaline phosphatase
Cytochrome a
Esteraae
Amylase
Carboxylase
Llpase
10-'
io-»
10"
10"
10-
10-'
10"
10-'
Accumulation of phosphoglycerlc acid
Increase blood organic phosphate?
Lower Inorganic phosphorus?
As above
Cellular anoxia
Accumulation of lower fatty acids
Increase In salivary carbohydrates
Increase in pyruvate
Accumulation of higher fatty acids
Source: Adapted from Hodge and Smith, 1965, Table LIV, p. 183. Reprinted by
permission of the publisher.
-------
268
TABLE 6.11. EFFECTS OF INORGANIC FLUORIDE COMPOUNDS ON ENZYME SYSTEMS
Compound
Ammonium
f luorophosphate
Fluoride
Enzyme
Chollnestcrase
Pigeon liver cyclophorase
Animal and plant glutanlne
synthetase
Yeast glucose dehydrogenase
Anaerlnaae
Catalase
Phosphorylaae
Phosphatase, alkaline
Phosphomonoesterasea of
Concentration
0.01 H
O.OI> H
10"* H
10'* «
0.01 H
10-' M
-log(F) - 2.3-3.3
0.02 M
Appro* 0.5 M
lO-'-lO-1 H f
Effect
SOZ inhibition
Reduced oxygen uptake in pres-
ence of malate by SOZ
SOX inhibition of cobalt-
activated enzymes
SOZ inhibition of magnesium-
activated enzymes
30-401 inhibition
10Z inhibition
SOZ inhibition
6.AZ inhibition
SOZ Inhibition
25-60Z Inhibition
Potassium fluoride
Sodium fluoride
Tofulopaia utilia
Acid phosphatase of human
prostate
Steroid sulfatase of Patella
oulgata
Glucosulfatase of P. vulgata
Pyrophosphacase
Phosphatase of PeniailHum
ohryaoganum
Phosphatase, alkaline
Aspartaae
Enzymes of rat liver, kidney
homogenates
Cytochrome system
Aconltase
Cltrogenase
Esteraaes
Phosphatase, alkaline
Phosphorylase
Cholineaterase
Creatlne phosphoklnoae
Alkaline phoaphatase of adult
and embryonic guinea pig
cortex
Muscle ATPase
Penlcllllnaae
Glucuronldase
Amylase
a-Hydroxy acid oxidase, hog
kidney
Hexoklnaae
Phosphomutase (rabbit muscle,
heart, liver)
Phosphatase, acid
Cholinesterase
Acid phoaphatafles
Cozymase
Proatatic acid phosphatase
-log(F) -2.0
0.005 M
0.005 M
2.5 * 10'' M F
50 MM KF
0.01 M
0.1 M
0.0001 H F
Approx 0.001 M
0.01 H
0.01 M
0.003 M
0.01 M
0.2 M NaF
0.1 M NaF
0.01 « NaF
0.001 M NaF
1 » 10"' H NaF
6.5 x 10"* M NaF
0.02 W
0.002 H
ID'' H
0.2 M
1Z NaF
Up to 0.01 H
0.003 M
0.02 M
0.02 H
0.02-0.1 M
0.5 mg/ml of beef
serum .
10"' M NaF
0.001 H
About 98Z Inhibition in 6-
glycerol phosphate
About 90Z inhibition In yeaat
adenyllc acid substrate
About 65Z inhibition in phenyl
phosphate substrate
9Z inhibition
79Z Inhibition
Inhibited
No appreciable effect
Negligible Inhibition
Inhibit activation of acetate
without affecting pyruvate
oxidation, oxldative rate, or
level of adenlne nucleotidea
SOZ Inhibition
No effect
Slight Inhibition
Partial or complete Inhibition
No inhibition
Accelerates conversion of phos-
phorylase a to phosphorylase b
Almost complete Inhibition
SOZ inhibition
Detectable inhibition
21Z Inhibition of forward
reaction
100Z inhibition of forward
reaction
No effect
Hydrolysis of ATP reduced to
87Z; hydrolysis of inositine
triphosphate reduced to 36Z
(normal 46Z)
Hydrolysis of ATP reduced to
3SZ; hydrolysis of Inositine
triphosphate reduced to 12Z
Ineffective
Complete Inhibition of hydrol-
ysis of dehydroelpsndrosterone
sulfurlc ester
No effect
No inhibition
No effect
43-48Z Inactlvatlon
Inhibition
Strong inhibition
80Z Inhibition
Inhibited
Protected against thermal
denaturatlon
-------
269
TABLE 6.11 (continued)
Compound
Enzyme
Concentration
Effect
Sodium monofluoro-
phosphate
Sodium, potassium,
and ammonium
fluorides, sodium
fluorosillcate
Tantalum potassium
fluoride
Pyrophosphatase
Potato acid, alkaline
pyrophosphatases
Potato acid phoaphatase
Phosphataae, acid
(Basldlomycetes)
Fhosphatase, alkaline
Intestinal alkaline phosphatase
Sulfatase A of ox liver
Enolaae
Phosphataae, acetyl
Rat liver homogenate, kidney
homogenate
Homogenate of Flexner-Jobllng
tumor
Homogenate of human flbroaarcoma
Mitochondria of Flexner-Jobllng
tumor
Hoaogenate of mouse hepatoma
98/15
Homogenate of mouse adrenal
cortical tumor
Homogenate of mouse Novikoff
hepatoma
Homogenate of mouse C3H mammary
carcinoma
Water-soluble enzymes of
streptococci
Catechol oxldase
Succino dehydrogenaae
Fhosphatases of cell membrane of
Propionibaotarium pentoaacwn
Carboxylase
Enolaae
Esterase
Llpase
ATPase
Decarboxylase
Chollnesterase
Decarboxylase of Paeudomonaa
fluorgaaanB
Fhosphorylaae
Alkaline phosphorylaee
Amylase
Succlnic dehydrogenase
0.001 M
10'' M NaF
10"' M MaF
0.02 M
6.35 » 10'* M
0.01 M
0.01 M NaF
0.01 M NaF
0.125 aH
0.01 M
0.05 M
0.01 M
0.01 H, 0.03 H
0.01 H, 0.03 H
0.01, 0.03 H
0.01 H
0.01 M
0.01 H
0.01 H
42 ug NaF
0.02 M
0.1 H
0.02 M
0.1 H
0.023 M f
2.4 x 10-
0.5-1.67
ID"1 H
10'* M
0.1 H
1.5 « 10-
H
10-
M NaF
1.3 mg
1:3000
0.01 and 0.001 H F
Inhibition >90Z
Inhibited
Inhibited
Nearly complete inhibition
Inhibition
Complete Inhibition
10Z inhibition
95Z inhibition
Inhibited fermentation, respira-
tion yeast
No inhibition
50Z inhibition
Inhibited net breakdown of high-
energy phosphate
Increased respiratory rate
Increased respiratory rate
Increased respiratory rate
Inhibited respiratory rate
Inhibited respiratory rate
Inhibited respiratory rate
Increased respiratory rate
Inhibited arsenolysls of
cltrulllne
39Z Inhibition
95Z inhibition
37Z inhibition
50Z inhibition
Fhosphatases of cell membrane
inhibited in organisms grown
in 0.023 H F solution
63Z Inhibition
43-45* Inhibition
Inhibition >85Z
7Z inhibition
40Z Inhibition
Depressed enhancing effect of
pentachlorophenol
50Z Inhibition
Inhibited frog rectus muscle
Inhibition
0.0021 H
0.002 M
1.7-8550 ppm F in
saliva
0.76-760 ppm F in
substract
50Z Inhibition
SOZ inhibition
No effect
No effect
1 x 10-* H TaK,F,
No significant effect
Source: Adapted from Hodge and Smith, 1965, Table till, p.
Reprinted by permission of the publisher.
177-182. Data collected from several sources.
events that results in the observed hormone or other effect. The ampli-
fication may be considerable. The action of the cyclic AMP is stopped
by rephosphorylation to adenosine triphosphatase (ATP) by a phosphodies-
terase. The effect of fluoride on the system hindered the discovery of
adenylate cyclase and cyclic AMP. In 1956, Sutherland and co-workers (as
cited in Robison, Butcher, and Sutherland, 1971) studied the effect of
glucagon and epinephrine on the action of liver phosphorylase on glycogen,
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270
by adding fluoride routinely to block the action of liver phosphorylase
phosphatase. The fluoride was added to maintain the activity of any active
glycogen phosphorylase formed. But fluoride stimulates adenylate cyclase,
and it was not until fluoride was omitted from the mixtures that the hor-
mone effects were noted. The fluoride effect on fat-cell ghosts parallels
that of the hormone, as shown in Figure 6.9. Loss of activity muscle
homogenates also follows a parallel course for the hormone and for fluo-
ride, as shown in Figure 6.10.
The difference in effect of fluoride on intact cells and on cell
homogenates, in this case of cells from adipose tissue, is shown in Table
6.12. In both experiments cited, the stimulation by fluoride in the
broken cells was well above that due to the hormone. While fluoride has
been found to strongly stimulate the activity of adenylate cyclase where
it occurs in practically all broken cell systems studied, it has relatively
little effect on intact cells and tissues. The reason for this is not
known. The adenylate cyclase system is highly organized in its situation
in the membrane. It may be that fluoride, in spite of the fact that it
penetrates into cells (Section 6.3.2.3), does not locate where it can exert
much action unless the cell's organization is disrupted. The compartmen-
tation serves the function of keeping the cell's adenylate cyclase from
being continuously stimulated by fluoride, as there is no obvious way for
its action to be turned off, except possibly by interacting with metal
ions such as calcium and magnesium in the cell.
ATVIMH)
0 S 10 tl 20
HO, l«ln
Figure 6.9. Effect of varying concentrations of ATP and Mga on
adenyl cyclase activity in fat cell ghosts: (a) activities are measured
at fixed concentration of Mg (5 mW); (b) activities are measured at
fixed concentration of ATP (5.84 mW). Source: Adapted from Birnbaumer
et al., 1970, The Actions of Hormones on the Adenyl Cyclase System,
Figure 4, p. 195. In: Role of Cyclic AMP in Cell Fimctiont P.
Greengard and E. Costa, eds. Raven Press, New York. Reprinted by
permission of the publisher.
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271
OUNIOWC »MJI
10 15
AOINO IKrl
Figure 6.10. Loss of adenyl cyclase activity in a rabbit skeletal
muscle homogenate at 4°C. Source: Adapted from Robison, Butcher, and
Sutherland, 1971, Figure 2.4, p. 38. Reprinted by permission of the
publisher.
TABLE 6.12. EFFECT OF EPINEPHRINE AND FLUORIDE ON CYCLIC AMP
FORMATION BY ADIPOCYTES BEFORE AND AFTER HOMOGENIZATION
Experiment
Conditions
Cyclic AMP
(millimoles x 10"7/g)
Whole cells
Broken cells
I
II
Control
Epinephrine (1 ug/ml)
NaF (0.01 M)
Control
Epinephrine (1 yg/ml)
NaF (0.01 M)
2. it
20.4
3.2
3.8
10.8
4.9
7.8
8.7
33.3
13.0
96.1
145.2
experiments I and II were performed at different times using
different preparations of adipose tissue. For the experiments
involving whole cells, adlpocytes were prepared by the method of
Rodbell and incubated in the absence of added ATP or Mg2*. For the
experiments with broken cells, the adlpocytes were homogenized in
an isotonlc tris buffer (experiment I) or in a hypotonic glycyl-
glycine-MgSO* buffer (experiment II) and incubated in the presence
of 2 mW and 3 mW MgSO«. Caffeine (1 mW) was present in all cases.
Source: Adapted from Butcher and Sutherland, 1971, Table
2.111, p. 40. Reprinted by permission of the publisher.
Fluoride has been used as a probe to bring out changes in the devel-
opment of the adenylate cyclase system. An example is given in Figure
6.11, which shows the results of a study by Schmidt et al. (1970) on ade-
nylate cyclase activity in particulate preparations from homogenized rat
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600
ORNL-DWG 79-20887
500
400
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3
200
100
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9 13
AGE (days)
17
23
Figure 6.11. Effect of increasing concentrations of sodium fluoride
on brain adenyl cyclase activity in rats. Source: Adapted from Schmidt
et al., 1970, Figure 4, p. 59. Reprinted by permission of the publisher.
brain. Robison, Butcher, and Sutherland (1971) cited other studies show-
ing the effect of developing at different times in different organs and
varying among animals. They interpreted the results as showing that in
the course of development, an inhibitory influence that can be reversed
by fluoride (as 10 mW sodium fluoride) is superimposed on the adenylate
cyclase system.
Menon, Giese, and Jaffe (1973) studied hormone- and fluoride-sensitive
adenylate cyclases in human fetal tissues. The enzyme preparations from
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273
all tissues were stimulated by fluoride, but not all by the appropriate
hormones. This indicated that some tissues develop their receptors or
activate the mechanism sooner than others, leading the authors to postu-
late that cyclic AMP response may be a factor in control of developmental
processes. A functional heterogeneity of human fetal anterior pituitary
cells has been shown by Groom, Cooke, and Boyns (1971). While cyclic AMP
stimulated release of both luteinizing hormone and follicle-stimulating
hormone, fluoride augmented release mainly of follicle-stimulating hormone.
The complexity of the adenylate cyclase system was shown by the differen-
tiation of fluoride-stimulated and non-fluoride-stimulated components pre-
pared from beef brain cortex enzyme in a study by MacDonald (1975), one
component being activated by sodium fluoride and the other inhibited.
6.4.1.2.1 Fluoride and other cyclic nucleotidases Another cyclic nucle-
otide, guanosine 5'-phosphoric acid (cyclic GMP) made from guanosine 5'-
triphosphate (GTP) as cyclic AMP is made from ATP, has been found in all
mammalian tissues studied (Hardman and Sutherland, 1969), usually in lower
concentration than cyclic AMP. In contrast to its effect on adenylate
cyclase, fluoride does not generally stimulate guanylate cyclase. Rodbell
et al. (1971) found inhibition of fluoride stimulation of a glucagon-
sensitive adenylate cyclase system from rat liver by guanyl nucleotides.
Hosey and Tao (1975) found a similar inhibition of the system from rabbit
red cells. These studies of broken cells are of interest because they
indicate how factors in the cell affect the overall response, modulating
the effect of the hormone on the outside. Yamashita and Field (1972) found
that in intact thyroid cells (but not in liver), the levels of cyclic GMP
and the incorporation of tritiated guanine into cyclic GMP increased in
response to sodium fluoride. This suggests that in at least one intact
tissue, fluoride activates a guanylate cyclase.
6.4.1.2.2 Mechanism of fluoride stimulation of adenylate cyclase
Roberecht et al. (1975), in studies of the stimulation of amylase secre-
tion by either pancreozymin or fluoride in the perfused rat pancreas,
noted an effect of fluoride anterior to a possible direct effect on the
adenylate cyclase system. They postulated that while the hormone acts on
the receptor, the fluoride acts by causing variations in the phosphoryla-
tion of membrane proteins. Aspects of possible mechanisms of stimulation
by hormones and fluoride are given in the following schemes. Perkins and
Moore (1971), studying activation of adenylate cyclase in membrane frag-
ments of rat cerebral cortex, considered that fluoride acts by dissociat-
ing some part of the adenylate cyclase complex to relieve inhibition of
the enzyme, this action being complementary to the action of the hormone.
Another activation scheme is given in Figure 6.12 (Najjar and
Constantopoulos, 1973). Using as an analogy the action of fluoride on
phosphoglucomutase, the authors postulated that fluoride or the hormone
accepts a phosphate group directly from the cyclase (single-enzyme system)
or from a phosphatase to activate the cyclase (multi-enzyme system) . A
criticism of this scheme is that fluoride and the hormone probably do not
act at the same site; however, they must act very near to each other (per-
haps on the same complex), as shown by the histochemical studies of heart
and skeletal muscle stimulated by glucagon, epinephrine, and fluoride
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274
ORNL-DWG 77-5322R
ADENYLATE CYCLASE SYSTEM
SINGLE ENZYME SYSTEM
H or F"
(Inactive) C-p - C ( Active )
NTP
NDP
Kinase VUTO
cAMP /NTP
/
K,C,P-p
Active
Cyclase
Multienzyme System
Inactive
CyclaM HX.F"
NDP
Inactive
Cyclate
Phosphatase
Kinase
cAMP Active
Cyclase
cAMP
H - HORMONE. F - FLUORIDE. NTP - NUCLEOSIDE TRIPHOSPHATE.
C DEPHOSPHORYLATEO ADENYLATE CYCLASE. Co THE PMOSPHOHYLATED FORM
K - ADENYLATE CYCLASE KINASE WHICH MAY EXIST IN THE PHOSPHO AND
DEPHOSPHO FORM. ACTIVE AND INHIBITED RESPECTIVELY.
P - DEPHOSPHORYLATED ADENYLATE CYCLASE PHOSPHATASE. Pp THE
INHIBITED PHOSPHORYLATED FORM
Figure 6.12. The proposed mechanism of activation of adenylate
cyclase system. Source: Adapted from Najjar and Constantopoulos, 1973,
Figure 1, p. 89. Reprinted by permission of the publisher.
(Schulze, Krause, and Wollenberger, 1972). The authors noted that of the
known ATP-splitting enzymes, adenylate cyclase is the only one activated
by fluoride; others are inhibited or not affected. It is interesting to
note that along with a primary direct effect of fluoride on brain adenylate
cyclase which increases production of cyclic AMP, Katz and Tenenhouse
(1973) found an indirect effect of inhibition by fluoride of hydrolysis
of ATP and ADP. Since these are inhibitory to phosphodiesterase, the
secondary action of fluoride indirectly kept the phosphodiesterase from
rephosphorylating the cyclic AMP to ATP, thus maintaining its level.
A highly formal model for adenylate cyclase action is shown in Figure
6.13. Discriminators (hormone receptors) on the surface of the membrane
are postulated to act through transducer components to influence an ampli-
fier molecule, which is the catalytic component of the complex. Fluoride
is postulated to act on a site on the amplifier in such a way (the hormone
also having this effect) as to enhance the affinity of a nonsubstrate site
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275
ORNL-OWG 79-20907
HORMONES
DISCRIMINATORS
TRANSDUCERS
AMPLIFIER
ATP
c-AMP
Figure 6.13. A schematic representation of the adenylate cyclase of
the cyclase-PDE model cyclic AMP generating system. Source: Davies and
Williams, 1975, Figure 2, p. 4. Reprinted by permission of the publisher.
for magnesium such that the magnesium binding enhances the activity of the
substrate-binding site. While Severson, Drummond, and Sulakhe (1972) found
that binding of magnesium enhanced reactivity, they did not find that the
association constant, A^, for this binding was altered by fluoride. They
considered that fluoride, metal ions, and the hormone all act to increase
the maximal velocity of the reaction by a "V" allosteric mechanism.
de Ha8n (1974) criticized the concept that there is a regulatory
binding site for magnesium whereby the action of fluoride and hormones
is affected. Magnesium ATP is seen to be the true substrate; ATP alone
is inhibitory. It is postulated that hormones, as well as fluoride,
decrease the sensitivity of the adenylate cyclase toward free ATP. Par-
allel to this, the maximal velocity is increased. Both effects are caused
by an equilibrium conformational change in the enzyme. This scheme
stresses steady-state operation of the system, with feedback from substrate
binding and other factors influencing receptivity to the hormone.
6.4.1.3 Fluoride and the Thyroid Gland Because both are halogens it
was once thought that fluorine might be antagonistic to iodine and thus
be goitrogenic. However, it seems that while chlorine and bromine are
slightly concentrated by the thyroid gland, fluorine is not (Demole, 1970).
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276
Fluoride, at a pharmacological dose of 50 to 100 mg daily, does have a mild
antithyroid effect in hyperthyroid patients but not in normals. At one
time fluoride was used in the treatment of exophthalmic goiter. However,
the therapeutic action is inconstant and transitory, and such medication
is obsolete. Fluorine-containing drugs synthesized for treatment of thy-
roid disorders have been a disappointment. The question of thyroid-
fluoride effects has been reviewed by Demole (1970) whose conclusions
were: (1) fluoride does not accumulate in the thyroid; (2) fluoride does
not affect the uptake of iodine by thyroid tissue; (3) pathological changes
in the thyroid show no increased frequency in regions where the water is
fluoridated; (4) administration of fluoride does not interfere with iodine
prophylaxis for endemic goiter; and (5) the beneficial effect of iodine
in threshold dosage to experimental animals is not inhibited by even high
doses of fluoride.
Differences in the action of fluoride, a thyroid stimulating hormone
(TSH), and other stimulators were shown by Pastan, Macchia, and Katzen
(1968). Thus while fluoride increased glucose-1 and glucose-6 oxidation,
increased incorporation of phosphate into phospholipid, and stimulated
adenylate cyclase in various broken cell preparations, it failed to induce
the formation of pseudopods or intracellular droplets. Willems, Berberof-
Van Sande, and Dumont (1972) similarly found an inhibitory effect of fluo-
ride on accumulation of intracellular colloid droplets and secretion. They
postulated that this was due to inhibition by fluoride of aerobic glycol-
ysis in the follicular cells.
In studies with intact mouse thyroid glands, Williams and Wolf (1971)
and Kendall-Taylor (1972) found that preincubation of the glands with flu-
oride (3 mW sodium fluoride) blocked the response to both TSH and cyclic
AMP (adenosine-3,5'-monophosphate); iodoprotein was also released. These
effects were considered to be due to metabolic toxicity of fluoride with
secondary membrane-damaging effects; however, caution in interpretation
was urged because of the multiple actions of the various agents (hormones,
prostaglandins, and fluoride) and concentration effects.
McLaren (1976) reviewed the literature on the relationship of fluo-
ride and the thyroid gland, with attention to reasons (e.g., physiological
and experimental) for inconsistencies in the published data. Some reten-
tion or loading of the thyroid by fluoride is considered to occur. Fluo-
rides at sufficient concentration are seen to produce morphological changes,
However, the lower level of intake at which this may occur is open to
discussion.
6.4.1.4 Fluorides and Cell Growth Berry and Trillwood (1963) reported
that fluoride at concentrations of 0.045 to 4.5 ppm in the culture media
reduced the growth of HeLa cells and of strain L mouse fibroblasts. The
report caused concern since these concentrations were described as being
equivalent to those recommended for use in fluorldation of drinking water.
Other authors, however, found different results. Albright (1964, 1966),
using mouse leukemic lymphoblasts, found inhibition did not occur below
8 to 9 ppm. At 20 ppm, a growth inhibition of 29% in seven days was ob-
served. This inhibition could be partially reversed by pyruvate but not
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277
by citrate. More than one mechanism of inhibition was indicated, one
probably being the blocking of enolase. Armstrong et al. (1965), using
HeLa cells to repeat and extend the work of Berry and Trillwood and also
using esophageal cells, found no effect of fluoride on cell multiplication
or on protein synthesis up to 10 ppm; at 15 ppm an incipient retardant
effect on growth of the esophageal cells was noted. Albright (1964, 1966)
and Armstrong et al. (1965) emphasized that the cell-culture results
should be appraised in relation to the fluoride concentrations that really
exist in the body fluids. With quick renal excretion and bone as a sink,
plasma fluoride concentrations and concentrations in the soft tissues are
well below the concentrations showing inhibitory effects in vitro.
The importance of intracellular-extracellular fluoride ratios is
shown by the experiments of Suttie et al. (1974), who developed a fluoride-
resistant strain of mouse fibroblast cells, able to grow in media contain-
ing 70 ppm fluoride. Although the parent cells at 50 ppm fluoride had an
intracellular to extracelluar fluoride ratio of 0.3, the ratio of the
resistant cells was 0.03.
6.4.1.5 Fluorides and Cell Permeability Fluoride has an action on per-
meability of membranes. Part of this action is due to inhibition of eno-
lase and other metabolic perturbations and part to a direct effect on the
membrane itself, as shown by the study of Lepke and Passow (1967) with
nonmetabolizing ghosts of human erythrocytes. Fluoride at a concentration
of 40 mM (760 ppm) caused potassium loss from potassium-loaded ghosts into
isotonic sodium chloride solutions at about the same rate as from similarly
treated intact metabolizing cells. If this effect occurred, it would be
obscured by metabolic effects at lower physiologic concentrations.
Feig, Shohet, and Nathan (1971), following Keitt's (1966) lead of
using fluoride inhibition of enolase as a model system for study of in-
herited pyruvate kinase deficiency, found multiple effects of fluoride.
Membrane ATPase was inhibited 40% at 1 mW (19 ppm) and completely inhib-
ited at 5 mW; however, the incorporation of fatty acids into membrane
phospholipids was unaffected until all the ATP was used. Fluoride was
shown to react directly with red cell membranes in the presence of cal-
cium, the combination inducing a massive cation leak. A higher concentra-
tion (10 mW) was needed for this effect than for the inhibition of enolase
or ATPase. Addition of oxidant (methylene blue) regenerated NAD, which
permitted some formation of ATP beyond the enolase block, prevented the
massive cation and water loss (but not the normal cation leakage), and
reestablished membrane phospholipid renewal.
Millman and Omachi (1972) found active sodium extrusion from red
cells and NAD concentrations to decrease simultaneously on addition of
graded levels of fluoride starting at 0.5 mW. Figure 6.14 shows the ef-
fects of 5 vM fluoride and 10 mAf pyruvate on 22Na release from red cells
and on cellular NAD concentration. It is postulated that decrease in
pyruvate due to fluoride inhibition of enolase causes a drop in the sub-
sequent formation of NAD. NAD is utilized by the enzyme glyceraldehyde-
3-phosphate dehydrogenase. As the level of NAD falls, so does the activity
of the enzyme, followed by proportionate decreases in the rates of phos-
phoglycerate kinase and Na,K-ATPase.
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278
1400
ORNL-DWG 79-20908
[CELL NAD]
(nmoles/ml
ERYTHROCYTE)
PYRUVATE 70
CONTROL 66
FLUORIDE
+ 79
PYRUVATE
FLUORIDE 44
30 60 90
INCUBATION (mln)
120
Figure 6.14. Effect of pyruvate on 22Na release and cellular NAD
concentration in fluoride-treated and control erythrocytes. Source:
Adapted from Millman and Omachi, Figure 5, p. 344. Reprinted by permission
of the publisher.
From the above studies, it is seen that at sufficiently high concen-
trations fluoride may be a factor, although, perhaps, only a minor one,
in the dynamics of transport of electrolytes and fluids across cell
membranes.
6.4.1.6 Fluoride and Protein Synthesis Hardesty et al. (1973) showed
that centrifugation of ribosome material from normal cells (reticulocytes)
gave mostly aggregated material but gave a sharp peak of 78S material from
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279
ones incubated in fluoride. The sodium fluoride-treated ribosomes, if put
into a cell-free protein-synthesizing system without fluoride, could in-
corporate ^-terminal value and carry on with peptide elongation. However,
regular ribosomes in the presence of sodium fluoride were inhibited. Thus
fluoride appears to block a reaction of peptide initiation with concomitant
accumulation of an initiation complex, explaining the resumption of chain
elongation on removal of the fluoride.
Similar results were found by O'Rourke and Godchaux (1975). In a
reticulocyte lysate system, some time was needed for polysome breakdown.
Meanwhile, fluoride (at a level of 30 raff) allowed chain elongation but
little initiation of new chains.
Marks et al. (1965) postulated that the derangement of the protein-
synthesizing apparatus was secondary to inhibition of fluoride of ATP
production, but this was not observed by Freudenberg, Halbreich, and
Mager (1970).
The retention of t-RNA and messenger RNA on ribosomes following flu-
oride treatment (10 mftf), postulated by Hardesty et al. (1973), is supported
by the work of others (Baglioni, Jacobs-Iorena, and Meade, 1972; Geraghty
et al., 1973; Terada et al., 1972). On removal of fluoride, polysomes
reform and protein synthesis may resume. The dissociation of polysomes
by fluoride has also been studied in cells other than reticulocytes for
instance, in HeLa cells (Baglioni, Jacobs-Iorena, and Meade, 1972) and
mouse plasma tumor cells (Bleiberg, Zauderer, and Baglioni, 1972). In
the latter study, addition of fluoride (15 raff) to mouse myeloma cells in
culture caused disaggregation of polysomes and release of the fraction
of ribosomes bound to the endoplasmic reticulum membrane. Removal of
fluoride caused reaggregation and rebinding, and synthesis and secretion
of immunoglobulin resumed.
Godchaux and Atwood (1976) studied the structure and function of
the initiation complexes that accumulate during inhibition of protein
synthesis by fluoride (20 to 30 raM potassium fluoride). Deacylated
methionyl-t-RNA was found in the complex. The authors postulated that
fluoride slows the use of the acylated RNA, allowing a deacylating enzyme
to remove the methionine.
6.4.1.7 Fluoride in Inflammation, Wound Healing, and Bone Resorption
Stone and Willis (1968) studied interferences to inflammatory processes
involved in the healing of skin disorders, skin bacterial infections, and
the like, and found enhancement of inflammation by fluorides. Application
of 0.5% (5000 ppm) fluoride by patch over skin scratches caused the forma-
tion of intradermal pustules. The authors felt that fluoride did not
induce inflammation but enhanced it by exaggerating its early cellular
phases. Joseph and Tydd (1973), studying regeneration of skin in the
rabbit ear, considered that healing was stimulated by a wound hormone
produced by cell damage and that fluoride might increase early cell dam-
age and thus provide the stimulus. Increased acid phosphatase in the
fluoride-treated tissues, indicating lysosomal breakdown, supported this
hypothesis. Figure 6.15 shows the effect of fluoride at two concentration
levels on the regeneration rates.
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ORNL OWC 77 5323
100
80
- 60
o
£
Z
40
DC
O
20
O CONTROLS
RABBITS RECEIVING DRINKING
WATER CONTAINING 10 ppm
SODIUM FLUORIDE
RABBITS CONTAINING DRINKING
WATER CONTAINING ISO ppm
SODIUM FLUORIDE
14
21 28
TIME (day*)
35
42
49
Figure 6.15. Effect of fluoride at two concentration levels on the
regeneration of skin in the rabbit ear. Source: Adapted from Joseph and
Tydd, 1973, Figure 1, p. 165. Reprinted by permission of the publisher.
Hars and Massler (1972) reported a beneficial effect of fluoride in
dental surgery. Following a single injection of 1% stannous fluoride
(0.3 ml) or 2% sodium fluoride (0.3 ml) into tooth extraction clots in
rats, there was a lessening of bone resorption in the area around the
socket. There were no noticed toxic effects on cellular morphology or
bone structure, and healing of the epithelium and the subjacent tissue
was maintained. The authors suggested the use of fluoride following
extractions and tooth transplant and replant operations.
6.4.1.8 Functional and Cytochemical Effects Manocha, Warner, and
Olkowski (1975) maintained squirrel monkeys on distilled water and water
containing 1 and 5 ppm fluoride for 18 months. Water consumption was
higher at the higher fluoride intake. No changes in the nervous system
were found. Slightly enhanced activity of citric acid cycle enzymes was
noted in the liver of the higher-intake animals, and their kidneys showed
some cytochemical changes. The activities of glomerular acid phosphatase,
citric acid cycle, pentose shunt, and lysosomal enzymes were increased,
indicating some degree of metabolic stress on the kidneys due to the higher
fluoride regime and perhaps some catabolism. It should be noted that
these symptoms resulted from a fluoride intake near the upper limit of
the physiological range.
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281
L8we (1974) found some deterioration (flocky decay) of myofilaments
of smooth muscle cells of guinea pig ileum. This deterioration was attrib-
uted to inhibition of glycolysis following incubation of the cells in 1 mW
fluoride (19 ppm). This concentration is considerably higher than what
these cells would ever encounter in vivo.
Czechowicz, Osada, and Slesak (1974) studied the effect of prolonged
administration of sodium fluoride (daily intramuscular injection of 4 mg/
kg for three months) on the metabolism of Purkinje's cells in the cere-
bellar cortex of guinea pigs. There was an intensification of the meta-
bolic activity of the mitochondria and activation of membrane transport
enzymes. The authors postulated that the changes reflected excitation of
neurons by the added fluoride.
Fluoride (0.1 to 10 mftf sodium fluoride) was shown to have an anti-
curare effect (increasing as the fluoride concentration increased)
(Koketsu and Gerard, 1956), sensitizing postsynaptic receptors to acety-
choline following depression of end-plate potentials by the curare (5 x
10~6 tubocurarine). Jacobs and Blaber (1971) studied this action at the
neuromuscular junction of cat tenuissimus muscle. Transmitter store was
increased from a control value of 1042.96 ± 175.75 to 1465.19 ± 150.45,
and transmitter release was increased from a control value of 0.2261 ±
0.0310 to 0.2318 ± 0.0241 by 8 mW fluoride over the 3 yg tubocurarine
block. Part of the fluoride effect was considered to be displacement of
the drug from presynaptic sites. Fluoride acts as a noncompetitive,
reversible inhibitor of erythrocyte cholinesterase (Heilbronn, 1965a).
It also has been shown to reactivate cholinesterase blocked by organo-
phosphorus inhibitors at concentrations of 0.5 to 5 x 10~3 M sodium fluo-
ride (Heilbronn, 19652?) and 2 and 4 mA/ sodium fluoride (Blaber, 1970) .
Thus fluoride seems to have both pre- and postsynaptic effects.
Fluoride is one of the positive inotropic agents affecting in vitro
heart muscle contraction (Robison, Butcher, and Sutherland, 1971). The
response is seen at slow frequencies of contraction and at fluoride con-
centrations of 0.11 to 4.3 mW (Berman, 1966) and is reflected as a pro-
longation of the active state of contraction (Reiter, 1965).
6.4.2 Fluoride and Teeth
6.4.2.1 Fluoride, Fluorosis, and Tooth Health - Fluoride is utilized in
the calcification of teeth in utero (Section 6.3.2.4.1). It is also pres-
ent in the enamel before teeth erupt. Maier (1972) detailed how fluoride
was found to have an effect on teeth health. Eager (1901), an American
physician in Naples, Italy, upon examining prospective immigrants to the
United States, reported the severe tooth mottling observed in persons
from a small nearby community. He postulated that volcanic emanations
were the cause, either in the air or forming a solution in the water.
Cases from communities elsewhere in the world were then reported. In
1925 and 1928 the communities of Oakley, Idaho, and Bauxite, Arkansas,
respectively, where mottling was a problem, changed their- water supplies
on the basis of a recommendation by dentist Dr. F. S. McKay. Dr. McKay
thought that something in the water supply was responsible for the mot-
tling, and after the water supplies were changed, no new cases appeared.
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282
However, fluoride was not yet implicated. A report by Kempf and McKay
(1930) was read by officials of the Aluminum Company of America (ALCOA).
These ALCOA officials were concerned that the dental defects in persons
living in Bauxite might be due to ingestion of aluminum. Accordingly,
water samples from Bauxite were sent to ALCOAfs laboratory in Pittsburgh
where they were analyzed under the direction of the laboratory's chief
chemist, Dr. H. V. Churchill. Analysis of the water gave 14 ppm fluoride.
Water samples from other communities where tooth mottling was a problem
were also analyzed by the company, and high fluoride levels were found.
Fluoride was, therefore, indicated as the cause. The next step was to
confirm these findings in animal tests. This, however, had already been
done by Smith and co-workers in Arizona. Smith et al. (1931) produced
tooth mottling in rats by feeding them fluoride. In addition to the anal-
ysis work of Churchill and the research of Smith et al. (1931), Velu (1931)
in North Africa also concluded that fluoride was involved in tooth mot-
tling. By giving sheep in North Africa water saturated with a fluoride-
bearing rock phosphate, Velu (1932) produced a tooth mottling similar to
that affecting many Moroccans. Meanwhile, the low incidence of caries in
mottled teeth was noted, and appreciation of the balance between the ben-
eficial effect of fluoride at low concentrations and deleterious effects
at higher concentrations was obtained. During the decade 1937 to 1947,
Dean did extensive work on chronic endemic dental fluorosis using rigorous
epidemiological standards. Using the data of Dean, Arnold, and Elvove
(1942), Hodge (1950) showed that the decrease in dental caries was a lin-
ear function of the logarithm of the fluoride concentration. The increase
in fluorosis index is also log-linear, showing both to be true pharmaco-
logic responses. This is shown in Figure 6.16, which includes the results
of Dean, Arnold, and Elvove (1942) and Striffler (1958). Water intake
changes with temperature and a graph of the relationships among fluoride
levels, fluorosis, and ambient temperatures are shown in Figure 6.17.
35
HI
if
ss
8?
OMHL DWG JJ W74
» i
8
10 a
o« 0.1 14
FLUORIOt IN DftlNKINO WATM Ippml
Figure 6.16. Relation between decayed, missing, and filled teeth
(broken line at left), severity of fluorosis (solid lines), and fluoride
concentration in water (logarithmic scale). Source: Adapted from Hodge
and Smith, 1965, Figure 35, p. 465. Data collected from several sources.
Reprinted by permission of the publisher.
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ORNL DWG 77 S3JS
OBJECTIONABLE FLUOROSIS
FLUORIDE REMOVAL INDICATED
MEAN ANNUAL TEMPERATURES
APPROXIMATELY 70°F
APPROXIMATELY BO°F
0.4
0.6
0.8 1.0 1.2 1.4
FLUORIDE CONCENTRATION (ppml
1.6
1.B
2.0
Figure 6.17. Relationship among fluoride levels, fluorosis, and
ambient temperatures. Source: Adapted from Maier, 1972, Figure 13,
p. 32. Data collected from several sources. Reprinted by permission of
the publisher.
Galagan and Vermillion (1957) derived a formula for fluoride: parts per
million of fluoride = 0.34/2?, where E is the estimated average daily water
consumption of children through ten years of age in terms of ounces of
water per pound of body weight. It may be obtained from the equation
E = 0.038 + 0.0062 x average maximum temperature in °F. This formula is
used in making up the U.S. Public Health Service Drinking Water Standards.
Excess fluoride results in dental mottling. The mottling occurs
when enamel is being laid down; beyond 12 to 14 years teeth can no longer
be mottled, whatever the fluoride intake. Very mild fluorosis is present
in about one resident in five at a fluoride drinking water concentration
of 1 ppm (Figure 6.16). In its mild form caused by exposure to 2 ppm
fluoride in drinking water, fluorosis is manifested as chalky white flecks
on the teeth; more severe forms of fluorosis (from exposure to 4 ppm flu-
oride in drinking water) may cause the flecks to show a brown discolora-
tion, which is no doubt secondary to the actual histological damage. McKay
and Black (as cited in Bhus'sry, 1970) showed a relative lack of interpris-
matic substance in the mottled areas, and Williams in 1923 (as cited in
Bhussry, 1970) showed easier penetration of dyes into the mottled areas
than into sound enamel. Later studies using microradiography, polarized
light, and other techniques confirmed the histologic damage, showing
irregular hypomineralization in the mottled areas.
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284
The effect of fluoride in the mottling process seems to be mainly
on the ameloblasts. In experimental animals the presence of excess flu-
oride caused thickening of the cell walls, elongation of the nucleic,
and disruption of the internal cell organization (Fleming, 1953). Kruger
(197Q&) showed distension of the endoplasmic reticulum and enlargement of
mitochondria in ameloblasts from young rats; the effects were proportional
to time after injection and dose of fluoride (0.1, 3.0, and 7.0 mg of
fluoride per kg body weight). Episodes of fluoride administration can
be followed in the teeth by resulting paired hyper- and hypomineralized
zones, followed by normal mineralization as shown by Walton and Eisenmann
(1974).
Kruger (1970a) showed a reduction in the uptake of proline by amelo-
blasts in the presence of mottling doses of fluoride. In a later study,
Kruger (1972) observed increased uptake of serine at submottling doses and
reduced uptake at mottling doses. Proline is important in collagen and
also in the interprismatic fibrillar material. Glimcher and Krane (1964)
identified serine phosphate in bovine enamel matrix, and its presence
there was considered to satisfy some of the criteria for crystal growth.
The stimulating effect of fluoride on serine uptake at the lower, submot-
tling doses supported the general observation of Hodge and Smith (1968)
that "the primary effect of small doses of fluoride is the stimulation of
the osteocyte (or the ameloblast). Larger doses impair the function of
the osteocytes and the ameloblasts."
Dean's conclusions on fluoride in the water and dental health follow
(as cited in Maier, 1972). The conclusions are the following: (1) When
the fluoride level exceeds about 1.5 ppm, any further increase does not
significantly decrease the decayed, missing, and filled (DMF) incidence
but does increase the incidence and severity of fluorosis. (2) In a tem-
perate climate at a level of about 1.0 ppm, optimal effects are observed
maximal reduction in caries with no esthetically significant mottling.
Among 12- to 14-year-old children, DMF rates in permanent teeth were re-
duced by about 60%. (3) Fluorosis can be produced only during the period
of calcification of the teeth (i.e., up to about 12 years), not thereafter.
(4) Once lesions of fluorosis are formed, they cannot be repaired (as by
medicinal or dietary influences) either during the calcification period
or thereafter. (5) Fluorides appear to be the only agents ordinarily a
part of the diet that have an influence on enamel formation. (6) After
calcification is completed, the structure of the enamel remains unaltered
despite subsequent changes in the diet.
Although fluorides may be the only agents ordinarily a part of the
diet that have a direct influence on enamel formation, some substances
(e.g., trace elements) may interact with the fluorides and have an in-
direct effect on enamel formation. Hadjimarkos (1967) found that simul-
taneous administration of selenium and fluoride reduced the beneficial
effect of fluoride, while Stookey and Muhler (1964) showed that addition
of molybdenum enhanced it. Bibby and Little (1975) showed incorporation
of titanium, along with fluoride, in the organic part of the enamel and
gave special attention to the role of organic fluoride in enamel.
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285
6.4.2.2 Physiological and Biochemical Aspects of Caries Resistance and
of Fluorosis Research on the penetration of fluoride and associated
cations into the tooth surface led to the advent of fluoridated tooth-
paste. Hoerman et al. (1966), using electron-probe microanalysis, found
that fluoride applied in a stannous compound reached a level in the first
few microns of enamel of about 500 ppm, which represents about a 20% in-
crease over normal by observed levels. Slight acidification has been
shown to increase fluoride uptake. Friberger (1975) considered that two
factors largely explain this: (1) faster diffusion of hydrogen fluoride
than of F~, hindered by a hydration shell as well as by reaction with
counterions, and (2) faster recrystallization at lower pH.
Jongebloed, Molenaar, and Arends (1975), by scanning electron micro-
scopy, studied sections of extracted teeth subjected to artificial caries
attack and treatment with sodium monofluorophosphate, one of the agents
used in fluoridated toothpastes. The microscopy showed plugging of the
interprismatic channels by material derived from the monofluorophosphate.
The authors postulated that this clogging not only slowed the inroads of
caries but also hindered removal of dissolved material, allowing redepo-
sition when the caries attack subsided.
Levine (1976) reviewed the action of fluoride in caries prevention.
In spite of much research, the mechanisms of this therapy are not fully
understood. One possibility is reduction of enamel solubility by forma-
tion of fluorapatite. Increased crystallinity and increased precipitation
of mineral in the presence of fluoride may also be factors, as well as
the plugging mentioned above. Perdok (1962) presented evidence for a
greater degree of hydrogen bonding between enamel protein and mineral
material for fluorapatite compared with hydroxyapatite, resulting in a
lower lattice-free energy and enhanced resistance to acid attack. Fluo-
ride absorbed during development affects tooth morphology, causing rounder
tooth cusps and shallower fissures. However, the effect of this morpho-
logical alteration on caries resistance is considered minor. Fluoride
appears in dental plaque and has a bacteriostatic effect. Not only is
bacterial glycolysis inhibited but also synthesis of polysaccharides which
serve as a reserve for acid production and as a matrix which would hold
fermentation products against the enamel surface. Birkeland and Charlton
(1976), studying plaque removed from subjects in a 1 ppm fluoride area,
showed an increase of fluoride ion activity upon fall in pH, with a
resultant caries-resistant effect.
Although fluoride is important in enamel, the concentration there
is not as great as in other hard tissues. The content is highest in the
surface enamel. Thus, Weatherell and Hargreaves (1965), removing layers
of enamel from an incisor of a 38-year-old male resident in a district
where fluoride in the water was 0.5 ppm, found that fluoride concentra-
tions fell steeply at first and then leveled off from 500 ppm at the
surface to 50 ppm at about two-thirds enamel depth. Fluoride concentra-
tions in tooth parts are shown in Figure 6.18 (Yoon et al., I960). The
high concentration in the pulp chamber should be noted, reflecting a good
systemic supply of fluoride. The cementum, structurally related to bone,
had a fluoride concentration of 2390 ppm. Singer and Armstrong (1962)
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286
ALVEOLAR BONE
CORTEX
SPONGIOSA
LAMINA DURA
F(ppm)
fi
1
1
1 tt
2390
1084
Figure 6.18. Fluoride concentrations in portions of alveolar bone
and teeth. Source: Yoon et al., 1960, p. 569. Reprinted by permission
of the publisher.
and Weatherell (1966), on the basis of postmortem studies showing good
correlation between the fluoride content of the cementum (higher than
bone) and that of the skeleton, suggested analysis of cementum biopsy
samples as a way of estimating skeletal fluoride burdens. The patients'
histories would have to be considered when doing this, as shown by the
results of a detailed study by Stepnick, Nakata, and Zipkin (1975) of
the effects of age and fluoride exposure on the fluoride, citrate, and
carbonate content of human cementum. External fluoride exposure, disease,
and abrasion were factors obscuring the relation.
Fluoride content of the teeth increases during life, but the rate
of increase slows with age. Figure 6.19 (part a) shows the results at
different concentrations of fluoride in the drinking water for enamel,
and part b shows the results for dentin (Jackson and Weidmann, 1959).
The greater incorporation and the less pronounced plateau in the dentin
reflects the greater accessibility of this part of the tooth than the
enamel to systemic fluoride.
The importance of early intake of fluoride for caries prevention is
shown by the results of a study of 1500 children from infancy to 10 years
of age (Margolis et al., 1975). Diminution of caries, ranked from the
greatest retardation to the least, is listed: the group in a nonfluor-
idated community that had received a fluoride-vitamin supplement from
infancy, the group living in an area where water was fluoridated, the
group given fluoride-vitamin supplementation starting at age 4, and the
control group. These results indicate the importance of fluoride during
the infant years (0-4) for the reduction of dental caries.
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287
8
o
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45
40
35
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25
20
15
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r>
I I I I
- WEST HARTLEPOOL
A SOUTH SHIELDS
0 LEEDS
) dentin. Source: Adapted from Jackson
and Weldmann, 1959, Figures 1 and 2, p. 304. Reprinted by permission of
the publisher.
6.4.2.3 Control of Fluoride as a Public Health Measure On the basis
of the epidemiological studies of tooth mottling and tooth decay dis-
cussed in Section 6.4.2.1, adding fluoride to public water supplies in
which it was deficient was suggested by a number of authorities in the
late 1930s and early 1940s. The suggestion was actually implemented in
1945 in Grand Rapids, Michigan, Newburgh, New York, and Brantford, Ontario.
The U.S. Public Health Service (as cited in Maier, 1972) reported that
in 1971 over 86 million persons in the United States were using fluoridated
water, plus an estimated 9.5 million using public water that naturally
contained sufficient fluorides. This, at the time, was about 58% of the
people in the United States who were served by a public water supply.
Figure 6.20 shows the growth in fluoridation from 1960 to 1970. It was
reported in 1975 (Environmental Health Resource Center, 1975) that in
the United States nearly 100 million persons used optimally fluoridated
water, 115 million did not have its benefits, and some 150 million people
in 30 countries around the world were drinking fluoridated water.
The benefits of fluoridation as a public health measure are beyond
question. Cox (as cited in Hodge and Smith, 1965) evaluated data from
cities where fluoridation had been introduced and described fluoridation
as the most practical means of approaching the goal of sound teeth for
all children. The dental benefits of fluoride in drinking water also
extend to adults who continue to reside in communities with optimal
fluoridation.
Figure 6.16, relating the fluorosis index, dental caries, and fluo-
ride content of the drinking water, is shown in Section 6.4.2.1. Similar
data are presented in a different way in Figures 6.21 and 6.22. The
threshold for beneficial results is considered to be 0.5 ppm fluoride.
-------
288
55
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VTER SUPPLY
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POPULATION (in millions)
8 § § § 1
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/
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ION
/
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1961
1963
1965
1967
1969
1961
1963
1965
1967
1969
Figure 6.20. Communities, water-supply systems, and population
served with fluoridated water, 1960-1970. Source: Adapted from Maier,
1972, Figure 10, p. 26. Reprinted by permission of the publisher.
ORNL-DWG 77-5327
NUMBER
OF
CITIES
STUDIED
NUMBER
OF
CHILDREN
EXAMINED
NUMBER OF PERMANENT TEETH
SHOWING DENTAL CARIES EXPERIENCE
PER 100 CHILDREN EXAMINED
9 100 200 300 400 500 600 700
FLUORIDE |
CONCENTRATION
OF PUBLIC
WATER SUPPLY
(ppm)
11
3
4
3867
1140
1403
847
<0.5
0.5 TO 0.9
1.0 TO 1.4
Figure 6.21. Relationship between fluoride concentration of public
water supply and number of dental caries in permanent teeth of children.
Source: Adapted from Maier, 1972, Figure 4, p. 18. Reprinted by per-
mission of the publisher.
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289
1400
ORNL-DWG 77-5328
140
DENTAL CARIES EXPERIENCE
DENTAL ruionosis
FLUOMOE (O»3.i z* 1.9 14 1.2 1.2 u 1.2 oj o^ 0* o.2 o.f O4 as oj oo O-Z oz ai 0.2 oxi o.i ai ao ai ai
(PPM)
SfcS>js*33^B53|
s!22S3S!52dg2s!!
i '.II
w K a
I i
Figure 6.22. Relationship between dental caries prevalence
(permanent teeth) and fluoride ingestion as measured by percentage of
children showing dental fluorosis in 8576 selected 12- to 14-year-old
children in 27 cities. Source: Adapted from Maier, 1972, Figure 3,
p. 17. Reprinted by permission of the publisher.
The trade-off between fluorosis and caries prevention is clearly seen in
Figure 6.22; the optimum fluoridation level in a temperature climate is
considered to be about 1.0 ppm.
The long-term result of fluoridation in Grand Rapids, Michigan, is
shown in Figure 6.23. The fluoride content of the water was 0.15 ppm
before fluoridation and was raised to 1.0 ppm. After 15 years the curve
of DMF teeth for Grand Rapids was approaching that of Aurora, Illinois,
where the water is naturally fluoridated at 1.2 ppm.
The reduction of caries incidence from the Grand Rapids' baseline
before fluoridation is very notable and is similar to the reduction in
-------
290
16
12
u
cc
UJ ^
a. 8
X
ORNL OWO 77532*
GRAND RAPIDS
BEFORE FLUORIDATION
16
12
RAPIDS f
10 YEARS AFTER -'GRAND
FLUORIDATION X RAPIDS
* 15 YEARS AFTER
FLUORIDATION
9 10 11 12
AGE LAST BIRTHDAY
13
14
16
16
Figure 6.23. Reduction in caries incidence in permanent teeth of
children from Grand Rapids, Michigan, after 10 and 15 years of fluoridation.
Source: Adapted from Maier, 1972, Figure 6, p. 20. Reprinted by per-
mission of the publisher.
all other communities studied. Fluoride is mainly effective in reducing
the number of caries when taken during the period of tooth formation. As
seen in Section 6.2, it is also useful for offsetting osteoporosis in
middle-aged and elderly people. Because of the slow turnover of enamel
material, the tooth effect largely lasts through life.
6.4.2.3.1 Possible countraindications to fluoridation From time to
time, various ills (e.g., acne, allergies, headaches, and numbness) have
been attributed to fluoride in the water. Aside from a few well-documented
cases of fluoride contact dermatitis under special circumstances (Smith
and Hodge, 1959), the purported cases turn out to have no basis in fact.
Perkins (1952) claimed that cancer deaths in Grand Rapids rose after flu-
oridation; however, this was refuted by Swanberg (1953), who found that
the opposite was actually true. A report issued by The National Health
Federation and published in the Congressional Record of July 21, 1975 (as
cited in Wolman, 1976), linked cancer mortality patterns in certain U.S.
counties to artificial fluoridation of water. In refutation, an exhaustive
study of cancer statistics in the United States over a 20-year period
(1950 to 1970), made by the National Cancer Institute (as cited in Wolman,
1976), "provides no support for recent claims that fluoridation of water
supplies in the U.S. has increased the risk of cancer" and adds that "no
significant excess mortality from cancer could be detected up to 15 years
after fluoridation in areas where 95% of the population had been abruptly
and continuously exposed." In fact, "reduced mortality from cancers of
the brain and nervous system in communities with high levels of natural
-------
291
fluoride" was actually found. Doll and Kinlen (1977) reported that a 1976
statement by the Royal College of Physicians that "there is no evidence
that fluoride increases the incidence of mortality of cancer in any organ"
was challenged on merits of the July 21, 1975, report in the Congressional
Record (as cited in Wolman, 1976) . Doll and Kinlen reexamined the same
census data that were evaluated in the report in the Congressional Record
and found that when age, sex, and ethnic group were taken into account,
the ratio between observed cancer mortality and expected cancer mortality
actually fell slightly in the cities using fluoridated water supplies.
Thus, the National Cancer Institute's refutation of the Congressional
Record study was reaffirmed. In one other study, Erickson (1978) compared
the mortality rates (blacks and whites only) in 24 cities with fluoridated
water supplies and 22 cities with nonfluoridated water supplies, and found
no evidence of fluoride causing any harmful effects. Other claims of del-
eterious effects of fluoride from fluoridation of public water supplies
were commented on by Rubini (1969) and Bronner (1969) and were shown to
be without foundation.
6.4.2.3.2 Vehicles other than water for fluoridation Vehicles other
than water have been suggested for fluoride administration, such as tab-
lets, milk, table salt, or topical application. The question was consid-
ered by the Nutrition Committee of the Canadian Pediatric Society (1972),
and techniques other than water fluoridation were found to be of interest
mainly to special population groups or as a means of supplementation where
water of optimum fluoride content was not available. While fluoridation
of public water supplies is still the best general way of ensuring adequate
intake of fluoride by the general population, changes in food and water
intake patterns and increasing use of fluoridated water in food processing
make it necessary to monitor the amounts of fluoride people are actually
consuming. Prival and Fisher (1974) considered the question and claimed
that fluoride intakes are rising. One method of monitoring considered
useful is the so-called "market-basket" approach, which is analysis of
the fluoride content of a typical two-week diet of a 16- to 19-year-old
male. The authors suggested periodic surveys of dental fluorosis in
selected artificially fluoridated areas as a basic way of detecting any
trend toward increase of fluoride intake above optimum.
6.4.3 Toxicity of Fluorine and Fluorine Compounds
6.4.3.1 Chronic Toxicity, Fluorosis Chronic toxicity of fluoride is
manifested chiefly in the bones where incorporation of fluoride modifies
the chemical composition of bone (Weidmann and Weatherell, 1970). Fluo-
ride is a unique ion because it continues to deposit in calcified struc-
tures after the other constituents have reached a steady state (Zipkin,
1970). While the calcium-phosphorus ratio remains unchanged, carbonate
and citrate are lowered and magnesium increases. A relation between flu-
oride intake and calcium deposition has been noted by many authors. In
spite of the chemical changes, the physiology of the skeleton is not
grossly changed by consumption of water containing as much as 8 ppm fluo-
ride (Zipkin, 1970). At about this level on long-term intake, chemical
fluorosis may be noted. In its early stages, fluorosis is evidenced by
an increased opacity of the bone to X rays.
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292
Roholm (1937a) studied workers in the cryolite industry exposed to
high levels of fluoride and described the three following stages in the
evolution of skeletal fluorosis, as distinguished radiologically: (1)
The spinal column and pelvis show roughening and blurring of the trabec-
ulae, or fibrous parts, reflecting both early ectopic calcification and
also disorganization in the protein-matrix part of the bone. (2) The
trabeculae merge together, and the bone has a diffuse structureless
appearance. Contours become uneven, the medullary cavities may be nar-
rowed, and the ligaments show calcification. (3) The bones appear as
marble-white shadows with a woolly configuration. The bones of the ex-
tremities show irregular periosteal thickening with calcification of
ligaments and muscular attachments. The cortex of the long bones is thick
and dense, the medullary cavity is diminished, and the interoseous mem-
branes, such as between the tibia and fibula and between the radius and
ulna, show calcification.
Singh et al. (1962) studied the skeleton of an individual who had
lived in an area of 9.5 ppm water fluoride content. The bones were heavy,
irregular, and dull-colored. Multiple exostoses were present, particularly
around sites of insertion of muscles and tendons. In the spine, ligaments
were calcified and vertebrae were fused at many places and thickened, re-
sulting in pressure on the spinal cord. These changes, and other cases
studied showing exostoses around joints, explain the crippling and pain
associated with severe fluorosis.
It is paradoxical that the increased calcification is accompanied
by bone resorption. Fluoride stimulates both the osteoblasts and the
osteoclasts; therefore, bone destruction may proceed side by side with
bone formation. Because of this, x-ray pattern may resemble that of
Paget's disease and other bone diseases such as osteosclerosis and osteo-
malacia without elevated fluoride.
It is considered that 4 to 5 mg of fluoride is the daily limit that
may be ingested without hazardous body storage (Singh and Jolly, 1970).
In areas of endemic fluorosis, levels of ingestion of over 8 mg daily
are common, and levels in industrial situations may be 15 to 20 mg daily.
Fluoride levels in bone in fluorotic individuals cover a wide range.
It is unlikely that there is a critical threshold of fluorine in the bone
for development of fluorosis. (However, a critical threshold would be
difficult to determine since the fluoride concentration in bone has to
be greater than 5000 ppm before there is an increase in x-ray absorption.)
Rather, the level in the bone represents the past history of the individ-
ual. If this history involved intake of fluoride such that cellular metab-
olism was perturbed for a sufficient time, fluorosis resulted. Once in
the bones, fluoride causes no problem (see Weatherell, 1966).
Since all the details of bone calcification and metabolism are not
known, it is also not known exactly how excess fluoride interferes with
normal bone processes. As discussed by Weatherell (1966), fluoride may
inhibit enzymes of the bone matrix, may perturb the transport of metabo-
lites across bone cell walls, or may interfere with the synthesis of
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293
matrix precursors. Along with this is increased osteogenesis, as evidenced
biochemically by increase in serum alkaline phosphatase.
Fand (1973) discussed other aspects of fluorosis in addition to
dental and skeletal lesions. On long-standing fluorosis, neurological
symptoms may occur that have been designated as a radiculomelopathy by
Singh and Jolly (1961). A hypochromic microcytic anemia with defective
marrow erythrocyte formation has been noted. There may be increased serum
alkaline phosphatase activity, along with increased serum inorganic phos-
phorus, reduced serum calcium, and increased urinary calcium. Premature
aging and signs of hypoadrenocorticalism characterized by decreased urinary
17-ketosteroids may be noted. Digestive disturbances, including a chronic
catarrhal gastritis, occur.
Patients with renal insufficiency would not eliminate fluoride as
easily as healthy persons and might show signs of fluorosis at lower
concentrations than the general population. However, as mentioned in
Section 6.3.2.1, fluoride is largely eliminated passively. The conse-
quence of this is that most nephritic conditions do not have much effect
on fluoride excretion. Studies of fluoride excretion in normal and
nephritic persons and in experimental animals with kidney injury (Hodge,
Smith, and Gedalia 1970; Weatherell, 1966) prove this to be true.
The use of fluoridated water for hemodialysis has caused some alarm.
Posen et al. (1968, as cited in Aaron 1969) suggested that the fluoridated
water (0.9 to 1.0 ppm) of Ottawa, Canada, was a contributing factor to
the high incidence of renal azotemic osteodystrophy in 16 patients on
long-term hemodialysis. Aaron's discussion (19.69), however, discounted
this, as osteodystrophy is common in patients with chronic renal failure,
including those receiving long-term dialysis with nonfluoridated water.
Parsons (1974) considered the question and found no significant differences
in fluoride retention in patients dialyzed against fluoridated water in
Newcastle and nonfluoridated water in London. There was no convincing
correlation between the degree of fluoride retention found in uremic bone
and the prevalence of uremic osteodystrophy. Parsons suggested that flu-
oride in the hemodialysis water may actually be beneficial in opposing
the demineralizing process of long-term dialysis. However, Cordy et al.
(1974) compared hemodialysis patients using nonfluoridated water with those
patients using fluoridated water. In agreement with Posen et al. (1968,
as cited in Aaron, 1969) they concluded that patients maintained on long-
term hemodialysis (several years) using fluoridated water will show an
unacceptable frequency and degree of osteomalacia.
There are several methods of monitoring for fluoride hazards. In
most urban areas the fluoride concentration in the drinking water is
routinely determined. However, analysis of typical water supplies are
required to show that a hazard exists in rural areas. Where persons are
exposed to unknown amounts of fluoride, such as dusts and fumes in indus-
trial situations, authorities agree that monitoring of urinary fluoride
would provide adequate information concerning fluoride exposure. "Air
sampling forms the basis for good industrial hygiene control; urine anal-
ysis gives reliable evidence of the effectiveness of the protective pro-
gram" (Hodge and Smith, 1972). Walbott (1970) criticized this philosophy
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294
on the basis of individual variations, but it remains an effective and
practical approach when applied systematically.
Threshold limit values for a number of fluoride compounds, including
some fluoroorganics, are given in Table 6.13. Most of the compounds for
which threshold limit values have been recommended do not present air pol-
lution problems, and many not even workroom problems. In most cases, the
industrial exposure concentrations are significantly below these values.
TABLE 6.13. THRESHOLD LIMIT VALUES OF VARIOUS FLUORINE COMPOUNDS
Fluoride-containing
substance
ACGIHa threshold
limit value
(ppm) (mg/m3)
Pennsylvania
short-term limit
Boron trifluoride*
Bromine pentaf luoride
Chlorine trif luoride*
Dichlorodifluorome thane
Dichloromonof luoromethane
Dichlorotetraf luoroe thane
Di f luorodibr omome thane
Fluoride (F~)
Fluorine
Fluorotrichloromethane
Hydrogen fluoride*
Nitrogen trifluoride
Oxygen difluoride
Perchloryl fluoride
Selenium hexafluoride
Sodium fluoroacetate (1080)
Sulfur hexafluoride
Sulfur pentaf luoride
Sulfuryl fluoride
Tellurium hexafluoride
l,l,l,2-Tetrachloro-2,2-
difluoroethane
1,1,2, 2-Tetrachloro-l , 2-
difluoroethane
l,l,2-Trichloro-l,2,2-
trifluoroethane
Tr i f luoromonobromome thane
American Conference of
1
0.1
0.1
1000
1000
1000
100
0.1
1000
3
10
0.05
3
0.05
1000
0.025
5
0.02
500
500
1000
1000
Governmental
3
0.7
0.4
4950
4200
7000
860
2.5
0.2
5600
2
29
0.1
13.5
0.4
0.05
6000
0.25
20
0.2
4170
4170
7600
6100
Industrial
1 ppm for 5 win
0.1 ppm for 5 min
10 mg/m* for 30 min
0.5 ppm for 5 min
3 ppm for 15 min
Hygienists.
, V«-tafln
Source: Reprinted from Fluondea, Publ. 1922, p. 231, with the
permission of the National Academy of Sciences, Washington, D.C.
As noted, the threshold limit value for inorganic fluoride is 2.5
mg/m3. A few countries consider this too high and recommend 1.0 mg/m3
instead. The countries included are the Soviet Union, Poland, Hungary,
Czechoslovakia, and East Germany. It should be noted, however, that the
philosophy of the Soviet Union hinges on finding the smallest dose or the
lowest concentration that produces a reproducible effect of any sort; in
the case of hydrogen fluoride, for example, the results of a test using
a transmitted impulse from the olfactory nerve of a dog inhaling hydrogen
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295
fluoride in air were used. An air-quality standard for fluoride of 0.01
mg of fluoride per cubic meter for a 24-hr average concentration with a
maximum allowable single peak concentration of 0.03 mg/m3 in the ambient
air of inhabited areas, has been established in the Soviet Union and sev-
eral other eastern countries (National Academy of Sciences, 1971, pp. 230-
231). The National Academy of Sciences document questions the practicality
of such low limits and considers them more representative of a final goal
to be achieved than a true reflection of an existing situation.
Zielhuis (1974) discussed differences between the United States and
the Soviet Union in their approach to setting permissible limits for res-
piratory exposure to chemical agents in industry. In the United States,
research is often focused on cells or organs; in the U.S.S.R. the emphasis
is on central nervous system effects (Ryazanov, 1962). Thus, differences
arise in interpretation of biological changes regarding health. Zielhuis
(1974) made a plea for exchange of basic data because the two approaches
clearly complement each other.
For the general population, water is the chief source of fluoride.
The close relationship between fluoride concentrations in water and in
urine is shown in Figure 6.24. Largent (1961) proposed that an average
urinary excretion of at least 8 mg of fluoride per liter over a period
of more than five years would be required to corroborate a diagnosis of
skeletal fluorosis. This prediction was supported by the findings of
Sankaran and Gadukar (1964). They found levels of urinary fluoride excre-
tion of 8 to 22 ppm in 6 cases of early to advanced human skeletal
fluorosis.
The mobilization of fluoride as evidenced by continued urinary excre-
tion on withdrawal of fluoride was mentioned in Section 6.3.2.2. Such
excretions chiefly result from the osteoclastic activity of normal bone
cycline (Hodge and Smith, 1965). Fluorotic patients brought to a normal
regime showed that the release of fluorine from the bone into the blood
and thence into the urine slowly declined over a period of several years
half-life of eight to ten years (Forbes et al., 1978).
A simple diagram of bone dynamics is given in Figure 6.25. At doses
below poisoning levels and below levels where crippling fluorosis may
ensue, fluoride stimulates bone formation, induces partial resorption,
and causes changes in the degree of mineralization. Since bone formation
prevails over enhancement of resorption, total bone mass increases. New
bone, rich in fluoride, resists osteoclastic action because of the decreased
solubility of fluorapatite as compared with hydroxyapatite. Feedback from
the process results in a secondary hyperparathyroidism. This leads to
osteoblastic as well as osteoclastic differentiation, the former causing
increased chondrogenesis and matrix formation. The high organic content
of bone thus formed accords with the observation, made histologically,
that the exostoses of fluorosis resemble fetal bone, where high osteo-
blastic activity is of course normal. The alterations of normal growth
and development produced by excess fluoride were summarized by Hodge and
Smith (1965) as: (1) acceleration of cortical remodeling, (2) dissocia-
tion of the normal sequences in osteogenesis, and (3) the production of
abnormal bone.
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296
ORNL-OWG 79-20915
Q.
O.
T
DRINKING WATER
URINE
IL
I
1 2 3
FLUORIDE IN DRINKING WATER (ppm)
Figure 6.24. Relationship between fluoride concentration of drinking
water and fluoride concentration of the urine. Source: Adapted from
McClure and Klnser, 1944, Figure 1, p. 1582. Reprinted by permission of
the publisher.
ORNL-DWG 79-20910
[F] IN
BONE
[F] IN
SERUM
HYPERPARA-
THYROIDISM
MAINTAINS
SERUM {CaH-)'
DIFFERENTIATION
Figure 6.25. Scheme of the effects of fluoride on calcium homeostasis
(osteocytic resorption) and bone metabolism (osteoclastic resorption).
The lines ending in a perpendicular bar indicate inhibition; those ending
in an arrow indicate stimulation. Source: Rich and Feist, 1970, Figure
4, p. 82.
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297
Fluoride effects on enzymes were discussed in Section 6.4.1. Roholm
(1937a) in his treatise on fluoride intoxication, pointed out that the
enzyme system most susceptible to fluoride is a lipase. Hodge and Smith
(1965) mentioned the findings of several authors: Leake et al. (1929)
noted that hepatic lipase activity was suppressed by in vivo intravenous
fluoride injections of 75 to 150 mg/kg fluoride, and Sievert and Phillips
(1959) reported curtailment of renal fatty acid oxidase activity by in
vivo fluoride concentrations of 0.1% and 0.15% of the diet feed. Burstone
and Keyes (1957) demonstrated that a fatty acid, esterase, was the chief
enzyme associated with bone formation, affected by in vivo sodium fluoride
injections of 0.1 ml of 0.05 M solution twice a day for three days. The
studies of Johnson (1960) on mineralization of collagen showed involvement
of phospholipids in the chemistry of the osteoblasts and in the transfor-
mation of osteoid material to bone. A constant finding of extensive serous
atrophy of the fatty marrow in the bones of animals maintained on very
high fluoride diets (900 ppm for 71 days) (Hodge and Smith, 1965) further
showed the importance of lipids in bone metabolism.
The osteosclerotic effect of fluoride and research done on wound and
fracture healing in the presence of fluoride have stimulated studies on
fluoride use in therapy of bone disorders. Gedalia and Zipkin (1973)
reviewed the question and concluded that fluoride therapy must still be
considered experimental because much work remains to be done on establish-
ing optimal dosages, on coupling fluoride therapy with other medications
(e.g., vitamins and hormones), and in the elaboration of fluoride compounds
more specific and less toxic than simple fluorides. On balance, however,
it appears that fluoride-induced osteosclerotic bone, although not as sat-
isfactory as original bone, is preferable to osteoporotic bone. According
to Hodge and Smith (1968), the benign nature of early skeletal fluorosis
and the mildness of the adverse reactions from fluoride doses as high as
60 mg daily make the risks of fluoride treatment acceptable.
An optic neuritis is, however, a possible contraindication. Neer
et al. (1966) studied a patient with relatively stabilized multiple mye-
loma with generalized osteoporosis and found a beneficial effect (pro-
gressively positive calcium, presumptive stabilization of bone crystal)
over three years at a fluoride dose of 27 mg daily. Carbone et al. (1968)
found that administration of fluoride following, or concurrent with, anti-
neoplastic treatment produced some benefit in myeloma patients with bone
lesions. Similarly, Compels, Votaw, and Martel (1972) found some benefi-
cial increase in bone density in some patients with multiple myeloma who
were receiving fluoride therapy. In contrast, Harley, Schilling, and
Glidewell (1972), in a double-blind study of 150 patients with multiple
myeloma, found no benefit from fluoride treatment and even a suggestion
that production of fluorosis might be detrimental to myeloma patients
because the new, low-quality, somewhat disorganized bone being laid down
would be an inroad for the myelomatous process.
The use of fluoride is probably of more benefit in developmental and
degenerative or metabolic bone disorders than in neoplastic-associated ones,
Whereas Albright and Grunt (1971) found only marginal benefit of fluoride
in 20 children and 5 adults with osteogenesis imperfects, Bernstein et al.
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298
(1963) found increased calcium retention, increased mineralization, and
some relief of bone pain in patients with postmenopausal osteoporosis,
urticaria pigmentosa with osteoporosis, and idiopathic osteoporosis. These
patients received doses of sodium fluoride of 50 to 200 mg/day (22 to 90
mg of fluoride). Bernstein et al. (1966) also found a lower prevalence of
osteoporosis, collapsed vertebrae, and back pain in residents over age 45
(particularly women) in a community of high fluoride water concentration
(4.0 to 5.8 ppm) as compared with residents of a community having a low
concentration of fluoride in the water (0.15 to 0.3 ppm). The male sub-
jects, however, showed little difference in the incidence of spontaneous
collapsed vertebrae as a function of fluoride water concentration. The
4.0 to 5.8 ppm level is, however, high for the general populace because
of the potential enamel defects (mottling) on developing teeth.
As seen in Figure 6.25, imbalance in bone formation on stimulation
with fluoride may arise from lack of calcium. Jowsey et al. (1972) found
that twice weekly administration of a combination of 50 mg of sodium flu-
oride, 50,000 units of vitamin D, and 900 mg of dissolved calcium was
beneficial in the treatment of osteoporosis. Zanzi et al. (1975) found
increases in skeletal mass in some, but not all, osteoporotic patients
on treatment with salmon calcitonin, sodium fluoride, and dissolved
calcium.
Shambaugh and Scott (1964) used sodium fluoride to induce or hasten
maturation and inactivation of otosclerotic foci in ear bones in order
to arrest progression in conductive and sensorineural hearing loss.
6.4.3.2 Acute Toxicity A reasonable estimate of a "certainly lethal
dose" of sodium fluoride for a 70-kg man is 5 to 10 g (Hodge and Smith,
1965). This corresponds to 70 to 140 mg/kg. Since sodium fluoride is
19/42 fluoride by weight, this corresponds to 2.2 to 4.5 g of fluoride,
or 32 to 64 mg per kilogram of body weight. Roholm (1937a) reported 4 g
of sodium fluoride as the smallest dose to cause death in an adult man.
Sodium fluoride used as a roach and ant powder may be carelessly kept
near food and mistaken for sugar or flour. Incidents of poisoning have
occurred this way. Pure sodium fluoride is white, but federal law now
requires that it be colored blue or green (National Academy of Sciences,
1971); nonetheless, accidents still occur. Other fluoride compounds are
also used as insecticides and rodenticides; they are as poisonous as sodium
fluoride on the basis of the amount of fluoride absorbed. Metcalf (1966)
listed the toxicities to insects of a number of inorganic fluoride com-
pounds. The toxicities generally are a function of the fluoride content.
To humans, the toxicity depends on the ease of absorption of the compound.
Thus, cryolite (Na3AlF«), which has a relatively low solubility and is a
natural product, has been used as a spray or as a dust for the control of
chewing insects. It is relatively innocuous to foliage and has a low tox-
icity to mammals; the oral LD30 in the rat is approximately 13,500 mg/kg.
Other fluorine-containing compounds in the home taken as recommended
(e.g., anticaries tablets, some pediatric formulations, and toothpaste)
are not hazardous. Hodge (1969), however, cautioned that some commercially
available rust removers contain dangerous quantities of hydrofluoric acid.
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299
Because of the resulting massive availability, fluoride compounds
are lethal at considerably lower doses when injected rather than ingested.
Thus, the 24-hr intraperitoneal LD90 of sodium fluoride for rats was 23
mg/kg, about one-fifth of the oral LDS0. Showing the importance of solu-
bility, the 24-hr LDSO for cryolite given intraperitoneally in rats was
25,000 mg/kg, while for calcium fluoride it was 1500 mg/kg (Hodge and
Smith, 1965).
The amount of fluoride absorbed into soft tissues seems to be the
most critical point in fluoride poisoning. Gettler and Ellerbrook (1939)
analyzed remaining fluoride in the internal organs of five persons fatally
poisoned. They estimated from these analyses that 105 mg is the smallest
absorbed lethal dose of fluoride in a 140-lb individual. On the basis of
known patterns of fluoride distribution, Hodge and Smith (1965) estimated
that the 105 mg of fluoride would represent 5% of the ingested dose, which
would have been 4 to 5 g of sodium fluoride. The 105 mg is the fraction
of the total absorbed fluoride remaining in the soft tissues at death.
They suggested that this be called the "smallest soft tissue burden."
There is no single cause of death in fluoride poisoning. Respiratory
blockage is certainly important but is not the only major effect. Hodge
(1969) grouped most of the acute fluoride effects into four categories of
major functional derangements: (1) enzyme inhibition, (2) calcium complex
formation, (3) shock, and (4) specific organ injury. Effects of fluoride
on various enzymes and enzyme systems are discussed in Section 6.4.1. At
acute levels these inhibitions may be contributory to death. Hodge and
Smith (1965) summarized the effects of the four categories. In acute poi-
soning, fluoride kills by blocking normal cellular metabolism. Fluoride
inhibits enzymes involved in essential processes, causing vital functions,
such as the origin and transmission of nerve impulses, to cease. Inter-
ference with necessary body functions controlled by calcium (e.g., blood
clotting and membrane permeability) may be equally important. Massive
impairment in the function of vital organs results from cell damage and
necrosis. Terminally there is a characteristic shock-like syndrome.
Fatal poisoning is rapid, death frequently occurring in 2 to 4 hr
(Hodge and Smith, 1965). When soluble fluoride is ingested, a catastrophic
series of events is set in motion. There is salivation, a burning sensa-
tion, nasal discharge, nausea, mucosal irritation, urination, vomiting
with blood, and diarrhea with blood. The pH of the stomach causes some
hydrogen fluoride to be formed. When this is regurgitated, extreme irri-
tation of the esophagus, throat, and upper respiratory tract ensues. There
is urticaria, muscular weakness, excitement and tremor, convulsion, and
fall of blood pressure (Greenwood, 1940). Initially there is an accelera-
tion and deepening of respiration that is followed by a general paralysis
of the vital nervous centers. Death occurs by general collapse; shock,
involving tetany, is a prominent characteristic. On autopsy, general
congestion of the organs is noted, with renal tubular degeneration. The
blood is slow to clot because of the calciprivic action of fluoride.
Poison and Tattersall (1969) described a number of cases of fluoride
poisoning suicidal, homicidal, and accidental. One woman died in 15
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300
min after taking 17.2 g of sodium fluoride. Numerous cases of fluoride
poisoning occurred in a mental hospital in Oregon (Lidbeck, Hill, and
Beeman, 1943). Roach powder was mistaken for powdered milk, added to
scrambled eggs, and served to patients in five wards. Some rejected the
dish because of a salty or soapy taste. Of 263 patients who ingested
the fluoride, 47 died.
Fluoride poisoning has no particular or special signs but resembles
poisoning from other violent gastrointestinal irritants, notably arsenic,
mercury, barium, and oxalic acid (Poison and Tattersall, 1969). It has
been mistaken for botulism. There is no specific treatment, except for
administration of calcium salts. Vomiting is usually spontaneous; if not,
an emetic should be given. Gastric lavage with limewater is effective.
Calcium chloride or milk by mouth may be given. A soluble calcium salt
may be given intravenously; calcium gluconate is often used. Because the
kidneys can excrete a great deal of fluoride and some fluoride is taken
up by the bones, if a patient survives the first few hours of poisoning,
chances of survival are good with supportive measures. Abukurah et al.
(1972) reported the case of a man who survived after ingesting 120 g of
sodium fluoride in a suicide attempt. Nausea and vomiting occurred imme-
diately and persisted for 1 hr prior to hospitalization. Tetanic contrac-
tions and ventricular fibrillation, requiring countershock and cardiac
massage, were features of the case. Fluid therapy and administration of
diuretics to protect against tubular necrosis and to increase excretion
of fluoride were effectively used to remove the patient from the acute
phase of poisoning. The patient recovered without sequelae. This is
generally the case in recovery from fluoride poisoning. Thus, except
for necrosis and burns, as in the case of exposure to hydrogen fluoride,
the effects of fluoride appear to be mainly reversible.
6.4.3.3 Toxicity and Hazards of Inorganic Fluoride Compounds
6.4.3.3.1 Hydrogen fluoride and hydrofluoric acid Exposures to hydrogen
fluoride, F2, and hydrofluoric acid (SiFi.) usually occur in industry.
Poisoning by hydrogen fluoride is rare. Although it is highly dangerous
because of its fluorine content and corrosive action, hydrogen fluoride's
extremely irritating nature serves as a warning. Used in water solution,
it can be extremely dangerous. It penetrates the skin easily, resulting
in deep burns that develop into abcesses. Hydrogen fluoride is as toxic
as other fluorides on the basis of fluorine content, but in cases of inha-
lation (as a gas or as vapors of an aqueous solution) the respiratory
inflammation and pulmonary edema due to its irritant nature tend to over-
shadow the general aspects of fluoride poisoning mentioned in the preced-
ing section. This is shown by the outcome of two cases described by
Greendyke and Hodge (1964). Two men at work noticed a bottle of hydro-
fluoric acid emitting fumes. The men attempted to remove the bottle, but
it exploded, showering them with acid and enveloping them in dense fumes.
Fellow workmen sprayed them with a fire hose, and a physician washed the
burns with bicarbonate and administered an opiate. The men were then
taken to a hospital. After 4 hr, one man died from intense inflammation
of his respiratory tract and gross hemorrhagic pulmonary edema, in spite
of a tracheotomy. An autopsy showed bloody mucus in the stomach as well
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301
as the lungs; the fluoride blood level was 4 ppm. The other man died
after 10 hr from cardiac arrest and apnea. Autopsy findings were similar
to those of the other victim.
Because these men were 85 miles from a hospital and several hours
elapsed before they were treated, it is possible they might have survived
with earlier treatment; however, it is difficult to know what to do to
counteract lung damage. Mayer and Guelich (1963) estimated that hydrogen
fluoride contamination from splashes of concentrated hydrofluoric acid,
particularly in the chest area and breathing zone, could produce concen-
trations of 10* to 10s ppm that might do irreversible, fatal damage to
lung tissue in less than a minute. It may be noted that hydrofluoric
acid is used in industry as an aqueous solution in concentrations up to
70% and as a pure liquid under pressure. The vapor pressures of aqueous
solutions are such that an inhalation hazard probably exists only with
solutions containing more than 60% hydrogen fluoride (Mayer and Guelich,
1963). Enough hydrogen fluoride can be absorbed through the skin that
systemic fluoride poisoning results. This is shown in a case studied by
Burke, Hoegg, and Phillips (1973). In a laboratory accident, a techni-
cian's face, neck, and arm were sprayed with liquid hydrogen fluoride.
The man was placed in a shower and washed for 15 min. In the hospital,
under general anesthesia, the skin burns were infiltrated with calcium
gluconate. The patient showed signs of general fluoride poisoning, with
stupor and polyuria. Urine fluoride analyses showed he had absorbed a
total systemic dose of at least 404 mg of fluoride from an estimated 5 g
of hydrogen fluoride spilled on about 2.5% of his body surface. The
patient recovered without sequelae, except for skin burns which were
repaired by plastic surgery.
6.4.3.3.2 Elemental fluorine Fluorine is more toxic than hydrogen
fluoride. The U.S. safe standard (Hamilton and Hardy, 1974) for exposure
to hydrogen fluoride is 3 ppm compared to 0.1 ppm for fluorine. For flu-
oride salts in air (dusts and fumes) it is 2.5 mg/m3. Fluorine causes
burns, as does hydrogen fluoride. As described by Dreisbach (1971),
inhalation of hydrogen fluoride or fluoride causes coughing, choking,
and chills lasting 1 to 2 hr after exposure. Over one or two days, fever,
coughing, chest tightness, rales, and cyanosis develop, indicating pulmo-
nary edema. The symptoms progress for a day or two and then regress
slowly over a period of a few weeks.
Some exposure limits have been given in the Hygienic Guide series
of the American Industrial Hygiene Association (1965). The maximum atmos-
pheric concentration for an 8-hr exposure, as determined by experiments
with animals, was 0.1 ppm. Short exposure tolerance, as observed in two
men exposed very briefly, was 25 ppm. This caused sore throat and chest
pain for 6 hr. The volunteers felt they could not tolerate 50 ppm. One
ppm for 1 hr was not expected to cause injury. Atmospheric concentrations
immediately hazardous to life are not known for humans, but test animals
have died at concentrations ranging from 10,000 ppm for 5 min to 200 ppm
for 3 hr. Keplinger and Suissa (1968) found only slight irritation upon
exposure of volunteer human subjects to 25 ppm but marked irritation of
eyes and nose at 100 ppm. Largent (1949) gave the progression of effects
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302
with concentrations of gaseous fluorides (e.g., hydrogen fluoride and F2
giving rise to hydrogen fluoride). No local immediate systemic effects
were noted at 3 ppm, but at 10 ppm many persons experienced discomfort.
At 20 ppm, all persons complained and objected seriously to staying in
the environment. Brief exposures to 60 ppm caused definite irritation
of the conjunctivae and nasal passages and tickling and discomfort of the
pharynx and trachea. The highest concentration tolerated was 120 ppm for
less than 1 min by two men.
Some effects of fluorine are qualitatively different from those of
neutral fluorides or of hydrogen fluoride. Hodge and Smith (1965) sug-
gested that perhaps it is not F2 but some highly reactive product (e.g.,
OF2) that is responsible for the respiratory irritation when F2 is
released in air.
Ricca (1970) reviewed the pathotoxicology of elemental fluorine,
with particular attention to the physiochemistry of fluorine reactions
with animal proteins and lipids. Fluorine can react directly with organic
compounds to yield free radicals without the requirement of an initiator.
Disruption of the fluorine molecule gives hydrogen fluoride, a free-
radical fluorine atom, and a free-radical organic moiety. Addition of
fluorine across double bonds is also an important feature of fluorine
reactivity. Some C-F and N-F fluorosubstituted compounds are potent com-
petitive inhibitors of natural substrates or may take the place of natural
organic molecular building blocks. Chemical bonds may be broken by fluo-
rine attack, causing aberrations in metabolic chains. Finally, fluorine
elimination shows differences from that of fluorides. Ricca attributed
the effects of fluorine to formation of hydrogen fluoride and fluoride,
plus the special effects of fluorine itself. On the basis of his own
work and a survey of the literature, Ricca suggested the following limits:
an emergency exposure limit of 25 ppm for 5 min, an emergency tolerance
limit of 15 ppm for 10 min, and a threshold limit value of 1.0 ppm for
8 hr.
6.4.3.3.3 Silicon tetrafluoride Silicon tetrafluoride, used to make
fluorinated compounds, is gaseous and has effects and toxicity similar
to those of hydrogen fluoride (Greenwood, 1940). Hydrofluorosilicic acid
and soluble salts have actions similar to those of hydrofluoric acid and
fluorides. Roholm (1937&) analyzed a disastrous fog that occurred in the
Meuse Valley near Liege, Belgium, in 1930. He concluded that the disaster
may have been due to acute fluoride poisoning that resulted from gaseous
fluorine compounds (HF, SiF*,) liberated by certain factories in the area
in conjunction with an unusually dense fog. Heavy fumes of fluorosilicic
acid are generated from SiF<, in moist air. Several thousand persons suf-
fered acute pulmonary attacks, and 60 deaths were reported.
6.4.3.4 Fluorine in Pesticides Fluoride sprays were introduced in the
early decades of this century partly to replace arsenate sprays with their
residue problems, particularly lead arsenate. Use was considerable at
one time, and sodium fluoride, sodium and barium fluorosilicates, and
cryolite were used most extensively (Hodge and Smith, 1965). However,
by the late 1960s, more effective insecticides became available, and the
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303
use of all types of fluoride insecticides virtually ceased (National
Academy of Sciences, 1971). In view of the relatively small amounts now
used, it does not appear that there is widespread hazard from either in-
organic or organic fluorine-containing insecticides.
6.4.3.5 Toxic Plant Fluorocarbon, Lethal Synthesis Some plants synthe-
size fluoro compounds that are toxic or that become toxic by metabolic
conversion (lethal synthesis). The first discovered was fluoroacetate
(Marais, 1944), which is found in leaves of the plant Diohapetalum cymosum
in South Africa. Peters (1972) cited the number of plants known to con-
tain fluoroacetate at about 36. Fluorooleic acid, with smaller amounts
of shorter chain fluoro acids (Peters, 1972), are found in West Africa in
the seeds of Didhapetalum toxicarium. Microorganisms can process these
fluoro compounds to make, for instance, fluoromalonate from fluoroacetate
(Pattison and Peters, 1966), or to degrade the compound completely. The
toxicity of the compounds in animals is due to conversion to fluorocitrate,
which blocks the tricarboxylic metabolic cycle. A "delayed convulsive
action" results. The compounds are very toxic: Pattison and Peters (1966)
estimated the lethal dose of fluoroacetate in man to be between 5 and 20
mg/kg. Pattison (1959) discussed other cases of human poisoning. Peters
(1972) stressed the need for finding an antidote to poisoning by fluoro-
acetate and similar compounds. Fluoroacetate is a commerical rodenticide
and insecticide and could present a danger to humans if used indiscrimi-
nately. Yu and Miller (1970) reported the presence of fluoroacetate in
a few samples of crested wheat grass collected near a phosphate factory
in Montana. Cheng et al. (1968) and Lovelace et al. (1968) reported that
cultivated plants such as crested wheat grass and soybeans may have a
certain amount of fluoroacetate and fluorocitrate, the amounts found,
however, being too small to present a hazard.
6.4.3.6 Fluorine Compounds, Including Fluoroorganics Rudge (1962)
mentioned that the physiological properties of fluorine and its compounds
cover the complete gamut, from the innocuous through the beneficial to
the extremely toxic. The saturated fluorocarbons can be classified in
the innocuous range. Some of these, such as Teflon (polytetrafluoroeth-
ylene), are among the most inert chemical substances known. There is a
great deal yet to be learned about the relationship between chemical con-
stitution and physiological behavior of fluorine-containing compounds.
Fluothane (CF3CClBrH) is a potent anesthetic with relatively few side
effects, whereas 2,2'-hexafluorodiethyl ether (CFgC^OCE^CFa) causes
convulsions when inhaled. While tetrafluoroethylene (CF2=CFa) appears
to be nontoxic, most of the higher unsaturated fluorocarbons and chloro-
fluorocarbons are very toxic. Sulfur pentafluoride (S2F10) is extremely
toxic, causing pulmonary edema. However, sulfur hexafluoride is so inert
it 'nay be breathed in 80% concentration by volume when mixed with oxygen
with no adverse physiological effects except for a slight narcosis
(Rudge, 1962).
Clayton (1966) reviewed the mammalian toxicology of organic compounds
containing fluorine. Cook and Pierce (1973) noted the tendency of unsat-
urated fluoro compounds to be toxic and considered the mechanism of this
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304
effect. Table 6.14 shows data collected on the toxicities of some chloro-
olefins and fluoroolefins. While admitting some toxic effect due to
hydrolysis, Cook and Pierce (1973) showed that the toxicity of halogenated
olefin directly reflects its reactivity to nucleophiles. Thus, substitu-
tion of fluorine for hydrogen makes the double bond in the compound
(CF3)2OCF2 more susceptible to nucleophilic attack than the double bond
in the compound CF2=CF2, and the toxicity follows the same pattern. The
chief toxicity of the fluoroolefins is apparently due to their activity
as biological alkylating agents. The authors warn that whenever one works
with a polyfluorinated olefin of high nucleophilic susceptibility and
there is an absence of specific toxicological information, extraordinary
safety precautions should be taken.
6.4.3.6.1 Toxicities of propellants and refrigerants Table 6.15 shows
the results of tests done mainly in the 1930s on the acute inhalation
toxicity of various fluoromethanes. The compounds were developed as fire-
extinguishing agents or refrigerants, and therefore the test design fea-
tured exposure of up to 2 hr only. As seen, the fluorinated compounds
are generally in the high Underwriters' Laboratories (UL) class (i.e.,
show low toxicity).
TABLE 6.14. OLEFIN TOXICITIES
Olefin
LC90a
(ppm)
ALC6
(ppm)
CHa^IHF 800,000
CHa^Fa 128,000
CFa'-CFa
CHCl-CCla
CF9CF-CF2
CF9CF-CHCF9
trans
oia
(CF,)aC=CFa
40,000
32,000
3,000
3,240-13,365
(2 hr)
1,000
7,560 (2 hr)
61 (1 hr
179 (1 hr)
0.76
8,000
4,000
1,000
200
100
T.ethal concentration for 50% of
animals, 4-hr exposure.
"Approximate lethal concentration,
4-hr exposure.
Source: Adapted from Cook and
Pierce, 1973, Table 1, p. 337. Reprinted
by permission of the publisher.
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305
TABLE 6.15. INHALATION TOXICITY OF FLUOROMETHANES
Exposure
Group
A
B
C
Structure
CHC1,
CHClaF
CHClFa
CHF,
CCU
CC1,F
CClaF,
CC1F,
CF»
CH,C1
CHjClj
CHClaF
CC12F2
Concentration
«>
2.0
10.0
20.0
20.0
2.0
10.0
20.0
20.0
20.0
2.0
5.0
10
20
Time
(hr)
2
1
2
2
1
2
2
2
2
2
2
1
2
Fatal
+
+
+
+
+
+
UL>
class
3
4-5
5a
6a
3
5a
6
6
6°
4
4-5
4-5
6
TLV"
50
1000
(1000)
(1000)
10
1000
1000
(1000)
(1000)
100
500
1000
1000
Underwriters' Laboratories classification; the higher the value,
the lower the toxicity.
''Threshold limit value assigned by the American Conference of
Governmental Industrial Hygienists, 1964 values; figures in parentheses
indicate provisional values.
cBased on data from Haskell Laboratory.
Source: Adapted from Clayton, 1967, Table I, p. 338. Reprinted
by permission of the publisher.
Clayton remarked that the "1000 ppm" level is somewhat arbitrary.
Values given by Cook (1945) ranged from 5,000 ppm for dichlorofluoromethane
to 100,000 ppm for dichlorodifluoromethane. The values were subsequently
lowered to 1000 ppm, not because of toxicity but on the premise that good
engineering practice demands that no environmental contaminant should be
allowed to exceed 1000 ppm (8-hr average). Only carbon dioxide has a
threshold limit value greater than 1000 ppm, namely, 5000 ppm.
Since the early studies of fluorocarbons, considerable work has been
done on the solubilities in blood, pharmacokinetics, and long-term toxic-
ities of fluorocarbons. Thus Dolley et al. (1970) and Paterson, Sudlow,
and Walker (1971) studied the blood levels of fluorinated hydrocarbons in
normal and asthmatic individuals after inhalation of pressurized aerosols.
The aerosols are used to deliver adrenergic bronchodilator drugs, and the
medication is often overused. Another abuse is inhalation of aerosols to
become mildly stimulated and intoxicated. Deaths have resulted from this
practice, apparently due to cardiac arrhythmia caused by the sensitizing
effect of the fluorocarbons to circulating catecholamines (Bass, 1970).
The propellants were found in the blood after inhalation, but in consider-
ably lower concentration than when fluorocarbons were used as anesthetics.
It was felt that even with overuse there was no great hazard. The fluoro-
carbons are fat-soluble, accounting for the degree of absorption observed.
Chiou and colleagues studied the absorption, distribution, and elimi-
nation of fluorocarbon aerosol propellants in dogs (Chang and Chiou, 1976;
-------
306
Niazi and Chiou, 1976), humans, monkeys, rats, and mice (Niazi and Chiou,
1975). The propellants were found to have a longer biological half-life
than previously thought and to undergo extensive distribution in the body.
Results with dogs on intravenous injection of a single dose of fluorocar-
bon, in this instance dichlorotetrafluoroethane, showed a three-compartment
distribution, with half-lives of 1.3, 9.6, and 50.8 min, respectively, for
the initial, intermediate, and final disposition phases. Two hours were
required to achieve pseudo distribution equilibrium. There was a triexpo-
nential decay curve of fluorocarbon in the blood, and 84% of the propel-
lant was cleared from the blood passing through the lungs in each cycle.
Compartments were considered to be based on whether the tissues were
vessel-rich or vessel-poor, on fat solubility of the fluorocarbon, and on
interactions such as protein binding and other complexations. The reten-
tions found have implications for the toxicity profiles of fluorocarbons.
Aviado (1974) reviewed the toxicity of 15 propellants used in aero-
sols. Chronic and acute inhalation toxicity, acute cardiovascular tox-
icity (e.g., cardiac arrhythmias and myocardial depression), and acute
bronchopulmonary toxicity were the chief reported effects. Propellants
were divided into four categories (Table 6.16). The classifications are,
in some instances, more severe than the previous UL ratings (Table 6.17).
TABLE 6.16. CLASSIFICATION OF PROPELLANTS BASED ON TOXICITY TO
RESPIRATORY AND CIRCULATORY SYSTEMS
Fluorocarbon Underwriters' Frequency
Name of propellant Laboratories of use in
classification aerosols
Low-pressure propellants of high toxicity
Trichlorofluoromethane FC 11 5a 93
Dichloromonofluoromethane FC 21 4-5
Trichlorotrifluoroethane FC 113 4-5
Trichloroethane 4-5 1
Methylene chloride 4-5 8
Low-pressure propellants of intermediate toxicity
Dichlorotetrafluoroethane FC 114 6 36
Monochlorodifluoroethane FC 142b 5a 2
Isobutane 5b 37
Octafluorocyclobutane FC C-318 6
High-pressure propellants of intermediate toxicity
Dichlorodifluoromethane FC 12 6 153
Monochlorodifluoromethane FC 22 5a
Propane 5b 6
Vinyl chloride 4-5 1
High-pressure propellants of low toxicity
Chloropentafluoroethane FC 115 6
Difluoroethane FC 152a 6 5
Source: Adapted from Aviado, 1974, Table 2, p. 371. Reprinted by
permission of the publisher.
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307
TABLE 6.17. COMPARATIVE LIFE HAZARD OF CASES AND VAPORS
Croup number
and definition
Not used as
propellents
Used as propellents
Low pressure
High pressure
Croup 1: Gases or vapors
which In concentrations of
O.SZ to l.OZ for durations
of exposure of 5 mln are
lethal or produce serious
Injury
Group 2: Gases or vapors
which in concentrations of
O.SZ to l.OZ for duration
of exposure of 30 mln are
lethal or produce serious
injury
Group 3: Cases or vapors
which in concentrations of
2.0Z to 2.SZ for duration
of exposure of 1 hr are
lethal or produce serious
inlury
Group 4: Gases or vapors
which in concentrations of
2.0Z to 2.SZ for duration
of exposure of 2 hr are
lethal or produce serious
injury
Between groups it and S:
Gases or vapors less toxic
than group 4
Group Sa: Gases or vapors
much less toxic than group
4 but more toxic than
group 6
Croup 5b: Gases or vapors
which available data indi-
cate would be classified
as either group S or
group 6
Group 6: Gases or vapors
which In concentrations up
to at least 20Z for dura-
tion of exposure of 2 hr
do not appear to produce
Injury
Sulfur dioxide
Ammonia
Methyl bromide
Carbon tetrachlorlde
Chloroform
Methyl formate
Dlchloroethylene
Methyl chloride
Ethyl bromide
Ethyl chloride
Carbon dioxide
Ethane
Chlorotrlfluoro-
methane (FC 13)
Trichloroethane
Methylene chloride
Trlchlorotrlfluoroethane
(FC 113)
Dlchlorofluoromethane
(FC 21)
Trichlorofluoronethane
(FC 11)
Monochlorod1fluoroethane
(FC 142b)
Isobutane
nichlorotetrafluoroethane
(FC 114)
Octafluorocyclobutane
(FC C-318)
Vinyl chloride
Monochlorodifluoromethane
(FC 22)
Propane
Dichlorodlfluoromethane
(FC 12)
nifluoroethane (FC 152a)
Chloropentafluoroethane
(FC 115)
Tlot tested by Underwriters' Laboratories but estimated to belong In the group.
Source: Adapted from Avlado, 1974, Table 1, p. 368. Reprinted by permission of the publisher.
For instance, octafluorocyclobutane, given a UL rating of 6, appears in
the "low-pressure propellents of intermediate toxicity" category in the
proposed classification. The hazards of fluoro compounds and of other
gases and vapors are compared in Table 6.17.
Alarie, Choby, and Poel (1972) observed alveolar instability and
death in rats following intravenous administration of 0.5 to 0.8 ml of
tetrachlorodifluoroethane (TCDF). Because of its immiscibility with water,
low surface tension, and ability to solubilize lipids, TCDF is apparently
able to remove the surfactant normally present on the alveolar surface,
-------
308
with consequent exudation and alveolar collapse. Although the experimental
conditions were admittedly severe, they nevertheless indicated the danger
due to the fat-solubilizing nature of the fluorocarbons.
In contrast with the study of Alarie, Choby, and Poel (1972), Bohning
et al. (1975) found no effect of the fluorocarbons fluorotrichloromethane
(FC-11) and dichlorodifluoromethane (FC-12) on tracheobronchial particle
deposition and mucociliary clearance in donkeys. The animals were inter-
mittently exposed to 1000-ppm concentrations over a period of about 13
months. The authors noted that broncopulmonary changes have, however,
been observed in mice (Brody, Watanabe, and Aviado, 1974) and in humans
(Brooks, Mintz, and Weiss, 1972; Sterling and Batten, 1969) at higher
concentrations of the propellants. The conclusion is that the threshold
limit value of 1000 ppm is quite reasonable.
Flowers, Hand, and Horan (1975) studied the concentrations of fluoro-
alkanes associated with cardiac conduction system toxicity. No deaths
ensued in dogs exposed for 10 min to FC-11 at concentrations below 15%.
At concentrations between 15% and 17%, eight animals survived and seven
died. No animal survived a 10-min exposure to a concentration in excess
of 21%. For FC-12, concentrations greater than 95% were necessary to
produce death in 10 mln, with severe oxygen deficit. The results for
PC-11 are summarized in Figures 6.26 and 6.27. The narrow margin between
CMMtlOMi 77»i»"
MO
O
O M
I
t
1S-17 174-21 214
CONCENTRATION Of FMEON 11 1%)
I 1NO CHANGE IN SUBINTE «VAt» OF fUL»E («ATE SEGME NT. ' 10* CHANGE
IN BAM LINE MATE
{<» REVERSIBLE ALTERATION* IN CAMOIAC CONDUCTION OH PACEMAKEH FUNCTION
LETHAL NEtfONtEi
Figure 6.26. Effect of Freon 11 on cardiac conduction in dogs. Source:
Adapted from Flowers, Hand, and Horan, 1975, Figure 8, p. 360. Reprinted
by permission of the publisher.
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309
ORNL-OWG 804113
EARLIEST REVERSIBLE CHANGE - 15.0%
EARLIEST IRREVERSIBLE CHANGE - 15.5%
UNIFORMLY IRREVERSIBLE CHANGE - 21.5%
o
6
1
1
3D-
SB <
> I°AVBAJR
--SB
ST
» nan
*-NSR
* NSR
MCD
REVERSIBLE CHANGES, 1S%-21.0%
LETHAL CHANGES, 16%-21.5%
MORE COMPLEX ARRHYTHMIAS
22 ASYSTOLE
2 VENTRICULAR FIBRILLATION
NO ANIMAL WITH VENTRICULAR ESCAPE SURVIVED
NO ANIMAL WITH VENTRICULAR TACHYCARDIA SURVIVED
Figure 6.27. Freon 11 results: note narrow margin between concen-
tration eliciting earliest detectable yet reversible change and concen-
tration of the first lethal result. Source: Adapted from Flowers, Hand,
and Koran, Figure 9, p. 360. Reprinted by permission of the publisher.
the concentration of the first lethal results should be noted. The study
sounded a note of alarm because lethal concentrations of fluorocarbons
can be reached by "sniffing" and indeed have been. The study also empha-
sized that the concentrations are orders of magnitude higher than those
found in certain areas (use of fluorocarbon-propelled hair sprays in
beauty salons was mentioned). Thus to uniformly produce death in the
test animals, a continuous 10-min exposure to 21.5% FC-11 (215,000 ppm)
was required. Peak concentrations in samples obtained over several months
from a beauty salon did not exceed 310 ppm, which is well below the indus-
trial threshold limit value of 1000 ppm, whereas simulated sniffing episode
samples reached 350,000 and 400,000 ppm. Where use is fairly heavy, good
ventilation is recommended.
Paulet and Lessard (1975) studied the action of FC-11 and FC-12 on
smooth muscle. Both gases, bubbled into the muscle nutritive solution
to give various concentrations, reduced the amplitude of spontaneous con-
tractions of both Isolated rat uterine muscle and isolated rabbit duodenum
muscle. Base tonus of the rat muscle was not much affected by either gas;
with rabbit muscle, FC-12 increased tonus while FC-11 decreased It. The
effects of both compounds were shown to be musculotropic, not neurotroplc,
and to be reversible, even after prolonged inhibition. The two gases did
not modify the action of acetylcholine, adrenalin, histamlne, or oxytocin
on the muscles.
-------
310
Paulet, Roncin, Vidal, Toulouse, and Dassonville (1975) also reported
on the effect of fluorocarbons on the general metabolism of rats, rabbits,
and dogs. In single inhalation exposure experiments, only FC-11 produced
metabolic reactions; for example, at 5% a slight hyperglycemia with lac-
tacidemia was produced. In prolonged exposure experiments (inhalation 2
hr/day for five days), only FC-11 at 5% produced the following slight meta-
bolic modifications: decrease in oxygen uptake, increase in glycemia and
lactacidemia, slowing of hepatic glycogen secretion, increase in respira-
tory quotient, decrease in blood urea, and a small increase in free fatty
acid. All of these changes could be explained by a slowing of cellular
oxidation.
As studied by Paulet, LanoS, Thos, Toulouse, and Dassonville (1975),
FC-11 and FC-12, when inhaled in concentrations varying from 0% to 5%
(FC-11) and from 0% to 50% (FC-12), rapidly diffused into the blood, cere-
brospinal fluid, urine, and bile; a balanced condition is quickly estab-
lished. This effect is similar to the results of Nlazi and Chiou (1976).
The rapid appearance (1 min) of the gases in the cerebrospinal fluid is
noteworthy, explaining the often observed stimulating or depressing action
of fluorocarbons on the central nervous system. Elimination takes place
primarily through the lungs (98%) and is completed 20 to 50 min after
fresh air is inhaled. Bile and urine constitute only a minor pathway
of excretion.
6.4.3.6.2 Fluorine-containing anesthetics Krantz and Rudo (1966)
reviewed the history of the introduction of fluorinated anesthetics and
their chemistry and use. Fluorine does not appear to increase the potency
of a compound per se; it decreases flammability and augments the stability
of associated halogens in the molecule. Saturated and unsaturated cyclic,
branched, and straight-chain compounds containing fluorine and other halo-
gens have been examined for use as anesthetics. While inhalation is the
most common route of administration, injection of an emulsion has also
been tried (Krantz et al., 1961). This allows use, with simplicity and
accuracy of dosage, of compounds not otherwise usable because of low vola-
tility. The injected agents are excreted by the lungs. Some fluorinated
compounds can cause excitation as well as anesthesia, and this has ruled
out their use. In the use of an anesthetic, effects on the heart, respi-
ration, and the central nervous system must be considered, as well as
toxic side effects such as hepatotoxicity and nephrotoxicity. Toxicity
may arise from cell injury due to fatty infiltration and from effects of
breakdown products if they exist. The toxicities of several of the flu-
orinated anesthetics used are considered in the following paragraphs.
Fluoromar or fluroxene (trifluoroethyl vinyl ether, CF3CH2OCH=CH2)
was the first fluorinated compound used for human anesthesia. It is use-
ful for both light and deep anesthesia. Fluoromar is an excellent anes-
thetic because fluoride is not liberated by metabolic processes of the
body, there is no hepatic impairment, and recovery is rapid with early
return of reflexes. According to Morris (1963), it is the only halogen-
ated drug not producing hepatic damage. However, it is somewhat lacking
in potency compared with some of the other fluorinated anesthetics.
-------
311
Halothane or fluothane (CF3CHBrCl) undergoes some biotransformation
in the body. It is more soluble in tissue compartments than in whole
blood and causes some hepatotoxicity (Jones, Margolis, and Stephen, 1958);
however, it causes less hepatotoxicity than chloroform. Because halothane
causes some hepatotoxicity and decreases uterine tone, it is not recom-
mended for patients with known liver or biliary tract disease or for
obstetrical use. An azeotropic mixture of halothane and ether is a
highly effective anesthetic.
The biotransformation of halothane was studied by Airaksinen,
Rosenberg, and Tammisto (1970). Trifluoroacetic acid, the main metabo-
lite found in the urine of man after halothane anesthesia, was probably
formed through trifluoroethanol and trifluoroacetaldehyde. The results
indicated that toxicity was chiefly caused by the blocking of essential
thiol groups (-SH) by the aldehyde, or a compound derived from it, before
oxidation to trifluoroacetic acid.
Methoxyflurane (CH3OCFaCCl2H) has been extensively used as an anes-
thetic. Its relatively low vapor pressure allows some safety in adminis-
tration. Its elimination is slow because of absorption by adipose tissues.
Slow induction, slow emergence, and hypotension during anesthesia are
disadvantages, but the quality of anesthesia is good. Some nephrotoxicity
of methoxyflurane has been noted due mainly to fluoride released from the
compound by hydrolysis (Hook, 1971; Mazze, Shue, and Jackson, 1971; Taves
et al., 1970). Methoxydifluoroacetic acid is also produced. Cases of
secondary hyperoxaluria following methoxyflurane anesthesia, with actual
deposition of calcium oxalate crystals in the tubules if renal function
was sufficiently compromised, were studied by Frascino, Vanamee, and Rosen
(1970). There was enough concern that the National Academy of Sciences-
National Research Council Committee on Anesthesia issued a "Statement
Regarding the Role of Methoxyflurane in the Production of Renal Dysfunc-
tion" (National Academy of Sciences and National Research Council, 1971).
It was considered that a chief mechanism of action was an effect of fluo-
ride (from hydrolysis of the methoxyflurane) that rendered the distal
renal tubules unresponsive to antidiuretic hormone. Figure 6.28 shows
the serum levels of fluoride and "organic acidlabile fluoride" in patients
at various times after methoxyflurane anesthesia. Since the two metabo-
lites are not volatile, they are eliminated by the kidneys, not the lungs.
It was suggested that levels might be lowered and the nephrotoxicity mini-
mized by management of fluids and electrolytes.
Creasser et al. (1974) and Dahlgren (1977) reported on the effects
of methoxyflurane used as an analgesic in obstetrics. In the study by
Creasser et al. (1974), methoxyflurane exposure to 22 obstetric patients
consisted of 65 to 240 min intermittently self-administered during labor
and 5 to 70 min of awake analgesia during vaginal delivery. Some altera-
tion in renal function was observed in the methoxyflurane group but not
in the control group as indicated by an increase in blood urea nitrogen,
serum uric acid, and serum creatinine following delivery. However, post-
partum observation in the control group was limited to 24 hr and in no
instance was any measured value in the control group significantly dif-
ferent from the measured values in the methoxyflurane group at 24 hr post-
partum. The polyuric form of renal dysfunction is known to occur when
-------
312
60
- 50
9 40
o:
O
u.
o 30
o
o:
o
? 20
ORNL-OWC 79-209H
1200
OALF
I-
-W-
-I I-
1000 -
UJ
o
5
o
800 3
UJ
600
§
Q
U
400 y
<
o
K
O
200 S
a
UJ
UJ
100
(234
TIME AFTER METHOXYFLURANE ANESTHESIA (days)
Figure 6.28. Serum fluoride and "organic acid-labile fluoride"
(OALF) concentrations of all samples taken from 15 patients at various
times after the end of anesthesia. The numbers are numbers of samples
included in the means; bars are standard errors of the means. Source:
Adapted from Fry, Taves, and Merin, 1973, Figure 1, p. 41. Reprinted by
permission of the publisher.
serum inorganic fluoride concentrations reach 80 to 175 micromoles per
liter, but it was not observed in the patients studied by Creasser and
co-workers where the mean peak serum inorganic fluoride level was only
21.9 micromoles per liter. Although methoxyflurane analgesia during labor
and vaginal delivery provided acceptable patient analgesia without fetal
depression at birth, the presence of increased methoxyflurane metabolites
(inorganic fluoride and oxalic acid) which might cause some alteration in
renal tests suggested to Creasser et al. (1974) that there was a need to
control the total dose of methoxyflurane administered to the mother.
Dahlgren (1977) studied the renal and hepatic effects of the admin-
istration of a mixture of nitrous oxide and methoxyflurane as an analgesic
to women in labor; comparison was made to women in labor who were admin-
istered only nitrous oxide. In an earlier study Dahlgren observed that
when using an analgesic mixture of thiopentone and methoxyflurane, thio-
pentone and halothane, or thiopentone and pethidine a transient disturbance
of renal and hepatic function was associated with methoxyflurane (Dahlgren
and Goodrich, 1976, as cited in Dahlgren, 1977). Dahlgren (1977) designed
a study to test if renal and hepatic disturbances were associated with
methoxyflurane and nitrous oxide analgesia and if signs of distal tubular
dysfunction could be detected in neonates. The results of his studies
with 75 women who received only nitrous oxide analgesia and with 126 women
who received the methoxyflurane and nitrous oxide mixture (29 received a
dose greater than or equal to 10 ml and 75 received a dose less than or
-------
313
equal to 5 ml) indicated that hepatic and renal functions were affected
in the groups exposed to the nitrous oxide/methoxyflurane mixture (espe-
cially the high dose methoxyflurane group). This was indicated by statis-
tically significant increases in serum sodium, serum creatinine, blood
urea, serum uric acid, glutamic oxalacetic transaminase, and glutamic
pyruvic transaminase. The neonatal capillary concentrations of uric acid
also showed dose-dependent increases in response to methoxyflurane.
Dahlgren stated that: (1) the significant differences between the nitrous
oxide group and the nitrous oxide/high dose methoxyflurane group in serum
sodium, serum creatinine, blood urea, and uric acid concentrations were
in agreement with the results of other researchers and (2) as in the study
by Robertson and Hamilton (1973) the major influence of the methoxyflurane
anaesthesia was on serum uric acid concentrations. Robertson and Hamilton
(1973, as cited in Dahlgren, 1977) suggested that the increase in serum
uric acid concentrations was a toxic effect of the fluoride ion on the
ability of the distal tubules to secrete uric acid.
Enflurane (CF2HOCF2CC1FH) was developed to replace halothane and,
for some uses, methoxyflurane. It undergoes biotransformation, but to a
lesser degree than methoxyflurane. Thus Barr et al. (1974) found that it
took 6 to 10 hr of 2.5% enflurane anesthesia to develop vasopressin-
resistant polyuric renal dysfunction in rats similar to that resulting
from 1.5 hr of 0.25% methoxyflurane. Peak serum inorganic fluoride levels
were similar for both compounds at about 1.14 ppm; however, the level
peaked earlier and returned to control values sooner after enflurane
than after methoxyflurane anesthesia.
Figure 6.29 shows serum inorganic fluoride levels in 102 patients
following enflurane anesthesia. The 102 patients were divided into three
groups using the following criteria: group one patients were without
pertinent medical or anesthetic history, group two patients had received
one previous enflurane anesthetic, and group three patients had all taken
barbiturates before enflurane anesthesia. For most individuals, the peak
fluoride levels in all three groups were about the same; however, with
methoxyflurane, fluoride levels might continue to rise or remain elevated
for days and with enflurane the fluoride level generally declines within
24 hr.
In spite of possible nephrotoxicity, methoxyflurane continues to be
used for obstetrical patients because of its valuable analgesic and anes-
thetic properties. Figure 6.30 shows plasma fluoride levels in mother
and child following use of methoxyflurane for delivery only, labor and
delivery, and delivery by cesarian section (mean exposure durations of
19.7 ± 5.9, 49.1 ± 23.9, and 39.6 ± 14.2 min respectively). The values
in all cases were considered tolerable, and no nephrotoxicity was noted.
Fry and Taves (1974) concluded that exposure of obstetrical patients to
methoxyflurane for as long as 30 min was probably safe. For general anes-
thetic use of methoxyflurane, Cousins and Mazze (1973) gave a number of
cogent recommendations as to dose, use of adjuvants, and type of surgical
intervention with exposure to be limited to 2 hr at the lowest feasible
concentration. They found the threshold inorganic fluoride level for
biochemical renal impairment to be about 50 micromoles per liter of plasma
-------
314
ORNL-DWG 79-20912
80
70
50
UJ
g
-------
315
ORNL-DWC 79-20914
24
20
12
MATERNAL FLUORIDE ISO
FETAL FLUORIDE t S.D
4 -
CONTROL I END OF
I ANESTHETIC
DELIVERY
2hr
24 hr
Figure 6.30. Plasma fluoride levels following methoxyflurane analgesia
for (a) delivery only, (2?) for labor and delivery, and (a) for caesarean
section (* indicates significant change from control). Source: Adapted
from Palahniuk and Gumming, Figures 1-3, pp. 294-295. Reprinted by
permission of the publisher.
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316
(0.95 ppm), with clinical high output renal failure becoming evident at
100 micromoles per liter (1.9 ppm).
Impurities in anesthetics may be hazardous. Torkelson et al. (1971)
studied the question of the acute inhalation toxicity of actual and poten-
tial trace substances in methoxyflurane by exposing rats to the vapors of
nine such compounds. None were found toxic enough to present a signifi-
cant hazard in the use of methoxyflurane as an anesthetic.
The fluorinated anesthetics show a lower mortality rate than the
anesthetics they replace and are a useful advance as anesthetics. What
hazards they do present (e.g., hepatotoxicity, renal toxicity, and cardiac
and circulatory sensitization) can be minimized by proper management and
selection of the best anesthetic for a particular use. It is likely that
research will improve the situation even further. Two questions, however,
need to be considered. One concerns the possible embryopathic, teratogenic
effects of anesthetics given during pregnancy and the effect on reproduc-
tion function. The other questions the effects on the offspring of indi-
viduals who constantly come in contact with halogenated anesthetics (e.g.,
anesthetists and operating room personnel). These questions are discussed
in Section 6.4.4.
6.4.3.6.3 Fluorinated compounds as blood extenders and other medical
uses Gollan and Clark (1966) pioneered the use of oxygenated liquid
fluorochemicals for organ perfusion and carried animals through alternate
episodes of breathing liquid fluorocarbon and then air (Clark and Gollan,
1966). Sloviter and Kamimoto (1967) introduced the use of emulsions of
fluorochemicals in water-protein solution in order that salts and metabo-
lites might be carried as well as gases. Geyer, Monroe, and Taylor (1968)
and Clark, Kaplan, and Becattini (1970) succeeded in keeping animals alive
whose blood was totally replaced with such emulsions.
Fluorinated compounds are considered to be inert in the sense that
no degradation occurs. They do, however, interact under some conditions
with cell substances and cell systems. For instance: in influencing the
metabolism of steroids (HOller and Breuer, 1975); causing possible struc-
tural changes in amino acids (Brown and Hardison, 1975); and interacting
with platelets and blood-clotting factors resulting in intravascular clot-
ting causing a marked increase in pulmonary artery pressure, dilation of
the right side of the heart, and terminating in fatal hypoxia (Sloviter,
1975). Okamoto, Yamanouchi, and Yokoyama (1975) studied the elimination
of fluoro compounds because their long retention prohibits their use in
some situations. There has been no clinical use yet of fluorochemicals
or other synthetic substances as erythrocyte substitutes (Sloviter, 1975),
but such use is not inconceivable. Use in extracorporeal circulation,
membrane oxygenation systems, and organ isolation experiments is also
possible. The field is very active. According to Clark et al. (1975)
the future use of highly fluorinated compounds in biology and medicine
lies in the great versatility that can result by changing their chemical
structure. In fact, numerous types of fluorinated compounds have already
been used; for example, cyclic ethers and other ring compounds and
straight- and branched-chain structures. The use of fluoro compounds In
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317
a liquid membrane configuration for blood oxygenation, to avoid the for-
mation of actual blood-gas interfaces that might cause damaging cellular
or protein alterations, is a relatively new development (Maugh, 1976).
Fluorinated compounds containing a heavier halogen in the molecule
have also been used as radio-opaque media. Examples are perfluorooctyl
bromide and perfluorohexyl bromide (Long et al., 1972) and perfluorooctyl
iodide and perfluorodecyl iodide (Clark et al., 1975). An interesting
application of a fluorinated compound was the trial of octafluorocyclo-
butane and other gases for vitreous replacement (Vygantas et al., 1973),
especially in treatment of retinal detachment. A gas was sought that
would be slowly reabsorbed. The results were encouraging, and no toxic
effects were noted.
6.4.3.6.4 Fluorinated fire-extinguishing agents Tables 6.18 and 6.19
show the lethal concentrations and toxicities of vapors from various
agents used in fire fighting. Bromotrifluoromethane is seen to be in a
higher UL class than even carbon dioxide. Table 6.20 shows the minimal
concentrations of various halogenated fire-extinguishing agents required
to produce characteristic reactions in rats, and Table 6.21 compares the
toxicity of several agents under various fire situations.
The best agent tried, bromotrifluoromethane (CF3Br), has been used
in portable extinguishers since 1959 by the U.S. Army and in specialized
situations such as protection against in-flight engine fires in commercial
aircraft. It is in some canister-type extinguishers that can be bought
by the general public and is used in preference to carbon dioxide where
space is at a premium; for example, to protect specialized equipment such
as computers. Its advantages are discussed by Mosbacher (1976). The
toxicity of pyrolysis products of fire-extinguishing agents in confined
TABLE 6.18. LETHAL CONCENTRATIONS OF SEVERAL
FIRE-EXTINGUISHING AGENTS
Compound
ecu
CHjBrCl
CBraFa
CBrClFa
CBrF,
Species
Rat
Guinea
Pig
Rat
Mouse
Rat
Rat
Rat
Time of
exposure
(min)
10
10
15
15
15
15
15
Lethal
concentration
(*)a
2.8
2.0
2.9-3.2
2.7-2.9
5.5
32
83
vapor mixed with air in all exposures.
Source: Adapted from Clayton, 1966, Table
2, p. 463. Data collected from several sources.
Reprinted by permission of the publisher.
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318
TABLE 6.19. TOXICITIES OF VARIOUS GASES ENCOUNTERED IN FIRE FIGHTING
Compound
Bromotr If luorome thane
Carbon dioxide
Difluorodibromoraethane
Bromochlorome thane
Carbon tetrachloride
Carbon monoxide
Methyl bromide
Formula
CBrFj
CO 2
CBr,Fj
CHjBrCl
CClt
CO
CH,Br
ULa
class
6
5a
4
3
3
2
2
ALC*
(Z vol)
83.2
65.7
5.5
6.52
2.86
1.5
0.59
ALC
decomposition
product
(Z vol)
1.4
2.0
0.2
0.4
0.032
1.6
/Underwriters' Laboratories.
Approximate lethal concentration in 15-min rat exposure; vapors
mixed with air in all exposures.
Source: Adapted from Clayton, 1966, Table 4, p. 464. Data
collected from several sources. Reprinted by permission of the
pub!isher.
TABLE 6.20. MINIMAL CONCENTRATIONS OF HALOGENATED FIRE-EXTINGUISHING
AGENTS REQUIRED TO PRODUCE CHARACTERISTIC REACTIONS IN RATSa
(ppm)
Reaction
Incoordination
Drowsiness
Limb twitching
and slight
body tremors
Convulsions and
acute body
tremors
Deep narcosis
Delayed death
(about 36 hr)
Liver damage
Death during
exposure
Chlorobromo-
me thane,
CHaBrCl
4,750
(26 min)
4,750
(26 min)
19,000
(17 min)
39,000
(30 min)
Trif luorobromo- Dlfluorodl-
methane, bromome thane,
CBrF, CBr,Fa
500,000 10,000
(26 min) (14 min)
15,000
(10 min)
30,000
(11-13 min)
Tetrafluorodl-
bromoethane ,
CBrFj-CBrF,
3,400
13,500
(14 min)
27,000
(9 min)
Carbon
tetrachloride,
ecu
9,000
(14 min)
9,000
(20 min)
15,500
(12 min)
18,000
(9-11 min)
18,000
18.000
27,000
Time of onset of reactions In parentheses.
Source: Adapted from Clayton, 1966, Table 9, p. 467. Data collected from several sources.
Reprinted by permission of the publisher.
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319
TABLE 6.21. TOXICITIES OF FIRE-EXTINGUISHING AGENTS
Condition
Toxlcity
Rapid fire extinguishing
Slow fire extinguishing12
Evolution of carbonyl halides
(slow extinguishment)
CBr,Fa>CH,BrCl>CBrF,
CBr,F2>CHaBrCl>CBrF,
ecu
CCU>CHaBrCl>CBrF,
Gasoline fire.
Source: Adapted from Clayton, 1966, Table 10,
p. 467. Data collected from several sources.
Reprinted by permission of the publisher.
situations is of some concern. Table 6.22 shows the mortality and response
of several mammalian species to pyrolyzed CF3Br. The total gas concentra-
tion (decomposed and undecomposed) was 10,000 ppm. The experimental con-
ditions were more severe than would usually be encountered by humans in
fire-fighting situations.
Bromotrifluoromethane shares with some other compounds, such as car-
bon tetrachloride and gasoline, the capability of causing the heart muscle
to react abnormally to elevated adrenaline levels. This might occur in
a stress situation such as a fire. The resulting cardiac arrhythmia can
cause death. Tests by Haskell Laboratory (1971) showed such cardiac sen-
sitization in dogs under adrenaline challenge starting at about 7.5 vol %
bromotrifluoromethane. In humans, central nervous system effects (e.g.,
lightheadedness and impaired reaction times) were observed when levels of
7% were breathed for 4 min, but no cardiac arrhythmias occurred at levels
TABLE 6.22. MORTALITY AND RESPONSE OF SEVERAL MAMMALIAN SPECIES TO PYROLYZED BROMOTRIFLUOROMETHANE (CF.Br)
CF.Br
concentration6
(Z vol)
50
2.5
1.0
0.75
0.50
Mortality
100
100
100
90
20
50
0
Animal response
Initial agitation, somnolence,
effect on equilibrium, dyspnea,
prostration
Slight agitation, dyspnea
Few reactions, slight dyspnea,
death in 48 hr
No reactions
Death occurred in mice within 3
days after exposure
Pathology
Pulmonary edema
Pulmonary edema
Pulmonary edema
Pulmonary edema
in animals
succumbing
Pulmonary edema
in mice
Species
Mice
Rats
Guinea pigs
Mice
Rats
Guinea pigs
Mice
Rats
Guinea pigs
Mice
Rats
Mice
Rats
Number
of
animals
10
10
5
10
10
5
10
10
5
10
10
10
10
^Exposure: Pyrolysis temperature 1000'C, 30 min.
Based on air mixed with decomposed and undecomposed CBrF,.
Source: Adapted from Clayton, 1966, Table 7. Data collected from several sources. Reprinted by
permission of the publisher.
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320
up to 10%. Rhoden and Gabriel (1972) studied the effect of CF3Br inhala-
tion on myocardial glycolysis in rats and showed respiratory depression,
hypoxia, and mobilization and intracellular accumulation of free fatty
acids. The Haskell report considered that in spite of possible deleteri-
ous effects, CF3Br is the safest gaseous extinguishing agent available.
Low concentrations are required to put out fires, and it acts quickly;
its toxic effects are less than those caused by products of the fire.
Its chief pyrolysis product, hydrogen fluoride, is toxic but gives warn-
ing by its extremely irritating nature.
The workroom threshold limit value for CF3Br is 1000 ppm (American
Council on Governmental Industrial Hygienists, 1971), but this is an arbi-
trarily set "industrial housekeeping" level (Section 6.4.3.6.1). Scholz
and Weigand (1964) found no behavior changes in animals inhaling CF3Br at
concentrations as high as 60 vol % (with oxygen) for a single 2-hr period
and no damage to health in workers engaged in the manufacture of CF3Br.
Rhoden and Gabriel (1972) drew a parallel between deaths caused by aerosol-
sniffing incidents and cardiac effects from CF3Br and were pessimistic
as to the desirability of its use in closed environments.
6.4.4 Teratogenesis, Mutagenesis, and Carcinogenesis On the basis of
the chemistry and of the enzyme, hormone, and other effects discussed in
preceding sections, inorganic fluoride under normal conditions would not
be expected to be teratogenic, mutagenic, or carcinogenic. In contrast,
some organic fluorinated compounds are indeed used experimentally as muta-
gens, and fluorinated compounds are also used as carcinogens. This is not
of environmental concern. Other fluorinated compounds such as 5-fluoro-
uracil are used as cancer-control agents (Heidelberger, 1972). On the
basis of differences in metabolism between cancerous and normal cells,
inorganic fluoride has been tried as one of a number of glycolysis inhi-
bitors in cancer treatment (Black and Kleiner, 1947; Black, Kleiner, and
Bolker, 1947, 1949). While the results were initially encouraging, at
least with some kinds of cancer, adaptation to the inhibitor(s) resulted
in no great long-term benefit, and the approach has been discarded.
Regarding inorganic fluoride effects on the general population,
controlled health studies have shown no greater incidence of birth defects
or of cancer in areas where water was fluoridated or where the level was
naturally high than in low-fluoride areas. The normality of the size and
development of children in the American Southwest, where drinking water
supplies contain up to 5 ppm fluoride, was never questioned, nor were any
differences in developmental rates found between children in Newburgh,
New York, where water was fluoridated to a concentration of 1 ppm, and
children in Kingston, New York, the control city with a community water
supply containing 0.06 ppm (National Academy of Sciences, 1971, pp. 198-
199). Schlesinger (1970) gave a detailed analysis of the Kingston-
Newburgh study. The stillbirths and maternal and infant mortality rates
in the two cities were compared for the five-year period prior to the
start of fluoridation and during the ten years of the study. The long-
term downward trends were similar in the two cities, and no changes could
be detected in the trend in Newburgh after fluoridation. The death rates
from cancer and cardiovascular diseases were also examined in the two
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321
cities and did not change, relative to each other, prior to or during
the period of the study.
Archer and Lundin (1967) compared lung cancer data from five groups
of miners exposed to a wide range of airborne radioactive particles (decay
products of radon). Included was a group of Canadian fluorspar miners.
The emphasis was on radiation damage, and no synergism with fluoride was
suggested. Kanisawa and Schroeder (1969) fed mice 10 ppm fluoride for
life and found neither suppression nor enhancement of tumors. Gorban,
Karpilovskaya, and Rubenchik (1974) have shown, however, that sodium flu-
ride added to the diet at 1.5 mg/kg daily for four months inhibited the
development of hepatomas induced in rats by p-dimethylaminoazobenzene and
also prevented increase in the level of glycogen in the liver.
Cecilioni (1972, 1974) reported that the mean cancer death rate in
the highly industrialized city of Hamilton, Ontario, was significantly
higher than in the less industrialized city of Ottawa, Ontario, during
1966 to 1971. Cecilioni attempted to correlate the cancer incidence and
mortality with industrial pollution by steel mills; fluoride is one of
several pollutants emitted. He presented evidence (e.g., hospital data
on respiratory diseases) that showed a good correlation between industrial
pollution and cancer incidence, but no one pollutant could be conclusively
implicated.
Several papers have been written that discuss the potential mutage-
nicity of inorganic fluoride compounds to laboratory animals and human
subjects. Guleva, Flotko, and Gatiyatullina (1972) subjected rats to
inhalation of cryolite (AlF6Na3) and its mixture with hydrogen fluoride.
While there were no changes in the mitotic activity of test corneal epi-
thelial cells as compared with the control ones, the rats presented a
high percentage of cells with chromosome aberrations in the bone marrow.
Jagiello and Lin (1974) explored the potentiality of fluoride as a muta-
gen in mammalian eggs. In vitro experiments with mouse, sheep, and cow
oocytes incubated in solutions containing up to 0.4 mg of sodium fluoride
per milliliter (181 ppm fluoride) disclosed a low incidence of anaphase
lags, suppression of polar body I, and fragmentation with rearrangement.
In vivo injection experiments showed only a minor effect on oocyte mei-
otic maturation. Species variations in sensitivity suggested, however,
an assessment of abnormal progeny from cows and ewes for chromosome
abnormalities in high-fluoride contaminated areas.
The mutagenic action of hydrogen fluoride, cryolite, and mixtures
of both on the chromosomes of.cells from albino rats and white mice (inha-
lation exposure of 6 hr/day, six days per week for two or five months),
and of the mutagenic action of sodium fluoride on the culture cells of
human leukocytes was studied by Voroshilin et al. (1973). Male albino
rats exposed for five months showed an increase in the frequency of cells
with chromosomal damage in the bone marrow when the cryolite concentra-
tion was 3.0 mg/m9 and when a mixture of cryolite and hydrogen fluoride
contained 0.5 mg/m3 and 0.25 mg/m3 respectively. A two-month exposure
of white mice, however, resulted in no increased frequency of transloca-
tions in testes cells when the hydrogen fluoride exposure concentration
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322
was 0.1 mg/m3 and the mixture concentration was 0.25 mg/m3 of cryolite
and 0.05 mg/m3 of hydrogen fluoride. Similarly, no increase in the fre-
quency of chromosomal aberrations was observed in the cell culture of
human leukocytes in the G0 stage at sodium fluoride concentrations of
1 v 10~3 and 3 x 10"3 Af; at higher concentrations sodium fluoride was
cytostatic.
Mohamed and Chandler (1976) divided 72 adult male highly inbred mice
into nine equal groups, with three groups being controls and the remaining
six groups exposed to 200, 100, 50, 10, 5, and 1 ppm sodium fluoride,
respectively, through the drinking water; mice were maintained on a low
fluoride diet. Four of the eight mice in each group were exposed for
three weeks and the other half for six weeks. Cytological examinations
on bone marrow cells and on spermatogenesis indicated the presence of
fragments, bridges, and other chromosomal abnormalities. The physiolog-
ical effect of sodium fluoride causing stickiness of chromosomes and/or
the occurrence of chromatid breakage followed by reunion to form structural
changes was suggested as the cause of these abnormalities. Mohamed and
Chandler stated that the analyses of their findings indicated that sodium
fluoride was a mutagenic agent with cumulative effects.
Brown et al. (1978) noted the results of Mohamed and Chandler (1976)
and conducted experiments to examine the rates of chromosome aberration
in bone marrow cells and in cells of testes from mice raised under various
fluoride intakes. In one experiment, Swiss mice that had been administered
50 ppm fluoride in the drinking water showed no difference in aberration
rate in the testis or marrow cells compared to a control group that had
received distilled water; both control and experimental groups were fed
low fluoride diets (0.5 ppm). In contrast to the results of Mohamed and
Chandler (1976), this experiment showed that chromosome aberrations were
not related to continuous fluoride intake. A second experiment by Brown
et al. (1978) in which adult male BALB/c mice were exposed to fluoride
concentrations of 0, 1, 5, 10, 50, or 100 ppm in the drinking water for
six weeks also showed no dose-related differences in chromosome aberration
rates of either marrow or testis cells. In addition, Brown and co-workers
tested fluoride for mutagenic activity in a microbial assay using both
Salmonella and Saccharornyces cells and found no evidence of mutagenicity.
Fluoride is known to have an antimutagenic action in some circum-
stances (Obe and Slacik-Erben, 1973). In studies of cultures of various
types and species of cells, including human ones, sodium fluoride alone
had no effect. However, it opposed the action of various polyfunctional
alkylating agents, apparently suppressing one or several of the events
that normally lead to breakage of chromosomes following attack of the
alkylating agents.
At high doses fluoride apparently is able to induce certain malfor-
mations in laboratory animals. Fleming and Greenfield (1954) administered
fluoride as sodium fluoride or calcium fluoride to female adult Webster
mice during gestation in cumulative doses as high as 600 to 700 ug CaF2
and 1000 to 1200 yg of sodium fluoride. Neonatal mice showed changes in
the structure of the jaws and teeth, retarded calcification of bone in
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323
the jaws, alteration of the cell structure of the ameloblast, and retar-
dation of the enamel matrix maturation. In another study, female Wistar
albino rats were given oral doses of sodium fluoride (2, 5, or 10 mg/g
daily) for 4 days from the 8th to the llth day (Group A) or from the llth
to the 14th day (Group B) of gestation (Goto, 1968). Fetuses observed at
term showed no external malformations; however, skeletal observations
showed that Group B fetuses had retarded ossification in the occiput,
sternbrae, metacarpal bones, metatarsal bones, and caudal vertebrae, and
in Group A some fetuses had various skeletal abnormalities. The delivered
young showed that three weeks after birth the retarded ossification was
restored to the normal condition. In addition, the growth of groups' A
and B sucklings was almost the same as the control sucklings. D'Angelo
and Esposito (1965) found that doses of 25 mg/kg (almost the minimal lethal
dose) given parenterally or orally to pregnant rats (D'Angelo and Esposito,
1965) produced fetal abnormalities of liver, kidneys, skull, jawbones,
and teeth.
Five articles are listed under the heading "Fluorine" in Shepard's
Catalog of Teratogenio Agents (Shepard, 1973). One is the article by
Fleming and Greenfield already discussed. A report by Schour and Smith
(1940) on the experimental and histologic analysis of mottled teeth and
a report by Smith and Smith (1935) on the occurrence of mottled enamel
in the temporary teeth are included. There is also a study by Spratt
(1950), using explanted chick embryos (in vitro studies), on the meta-
bolic basis of morphogenesis and differentiation as revealed by the use
of inhibitors. Fluoride had little effect on the developing central
nervous system but considerable effect on the heart. lodoacetate acted
oppositely. Spratt's explanation of this was the relatively greater
dependence of the heart tissue on glycolysis (fluoride's action on eno-
lase would block this) as contrasted with the dependence of brain tissue
on respiration. Duffey and Ebert (1957) extended Spratt's work, confirmed
the differential effect of fluoride, and carried the explanation further
to include the whole flow of electrons to oxygen, the two tissues having
different makeups with respect to this.
Data presented by Rapaport (1956) from births in 14 U.S. cities in
four states showed an apparent increase in mongolism with increase in the
fluoride content of the water. This conclusion was criticized on sampling
and statistical groups by Russell (private communication, 1962, as cited
in Hodge and Smith, 1965) and shown to be spurious. A study by Berry
(1958) in England and a study by Needleman, Pueschel, and Rothman (1974)
in Massachusetts also showed no relation between the fluoride content of
the water supply and the incidence of mongolism.
One final study also demonstrated that there is no association
between water fluoridation and congenital malformations (Erickson et al.,
1976). The incidence of selected malformations (including Down's syn-
drome) in areas with fluoride supplementation of public water supplies
was compared with the incidence of malformations in areas where the water
supply was deficient in fluoride; no substantial or significant differ-
ences were found.
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324
The possibility of birth defects and reproductive malfunction arising
from chronic exposure to halogenated anesthetics was mentioned in Section
6.4.3.6.2. The question of teratogenlcity of anesthesia was reviewed by
Smith (1974). Danger to mother and fetus from the anesthesia and anes-
thetics in operations during pregnancy has long been recognized; now con-
cern Is arising regarding the danger to anesthetists and other operating
room personnel from chronic exposure to inhalation anesthetics. Surveys
(e.g., questionnaires and examination of records) have shown an apparent
greater incidence of miscarriages, infertility, and birth defects in the
offspring of persons so exposed. The surveys have not yet been properly
statistically analyzed, and, as Smith points out, other factors may also
be implicated. Nonetheless, the available evidence suggests a need for
caution. Concern is such that the FDA proposes to study the question
further (Scott, 1976). If a danger is clearly shown, steps such as more
rigorous control of ventilation and of release of anesthetics in the
operating room (Whltcher et al., 1975), restriction in use of some anes-
thetics, different anesthetic mixtures, and greater use of Injection of
anesthetics as opposed to Inhalation in order to minimize release of the
agent may have to be instituted.
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325
SECTION 6
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SECTION 7
ENVIRONMENTAL DISTRIBUTION AND TRANSFORMATION
7.1 SUMMARY
Fluorine is widely used in industry, primarily as the mineral fluor-
spar, a metallurgical fluxing agent needed in the manufacture of steel,
and as hydrofluoric acid, the most important manufactured compound of
fluorine.
Since World War II, consumption of fluorides has increased greatly, and
the U.S. demand by the year 2000 is expected to be 1,900,000 to 2,500,000
metric tons (basis: contained fluorine). It is unlikely, however, that
this demand can be met domestically unless a practical method can be devel-
oped for recovering fluoride from wastes produced during phosphate rock
processing. If economical recovery is not feasible, future consumption
will depend on imports from Mexico, Spain, and Italy.
Major industrial emissions of fluoride to the atmosphere include coal
combustion, phosphorus and phosphate fertilizer manufacturing, steel and
aluminum production, and ceramic products manufacture. Natural emissions
result from weathering of rocks and minerals and volcanic activities.
Fluorine is ubiquitous in the earth's crust. Igneous rocks average
625 ppm fluoride, sandstones about 270 ppm, shales about 740 ppm, and
limestones about 330 ppm. Normal mineral soils average 200 to 300 ppm,
sandy soils containing less than clays. Soils high in phosphorus (either
naturally or as a result of fertilization) are enriched with fluoride;
so are soils near certain industrial activities.
Fluoride tends to persist in soils with high calcium or aluminum
content. Sandy, acidic soils favor development of soluble forms that
may leach or be taken up by plants. The plant depletion time for fluo-
ride in soil is estimated at 10,000 years.
Most natural waters .contain fluoride, but concentrations in uncon-
taminated surface and groundwaters usually do not exceed 0.3 ppm and 10
ppm respectively. Nearly all U.S. public water supply systems meet U.S.
Public Health Service standards for fluorides. Seawater of normal salin-
ity averages 1.4 to 1.5 ppm fluoride. Highly saline or acid springs in
active volcanic areas may contain up to 5000 ppm. Fluorides are removed
from most waters by chemical precipitation; sediments contain an average
of 730 ppm fluoride.
Fluorine may exist in the atmosphere as soluble gaseous fluorides
or soluble and insoluble dusts; it only rarely occurs in elemental form.
In uncontaminated rural areas, fluoride is present only in fractions of
a part per billion (ppb). Urban U.S. air usually contains less than 0.06
ppb, but average atmospheric fluoride concentrations may exceed 1.25 ppb
near some industries. Fluorides in the air return to earth as dusts or
in condensation or precipitation.
349
-------
350
Fluorides are removed from industrial wastes by precipitation or
sorption methods. Lime is frequently used to precipitate fluoride.
Sorptive methods involve passing fluoride wastes through scrubber towers
or columns packed with a suitable substrate such as alumina or charcoal.
7.2 PRODUCTION AND USAGE
Fluoride is widely used in industry and is expected to be in greater
demand in the future. The major industrial source of fluorides is fluor-
spar (fluorite), although cryolite, fluorapatite, and topaz may occasion-
ally be used (Worl, Van Alstine, and Shawe, 1973). In 1977 the United
States consumed nearly 1.2 million metric tons of fluorspar, 85% of which
was imported (Ch.enri.eal and Engineering News, 1978). Iron and steel pro-
ducers and the chemical industry are the chief consumers of fluorspar.
Iron and steel manufacturers use fluorspar chiefly in mineral form, but
most chemical applications require hydrofluoric acid which is obtained
by treating the mineral with sulfuric acid. In 1974, iron, steel, and
electrometallurgical fluxing accounted for 44% of the total U.S. consump-
tion of fluorspar, with the chemical industry a close second at 32.5%.
Nonferrous metal production, chiefly aluminum and magnesium, accounted
for 22%. The balance was distributed between ceramics and glass manufac-
ture (1.3%) and other miscellaneous uses (0.2%) (Wood, 1975). Uses of
important fluoride-containing compounds are given in Table 7.1, and
supply-demand relationships are illustrated in Figure 7.1.
World consumption of fluoride has greatly increased since World War
II. In spite of increased demand, however, domestic production has de-
creased. In 1970, the United States produced only 20% of the fluorspar
it consumed, importing the balance from Mexico, Spain, and Italy (Worl,
Van Alstine, and Shawe, 1973). Expected U.S. demand for fluoride in the
year 2000 is 1,900,000 to 2,500,000 metric tons (2,100,000 to 2,700,000
short tons) (Table 7.2). The rest of the world is expected to consume
5,000,000 to 6,000,000 metric tons (5,500,000 to 6,600,000 short tons)
(MacMillan, 1970). U.S. demand can be met domestically if an economical
method for fluoride recovery from wastes produced during phosphate rock
processing is devised. Otherwise, the presently known U.S. resources of
fluoride in fluorspar will be depleted in 25 years.
In the United States, most fluorspar is mined from deposits located
in Illinois and Kentucky. Important production also comes from Colorado,
Utah, Idaho, New Mexico, Montana, and Nevada (Largent, 1961). U.S. fluo-
ride resources (as fluorspar) are estimated at 4,900,000 metric tons
(5,400,000 short tons). As demand for fluoride increases, it is thought
that the rate of discovery of fluorspar reserves and the recovery of
fluoride from other sources will also increase (MacMillan, 1970).
7.3 DISTRIBUTION OF FLUORIDE IN THE ENVIRONMENT
7.3.1 Sources of Pollution
7.3.1.1 Industrial Sources Fluoride is emitted to the environment from
a variety of sources (Table 7.3). Most emissions result from processing
-------
351
TABLE 7.1. USES OF SELECTED FLUORIDE COMPOUNDS
Compound
Formula
Use
Aluminum trifluoride
Ammonium bifluoride
Antimony trlfluoride
Antimony pentafluoride
Calcium fluoride
Cryolite
Cupric fluoride
Perchloryl fluoride
Hydrogen fluoride
Lead fluoride
Lithium fluoride
Magnesium fluoride
Nitrogen trlfluoride
Oxygen difluorlde
Potassium fluoride
Potassium bifluoride
Silicon tetrafluorlde
Fluorosilicic acid
Sodium fluorosllicate
Potassium fluorosllicate
Zinc fluorosllicate
Silver fluoroslllcate
Barium fluorosilicate
Copper fluorosllicate
Sodium fluoride
A1F, Component of electrolyte melt in the manufacture and
refining of aluminum; in ceramics and glass; glazes
and enamels; welding rods
NtUHF] Frosting glass, boiler scale removal, wood treatment,
stain removal
SbF, Manufacture of Freon-type compounds
SbFj Oxidizing and fluorinating agent
CaFj Raw material for production of fluorine compounds,
production of plastics, steel manufacture, glass
manufacture, cement, abrasives, welding rods
Na,AlF. Aluminum manufacture, glass manufacture, enamels,
grinding wheels, insecticides
CuFj Construction of cathodes in nonaqueous galvanic
cells, flux in casting gray iron
ClOjF Oxidlzer for rocket engines, cutting and welding
metals, explosives
HF Etching and polishing glass, aerosol propellents,
foaming agents, cleaning fluids, plastics, petro-
leum, pickling metals, dyes, Pharmaceuticals, stain
removers, catalyst for high-octane aviation fluid
PbF, Fluorinating agent, raw material for lead tetrafluo-
rlde, underwater paints, special glasses
L1F Aluminum welding fluxes, zirconium and titanium braz-
ing fluxes, soft enamels and glazes, and depolar-
izer in fluorine manufacture
MgF» Flux in magnesium metallurgy, porcelain and pottery,
phosphor for cathode-ray screens, coating agent for
titanium pigments, antireflecting agent
NF, Rocket fuel oxidants, hydrogen-nitrogen trioxide
torches
OFj High-energy rocket propellent
KF Fire extinguisher for alkali metal fires, preparation
of silver-soldering fluxes
KHFj Electrolyte for preparing elemental fluorine, silver-
solder flux, frosting of glass
SiFt Manufacture of fluorosilicic acid, preparation of
concrete, oil production
HjSiF. Water fluorldatlon, disinfectant, wood preservative,
masonry hardener, treatment of skins and hides,
electroplating, glass treatment
Na3SlF« Opaciflcation of vitreous enamels and opalescent
glass, coagulation of latex, treatment of hides and
skins, zirconia pigment production, beryllium
extraction, insecticide
KjSiF, Chemical Intermediate, vitreous enamel frits
ZnSlF«*6H90 Laundry sour, wood preservative, plaster additive,
concrete additive
AgiSiF."4H,0 Antiseptic preparations
BaSiF. Opaclfler In enamel frits, insecticide, fungicide
CujSiF, Dyeing and hardening marble, insecticide, fungicide,
activating agent in flotation processes
NaF Rimmed steel manufacture, water fluoridatlon, heat
treating salts, stainless-steel pickling, soldering
and metallurgical fluxes, wood preservatives,
adhesives, insecticide, coated papers, fluxing
agent for vitreous enamels, antiseptic
-------
352
TABLE 7.1 (continued)
Compound
Formula
Use
Sodium bifluoride
Sulfur hexafluoride
Fluorosulfuric acid
Stannous fluoride
Uranium tetrafluoride
Fluorinated hydrocarbons
Fluoroethanols
Fluoro ethers and amines
Perchlorofluoroacetones
Fluorinated carboxylic acids
Fluorinated aromatic compounds
Perfluoroalkylsulfur fluorides
Polytetrafluoroethylene
Polychlorotrifluoroethylene
Polyvinyl fluoride
Polyvlnylldene fluoride
NaHF,
SF.
HSO.F
SnF,
Laundry sour and stain remover, bleach for leathers,
tin plating, stone and brick cleaner, glass etching
and frosting
Electrical equipment
Catalyst for alkylation of branched chain paraffins
and aromatic compounds, polymerization of mono-
olefins, electropolishlng metals
Dental preparations and dentifrices
Starting material for production of uranium metal and
UF.
Refrigerants, aerosol propellents, fire-extinguishing
agents, heat transfer agents
Anesthetics, drugs
Hydraulic fluids, heat transfer media, dielectric
fluids, selective solvents
Oil and water repellent textile coatings, acetal
resin solvents, adhesives, heat transfer agents,
pesticides
Rodenticides, insecticides
Lamprey irradlcants, dyes, Pharmaceuticals, organic
solvents, fungistats, anticonvulsants
Dielectric materials, solvents, thermally stable
fluids, inert polymers, polymerization initiator
Chemical gasketing and packing material, valves to
control gas and liquid flow, hoses, electronic
components, sealants, cooking utensil coatings,
bearings
Chemical process equipment, electrical wire and com-
ponents, organic seals and gaskets, outdoor protec-
tive coverings, electrical insulation, printed
circuits, sealants, gyroscopic fluids, lubricants
Metal coatings, wood and plastic lamlnanta, fabric
coatings, wall coatings, greenhouses and solar
stills, mold release films for resins, electrical
components
Piping, coatings for tanks, valves, and pumps,
instrument diaphragms, hoses, shipping containers,
electronic equipment
Source: Compiled from Standen, 1966.
-------
WORLD PRODUCTION
e/2.273e
I
ORNL-DWG 79-20913
1 I
U.S.S.R.
220e
PEOPLE'S REPUBLIC
OF CHINA
126e
THAILAND
187
FRANCE
130
SOUTH AFRICAN
REPUBLIC
104
EAST GERMANY
41e
MONGOLIA
90e
CANADA
68
UNITED STATES
151
MEXICO
539
SPAIN
191
ITALY
117
UNITED KINGDOM
84
WEST GERMANY
45
OTHER
180
401
80
26
9
2
27
IMPORTS
545
INDUSTRY STOCKS
1/1/73
170
GOVERNMENT STOCKPILE
BALANCE: 569
e/ ESTIMATE
SIC STANDARC
UNIT THOUSANC
INDUSTRY STOCKS
12/31/73
.S/148
U. S. SUPPLY
866
U. S. DEMAND
717
EXPORTS
1
KEY
CHEMICALS
237
IRON AND STEEL
PRODUCTION
(SIC 281)
293
NONFERROUS METAL
PRODUCTION
(SIC 3312)
153
CERAMIC AND GLASS
(SIC 3334)
9
IRON AND STEEL
FOUNDARIES
(SIC 3211)
19
OTHER
(S1C 332)
6
Figure 7.1. Supply-demand relationships for fluoride (all forms)
1975. Reprinted by permission of the publisher.
Source: Adapted from Wood,
01
-------
TABLE 7.2. SUMMARY OF FORECASTS OF U.S. AND WORLD FLUORINE DEMAND, 1973-2000
(thousand metric tons of contained fluorine)
Location 1973
United States
Total 717
Cumulative
Rest of world
Total 1,556
Cumulative
World
Total 2,273
Cumulative
2000
forecast range
Low
1,570
37,000
3,000
80,000
4,570
117,000
High
2,850
46,000
7,500
112,000
10,350
158,000
Probable
1985
1,570
13,600
3,640
30,000
5,210
43,600
2000
1,940
39,800
5,400
98,000
7,340
137,800
Probable
average annual
growth rate,
1973-2000
(%)
3.8
4.7
4.4
Source: Adapted from Wood, 1975, Table 10, p. 396. Reprinted by permission
of the publisher.
U)
-------
TABLE 7.3. SOLUBLE FLUORIDE EMISSIONS
Process
Coal burning for power
Open hearth steelmaking
Iron ore sintering
Iron ore palletizing17
Primary aluminum
production
Heavy clay products
Wet-process phosphoric
acld
HF alkylation
Expanded clay aggregate
Normal superphosphate
Electrothermal
phosphorus
Triple 'superphosphate"
Opal glass production
Blast furnace
Def luorinated phosphate
rock^
HF production
Enamel frit production
Copper smelting and
refining ,
Ammonium phosphate
Cement manufacture
Lead smelting and
refining
Current
Emission
(thousands
of tons
fluoride
per year)
27
25
18
18
16
10
6.4
5.8
5.3
5.0
4.1
3.8
3.3
2.8
1.8
0.7
0.7
0.6
0.3
0.3
0.2
Year
1970
1968
1968
1968
1970
1968
1970
1971
1968
1970
1968
1970
1968
1968
1970
1970
1968
1967
1970
1964
1967
Relat ive
confidence"
II
II
II
II
I
II
I
I
II
I
I
I
II
II
I
I
II
III
I
II
III
Year 2000 with current
Process
Primary aluminum
manufacture
Coal burning for power
Iron ore pelletizing'7
Expanded clav aggregate
Wet-process phosphoric
acid''
HF alkylation'"
Heavy clay products
»
Triple superphosphate
Electrothermal
phosphorus
Opal glass production
HF production
Iron ore sintering
Def luorinated phosphate
rock'* -
Blast furnace1'
Normal superphosphate
Enamel frit production
Cement manufacture
Copper smelting and
refining
Ammonium phosphate'
Open hearth steelmaking
Lead smelting and
refining
. prac t i ce
Emission
(thousands
of tons
fluoride
per v e a r )
141
86
39
25
22
16
10
7.3
6.6
5.5
5.3
4.8
2.7
2.6
1.4
1.1
0.8
1.6
0.8
0
2.4
Year 2000 assuming 99*
control efficiency
Process
Primary aluminum
manufacture
Coal burning for power
HF production
['1 ec t rothermal
phosphorus
Iron ore pelletizing
Wet~process phosphoric
acid-
Triple superphosphate
Expanded clay aggregate
Defluorinated phosph.ite
rock
HF alkvlation
Normal superphosphate
Heavv clav products
Opal glass production
Iron ore sintering
Blast furnace
Ammonium phosphate
Fnamel frit production
Copper smelting and
refining
Cenent manufacture
Open hearth st Of Irn.ik ing
Lead smeltim; and
refining
Emission
(thousands
of tons
f luorJde
per vear)
8.1
O.t
0.7
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.1
0.1
0.1
0. 1
0.1
0
-------
TABLE 7.3 (continued)
Process
Zinc smelting and
refining
Total for processes
considered
Current
Emission
(thousands 0
fluoride Vear confWence2
per year)
0.2 1967 III
155.3
1 '"." - -
Year 2000 with current practice
Emission
(thousands
, Process of tons
fluoride
per year)
Zinc smelting and 2.4
refining
384.3
Year 2000 assuming 99X
control efficiency
Process
Zinc smelting and
refining
Emission
(thousands
of tons
fluoride
per year)
<0.1
12.0
rBxcludes CaFs.
^Relative confidence levels: I excellent, II good. III fair to poor.
.Assumes no fluorspar addition to pellet.
includes pro rata allocation of gypsum pond fluoride emissions (estimated as
.Assumes 25Z of production uses lime pit disposal of acid sludges.
'Assumes no limestone other than that In pellets or sinter.
Source: Adapted from Robinson et al., 1972, Table 12. Reprinted by permission of the publisher.
6300 tons for 1970 and 21,000 tons for 2000).
in
ON
-------
357
phosphate rock; producing iron, steel, and aluminum; burning coal; and man-
ufacturing glass, ceramic, and clay products (Duncan, Keitz, and Krajeski,
1973; Robinson et al., 1972). Fluorides emitted by these processes are
primarily in the form of hydrofluoric acid, silicon tetrafluoride, or par-
ticulate matter (National Academy of Sciences, 1974). Major sources of
fluoride contamination are discussed extensively in National Academy of
Sciences (1971); that account is briefly summarized below.
7.3.1.1.1 Phosphate fertilizer production Phosphate rock mined in the
United States is usually converted to phosphate fertilizers, phosphoric
acid, or elemental phosphorus. During the grinding and drying of phos-
phate rock, dusts and gases containing fluorides may be liberated (Table
7.4). Gypsum settling ponds are also a source of atmospheric pollution
(Smith and Hodge, 1978). The chief gaseous pollutant produced is silicon
tetrafluoride, although hydrogen fluoride is also emitted (Russell, 1968).
In modern plants that practice good emission control, most of these fluo-
rides are removed from off-gases by water-spray towers or other types of
scrubbers.
7.3.1.1.2 Wet-process phosphoric acid production Sodium fluorosilicate,
potassium fluorosilicate, hydrofluoric acid, and fluorosilicic acid slur-
ries are produced during the manufacture of phosphoric acid. In some
coastal areas these wastes are dumped directly into the sea. In other
areas they are accumulated in settling ponds. Volatile fluorides are
usually not controlled in these ponds and constitute an atmospheric
emission source (Cross and Ross, 1969).
7.3.1.1.3 Brick, tile, pottery, and cement production Clays used in
manufacturing these products usually contain 0.02% to 0.3% fluoride. Dur-
ing the firing of brick, tile, and pottery, hydrogen fluoride and silicon
tetrafluoride are produced. During brickmaking, 30% of the initial fluo-
ride in clays may be emitted (Semrau, 1957). Gas and dust from kilns are
usually discharged untreated into the atmosphere. Fluoride-containing
frit is often used to color ceramics, thus providing another potential
emission (Wildblood, 1973).
7.3.1.1.4 Glass, enamel, and fiberglass production Fluorspar, cryolite,
and sodium fluorosilicate are often added to special-purpose glasses.
Gaseous and particulate fluorides escape to the environment during this
process. Vapor from etching solutions containing hydrofluoric acid or
ammonium bifluoride can escape to the atmosphere. Silicon tetrafluoride,
hydrogen fluoride, calcium fluoride, aluminum fluoride, sodium fluoride,
and sodium fluorosilicate are also produced during glass melting opera-
tions; overall, 10% to 20% of the fluoride in the raw materials is emitted
to the environment during glass manufacture (Semrau, 1957).
7.3.1.1.5 Metal casting, welding, and brazing Fluorides are used as
fluxes and coatings for molds in metal casting operations. Metal casting
produces hydrogen fluoride, silicon tetrafluoride, and boron trifluoride.
Efforts are seldom made to reduce atmospheric emissions of this nature.
-------
358
TABLE 7.4. FLUORINE EMISSIONS FROM PROCESSING PHOSPHATES
Process
Calcining phosphate
rock, bencf Iclatlon
Calcining phosphate
rock, def luorinat ion
Calcining phosphate
rock, def luorinatlon
Nodulizing phosphate
rock
Sintering phosphate
rock
Calcining phosphate
rock
Calcining phosphate
rock
Def luorinat Ing molten
phosphate rock
Phosphoric acid
manufacture
Elemental phosphorus
manufacture
Calcium-magnesium phos-
phate manufacture
Process
material
Phosphate rock
Phosphate rock
Phosphate rock, silica
Phosphate rock
Phosphate rock
Phosphate rock.
briquets
Phosphate rock.
pellets
Phosphate rock, silica
Phosphate rock, coke
Phosphate rock, silica
Phosphate rock,
silica and coke
Phosphate rock.
olivlne
Phosphate rock.
olivlne and silica
Phosphate rock.
olivlne
Process
equipment
Rotary kiln
Rotary kiln
Rotary kiln
Rotary kiln
Dwlght-l.loyd
machine
Rotary kiln
Shaft kiln
Rotary kiln
Electric furnace
Hearth furnace
Hearth furnace
Electric furnace
(for melting)
Hearth furnace
(for defluori-
natlon)
Shaft furnace
Electric furnace
Blast furnace
Electric furnace
Electric furnace
Electric furnace
Electric furnace
Input
fluorine
emitted
00
3
Almost nil
50-70
75
98
20-45
30
35-40
Almost nil
14
14
28
Small
84-95
72-86
90
92-96
70
90 or
greater
35
25
20-30
52
30
9.6
27-33
11
27-57
10-20
Remarks
Residence time short at
maximum temperature
Residence time 1 hr
Residence time 2 hr
Residence time in burning
zone 20-30 min
Residence time 30 mln
Moisture in charge
Melting without further
treatment
Melting time - 4-25 hr
Pool depth - 18 In.
Pool depth 3 in. , heat-
ing period 2 hr
Pool depth - 1.5-2.0 In.,
heating period 60-80
mln
About 17Z of emission in
particulate form
About 50Z of emission In
particulate form
About 16Z of emission In
particulate form
Batch operation
Continuous charging
Batch operation
Fusion time 1-2 hr
Continuous charging with
unfused material above
melting zone
Manufacture of Rhenanla
phosphate
Manufacture of calcium
metaphoaphate
Defluorination of
superphosphate
Manufacture of
superphosphate
Phosphate rock, soda
ash and silica
Phosphate rock
Rotary kiln
Combustion chamber
and absorption
tower
Triple superphosphate Rotary kiln
Phosphate rock, sul-
furlc acid
Mixer and den
8
80-85
78-82
16-42
30-35
Residence time - 27 mln
Extreme range
Average
Source: Adapted from Semrau, 1957, Table V, p. 98. Reprinted by permission of the publisher.
-------
359
Calcium fluoride or other inorganic fluorides are often used as
fluxing agents for arc welding. Hydrogen fluoride, silicon tetrafluo-
ride, and particulate fluorides are released during the welding process
(Pantucek, 1971). Fluoride concentrations of up to 10 rag per cubic meter
of air may be produced by welding in confined areas (Smith, 1967). Such
concentrations exceed the fluoride threshold limit value of 2.5 mg/m3 for
particulate fluorides set by the American Conference of Governmental In-
dustrial Hygienists. Silver soldering and brazing also release fluoride
particulates.
7.3.1.1.6 Phosphate and phosphate feed supplement production Silicon
tetrafluoride, hydrogen fluoride, and fluoride dusts are formed during
phosphate manufacture. Modern plants usually remove these pollutants by
spray towers or scrubbers. Slag from production furnaces contains about
3% fluoride and is usually solidified or sold as an agricultural liming
agent. Hydrogen fluoride is also produced during the manufacture of ani-
mal feed supplements; however, emissions from this process are small.
7.3.1.1.7 Aluminum production Aluminum electrolysis cells emit silicon
tetrafluoride, hydrogen fluoride, cryolite, aluminum fluoride, calcium
fluoride, and chiolite. Although aluminum manufacture has constituted a
significant source of emissions in the past, ambient air fluoride concen-
trations from aluminum plants are now generally low (Schmitt, 1963; Smith
and Hodge, 1978).
7,3.1.1.8 Steel production Fluorides constitute only a fraction of the
fumes produced by steel manufacturing. Primarily, calcium fluoride and
hydrogen fluoride are produced. These fluorides are usually efficiently
removed from off-gases, resulting in relatively low concentrations of
fluoride in gaseous emissions. As in aluminum production, however, the
aggregate total weight released is substantial (Smith and Hodge, 1978).
7.3.1.1.9 Petroleum refining Boron trifluoride and hydrogen fluoride
are used by the petroleum industry as alkylation catalysts in the produc-
tion of high-octane gasolines. Volatile fluorides may be released during
loading and unloading of chemicals and during disposal of waste products.
Tarry residues that release fluoride fumes when exposed to air are fre-
quently produced.
7.3.1.1.10 Rocket engine testing Fluorine and its compounds are used
as oxidizers in rocket fuels, and testing of rocket engines results in
fluoride emissions. Contamination may also result from burned purge gases
and discharges from pipe burnouts and spills (Ricca, 1966).
7.3.1.1.11 Pesticide application Among fluoride compounds used as pes-
ticides are sodium fluoride, sodium fluorosilicate, barium fluorosilicate,
cryolite, and various organic fluorides. Use of fluoride-containing prod-
ucts has declined in recent years due to the development of organic phos-
phates. Some uses, however, may still provide a direct environmental
emission.
-------
360
7.3.1.1.12 Coal combustion Coal combustion provides a significant envi-
ronmental input of fluoride. U.S. coals contain 25 to 143 ppm fluoride,
with an average of 60.9 ppm (Ruch, Gluskoter, and Shimp, 1974). Abernethy
and Gibson (1963) reported 10 to 190 ppm fluoride in U.S. commercial coals.
British coals contain 0 to 175 ppm fluoride, most containing less than 80
ppm (Crossley, 1944). A global average of 80 ppm in coal is suggested
by Bowen (1966). During combustion, about 50% of the fluoride contained
in coal is evolved as hydrogen fluoride, silicon tetrafluoride, and
particulates.
7.3.1.1.13 Atomic energy installations Gaseous diffusion plants use
uranium hexafluoride to separate isotopes of uranium. Due to strict con-
trol measures, emission of fluoride compounds is usually negligible, except
in cases of accidental release (Emler, Hulett, and Kalmon, 1971).
7.3.1.1.14 Other Additional industrial emission of fluorides results
from quartz etching, metal pickling, electroplating, addition of fluorides
to water, toothpastes, bleaches, drugs, incineration of wastes, and mining
(Waldbott and Oelschlager, 1974; Wood, 1973).
7.3.1.2 Natural Sources Natural sources of fluorides include minerals
and rocks in the earth's crust, precipitation, volcanoes, and fumaroles.
The fluoride content of minerals and rocks is discussed in Section 7.3.2.1.
7.3.1.2.1 Volcanoes and fumaroles Gaseous and particulate fluorides
are discharged by active volcanoes and fumaroles. Fluoride compounds in
volcanic gases include hydrogen fluoride, ammonium fluoride, silicon tetra-
fluoride, ammonium fluorosilicate, sodium fluorosilicate, potassium fluo-
rosilicate, and potassium fluoroborate. Fluorides of potassium, sodium,
calcium, and magnesium have also been identified, as well as trace amounts
of organofluorine compounds (Roholm, 1937; Stoiber et al., 1971). Volcan-
ism adds an estimated 1 to 7 * 109 kg of fluoride per year to the environ-
ment (Bartels, 1972; Carpenter, 1969).
7.3.1.2.2 Precipitation Precipitation collects atmospheric fluoride and
returns it to earth, providing a localized input (Table 7.5). Rainwater
in industrialized areas contains more fluoride than that in nonindustrial-
ized areas. Maclntire et al. (1949) found that rainwater averaged 0.29
ppm in a city, 0.30 ppm near a phosphate processing plant, and 0 to 0.02
ppm in a control area. Rainwater in a German industrial area averaged
0.28 to 14.1 ppm (Garber, 1970). In areas where much coal is burned, rain-
water adds an estimated 170 g of fluoride per hectare of land (Maclntire
et al., 1942). Global precipitation is estimated to provide 1.2 x 1010
kg (2.6 * 1010 Ib) of fluoride per year (Bewers and Haysom, as cited in
Bewers and Yeats, 1975).
7.3.2 Distribution in Rocks and Soils
7.3.2.1 Minerals and Rocks Fluoride in the lithosphere is primarily
associated with minerals, usually phosphates and silicates. The most
abundant fluoride mineral is fluorite (fluorspar, CaF2). Other economic-
ally important fluoride minerals are cryolite (Na3AlF6), sellaite (MgF2),
-------
361
TABLE 7.5. FLUORIDE CONCENTRATIONS IN ATMOSPHERIC PRECIPITATION
Location
Type
Number
Fluoride (ppm)
Range
of Newfoundland
Unspecified
Calcutta
Rain
Preoonsoon showers
Rain
Collected over 12
months near fertil-
izer factory
500 m ENE
500 m SW
1000 m NE
Collected over 3
months close to
another fertilizer
factory, three sites
Control
Collected over 12
months near industrial
area of Hamburg
Near
1000 m NE
1800 m
3000 m N
Control
0.001-1
0.02-0.4
5.3-14.1
0.79-3.3
3.1-6.3
0.61-1.6
0.16
0.41
0.41
0.28
0.61
0.19
Mean
Japan
England
California
Mojave Desert
Siberia
Kazakistan
Ukraine
Sierra Nevada
Czechoslovakia
Minnesota
Storm at sea, east
Rain
Rain
Rain
Rain
Snow
Snow
Rain
Snow
Snow
Snow
Fresh urban
Wilderness
Street, after
several weeks
Rain
Fresh urban
Snow runoff after
above rain
Rain
1
9
35
12
4
5
4
28
40
0.08-0.54
0.0-0.8
0.02-0.57
0.0-0.7
0.05-0.30
0.05-0.20
0.0-0.2
0.03-0.04°
a
t
1.62-3.2r
0.06
0.22
0.12
0.14
0.2
0.13
0.10
0.052
0.06
0.36
t
0.05?
0.05*
0.45a
0.7°.
0.22*
0.37«
2.41*
0.05
10.0
1.85
5.1
fIonic fluoride.
VTotal fluoride.
Ionic fluoride not detected.
Source: Adapted from Smith and Hodge, 1978, Table 7. p. 298. Reprinted
by permission of the publisher.
vllliaumite (NaF), bastnaesite [(Ce.La)(C09)F], fluorapatlte [Ca5(PO<,,C03)
3F], and topaz [AlaSiOA(F,OH)a.] (Worl, Van Alstine, and Shawe, 1973).
Virtually all rocks contain fluoride. Igneous rocks average 210 to
1000 ppm fluoride, and sedimentary rocks average 180 to 940 ppm (Fleischer
and Robinson, 1963). Hawkes and Webb (as cited in Shacklette, Boerngen,
and Keith, 1974) supplied the following values: ultramafic rock, 100 ppm;
mafic, 370 ppm; felsic, 800 ppm; limestone, 51 ppm; sandstone, 290 ppm;
and shale, 590 ppm. Kokuba (as cited in Shacklette, Boerngen, and Keith,
-------
362
1974) reported 100 to 800 ppm fluoride in volcanic rocks and 120 to 2400
ppm in plutonic rocks. Glass-rich volcanic rocks of the western United
States contain 20 to 4900 ppm fluoride (Coats, Goss, and Rader, 1963).
Bowen (1966) gave the fluoride content of igneous rocks as 625 ppm, sand-
stone as 270 ppm, shales as 740 ppm, and limestone as 330 ppm.
7.3.2.2 Soil Estimates of fluoride in the earth's crust range from
300 ppm (Largent, 1961) to 800 ppm (Murrmann and Koutz, 1972). Normal
mineral soils average 200 to 300 ppm fluoride (Bowen, 1966; Worl et al.,
1973). Of this, 10 to 40 ppm is extractable, and the concentration in
the soil solution is 0.1 to 0.5 ppm (Murrmann and Koutz, 1972). Gener-
ally, sand soils are low in fluoride, while heavier soils contain higher
concentrations. The high incidence of micaceous minerals and their weath-
ering products in clays probably accounts for the high fluoride content
of the latter (Table 7.6).
TABLE 7.6. FLUORIDE CONTENT OF CERTAIN
MICACEOUS CLAYS
Mineral Location Fluoride
(ppm)
Hydrous mica Platteville, Wis. 5800
Muscovite Staley, N.C. 400
Ordovician Chattooga County, Ga. 4500
bentonite Sevier Dam, Tenn. 7400
Sericite Guanajuato, Mexico 1800
Staley, N.C. 300
Source: Adapted from Robinson and
Edgington, 1946, Table 2, p. 347. Reprinted
by permission of the publisher.
Soils of the eastern United States contain 10 to 3680 ppm fluoride
(arithmetic mean, 340 ppm) while those of the western United States contain
10 to 1900 ppm (arithmetic mean, 410 ppm) (Figure 7.2). The difference
in fluoride content between the eastern and western areas is statistically
significant (1% level) and is probably due to differences in the fluoride
content of the parent materials (Shacklette, Boerngen, and Keith, 1974).
Robinson and Edgington (1946) analyzed 30 profiles of representative U.S.
soils (Table 7.7). The fluoride content ranged from a trace (undefined)
to 7070 ppm. The average fluoride content to plow depth (about 15.2 cm,
or 6 in.) was 292 ppm. Calcium chloride-extractable fluoride in United
Kingdom soils usually ranges from 0 to 0.2 ppm (Larsen and Widdowson,
1971). Labile (resin-extractable) fluoride averaged about 20 ppm. The
fluoride content varied with depth in some soils.
Soils rich in phosphorus tend to contain higher-than-normal fluoride
levels. A high-phosphate Tennessee soil contains as much as 0.83% fluoride
-------
ORIML-DWG 80-11484
36
30
. ,4- 92' 90' M- 86' B4- a?' » 7B' 76' 74' jy TO- 68' 66' 64'
:rT 1 1 1 1 1 1 1 1 1 < ' 1 « r=
J / » ^ * I »'
cTX^-T^A -;'Kf:--^-
~/c«- "*'> -V-;--VJ :!..:
:* V . / .^V^Xi--
4 Vx;. / . V. T-:"~
^$tStei$&
«MSk-->".%. ; ? /.; j ;^.
i s ,ss 2 x.. : ! 3v
^^*£ri&,^.V.«»»»-'
\. :». '.
\ _
114* 112' 110* 106' 106* IO4- 102* 100* M*
J L
92- 90'
J L
2' 80'
_1_
n*
»
74*
a-
Figure 7.2. Fluorine concentrations in surficial materials of the conterminous United States.
Source: Shacklette, Boerngen, and Keith, 1974, Figure 3, pp. 8-9.
u>
&
to
-------
364
TABLE 7.7. FLUORIDE IN SOILS
Soil type Location
Arredonda fine sand Gainesville, Fla.
Barnes loam La Bolt, S.D.
Brassua sandy loam North Graf ton, N.H.
Bridgeport loam Sheridan, Wyo.
Carrington loam Winthrop, Iowa
Chester silt loam Rockville, Md.
Falls Church, Va.
Unidentified clay loam Caribou County, Idaho
Colby silty clay loam Hays, Kan.
Fayette silt loam LaCross, Wis.
Depth
(in.)
0-36
0-9
9-17
17-33
33-60
0-3
3-4
4-9
9-19
19+
0-3
3-7
7-15
15-20
20-27
27-34
0-3
3-13
13-22
22-43
43-70
70-84
0-1
1-9
9-20
20-26
38-41
0-8
12-21
0-12
12-24
0-10
10-20
20-33
33-47
47-60
60-72
0-8
8-20
20-32
33-44
44-66
Fluoride
(ppm)
20
220
232
357
390
22
70
62
97
92
270
335
388
440
487
461
120
127
130
190
150
210
170
175
250
307
380
137
172
1610
3870
NDa
403
495
522
525
491
187
215
246
280
232
-------
365
TABLE 7.7 (continued)
Soil type Location
Frederick silt loam Fairfield, Va.
Greenville sandy loam Pretoria, Ga.
Hagerstown silt loam State College, Pa.
Hager s town , Md .
Holdredge silt loam Custer County, Neb.
Houston black clay Temple, Tex.
Kalkaska loamy sand Alger County, Mich.
Kirvin fine sandy loam Tyler, Tex.
Madison sandy loam Gainesville, Ga.
Depth
(in.)
0-2
2-11
11-16
16-36
36-56
»5-2
2-7
7-15
15-24
24-42
42-72
72-108
0-2
2-8
14-35
35-46
0-3
3-12
12-33
33-48
0-2
2-12
12-24
24-36
36-60
60-72
0-3
11-20
24-36
36-50
0-2
2-6
6-24
24-48
0-12
12-24
24-51
51-63
63-75
0-6
6-18
18-30
30-36
36-40
Fluoride
(ppm)
207
145
287
1032
1305
28
52
38
44
93
113
184
260
310
720
902
332
352
1832
1910
240
285
432
490
432
457
372
416
425
364
20
Trace
12
15
48
334
299
133
58
234
269
235
300
334
-------
366
TABLE 7.7 (continued)
Soil type
Marshall silt loam
Maury silt loam
Miami silt loam
Muskingum silt loam
Norfolk sandy loam
Oahu clay
Palouse silt loam
Shelby silt loam
... Depth
Location . .
(in. )
Clarinda, Iowa 0-13
13-24
24-45
45-71
Ashwood, Tenn. 0-2
2-12
12-25
25-40
40-60
60-90
Wayne County, Ind. 0-2
2-5
5-11
11-15
15-30
30-36
Zanesville, Ohio 0-7
8-13
14-24
25-46
47-72
Bests, Wayne County, N.C. 0-12
12-34
36-80
Oahu, Hawaii 0-10
10-25
25-40
Pullman, Wash. 0-20
20-33
33-62
62-75
75-84
Bethany, Mo. 0-7
8-12
12-20
20-24
24-48
48-60
48-
60-84
Fluoride
(ppm)
376
411
394
296
506
290
850
7070
4300
4080
95
130
135
187
400
452
316
390
344
326
365
42
70
95
120
87
55
369
364
360
389
358
276
444
487
468
438
442
306
420
-------
367
TABLE 7.7 (continued)
Soil type Location
Redding clay loam San Diego County, Calif.
Sharl:ey clay Houma, La.
Vernon fine sandy loam Guthrie, Okla.
Depth
(in.)
0-7
7-14
14-24
24-33
33-41
41-51
0-6
10-24
48-80
0-3
3-10
10-27
27-58
Fluoride
(ppm)
85
106
130
105
146
154
590
525
620
40
85
183
293
Not determined.
Source: Adapted from Robinson and Edgington, 1946, Table 1, p. 343.
Reprinted by permission of the publisher.
(Maclntire et al., 1949). Soils receiving annual applications of fertiliz-
ers, particularly superphosphates, have increased fluoride content. Super-
phosphates contain about 1% to 3% fluoride (Evans, Hoyle, and MacAskill,
1971; Larsen and Widdowson, 1971), 90% of which may accumulate in soil
(Robinson and Edgington, 1946). Annual application of fertilizers to
German soils has added 8 to 20 kg of fluoride per hectare (7.1 to 17.8
Ib/acre) (Oelschlager, 1971). Table 7.8 shows typical fluoride concentra-
tions of German fertilizers. The addition of 453.6 kg (1000 Ib) of super-
phosphate to 0.4 ha (1 acre) of soil can increase the fluoride content of
the plow layer by 7.5 ppm (Robinson and Edgington, 1946). Application of
500 kg (1102.3 Ib) of superphosphate per hectare (2.47 acres) raised soil
fluoride content by about 7 ppm in New Zealand (Stewart et al., 1974).
Hamilton (1974) estimated that annual fertilizer applications provide an
additional 5 to 30 kg of fluoride per hectare per year (4.5 to 26.8 Ib/
acre per year), of which 30 to 400 g (0.6% to 1.3%) is leached annually.
Soils near industrialized areas show elevated fluoride content due
to contamination. The fluoride concentration in the top 1.3 cm (0.5 in.)
of soil at a phosphorus extraction facility near Silverbow, Montana, ranges
from 265 to 1840 ppm (van Hook, 1974). Fluoride content decreases with
increasing distance from the facility. OelschlMger (1971) found that 2.1
kg of fluoride per hectare per year (1.9 Ib/acre per year) was accumulated
in soils in a large industrialized area.
-------
368
TA3LE 7.8. FLUORIDE CO»TE3rr OF PRINCIPAL
GEKMAS FECTTLIZEBS
Fertilizer
Bofaphospfaate 33.4-41,1
Brperphos 31.0-36.4
heoaoiapbMphat 15.0-27.7
Soperphcwphat 14,6-25.7
ThoBaspbosphat 0.01-0.14
Branatkalk 0,05-O.19
Merge1 0.06-O.27
DolcMltkalk 0.22
BBttentalk 3.9-10.2
Kalidongesalz (40Z) 0,02-0.03
Kaiflit 0,01-0,02
Scfwefelsaorefl laannf iV 0,003
Kalkaaaoasalpeter 0.01
laIkstickstoff 0,58
Stall*i*t (fresh ansre) 0,003
Source: Adapted froa Oelgchlagpr,
1971, Table 1, p. 81. Reprinted by per-
of the publisher.
7.3.3 Distribution in ifater
Fluoride is a nomal constituent of natural waters. dDContanlnated
surface waters (rivers, lakes, ponds, canals, creeks, and cisterns) usually
do not exceed a fluoride content of 0.3 ng/liter (Maier, 1972). The fluo-
ride content of surface waters varies depending on the source of the water
and the aaount of precipitation received (Worl, Van Alstine, and Shave,
1973). Table 7.9 gives the fluoride content of Borth American waters.
Livingston (1963) gave the fluoride content of world rivers as 0.1 to 0.2
ppm, Bowen (1966) suggested an average of 0.09 pp»- The fluoride content
of drinking water from aany different countries is given in Table 7.10.
Although soae of the extreme values are very high, average fluoride con-
centrations near 1 pp» are common.
Groundwaters (springs, wells, and infiltration galleries) «ay contain
as ocb as 67.2 ppa fluoride, but few contain nore than 10 pp» (Horl et
al., 1973). Large areas of the world have local groundwaters with vore
than 1.5 ppm fluoride. The fluoride content of groundwaters depends, in
part, on the nature of the rock through which they flow; alkalic igneous
rocks, dolonlte, phosphorite, and volcanic glasses give rise to high-
fluoride waters (Livingstone, 1963; Horl, Van Alstlne, and Soawe, 1973).
Groundwaters are the source of nost U.S. water supplies.
Fluorides are, of course, added to nany convunity water supplies to
help decrease the incidence of dental caries, Maier (1972) estimated that
-------
369
TABLE 7.9. FLUORIDE IB 1OKTH JtfKUCAS WATERS
Location
Date
Average
flaoride
Oaachlta liver near Nalvern, Ark,
Ouachlta River at Arkadelphla, Ark,
Soackover Creek aear Saackover, Ark,
Salton Sea, Imperial Valley, Calif,
Mono lake. Mono Coaaty, Calif,
Rush Creek near Memo lake, Calif.
Poos at Badvater, Death Valley. Calif.
Amargosa River aear Beatty, Bev.
Lake Tahoe at Bljoa, Bev.
Traekee River at Farad, Calif,
Pyraaid Lake at Svtcllffe, Bev.
Eagle take aear Sasawrille, Calif,
Lover Alkali Lake aear Eagleville, Calif.
Kiddle Alkali Lake near Odarrille, Calif.
Devils Lake, B.D.
Black Tiger Bay, Tovoabip 152, B.D.
Dry Lake, Towublp 155, B.D.
Free People* Lake, Tiwmlilp 151, I.D.
Rowd Lake, Towoobip 153, B.D,
Stlflfc Lake, Tomafilp 155, «,D.
Koorfgal River at Porthlll, Idaho
Flathead River at Colofeia Falla, Moat.
Pead Oreille River at Hetaliae Falls, Moat.
Colitfbia River above Dallas, Hash.
Hcrovik Lake aear Point Barrow, Alaska
East Onnallle Lake aear edge of Arctic
Coastal Plain
Chandler Lake, Brooks Range, Alaska
Token River at Eagle, Alaska
Ohio River at Dan 31
Ohio River at Dam 39
Ohio River at Dam 43
Ohio River at Shanneetovn, 111.
Ohio River at Dan 53
Allegheny River at Darren, Fa.
Oct. 1946-Sept, 1947
Oct. 1959-Sept. 1960
Oct. 19*9-Sept. 1950
Feb. 1954
Sept. 1956
Oct. 1953
Apr. 1964
Sept. 1953
Sept. 1953
Sept. 1955
May 1954
May 1954
May 1954
Bov. 1948
July 1950
Oct. 1949-Sept. 195O
Oct. 1949-Sept. 1950
Oct. 1949-Sept. 1950
Dec. 1958
Jane 1951
J»ly 1951
J»ly 1951
Aag. 1951
Apr. 1951-Sept. 1951
Oct. 1948-5ept. 1949
0.3
0.2
0.1
1.6
23
0.2
4,9
4.3
0.1
0.1
0.8
7,0
10.0
6,0
1.4
0.6
1.4
0.2
0,8
0,6
3.4
0.2
0,2
0.3
0.5
0.1
9.1
0,1
0.4
0.02
0.3
0.5
0.3
0.4
0.4
0.1
-------
370
TABLE 7.9 (continued)
Location
Clarion River near Piney, Pa.
Kiskiminetas River at Leechburg, Pa.
Casselman River at Harvedsville, Pa.
Youghiogheny River at Sutersville, Pa.
Mahoning River at Warren, Ohio
Tuscarawas River at Newcomers town, Ohio
Iowa River at Iowa City, Iowa
Cedar River at Cedar Rapids, Iowa
Wind River at Dubois, Wyo.
Wind River at Riverton, Wyo.
Bighorn River at Thennopolis, Wyo.
Little Missouri River at Medora, N.D.
Heart River near South Heart, N.D.
Grand River at Shadehill, S.D.
Cheyenne River near Hot Springs, S.D.
White River near Kadoka, S.D.
South Platte River at Juelsburg, Colo.
Republican River at Trenton, Kan.
Saline River near Wilson, Kan.
St. Francis River at Marked Tree, Ark.
White River at Batesville, Ark.
Black River at Black River, Ark.
White River at Newport, Ark.
Little Red River near Heber Springs, Ark.
Cinmarron River at Ute Park, N.M.
Arkansas River at Dardanelle, Ark.
Mississippi River near Baton Rouge, La.
Lehigh River at Catasauqua, Pa.
Delaware River at Dingmans Ferry, Pa.
Delaware River at Belvedere, N.J.
Delaware River at Trenton, N.J.
West Branch Susquehanna River at Lock
Haven, Pa.
Franks town Branch, Juniata River at
Huntingdon, Pa.
Codorus Creek near York, Pa.
Susquehanna River at Conowlngo, Md.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Feb.
Nov.
Oct.
Oct.
Oct.
Nov.
Oct.
Oct.
Mar.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Oct.
Sept
Date
1946-Sept.
1946-Sept.
1949-Sept.
1947-Sept.
1946-Sept.
1946-Sept.
1949-Sept.
1949-Sept.
1948-Sept.
1948-Sept.
1948-Sept.
1948-Sept.
1947-Sept.
1948-Sept.
1948-Sept.
1949-Sept.
1948-Sept.
1948-Sept.
1948-Sept.
1949-Sept.
1945-Sept.
1945-Sept.
1949-Sept.
1949-Sept.
1949-Sept.
1948-Sept.
1959
1944-Sept.
1944-Sept.
1944-Sept.
1944-Sept.
1945-Sept.
1947-Sept.
1948-Sept.
. 1958
1947
1947
1950
1948
1947
1947
1950
1950
1949
1949
1949
1949
1948
1949
1949
1950
1949
1949
1950
1950
1946
1946
1950
1950
1950
1949
1945
1945
1945
1945
1946
1948
1949
Average
fluoride
(ppm)
0.1
0.2
0.1
0.1
0.3
0.5
0.2
0.1
0.3
0.2
0.3
0.2
0.3
0.3
0.6
0.6
0.9
1.1
0.4
0.1
0.1
0.1
0.0
Trace
0.4
0.2
0.1
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.0
-------
371
TABLE 7.9 (continued)
Location
Date
Average
fluoride
(ppm)
Hudson River at Green Island, N.Y.
Lake Erie at Huron, Ohio
St. Lawrence River at Levis, Quebec
Cuyahoga River at Batzum, Ohio
Savannah River near Clyo, Ga.
Altamaha River at Doctortown, Ga.
Kissimmee River near Okeechobee, Fla.
West Palm Beach at Loxahatehee, Fla.
Hillsboro Canal at Sharvano, Fla.
Withlacoochee River near Holder, Fla.
Flint River at Bainbridge, Ga.
Chattahoochee River at Columbus, Ga.
Apalachicolu River near Blounstown, Fla.
Conasauga River at Tifton, Ga.
Oostanaula River at Rome, Ga.
Etowah River near Catersville, Ga.
Mobile River at Mt. Vernon Landing, Ala.
Ohio River at South Heights, Pa.
Ohio River at Dam 13
Ohio River at Dam 19
Tanana River near Tok Junction, Alaska
Tanana River at Big Delta, Alaska
Yukon River at Mountain Village, Alaska
Susitna River at Gold Creek, Alaska
Eklutna Creek near Palmer, Alaska
Ship Creek near Anchorage, Alaska
Brown Slough at Bethel, Alaska
Kenai River at Cooper Landing, Alaska
Gold Creek, Juneau, Alaska
Mackenzie River, Northwest Territory, Canada
Oct. 1958 0.0
Sept. 1950-.Sept. 1951 0.1
Aug. 1958 0.0
Oct. 1946-Sept. 1947 0.2
May 1938-Apr. 1939 0.0
May 1937-Apr. 1938 0.0
Mar. 1940-Feb. 1941 0.2
Mar. 1940-Feb. 1941 0.2
Oct. 1950-Sept. 1951 0.5
Oct. 1950-Dec. 1951 0.1
Oct. 1941-Sept. 1942 0.1
Oct. 1940-Sept. 1941 0.1
Dec. 1958 0.1
Oct. 1942-Sept. 1943 0.0
Oct. 1941-Sept. 1942 0.1
Oct. 1938-Sept. 1939 0.0
Dec. 1958 0.1
Oct. 1945-Sept. 1946 0.2
Sept. 1950 0.3
0.3
Mar. 1951-Sept. 1951 0.02
Oct. 1950-Sept. 1951 0.1
Jan. 1959 0.1
May 1951-Sept. 1951 0.2
Dec. 1950-Sept. 1951 0.1
Oct. 1950-July 1951 0.1
Sept. 1951 0.4
Oct. 1951-Nov. 1951 0.1
Oct. 1948-July 1949 0.1
July 1958 0.0
Source: Compiled from Livingstone, 1963, Tables 10-12, 25, and 26, pp.
G13-G20.
-------
372
TABLE 7.10. THE OCCURRENCE OF FLUORIDE IN DRINKING WATER FROM VARIOUS COUNTRIES
Location
North America
United State*
Alabama
Art con*
Arkansee
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illlnola
Indiana
Iowa
Kanaaa
Kentucky
Louie Ian a
Main*
Maryland
Massachusetts
Michigan
Mlnneaoea
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
Couth Dakota
Tenneaeee
Texae
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Canada
Mexico
Cuba
Fluoride
Average
0,10
0.12
0.09
0.21
0.20
0.49
0.25
0.)
0.11
0.04
0.12
0.22
0,16
0.11
0,08
0,09
0.13
0.17
0.03
0,06
0.08
0,41
0,02
0.12
0.14
Range
0-6,8
'1,0-33.3
0,0-3.0
0-7
0-5
0-0,4
0-0,2
0-2,5
0.0-2,0
0-2,22
0.3-5.0
0-4,0
0-2.0
0-2.8
0-10.0
0-3.9
0-6.0
0-0.4
0-5
0-8
0-2.0
0-3,2
0-6.0
0-5,0
b
0-2
0-9
0-0,5
0-2.1
0-12.0
0-1.3
0-4.2
0-7.5
0-3.0
0-2,4
0-0.5
0-2,0
0-0.8
0-7.0
0-1.2
0-2.0
0-7.2
0-5
0-0.1
0-7.5
0-5,0
0-0,6
0-2,0
0,1-1,2
0-1.2
0.1-17.5
0-0.4
Locat Ion
South America
Argentina
Brail 1
Ecuador
Peru
Europe
Austria
Belgian
Cyprus
Ccechos lovskls
England
Finland
France
Germany
Hungary
Ireland
Italy and
Sicily
Luxembourg
Netherlands
Norway
Poland
Portugal
Russia
Spain
Sweden
Bwltierland
Yugoslavia
Africa
South Africa
East Africa
(Kenya)
Tanganyika
Asia
Chins
India
Japan
Korea
Israal
Iran
Australia
New Guinea
Papua
New Zealand
Fluoride (ppm)
Average Range
0-1,6
0-0.60
0-6.3
0-1.4
0.38-0.8
0-1.68
0-3.6
0-28,00
0-4,5
0.57
0-7
0-4.90
0-5.14
0-0,2
0-7.1
0.02*1,23
0-2
0.01-0.07
0-1.1
-22.8*
0-4.6
0.0-6,3
0,0-1.12
0.01-1,42
0-4,16
Trace- 33.0
0-<30
Traca-95
0-13,0
0->3,0
0.02-20.0
0,8-10,0
0.3-1,50
0.0-<1,0
0,0-13.5
0.0-<0,55
0.0-<0,55
0-0.9
^Mineral waters only.
No records.
Sources Adapted from Cholok, 1939, Table VII, p.
of the publisher.
505, Reprinted by permission
-------
373
83 million persona were being served by artificially fluoridated systems
In the United States as of 1970. The U.S. Public Health Service limit for
fluoride In drinking waters varies, baaed on the annual average maximum
dally air temperature (Table 7.11), because water consumption Increases In
warmer weather. Most U.S. water supplies (Figure 7.3) meet the U.S. Public
Health Service criteria for fluoride. Eastern and central U.S. water sup-
plies sampled In the 1940s contained a mean of 0.3 ppra (Kehoe, Cholak, and
Largent, 1944). A 1962 survey (Durfor and Becker, 1964) of public water
supplies of the 100 largest U.S. cities showed 0.0 to 7.0 ppm fluoride,
with a mean of 0.4 ppm. Of the systems sampled, 92% contained less than
1 ppm. In 1970, McCabe et al. (1970) found that 52 of 969 U.S. supply
systems exceeded the recommended limit, and 24 exceeded the mandatory
limit. The maximum fluoride concentration encountered was 4.4 ppm.
TABLE 7,11. U.S. PUBLIC HEALTH SERVICE
RECOMMENDED LIMITS FOR FLUORIDE CONCENTRATION
Annual average
of maximum daily
air temperatures
Recommended fluoride
control limits
(mg/liter)
Lover Optimum Upper
50,0-53.7
53.8-58.3
58.4-63.8
63.9-70.6
70.7-79.2
70.3-80.5
0.9
0.8
0.8
0.7
0.7
0.6
1.2
1.1
1.0
0.9
0,8
0.7
1.7
1.5
1,3
1.2
1.0
0.8
Source; Adapted from U.S. Department of
Health, Education, and Welfare, 1962, Table 1,
p. 38.
Seawater usually contains more fluoride than freshwater, averaging
about 1.4 to 1.5 ppm In waters of normal salinity (Bowen, 1966; Carpenter,
1969; Goldechmldt, 1954; Rlley, 1965). Waters that art- highly saline ex-
hibit Increased fluoride concentrations. The Great Salt Lake, Utah, con-
tains 14 ppm fluoride. Highly saline lakes In Kenya, Africa, contain up
to 1627 ppm (Worl, Van Alstlne, and Shawe, 1973).
Thermal waters are also enriched in fluoride. Hot waters In areas of
recent volcanlsm, with pH 5 to pH 9, contain 1 to 12 ppm fluoride (Mahon,
1964). Warmwater springs also have an upper limit of about 12 ppm. Acid
springs In active volcanic areas may contain 5000 to 6000 ppm fluoride.
Sediments often become a sink for fluoride. Total fluoride In recent
oceanic sediments ranged from 450 to 1100 ppm (Carpenter, 1969), with an
average of about 730 ppm (Worl, Van Alstlne, and Shawe, 1973). The fluo-
ride contents of sediments from the Pacific, Atlantic, and Indian oceans
-------
ES 80-10475
OJ
Figure 7.3. Maximum fluoride content of U.S. waters (by counties). Source: Adapted from
Fleischer and Robinson, 1963, Figure 3, p. 69.
-------
375
appeared to be identical (Shishkina, 1966). There is no apparent differ-
ence in the fluoride content of bottom sediments of freshwater and salt-
water lakes (Mun, Bazilevich, and Budeyeva, 1966).
Pore solutions extracted from sediments are enriched in fluoride.
Interstitial waters in Georgia salt marshes show fluoride enrichment when
compared with surface waters of the same chlorinity (Windom, 1971). The
enrichment mechanism is thought to result from the uptake of fluoride from
water by plants, followed by release of the fluoride to the sediments after
plant death.
7.3.4 Distribution in Air
Fluorides enter the atmosphere as elemental fluorine, soluble gaseous
fluorides (e.g., hydrogen fluoride), or soluble dusts (e.g., sodium fluo-
ride) and insoluble dusts (e.g., cryolite) (Hodge and Smith, 1970). The
fluoride concentration in ambient air depends on the amount of fluoride
emitted, the distance from the source, the meteorological conditions, and
the topography of the area (Davis, 1972). Total U.S. atmospheric fluoride
emissions were about 150,500 metric tons per year as of 1970 (Smith and
Hodge, 1978).
In rural areas where no industrial contamination exists, the atmos-
pheric fluoride concentration is very low (fractions of a part per billion)
(Hodge and Smith, 1972); urban air normally contains from less than 0.1
to 2.4 ppb (Tables 7.12 and 7.13) (Hodge and Smith, 1970). During 1966
to 1968, the National Air Surveillance Network collected over 11,300 24-
hr samples of suspended particulates at urban and nonurban sites (Table
7.14). Of all urban measurements, 88% were below the limit of detection
(0.05 yg/m3) while over 98% of nonurban samples were below the limit. No
geographic pattern of fluoride occurrence could be established (Thompson,
McMullen, and Morgan, 1971).
Due to the burning of coal and other fossil fuels, atmospheric fluo-
ride usually increases during the winter months. For example, during one
nonheating season the atmosphere of British cities contained an average
of about 0.03 yg/m3. The fluoride concentration during the heating season
averaged about 0.05 yg/m3 (Lee et al., 1974). A similar winter increase
is found in National Air Sampling Network data for 1953 to 1957 (U.S.
Department of Health, Education, and Welfare, 1958) and in a study by
Schneider (1968).
Fluoride is often concentrated in atmospheres near industrial opera-
tions (Table 7.15). Before controls were instituted, an aluminum plant in
Oregon once released an average of 3175.2 kg (7000 Ib) of fluoride per day
(Savara, Noyes, and Suher, 1954). Since that time, controls have greatly
reduced emissions. Schneider (1968) measured airborne fluorides near in-
dustrialized Duisburg, Germany, and found that 90% of the samples contained
0.5 to 3.8 yg of fluoride per cubic meter, with a mean of 1.3 yg/m3. Air
near an aluminum reduction plant in Scotland contained 220 yg/m3 (Agate et
al., 1949). One mile from the factory the concentration dropped to 40
yg/m3. Hluchan, Mayer, and Abel (1968) found an average of 140 yg/m3 near
-------
376
TABLE 7.12. FLUORIDE IN PARTICULATE
MATTER COLLECTED FROM THE AIR OF
U.S. CITIES
Average
City fluoride value
(ppm)
Los Angeles 0.45
Los Angeles (1954) 1.10
Detroit 0.05
Philadelphia 0.29
Chicago 0.04
New York 0.25
Cincinnati 0.25
Kansas City 0.01
Portland 0.00
Atlanta 0.06
Houston 0.00
San Francisco 0.45
Minneapolis 0.07
Charleston 0.00
Louisville 0.00
Pasadena 0.50
Source: Adapted from Cholak, 1959,
Table II, p. 502. Reprinted by permission
of the publisher.
TABLE 7.13. THE OCCURRENCE OF FLUORIDE IN
THE ATMOSPHERE OF SOME U.S. COMMUNITIES
Fluoride (ppb)
vocation
Cincinnati (1957)
New York
Yonkers (summer)
Spokane
Portland, Oregon
Rural
Salt Lake City
Logan, Utah
Canada-Washington Border
San Francisco area
Mean
0.35
2.0
1.6a
0.3
0.02
0.3a
Range
0.04-1.20
0.2-0.4
0.6-0.8
0.05-1.0
0.2-0.4
Single determination.
Source: Adapted from Cholak, 1959,
Table III, p. 502. Reprinted by permission
of the publisher.
-------
377
TABLE 7.14. FLUORIDE IN URBAN AND NONURBAN U.S. AIR, 1966-1968
Number of samples with fluorine
Year
1966
1967
1968
1966-1968
1966
1967
1968
1966-1968
Number
of
stations
100
122
147
29
30
29
Number
of
samples
2521
2967
3687
9175
711
729
724
2164
content in the
<0.05
Pg/m9
Urban
2161
2612
3287
8060
Nonurban
687
721
724
2132
0.05-
0.09
Pg/m9
152
134
103
389
24
5
0
29
ranges
0.10-
0.99
Pg/ms
206
212
290
708
0
3
0
3
shown
1.00
2
9
7
18
0
0
0
0
Maximum
fluoride
content
(Pg/m3)
1.89
1.74
1.65
0.09
0.16
<.05
Source: Adapted from Thompson, McMullen, and Morgan, 1971, Table IV, p.
486. Reprinted by permission of the publisher.
-------
378
TABLE 7.15. FLUORIDES IN AIR NEAR INDUSTRIAL OPERATIONS
Operation
Airborne fluoride
Chemical manufacturing including A1F,,
aluminum metal in or near Odda, West-
ern Norway
Aluminum smelter on Tlwai Peninsula
opposite Bluff, New Zealand
Aluminum works, lower Fricktal,
Switzerland
Aluminum reduction plants near Massena,
New York
Aluminum reduction plant
Brick works
Gaseous diffusion for separation of
uranium isotopes
Glazed tile manufacturing
Phosphate fertilizer manufacturer,
gypsum pond, Manatee County, Florida
Phosphoric acid manufacturing
Steel manufacturing
Maximum dally concentrations 5-103 ug
F/m1, mean concentrations 2.6-15.7 ug
F/m', summer 1972, within 5 km
0.3-0.A ppb, 4-km downwind
0.012-0.185 mg accumulated per month per
dm1 of sampler filter surface. Amounts
varied with distance from source and
wind direction.
53 seven-day ambient air samples col-
lected at six sites over a period of
approximately 10 weeks, range 0.1-2.0
ppb
Lime-impregnated paper samplers during a
12-month period at three sites prior to
start-up showed 0.2-0.5 ug/dm1 per day,
mean 0.35 ug/dm1 per day; 1.6-4.6 km
north of plane. Samples at all sites
increased to a maximum of 5 ug/dm1 per
day after completion of start-up.
Background levels 5 km from plant
Mean of 31 samples 500 m NE of plant, 6.4
ug F/m1
Mean of 12 samples 1000 m NE-NNE of
plant, 1.9 ug F/m'
Mean of six samples 300 m S-SSE of plant,
1.4 ug F/m'
Total of 572 samples collected at four
locations. Maximum concentrations at
different sites, 4 ± 0.3 to 5 t 0.4 ppb
F; means at different sites, 0.8 i 0.1
to 1.0 i 0.2 ppb F
0.020-0.043 ppm in the environmental air
Pond water, 2810-5150 mg F/liter, evolv-
ing up to 0.094 Ib F/acre per day
20 kg F discharged dally to atmosphere;
10Z as apatite, 90Z in gaseous state as
SIP* and HF. 0-10 ug/m* in an area of
15.2 km1 over ten-year period
0.211-1.012 ug F/m'
Source: Adapted from Smith and Hodge,
permission of the publisher.
1978, Table 10, p. 301. Reprinted by
an aluminum factory in Czechoslovakia. Averages up to 3.90 yg/m3 were
recorded near Jacksonville, Florida, phosphate plants (Sheehy et al.,
1963). Before these plants began operations, averages up to only 1.79
pg/m3 were recorded.
The fluoride released during aluminum production is primarily in
particulate form. Total fluoride emitted by a Maryland aluminum plant
is composed of 64% particulate, 23% fluoride attached to particulate,
and 13% free gaseous fluoride (Israel, 1974). A similar distribution
was reported by Okita et al. (1974).
Emissions of fluorides in other selected industrial operations are
discussed by Kaltreider et al. (1972), Krechniak (1969), Leidel et al.
(1967), Luxon (1963), and Smith and Hodge (1978).
-------
379
Attention has recently been focused on the concentrations of fluoro-
carbons present in the atmosphere. Important among these are Fluorocarbon
11 (CFC13) and Fluorocarbon 12 (CF3C12). Fluorocarbon 11 is used mainly
as an aerosol propellant and a blowing agent for foam products. Fluoro-
carbon 12 is used in refrigeration and cooling systems (Anonymous, 1975a).
Both of these compounds are found in concentrations of 0.05 to 0.1 ppb in
air of remote areas and up to several tenths parts per billion in urban
areas (Howard and Hanchett, 1975). Approximately 250 x 106 kg (551 x 106
lb) of fluorocarbons was released to the atmosphere from the United States
in 1972 (Figure 7.4), and losses from non-U.S. sources are believed to be
of similar magnitude.
600
ORNL-DWG 79-20885
500
T 400
o
o>
"b
£ 300
>
o 200
100
u.s. TOTAL;
OTHER
ENVIRONMENTAL
RELEASE-
1
0»
o*
0»
o*
0»
I
OTHER
1940
1950
1960
1970
1980
-1990
Figure 7.4. U.S. production and environmental release of fluorocar-
bons. Data to 1972 based on known production information. Trends were
extrapolated to 1978, and then release calculations were made on the basis
of the following assumptions: (1) zero production after 1978 (ooooo) and
(2) no aerosol propellant use, with production for refrigerant and other
uses remaining equal to the 1978 levels (). Source: Adapted from
Howard and Hanchett, 1975, Science, Vol. 189, 18 July 1975, Figure 1,
p. 217. Copyright 1975 by the American Association for the Advancement
of Science. Reprinted by permission of the publisher.
-------
380
The high stability of fluorocarbons released to the environment allows
them to diffuse to the upper atmosphere where they may be involved in the
destruction of stratospheric ozone (Os). In laboratory studies, Fluoro-
carbon 11 and Fluorocarbon 12 decompose in the presence of high energy
ultraviolet radiation (as in sunlight) to yield intermediate carbene and
chlorine atoms. The liberated chlorine atoms catalyze reactions that
destroy 03 (Anonymous, 19752?; Cicerone, Stolarski, and Walters, 1974;
Cicerone, Walters, and Stolarski, 1975; Molina and Rowland, 1974). It
has not been conclusively determined to what extent these reactions occur
in the stratosphere (Interagency Task Force on Inadvertent Modification
of the Stratosphere, 1975; Interdepartmental Committee for Atmospheric
Sciences, 1975). If ozone is destroyed faster than it is formed by nat-
ural reactions, increased radiation will be allowed to reach earth,
resulting in a health hazard.
Due to the potential health risk, the nonessential use of fluoro-
carbons in aerosol sprays was banned in the United States in 1978. Even
with this curtailment, however, about 100 x 1Q6 kg (220 x 10* lb) will be
emitted annually during the next ten years (Figure 7.4). Furthermore, to
be effective, a worldwide fluorocarbon ban must be implemented. Howard
and Hanchett (1975) concluded that "restrictions of fluorocarbon produc-
tion and use in the United States would only partly reduce, rather than
end, destruction of stratospheric 03, if, in fact, the chlorine-catalyzed
03 destruction due to fluorocarbon compounds can exceed all natural sinks
of stratospheric 03."
7.4 ENVIRONMENTAL FATE
7.4.1 Mobility and Persistence in Soils
In alkaline soils, fluoride usually precipitates as calcium fluoride
or forms soluble compounds with group I cations and magnesium (Mg), calcium
(Ca), strontium (Sr), or barium (Ba) (Murrmann and Koutz, 1972). Soluble
fluoride compounds are almost completely fixed in soils of pH 6.5 or above
if sufficient calcium carbonate (CaC03) is available (Brewer, 1966). In
situations where liming is not desirable, gypsum (CaS04) or some other
neutral calcium salt will accomplish the same result. If adequate calcium
is not present, fluoride may be fixed as aluminum silicofluoride (Maclntire
et al., 1949). Sandy acidic soils favor development of soluble forms of
fluoride (Shacklette, Boerngen, and Keith, 1974).
Fluoride tends to persist in most soils; it is strongly absorbed by
soil colloids and cannot be displaced by common anions such as chloride or
sulfate (Murrmann and Koutz, 1972). Maclntire, Sterges, and Shaw (1955)
studied the retention of fluoride by four acidic soils over a four-year
period (Table 7.16). The retention of fluoride was proportional to soil
aluminum content; it was immobilized as the insoluble aluminum silicofluo-
ride. Inputs of 2237 kg (4932 lb) of CaFa to phosphatic soils over a ten-
year period resulted in leaching losses of only 2.5% of the added fluoride
(annual rainfall of 129.5 cm, or 51 in.). Only after seven years did
drainage waters contain as much as 1 ppm fluoride.
-------
381
TABLE 7.16. FLUORIDE RETENTION FROM 200- AND 800-Ib APPLICATIONS OF HYDROFLUORIC ACID IN POUR SOILS
HP addition
Annual outgo of fluorine (Ib per 2,000,000 Ib of soil)
Rate0
Depth
1st
2nd
3rd
4th Total
Increase
(Ib) «
Retention
(Ib) OO
Final
Hartsells sandy loan
None
200
200
800
800
To
In
To
In
surface
full depth
surface
full depth
1.1
1.1
4.5
3.5
79.4
0.7
1.0
2.3
4.4
17.2
0.8 0.5
1.6 1.2
4.0 3.7
12.4 16.6
28.2 23.4
3.1
4.9
14.5
36.9
148.2
1.8
11.4
33.8
145.1
0.9
5.7
4.2
18.1
198.2
188.6
766.2
654.9
99.1
94.3
95.8
81.9
4.1
4.2
4.1
4.3
4.4
Clarksvllle silt loam
None
200
200
800
800
None
200
200
800
800
None
200
200
300
800
To
In
To
In
To
In
To
In
To
In
To
In
surface
full depth
surface
full depth
surface
full depth
surface
full depth
surface
full depth
surface
full depth
1.2
3.8
7.3
126.3
139.6
3.5
2.5
5.0
3.0
10.0
4.9
6.6
7.7
48.0
73.1
0.8
1.9
3.1
23.9
20.3
1.1
1.2
2.0
2.0
4.3
1.3
4.4
4.1
15.9
31.1
0.9 0.5
1.3 0.6
2.7 2.3
23.6 17.5
20.0 16.6
Haury silt
1.7 0.7
3.6 0.8
2.4 1.1
4.5 0.8
4.6 3.6
Baxter silt
1.7 0.8
3.6 2.9
5.6 4.3
19.8 17.9
27.6 26.7
3.4
7.6
15.4
191.3
196.5
loam
7.0
8.1
10.5
10.3
22.5
loan
8.7
17.5
21.7
101.6
158.5
4.2
12.0
187.9
193.1
1.1
3.5
3.3
15.5
8.8
13-0
92.9
149.8
2.1
6.0
23.5
24.1
0.6
1.8
0.4
1.9
4.4
6.5
11.6
18.7
195.8
188.0
612.1
606.9
198.9
196.5
796.7
784.5
191.2
187.0
707.1
650.2
97.9
94.0
76.5
75.8
99.6
98.3
99.6
98.1
95.6
93.5
88.4
81.3
4.5
4.8
4.6
4.8
4.9
5.2
5.2
5.2
5.0
5.1
4.9
4.8
4.6
4.5
4.5
^Pounds of fluorine per 2,000,000 pounds of soil.
Respective to 200- and 800-Ib additions of fluorine.
"initial pH values: Hartsells, 5.40; Clarksville, 5.6; Haury, 5.3; and Baxter, 5.2. Rainwaters per
annum for the four successive years were 57.5, 39.9, 44.0, and 40.7 in. respectively. Drainage waters were
in range of 45Z to 50Z of precipitation.
Source: Adapted from Maclntire, Sterges, and Shaw, 1955, Table III, p.
of the publisher.
780. Reprinted by permission
The amount of fluoride removed from soils by seepage water is small.
Oelschlager (1971) collected groundwater samples from 30 widely separated
forest and agricultural areas in Germany. Fluoride removed in seepage
varied from 20 to 400 g/ha (0.02 to 0.4 Ib/acre), or about 0.5% to 6.0%
of the yearly added increment.
7.4.2 Mobility and Persistence in Water
In water, fluoride exists in both dissolved and undissolved forms.
The undissolved fluoride, transported in or on clay minerals suspended in
the water is eventually removed by sedimentation (Hamilton, 1974). Dis-
solved fluorides are usually present as the fluoride ion F~, particularly
in dilute solutions and at neutral pH (Borei, as cited in Largent, 1970).
As pH increases, the proportion of F~ decreases while HFa~ and undissoci-
ated HF increase. Dissolved fluorides readily precipitate as sediments
in waters high in calcium. In marine waters, about 4 * 10xl g of fluoride
per year are removed by incorporation into calcium carbonates (Table 7.17).
Incorporation into calcium phosphates is apparently the second most impor-
tant removal process. Assuming that the removal of fluoride from seawater
-------
382
TABLE 7.17. RATES OF REMOVAL OF FLUORIDE
FROM SEAWATER DUE TO INCORPORATION INTO
VARIOUS MINERALS
Fluoride
Mineral removal rate
(g/year)
Calcium carbonate 4.0 x io11
Calcium phosphates <2.6 x io11
Authigenic montmorillonites
-------
383
TABLE 7.18. FLUORIDE WASTE TREATMENT PROCESSES
Process
Lime addition
Alum coagulation
Hydroxylapatlte beds
Synthetic
Bone char
Alumina contact beds
Initial fluoride
concentration
(rag/liter)
1000-3000
1000-3000
500-1000
3.6
12-13
10
6.5
9-12
8
9
20-40
Final fluoride
concentration
(mg/liter)
10
20
7-8a
20-40
0.6-1.5
0.5-0.7
1.6
1.5
0.6
1
1.3
2-3
Current
application
Industrial
Industrial
Industrial
Industrial
Municipal
Municipal
Municipal
Municipal
Municipal
Municipal
Industrial
(lab scale)
Industrial
After 24-hr settling.
Source: Adapted from Watson, 1973, Table 36, p. 179.
permission of the publisher.
Reprinted by
compounds (Staebler, 1974, 1975; Watson, 1973; Zabban and Jewett, 1967).
Further reductions (down to about 1 mg/liter) are affected by the addition
of a second chemical such as magnesium hydroxide or aluminum sulfate
(Miller, 1974; Skripach et al., 1970; Watson, 1973). The fluoride sludge
resulting from the operations is normally disposed of as landfill (Ottinger
et al., 1973).
Other techniques involve passage of gaseous- or liquid-fluoride
wastes through a contact bed or slurry. The fluoride is removed by reac-
tion with the bed matrix. Bed media include hydroxyapatite, ion exchange
resins, activated alumina, iron, and charcoal (Kelly, 1974; Navratil,
1968; Ottinger et al., 1973; Reiter, 1972; Skripach et al., 1970; Watson,
1973).
-------
384
SECTION 7
REFERENCES
1. Abernethy, R. F., and F. H. Gibson. 1963. Rare Elements In Coal.
Bureau of Mines Information Circular 8163, U.S. Department of the
Interior, Washington, D.C. pp. 20-21.
2. Agate, J., G. Bell, G. Boddie, R. Bowler, M. Buckell, E. Cheeseman,
T. Douglas, H. Druett, J. Garrad, D. Hunter, K. Perry, J. Richardson,
and J. de V. Weir. 1949. Industrial Fluorosis. A Study of the
Hazard to Man and Animals near Fort William, Scotland. A Report to
the Fluorosis Committee, Medical Research Council Memorandum 22, His
Majesty's Stationery Office, London. 131 pp.
3. Anonymous. 1975a. NBS Research Details Fluorocarbon Breakdown in
Upper Atmosphere. J. Air Pollut. Control Assoc. 25(10):1060-1061.
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SECTION 8
ENVIRONMENTAL INTERACTIONS AND THEIR CONSEQUENCES
8.1 SUMMARY
Fluoride cycles naturally among the lithosphere, atmosphere, hydros-
phere, and biosphere. Man's activities, however, have resulted in new
routes of fluoride transfer as well as additional flow through existing
paths.
Food and water normally provide nearly all man's fluoride intake,
and most foods and beverages contain fluoride in at least minute amounts.
Certain foods and food products, such as seafoods, bonemeal, and tea, con-
tain higher than normal levels. With these exceptions, food averages 0.1
to 0.3 ppm fluoride; consequently, dietary intake of fluoride is small
and relatively constant, usually ranging from 0.20 to 0.80 mg/day in the
United States.
A slow but steady accumulation of fluoride occurs in most animals.
The increase is restricted almost entirely, however, to the skeletal tis-
sues. Biomagnification of fluoride occurs at the lower end of the food
chain; however, because fluoride is largely localized in skeletal tissues
the uptake of fluoride in humans or other animals near the top of the
food chain is not materially increased.
8.2 ENVIRONMENTAL CYCLING OF FLUORIDE
The environmental cycle for fluoride is presented in different ways
in Figures 8.1 and 8.2. In the natural cycle, fluorides move from the
i. -y
OCFOUTIONOFy
HDIMENTS
Figure 8.1. Environmental transfer of fluoride. Source: Reprinted
from Fluorides, Publ. 1922, p. 30, with the permission of the National
Academy of Sciences, Washington, D.C.
392
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393
ORNL-DWG 79-20897
'GASEOUS F
PARTlCULATf. F
RIVERS/ LAKES GROUND WATER
EXCRETA
VOLCANO
TLCHNOLOGY
Figure 8.2. Dispersion of fluoride in the biosphere. Source:
Hodge and Smith, 1972, Figure 1, p. 164. Reprinted by permission of the
publisher.
lithosphere to the atmosphere by way of volcanism or entrainment of soil
particles. Routes from the hydrosphere to the atmosphere include vapori-
zation and aerosol formation. Atmospheric fluoride returns to the hydros-
phere and lithosphere in precipitation or by deposition of particulates.
Fluoride also travels from the lithosohere to the hydrosphere by leaching
and erosion and returns by sedimentation (National Academy of Sciences,
1971).
The biosphere serves as an intermediate repository for part of the
fluoride that passes from the atmosphere to the lithosphere. Fluoride
in vegetation is returned directly to the lithosphere in plant wastes or
enters the food chain and is returned in animal wastes.
Man's activities result in new routes of fluoride transfer and addi-
tional flow in the existing ones. For example, industrial processing
involving fluorides results in a direct atmospheric emission, and lithos-
pheric fluoride is increased by industrial effluents and waste waters,
resulting in an increase in the fluoride burden of other phases of the
environment (National Academy of Sciences, 1971).
8.3 FLUORIDE IN FOODS
The principal sources of fluoride intake for humans are food and
water. Factors affecting the fluoride content of foods include the local-
ity in which the food is given, the amount of fertilization and spraying
received, the type of food processing, and whether fluoridated water is
used in preparation (McClure, 1949; Myers, 1978; Waldbott, 1963). These
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394
factors change from place to place, resulting in varying amounts of fluo-
ride in foods produced in different localities. The extent of these
effects on the concentration of fluoride in U.S. foods can be seen in
Table 8.1. In general, recent analyses of edible red meat show only a
few parts per million of fluoride. Cereals usually contain less than 1
ppm, but samples containing 20 ppm have been reported. Vegetables and
tubers usually range from 0.1 to 0.4 ppm; hen eggs, 0.1 to 0.6 ppm; cow
milk, 0.1 to 0.6 ppm; nuts, 0.1 to 1.5 ppm; and fruits, less than 1 ppm
(Cholak, 1959; Hodge and Smith, 1972; McClure, 1949). Average concen-
trations of fluoride in foodstuffs from India appear somewhat higher
(Lakdawala and Punekar, 1973; Nanda, 1972; Sengupta and Pal, 1971). Bev-
erages, with the exception of tea which contains up to 0.52 yg of fluoride
per cup (Cook, 1969), are not important sources of fluoride (Table 8.1).
A few wines contain up to 6 ppm fluoride, but most contain less than 1
ppm (Hodge and Smith, 1970).
TABLE 8.1. FLUORIDE CONTEXT OF VARIOUS FOODS AND BEVERAGES
Food or
beverage
Wheat
Rye
Barley
Oat
Rice
Polished rice
Potato
Carrot
Lettuce
Spinach
Bean
Parsley
Citrus fruits
Other fruits
Dried plums
Apples
Pears
Oranges
Beverages ,
Tea, leaf
Georgian
Indian
Ceylon
Drink, 1 cup
Coffee
Wine and beer
White wine
Red wine
Nuts
Fluoride content
0»8/kg)
Cereals
0.1-1.2"
0.26-1.3
0.1-4.0
0.18-3.15
0.42-7.1
0.30
0.4-4.8
0.18-0.78
21.2
11.4
Vegetables
0.12-2.9
0.07-6.4
0.1-1.1
0.19-0.60
0.22-2.00
0.18-0.42
0.44-6.4
0.1-20.3
0.26,,
13.6fl
0.11-0.15
0.35
Fruits
0.03-0.36
0.07-0.36
0.11-1.32
0.35-2.1
0.08
0.61-0.64
1.07-1.11
0.31-0.41
spices, and products of
3.2-398.8
120
89
82.0
0.5
0.2-1.6
0.07-0. 24*
0.20-1.7*
0.084-0. 94"
0.3-1.5
Mean fluoride
content
Cog/kg)
0.93
1.53
1.18
0.45
U.56
0.28
0.28
2.82
vegetable origin
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395
TABLE 8.1 (continued)
Food or
beverage
Crude tea salt
(Indian)
Crude sea sale
(Greek)
Purified aea salt
(Greek)
Heats ,
Broiler
Mucton
Beef
Pork
Liver (beef)
Kidney (beef)
Hearc (beef)
Liver (pig)
Eggs
Milk
Cheese
Butter
Kefir
Fluoride content
(Bg/kg)
35-55
18-20
4
dairy products, and eggs
1.4
1.20
0.20-2.00
0.20-3.30
5.20-5.80
6. 90- 10. 10
2.30-2.70°
0.29
1.2
0.20-0.40
0.21-0.27.
0.09-0.32?
0.09-0.36?
0.06-0.10?
0.07-0.22
1.62
0.16-1.32
1.50 .
0.06-0.10^
Mean fluoride
content
(mg/kg)
Fish, fish products, and crustaceans
Codfish, fresh
Fillet
Haddock (fillet)
Herring (cleaned)
Herring (fillet)
Herring (Atlantic)
Tuna
Anchovy (In oil)
Sardine (In oil)
Mackerel
Fish scales
Clam
Shrimp
Sea urchin
Lobster
Fish protein
concentrate
frag /kg dry weight.
mg/llter.
3.73-4.34
1.9-3.2
2.7
5.06
28.5
5.36
2.3
3.52-4.00
2.83-3.18
5.0
4.12-4.40
3.19-3.89
5.0-10.0
1.34-1.83
2.27-2.53
2.87-3.20
1.99-2.18
20-760a
Source: Adapted from Kumpulalnen and Koivistoinen, 1977,
Tables V-IX, pp. 43-47. Data collected from various sources.
Reprinted fay permission of the publisher.
Certain foods and food products tend to be enriched in fluoride.
Seafoods, particularly fish and crustaceans, contain high concentrations
of fluoride due to constant exposure to seawater (Cholak, 1959). Animal
products such as bonemeal and gelatin are rich in fluoride because they
are made from skeletons and hides, which accumulate fluoride (Section 5)<
Fish protein concentrate contains as much as 761.0 ±0.1 ppm fluoride
(Ke, Power, and Regier, 1970); however, studies by Zipkin, Zucas, and
Stillings (1970) indicated that the fluoride in fish protein concentrate
is only one-fourth to one-half as available for deposition in various
hard tissues and the whole bodies of rats as is sodium fluoride.
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396
Commercially prepared baby foods may have relatively high concen-
trations of fluoride. Some samples of Pablum contained 4 to 12 ppm,
and orange juice and formula contained up to 1.0 ppm (Farkas and Farkas,
1974; Tinanoff and Mueller, 1978; Wiatrowski et al., 1975). Ericsson
and Ribelius (1971) reported formula preparations with up to 53 times
the fluoride levels of mother's milk. Ham and Smith (1950) calculated
that a four-month-old infant received 0.46 mg of dietary fluoride per
day. Wiatrowski et al. (1975) analyzed many baby foods and concluded
that dietary intake of fluoride ranged from 0.32 mg/day for one- to four-
week-old infants to 1.23 mg/day for infants four to six months of age.
These intakes may be compared with recommended fluoride intakes of 0.5
mg/day for children from infancy to three years of age that live in areas
where water is not fluoridated (Committee on Nutrition, 1972; McClure,
1970). Adair and Wei (1978) also concluded that infants fed with com-
mercially prepared formulas may be receiving fluoride in excess of rec-
ommended optimal daily doses.
Foods characteristically high in fluoride include seafood, bone
products, and tea. Foods with typically low fluoride content include
most fruits and vegetables. With these exceptions, foods produced far
from point sources of fluoride usually average 0.1 to 0.3 ppm fluoride
(Cholak, 1959). Foods grown near fluoride-emitting factories often con-
tain higher than normal concentrations of fluoride. For example, unwashed
winter cabbage grown near point sources in the Stoke-on-Trent area (Eng-
land) during 1965-1966 averaged 12.7 ppm fluoride (dry-weight basis), and
some unwashed summer lettuce from the same area contained almost twice
this concentration of fluoride (Jones, Harries, and Martin, 1971).
Many foods receive additional fluorides during processing, primarily
due to the use of fluoridated water (Table 8.2). Uptake of cooking-water
fluoride by vegetables is proportional to the fluoride content of water
TABLE 8.2. FLUORIDE CONTENT OF VARIOUS FOODS AND REVERACES
PROCESSED IN EITHER FLUORIDATED OR UNFLUORIDATED WATER
Food or beverage
Pork and bean*
Tomato aoup
Ginger ale
Bxtr
Mixed vagetablea
Green beene
Whol* potatoea
Diced carroti
Kernel corn
Grant paaa
Wax baana
Fluorlda
Unfluorldatad
watar
Liquid
0.04
0.02
0.30
0.30
O.U
0.13
0.30
0.10
0.15
Solid
0.27
0.37
0.20
O.J8
0.19
0.20
0.10
contant (pp*>)
Fluoridated
watar
Liquid
0.38
0.77
0.68
1.03
0.71
0.87
0.55
0.48
0.49
0.77
Solid
0.77
1.05
0.89
0.76
0.61
O.J6
0.60.
0.73*
Difference
(pp-)
+0.50
40.34
40.73
40. 38,,
40.68°.
40.69"
*0.38»
40.42°
40.36°
£Solid
Thla aaapla of wax bean waa aent aa an unfluorldated "control"
Howevar, aubaequent Investigation revealed that the product
had been proceeeed In a cannery uelng wall water containing 1.2 ppa)
F".
Source: Adapted from Harler and Roae, 1966, Food Technology/
Journal of Food Science, Vol. 31, pp. 941-946. Copyright by Inatl-
tute of Food Technologlate. Reprinted by panieelon of the publlaher.
-------
397
over the concentration range of 1 to 5 ppm, but frozen vegetables absorb
more fluoride than fresh vegetables, and those cooked in a saucepan take
up more fluoride than those cooked in a pressure cooker (Martin, 1951).
In general, water containing 1 ppm fluoride will increase the fluoride
content of processed foods and beverages by 0.5 ppm or more (Auermann,
1973; Marier and Rose, 1966). Thus, food processed with fluoridated water
may contain 0.6 to 1.0 ppm fluoride rather than the "normal" 0.2 to 0.3
ppm, providing an Increase of about 0.5 mg/day in the diet.
Despite the widespread occurrence of fluoride in foods, human intake
through diet is usually small and relatively constant, depending on con-
sumer age and environment (Table 8.3). Daily dietary Intake, Including
TABLE 8.3. ESTIMATED DAILY FLUORIDE INTAKE FROM FOOD AND DRINKING WATER3
Fluoride intake (rag)
Ag*
(years)
1-3
4-6
7-9
10-12
Body
weight
(kg)
8-16
13-24
16-35
25-54
From
drinking
water
0.390-0.560
0.520-0. 745
0.650-0.930
0.810-1.17
From
food
0.027-0.265
0.036-0.360
0.045-0.450
0.056-0.560
Total from
food and
drinking
water
0.417-0.825
0.556-1.11
0.695-1.380
0.866-1.73
Total fluoride
(nig/kg body wt)
0.026-0.103
0.023-0.085
0.020-0.068
0.016-0.069
Food (dry eubttance) contained 0.1 to 1.0 mg of fluoride per liter; drink-
ing water contained 1 mg of fluoride per liter.
Source: Adapted from Maler, 1971, Table 2. p. 390.
drinking water, has been established for many areas of the world (Tables
8.4-8.6). Daily Intake is usually at least 0.2 mg, and in diets rich in
fish, tea, or other fluoride-containing liquids, it can be as high as 5
mg or more (Auermann, 1973; Elliot and Smith, 1960; Prival and Fisher,
1974). Generally, men consume about 1.8 mg of dietary fluoride per day,
housewives about 1.3 mg, and children 5 to 14 years old, 0.6 mg (Cholak,
1960). Young adult males eat more heartily than other subgroups of the
population and consequently ingest more fluoride. In a 1967-1968 study,
the typical young adult U.S. male consumed 2.1 to 2.4 mg of fluoride per
day (San Filippo and Battistone, 1971). However, contemporary U.S. army
field rations contained less than half the fluoride in the typical civil-
ian diet (San Filippo, Battistone, and Chandler, 1972).
8.4 BIOACCUMULATION IN FOOD CHAINS
Ingestion of fluoride-containing materials by animals results in
a small but steady accumulation of fluoride within the body (National
Academy of Sciences, 1971). The fluoride accumulates almost exclusively
in the skeletal system (Hodge and Smith, 1970). Although accumulation
occurs, the overall retention of daily ingested fluoride is low due to
rapid elimination of fluoride by the body (Hodge and Smith, 1970) (Sec-
tion 5).
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398
TABLE 8.4. DAILY DIETARY FLUORIDE INTAKE
FOR VARIOUS COUNTRIES
Country
Canada
England
Japan
Newfoundland
Norway
Russia
Sweden
Switzerland
United States
Fluoride
in food
(rag)
0.18-0.3
0.3-0.5
0.47-2.66
2.74C
0.22-0.31
0.6-1.2
0.9.
°'5
0.2-0. 3d
0.34-0.80
Fluoride
in water
(ppm)
0.1
Trace ,
0.01-0.08°
Trace
0.01-0.07
0.2-0.3
0.1
Including 0.07-0.86 mg from green
tea. ,
Milligrams of fluoride ingested.
^Including 1 mg from tea.
exclusive of that in drinking water.
Source: Adapted from Hodge and
Smith, 1972, Table 2, p. 165. Reprinted
by permission of the publisher.
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399
TABLE 8.5. ESTIMATES OF TOTAL DAILY
FLUORIDE INTAKE IN THE UNITED STATES,
THE UNITED KINGDOM, RUSSIA, AND JAPAN
Daily fluoride intake
Country / x
' per person (mg)
Food
United States'3 0.2-0.3
0.25-0.32
0.45
0.25-0.55*
1.0-2.0°
United Kingdom 0.3-0.5
0.6-1.8d
Russia 1.18
Japan 4.5
Food and fluoridated drinking water
United States 2.5 (av 3.1)
0.34-3.13
United Kingdom 1.2-3.2
5.5
Japan 5.0
Estimates by various researchers.
One- to two-year-old children.
Fluoridated water used in food
preparation and preserving.
^Four beverages.
Source: Adapted from Jones, Harries,
and Martin, 1971, Table II, p. 603.
Reprinted by permission of the publisher.
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400
TABLE 8.6. FLUORIDE IN DIETS IN NORTH AMERICA
Diet
Fluoride
In food
(rag/day)
Fluoride
in liquid
dog/day)
Total
fluoride
(rag/day)
Three meals served to house staff at 0.27-0.32
Minnesota general hospital (excluding
water)0
Dally intake of one person In Cincinnati 0.155 (av) 0.299 (av)?
measured over 20 weeks" 0.54 (max) 0.75 (max)
Three restaurant meals In southern
Ontario0
Estimates from existing data on fluoride 0.2-0.3 1.0-1.5°
content of specific foods; assumed
water contains 1 ppm fluoride
Diets of three young women in Toronto 0.43-0.76 0.0-0.03
avoiding high-fluoride foods such as
fish and tea"
Analysis of market-basket samples
Baltimore"
Dallas"
Atlanta"
Minneapolis"
Four market-basket samples in Baltimore 0.78-0.90 1.3-1.5
(artificially fluoridated to approxi-
mately 1 ppm fluoride)
Calculated from diets of seven labora- 1.0-2.0 1.0-3.2
Cory workers, assuming all food proc-
essed in water at 1 ppm fluoride and
all drinking and cooking water at 1
ppm fluoride
Analyzed diets (designed for low calcium 1.2-2.7 1.6-3.2
content) of ten patients in Hlnes, 2.0 (av) 2.4 (av)
Illinois:.' water fluoridated to 1 ppm
Calculated value for one meal Including
high-fluoride mineral water and fish
0.457 (av)
0.18-0.3
1.2-1.8
0.43-0.79
0.8
0.9
2.1
2.3
2.1-2.4
1.9-5.0
3.6-5.4
4.4 (av)
3.3
?Water low In fluoride (<0.2 ppm).
Including tea.
.Includes water used for cooking as well as drinking.
In Baltimore and Minneapolis, water was fluoridated to approximately 1 ppm
fluoride.
^Reported fluoride levels in Dallas water vary from 0.2 to 0.7 ppm.
/These values are considered atypical by some authorities due to the probable
substitution of fluoridated water for low-fluoride beverages normally consumed by
these patients (Myers, 1978).
Source: Adapted from Prlval and Fisher, 1974, Table 1, p. 30.
Some data exist on fluoride accumulation in plants and animals
(Table 8.7; Sections 4 and 5) (Jones, Harries, and Martin, 1971; Martin
and Jones, 1971; Oelschlaeger, Feyler, and Schwarz, 1972), but there is
an absence of literature on the movement of fluoride in the natural food
chain (Kay, Tourangeau, and Gordon, 1975). Carlson (1973) and Kay et al.
(1975) reported that fluoride ingested by prey species accumulates in
predators that consume the prey. It is assumed that the fluoride in
predators results from consumption of prey skeletons. The retention of
fluoride is not great, however, and animals grown for human consumption
generally do not contain enough fluoride to significantly increase human
uptake (National Academy of Sciences, 1971). Thus accumulation of fluo-
ride through the food chain does not appear to be a serious problem under
normal circumstances.
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401
TABLE 8.7. BIOACCUMULATION OF FLUORIDE IN SELECTED PLANTS AND ANIMALS
Organism Tissue
Lichens Whole plant
Mosses Whole plant
Vegetation (all types)
Fluoride content"
(ppm)
475-990
134-190
70
140-600
78
20
6.1-10.7
10-70
Parameters of exposure
Air, 1-8 Ion from source, 4 or 12 months
Air, 15 km from source, 12 and 4 months
Air, 40 km from source, 4 months, control
Air, 1-4 km from source, 4 or 12 months
Air, 15 km from source, 12 months
Air, 40 km from source, 4 months, control
Control samples
Samples 4-14 miles from source, 200,0004-
Insects
Controls (all types) Whole body
Foliage feeders Whole body
Camblal feeders Whole body
Predators Whole body
Pollinators
Chipmunk
Whole body
Femur
Ground squirrel Femur
Deer mouse Femur
Deer (two species) Femur
Vegetation (all types)
Deer mouse
Shrew
Sparrow
Frog
Grass
Freshwater plants
Water hyacinth
Marine algae (several
varieties)
Eel grass
Femur
Femur
Bones
Bones
Leaf
Petiole
Leaves
100-1000+
3.5-16.5
21.3-255
8.5-52.5
6.1-170
58-585
50-303 (108.7)
200-13,333 (1000)
35-142 (105)
17-7168 (775)
(106.5)
28-6038 (1300)
86-635 (225)
124-9400 (1500)
1.6-6.4 (3.9)
6-456
(144)
288-1995
(494)
1315-10,500
84-565
1013-3527
392-1067
852-7880
10-30
up to 1330
(40.5)
25
60
2-22
0.2
Trace
acres
Samples 2 miles or less from source,
7040 acres
All specimens exposed to fluoride in air
and diets
Captured 50 miles from source
Captured within 1/2 mile of source
Same
Same; primary source of intake, insects
in diet
Same
Controls
Adults from assorted locations in pol-
luted area
Controls
From assorted locations in polluted area
Controls
From assorted locations in polluted area
Controls
From assorted locations in polluted area
Controls
From assorted locations in polluted area,
2 years (samples above 35 ppm all 2.5
km or less from source)
Controls
From assorted locations in polluted area,
2 years
Controls
From assorted locations In polluted area,
2 years
Controls
Captured near factory (aluminum smelter)
Controls
Captured near factory
Controls
Growing near factory
Exposed to water of unknown fluoride
content
Crowing naturally in water at 1 ppm
fluoride
Same
Growing naturally in seawater at 1.08 ppm
fluoride
Kept in seawater at 1.05 ppm fluoride, 72
days
Kept in seawater at 52 ppm fluoride, 72
days
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402
TABLE 8.7 (continued)
Organism
Algae (Cladophora)
Sand shrimp
Mud crab
Prawn
Mullet
Oyster
Blue crab
Brown trout
Trout
Ocean fish (various)
Clover
Spinach
Winter rye
Tissue
Total body
Total body
Total body
Total body
Soft tissues
Exoskeleton
Gills
Muscle
Exoskeleton
Muscle
Bone
Fillet
Soft tissues
Skeletons
Leaf and stem
Leaf
Leaf and stalk
Fluoride contenta
(ppm)
3.2
2.4
106
3116
169.6
1414
374
3248
141.8
7743
4-5
13-18
20-30
50-100
298
253
10
800
21
400-1700
1.3
3.5-5.7
558-6820
6-13
8-17
17-53
62-233
5.3
15.5
41.3
6.0
67.0
158
200
Parameters of exposure
Kept in seawater at 1.05 ppm fluoride, 72
days
Kept in seawater at 52 ppm fluoride, 72
days
Kept in seawater at 1.05 ppm fluoride, 72
days
Kept In seawater at 52 ppm fluoride, 72
days
Kept in seawater at 1.05 ppm fluoride, 72
days
Kept in seawater at 52 ppm fluoride, 72
days
Kept In seawater at 1.05 ppm fluoride, 72
days
Kept in seawater at 52 ppm fluoride, 72
days
Kept in seawater at 1.05 ppm fluoride, 72
days
Kept in seawater at 52 ppm fluoride, 72
days
Kept in seawater at 0. 5 ppm fluoride for
up to 60 days
Kept In seawater at 2.0 ppm fluoride for
up to 60 days
Kept in seawater at 8.0 ppm fluoride for
up to 60 days
Kept in seawater at 32 ppm fluoride for
up to 35 days
Controls, kept In seawater at 0.5-1.5 ppm
fluoride
Same
Same
Kept In seawater at 8 ppm fluoride for 30
days
Same
Living in stream with natural fluoride
content 1-14 ppm
Exposure unknown; assumed to be control
level
Living in seawater, 0.7-1.4 ppm fluoride
Same
Controls
100 ppm fluoride added to soil as NaF,
KF, or cryolite
600 ppm fluoride added to soil as NaF,
KF, or cryolite
1800 ppm fluoride added to soil as NaF,
KF, or cryolite
Control
280 ppm fluoride as NaF added to soil
560 ppm fluoride as NaF added to soil
Control
500 ppm fluoride as NaF added to soil
1000 ppm fluoride as NaF added to soil
1500 ppm fluoride as NaF added to soil
Figures in parentheses are average values, when available.
Source: Adapted from Groth III, 1975, Table 1, pp. 227-228. Data collected from several sources.
Reprinted by permission of the publisher.
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403
SECTION 8
REFERENCES
1. Adair, S., and S. Wei. 1978. Supplemental Fluoride Recommendations
for Infants Based on Dietary Fluoride Intake. Caries Res. 12(2):
76-82.
2. Auermann, E. 1973. Fluoride Uptake in Humans. Fluoride 6(2):78-83.
3. Carlson, C. E. 1973. Fluoride Pollution in Montana. Fluoride
6:127-137.
4. Cholak, J. 1959. Fluorides: A Critical Review. J. Occup. Med.
1:501-511.
5. Cholak, J. 1960. Current Information on the Quantities of Fluoride
Found in Air, Food, and Water. Arch. Ind. Health 21:312-315.
6. Committee on Nutrition. 1972. Fluoride as a Nutrient. Pediatrics
49:456-460.
7. Cook, H. A. 1969. Fluoride in Tea. Lancet (Great Britain) 2:329.
8. Elliott, C., and M. Smith. 1960. Dietary Fluoride Related to Fluo-
ride Content of Teeth. J. Dent. Res. 39(1):93-96.
9. Enno, A., G. Craig, and K. Knox. 1976. Fluoride Content of Prepack-
aged Fruit Juices and Carbonated Drinks. Med. J. Aust. 2(9):340-342.
10. Ericsson, Y., and U. Ribelius. 1971. Wide Variations of Fluoride
Supply to Infants and Their Effects. Caries Res. 5:78-88.
11. Farkas, C. S., and E. J. Farkas. 1974. Potential Effect of Food
Processing on the Fluoride Content of Infant Foods. Sci. Total
Environ. 2:399-405.
12. Groth, E., III. 1975. An Evaluation of the Potential for Ecological
Damage by Chronic Low-Level Environmental Pollution by Fluoride.
Fluoride 8:224-240.
13. Ham, M. P., and M. D. Smith. 1950. Fluoride Studies Related to the
Human Diet. Can. J. Res. 28:227-233.
14. Hodge, H. C., and F. A. Smith. 1970. Minerals: Fluorine and Dental
Caries. In: Dietary Chemicals vs. Dental Caries, R. S. Harris, ed.
Advances in Chemistry Series, No. 94. American Chemical Society,
Washington, D.C. pp. 93-115.
15. Hodge, H. C., and F. A. Smith. 1972. Fluorides. In: Metallic
Contaminants and Human Health, D.H.K. Lee, ed. Academic Press, New
York. pp. 163-187.
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404
16. Jones, C. M., J. M. Harries, and A. E. Martin. 1971. Fluoride in
Leafy Vegetables. J. Sci. Food Agric. 22:602-605.
17. Kay, C. E., P. C. Tourangeau, and C. C. Gordon. 1975. Fluoride
Levels in Indigenous Animals and Plants Collected from Uncontaminated
Ecosystems. Fluoride 8:125-131.
18. Ke, P. J., H. E. Power, and L. W. Regier. 1970. Fluoride Content
of Fish Protein Concentrate and Raw Fish. J. Sci. Food Agric. 21:
108-109.
19. Kumpulainen, J., and P. Koivistoinen. 1977. Fluorine in Foods.
In: Residue Reviews, Vol. 68, F. A. Gunther and J. D. Gunther, eds.
Sprlnger-Verlag, New York. pp. 37-59.
20. Lakdawala, D., and B. Punekar. 1973. Fluoride Content of Water and
Commonly Consumed Foods in Bombay and a Study of the Dietary Fluoride
Intake. Indian Med. Res. 61(11):1679-1687.
21. McClure, F. J. 1949. Fluorine in Foods. In: Public Health Reports.
U.S. Public Health Serv. 64(34):1061-1074.
22. McClure, F. 1970. Water Fluoridation: The Search and Victory.
Government Printing Office, Washington, D.C. pp. 176-190.
23. Maier, F. J. 1971. Fluoridation. Grit. Rev. Environ. Control
2(3):387-430.
24. Marier, J. R., and D. Rose. 1966. The Fluoride Content of Some
Foods and Beverages a Brief Survey Using a Modified Zr-SPADNS
Method. J. Food Sci. 31:941-946.
25. Martin, A., and C. Jones. 1971. Some Medical Considerations Regard-
ing Atmospheric Fluorides. HSMHA Health Rep. 86(8):752-758.
26. Martin, D. J. 1951. Evanston Dental Caries. Study VIII: Fluorine
Content of Vegetables Cooked in Fluorine-Containing Waters. J. Dent.
Res. 30:676-681.
27. Myers, H. M. 1978. Fluorides and Dental Fluorosis. In: Monographs
in Oral Science, Vol. 7, H. M. Myers, ed. S. Karger, Basel. 76 pp.
28. Nanda, R. 1972. Fluoride Content of North Indian Foods. Indian J.
Med. Res. 60(10):1470-1482.
29. National Academy of Sciences. 1971. Environmental Fate and Trans-
formation of Fluoride. In: Fluorides. Washington, D.C. pp. 29-42.
30. Oelschaeger, W., L. Feyler, and E. Schwarz. 1972. Fluorine Content
in the Smooth Tissues, Blood, and Milk of Ruminants Inside and Outside
the Emission Zones of Fluorine. Zentralbl. Veterinaenned. Reihe A
19(9):743-752.
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405
31. Prival, M. J., and F. Fisher. 1974. Adding Fluorides to the Diet.
Environment 16:29-33.
32. San Filippo, F., and G. Battistone. 1971. The Fluoride Content of
a Representative Diet of the Young Adult Male. Clin. Chim. Acta
31:453-457.
33. San Filippo, G. Battistone, and D. Chandler. 1972. Fluoride Content
of Army Field Rations. Mil. Med. 137(1):11-12.
34. Sengupta, S., and B. Pal. 1971. Iodine and Fluorine Contents of
Foodstuffs. Indian J. Nutr. Diet. 8:66-71.
35. Tinanoff, N., and B. Mueller. 1978. Fluoride Content in Milk and
Formula for Infants. J. Dent. Child. 45(1):53-55.
36. Waldbott, G. L. 1963. Fluoride in Food. Am. J. Clin. Nutr. 12:
455-462.
37. Wiatrowski, E., L. Kramer, D. Osis, and H. Spencer. 1975. Dietary
Fluoride Intake of Infants. Pediatrics 55(4):517-522.
38. Zipkin, I., S. Zucas, and B. Stillings. 1970. Biological Availabil-
ity of the Fluoride of Fish Protein Concentrate in the Rat. J. Nutr.
100:293-299.
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SECTION 9
ENVIRONMENTAL ASSESSMENT OF FLUORIDE
James L. Shupe, A. E. Olson, and H. B. Peterson
Utah State University
Logan, Utah
9.1 INTRODUCTION
Voluminous literature has been accumulated and reviewed regarding
fluorine and the biological aspects of its compounds. The literature is
extensive beyond the possibility of complete coverage; therefore, this
summary is one of judgment without pretense of completeness.
9.2 PROPERTIES AND ENVIRONMENTAL OCCURRENCES
Fluorine, a halogen, is a pale yellow acrid gas. It is a common ele-
ment, widely distributed, constituting 0.06% to 0.09% of the earth's crust.
Fluorine is highly reactive and rarely occurs in nature in the elemental
form but combines chemically to form fluorides. It appears in detectable
concentrations in most soils, rocks, waters, the atmosphere, vegetation,
and animal tissues. The most common chemical forms are hydrogen fluoride,
alkali fluorides, silicon tetrafluoride, sodium fluorosilicate, fluoro-
carbons, and the minerals cryolite, fluorapatite, and fluorspar.
Important naturally occurring fluoride sources include volcanic
activity, erosion of rocks and soils, and geothermal waters. Fluoride
occurs in a wide variety of minerals. Substantial quantities are present
in certain mineral and rock formations.
Major sources of fluorides used in industry include fluorspar (fluo-
rite), cryolite, and fluorapatite. The United States produces only part
of the fluorides it uses (20% in 1970) and imports the balance primarily
from Mexico, Spain, and Italy. If economical methods of recovering and
recycling industrial waste fluorides could be developed, the United States
could supply its own needs.
A variety of analytical methods are available for determining fluoride
content of many substances. The widely used spectrophotometric procedures
of the past have been largely superseded by the fluoride ion electrode
method which is quicker and more convenient than other methods for most
types of samples. Nevertheless, fluoride must first be separated from
often relatively large amounts of extraneous material without significant
loss of fluoride.
9.2.1 Soils
Soils may contain diverse fluoride forms in highly variable amounts.
In undisturbed and unpolluted soils, the quantity present generally in-
creases with depth. Analyses may vary from less than 10 ppm fluoride to
406
-------
407
10,000 ppm fluoride. Average fluoride values include: igneous rocks,
625 ppm; sandstones, 270 ppm; shales, 740 ppm; limestone, 330 ppm; and
soils, 200 to 300 ppm. Clays usually contain more than sandy soils. Flu-
orides tend to persist longest in soils with a high calcium or aluminum
content. Fluorides in sandy or acid soils are generally more soluble and
either leach out or are more available for take up by vegetation. Appli-
cation of phosphate fertilizers, irrigation with water of high fluoride
content, and certain industrial emissions may raise the fluoride content
of surface soils. However, these fluorides often are, or rapidly become,
relatively insoluble forms that are not readily available to plants grow-
ing on those soils.
9.2.2 Water
Fluorides are naturally occurring constituents of most waters.
Uncontaminated surface waters (e.g., rivers and lakes) usually contain
less than 0.3 ppm fluoride.
Groundwater sources such as springs and deep wells usually contain
somewhat higher fluoride levels. Fluoride content of groundwater is at
least partially dependent on the type of rocks the water flows over and
the temperature of the water. Alkalic igneous rocks, dolomite, phosphor-
ite, and volcanic gases are most likely to give water of high fluoride
content. Climatic conditions such as amount of rainfall and evaporation
rate also affect the fluoride content of groundwater. Warmwater sources
(including geothermal wells) are much more likely to have an elevated
fluoride level than are cold sources. Fluoride levels in warm sources
usually range up to about 15 ppm fluoride, although a few higher levels
have been reported.
Seawater usually averages about 1.4 to 1.5 ppm fluoride. Oceanic
sediments average about 730 ppm fluoride. The Great Salt Lake in Utah
averages about 14 ppm fluoride, but some analyses of lakes and potholes
in Kenya, Africa, range up to several hundred ppm fluoride.
The U.S. Public Health Service has recommended that drinking water
contain from 0.7 to 1.2 ppm fluoride (level dependent upon average ambient
air temperature) as the most efficient and economical method of providing
an optimal fluoride intake for development of caries-resistant teeth.
9.2.3 Air
Fluorides occur in the atmosphere either naturally or as industrial
emissions. The fluorides may be either in gaseous or particulate (dust)
forms.
Atmospheric fluoride levels are normally very low and are measured
in fractions of a part per billion (ppb) (often less than 0.05 ug/m3 ppb).
Some industrial emissions, dust storms, escaping volcanic gases, or com-
bustion products of winter heating may locally raise the above level by
8 to 20 times or more. Levels are dependent on amount of fluoride emit-
ted, distance of sampling site from source(s), meteorological conditions,
and area topography. Current estimates of total U.S. atmospheric fluoride
emissions are greater than 155,000 tons per year.
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408
One major source of concern for the atmosphere appears to be related
to the widespread release of certain fluorocarbons. Some of these com-
pounds have been widely used as aerosol propellants and as refrigerant
gases. The purported danger comes from the possible reaction of these
products with the ozone layer in the upper atmosphere. Some reactions
have been demonstrated in the laboratory. The ozone layer serves as a
shield from dangerously high levels of ultraviolet radiation from the sun.
Elemental fluorine is apparently not active in the reaction but is simply
present in the compounds in question. Efforts are underway to drastically
curtail the use and release of these fluorocarbons.
9.3 ENVIRONMENTAL INTERACTIONS
Fluorides naturally cycle among soils, water, air, and biological
forms. Pathways that fluorides may take within the environment are num-
erous and complex. Figure 9.1 illustrates some of the possible pathways
to plants, animals, and people. Man's activities, especially specific
industrial operations, have increased the quantities of fluorides being
cycled and the number of areas where the burden has been great enough to
induce some detrimental effects on some ecosystems.
9.3.1 Soils
Fluorides tend to persist in most soils. They are strongly absorbed
by soil colloids and combine with calcium or aluminum in alkaline soils
ORNL- DWG 79 -20883
Figure 9.1. Routes of fluorides in the environment. The multiple
sources may ultimately supply beneficial amounts or excessive quantities
to people.
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409
to form only slightly soluble compounds that are stable and long retained
under most conditions. Usually fluorides are not readily leached from
soils.
9.3.2 Water
Fluorides are found in water in both dissolved and undissolved forms.
Unless chemically altered, undissolved forms eventually settle out of the
solution. The amount of fluorides maintained in the dissolved state de-
pends on pH, temperature, and the presence of strongly associating ions
such as magnesium, calcium, carbonates, and phosphates.
9.3.3 Air
Most volatile inorganic fluoride compounds react with water vapors
to form less volatile compounds. These compounds are then removed from
the atmosphere by condensation or nucleation. Stable atmospheric partic-
ulate compounds usually fall out as dust. Some of the fluorocarbons may
persist in the atmosphere until they are decomposed.
9.3.4 Industrial Effluents
Steel and aluminum production, phosphate ore processing for fertil-
izers , production of phosphoric acid and a variety of other compounds,
coal combustion, and glass and ceramic manufacturing are sources of indus-
trial fluoride emissions. Welding and metal casting often use fluorides
as fluxes, and these are often released into the atmosphere with little
or no efforts made to capture them.
Industrial effluents containing excessive fluorides may have these
removed by several methods. Gaseous wastes are usually washed so that
the wastes are trapped in water. These wastes or water contaminated by
unwanted fluorides are usually treated with appropriate chemicals to form
precipitated forms, or the fluorides are absorbed in contact beds or slur-
ries. Chemicals that may be used, depending on the individual circum-
stances, include: lime or other calcium compounds, some magnesium or
aluminum compounds, ion exchange resins, or charcoal. The resulting
sludges of fluoride waste can be filtered and disposed of.
9.3.5 General Biological Aspects
The mode of action and effects of fluorides on biological systems
are important and complex. In optimal amounts fluorides are beneficial
to some vegetation, some animals, and man. In excessive amounts they
are detrimental.
The mechanisms by which fluorides function are not totally under-
stood. Effects of fluoride and the responses it elicits have been studied
on whole organisms and on various components such as cells, tissues, and
organs. At optimal concentrations, fluorides are reported to activate or
enhance a variety of physiological processes including reactions of some
enzymes and growth stimulation in vegetation. Excessive levels, however,
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410
induce adverse physiological responses such as inhibition of some enzyme
activities.
Physiological effects of fluoride on isolated cells and tissues may
be very different from its effects on the total organism. Extrapolation
of experimental laboratory test results to living systems should be done
cautiously because of these differences. Often, fluoride concentrations
used in laboratory tests far exceed those found in the environment. Be-
cause of the many factors and variables usually associated with fluoride
toxicosis, extrapolation of confined experimental data to practical situ-
ations is often difficult. Likewise, it is often difficult to scientif-
ically prove that fluorides are responsible for some of the adverse and
detrimental effects sometimes attributed to them.
9.4 MICROORGANISMS
Many bacteria, yeast, fungi, algae, protozoa, and viruses are known
to metabolize some fluoride compounds, but the ability varies among spe-
cies. There is no evidence that fluorides are essential to microorganisms.
As in higher organisms, excessive fluorides are toxic. The tolerance
levels vary widely among organisms. Resting or reproductive stages such
as spore forms are much more resistant to effects of excessive fluoride
than are vegetative cells. Some organisms can adapt to gradual increases
in environmental fluoride levels and increase their tolerance levels;
o thers canno t.
Many experiments that showed detrimental effects to various micro-
organisms were conducted with fluoroorganic compounds. Whether the effects
noted were due to the presence of fluoride alone or because of some bio-
chemical effects of the entire compound is open to speculation.
Organisms may accumulate fluorides with no observable effects, but
some, particularly lichens, may develop visible lesions that vary with
species and amounts of fluoride accumulated. Lichens have thus been used
as indicators of fluoride air pollution.
Toxic effects that have been reported include: developmental alter-
ations and morphological changes, growth and reproduction inhibition, and
(in applicable species) reduction in infectivity. Additional effects may
include inhibition of respiration, carbohydrate catabolism, protein syn-
thesis, and photosynthesis.
9.5 VEGETATION
Fluorides are in almost all vegetation in small amounts and may be
essential to most vegetative growth. Usual concentrations in vegetation
grown in normal soils, in unpolluted areas, range from about 2 to 20 ppm
fluoride of dried plant material. In some industrial areas, the concentra-
tion in vegetation may be 10 to 20 times greater than normal. Fluorides
are emitted in both gaseous and particulate forms from some industrial
operations. Hydrogen fluoride and silicon tetrafluoride are the predom-
inant gaseous forms and the forms most injurious to crops. Some vegeta-
tion seems to accumulate fluorides in amounts roughly proportional to the
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411
concentration in air. There is no such correlation between fluoride con-
centration in the soils and fluoride accumulation in vegetation grown on
these soils.
One effect of fluoride in vegetation is the unseen buildup and con-
centration of fluoride in and on the vegetation. This affect may not be
as well related to air quality as are the effects of foliar symptoms,
growth, and physiology. The ingestion of vegetation containing high levels
of fluoride may adversely affect animals even though the plants evidence
no visible changes.
9.5.1 Sources of Fluorides to Vegetation
Fluorides in the soil are usually not in a chemical form that can
be readily assimilated by vegetation. Soils near or above neutrality,
those that are calcareous, and those high in clay retain fluoride in
forms not generally available to plants.
The nature of the plant species and the availability of major nutri-
ents in the soil also affect the amount of fluoride absorbed through roots.
There is not a simple direct relationship between concentrations of fluo-
ride in soil and in plant tissue because fluoride availability is strongly
pH dependent.
Vegetation may become contaminated with fluorides when fluoride-
containing soil is splashed onto the foliage by rain or sprinkled irriga-
tion water. Also, windblown dust from surface soils high in fluorides
may contaminate the vegetative parts that animals consume.
Usually waters contain less than 1 mg/liter fluoride although some
geothermal and effluent waters may contain many times this amount. Most
industrial effluent waters now have contamination limits imposed by state
and federal laws. Limited quantities of these waterborne fluorides may
reach plants through their roots, but considerable quantities may be ab-
sorbed from the water or adhere on the foliage when crops are sprinkler
irrigated. Waters high in fluoride when applied to the soil leave their
fluoride fixed on the surface soils, thus increasing the fluoride content.
Dust or splash from these surface soils can add fluoride to the foliage
of the crops. This is an indirect route of fluoride from the water to
the plant.
Fluorides are released to the atmosphere in various ways: from vol-
canic activity and geothermal wells; from the manufacture of brick, fertil-
izers, ceramics, aluminum, and steel; from coal combustion; and in the form
of gaseous hydrogen fluoride, silicon tetrafluoride, and fluoride particu-
lates. In rural and urban areas, atmospheric fluoride concentrations are
usually less than 0.05 mg/m3. Localized atmospheric concentrations near
industrial operations may be much higher. Most of the recognized damage
to vegetation attributed to fluoride is caused by the absorption of gase-
ous fluorides (HF and SiF«.) through the leaves. Tissue-fluoride content
increases with increased time of exposure and with increased atmospheric
concentrations.
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412
9.5.2. Fluoroorganic Compounds
More than two dozen exotic plant species are known to synthesize
fluoroorganic compounds. Notable among these are Dichapetalum cymosum
from Africa and Acaoia georgina from Australia. Both of these plants
can remove inorganic fluorides from the soil and convert them, in lethal
amounts, to compounds such as fluoroacetate within the plant. Such com-
pounds are extremely toxic to animals, but the plants are not adversely
affected. It has been reported that, under certain conditions, fluoro-
acetate may also be synthesized by some cultivated crop plants such as
soybeans and crested wheat grass; however, this observation is not well
established. Fortunately, as far as is known, the accumulation of fluoro-
organic compounds in these and other cultivated plants is only in trace
quantities.
9.5.3 Symptoms and Susceptibility
The expression of inorganic fluoride-induced foliar lesions in vege-
tation varies considerably, depending upon the class of vegetation (narrow-
leaved and broad-leaved), its relative susceptibility to fluoride, the
concentration in the air, and duration of exposure. The symptoms produced
in a given plant by a high fluoride concentration for a short duration
may be different from those produced by a low fluoride concentration for
a long duration.
Plants exhibit an extremely broad range of tolerances to fluoride,
as well as to other air pollutants. Great differences in susceptibility
are found, not only among different species, but also among varieties of
the same species. The resistance of species such as camellia, cotton,
and celery to fluoride may be contrasted to the extreme susceptibility of
gladiolus, Chinese apricot, Italian prune, and developing needles of pon-
derosa pine. Differential responses may also be found among varieties of
gladiolus, sweet corn, and sorghum, although the degree of difference is
not as great. In gladiolus, dark-flowered varieties have been reported
to be more resistant to fluoride than the lighter-flowered varieties. A
similar situation has also been observed among certain conifers, such as
ponderosa pine, that have phenotypic variants among the natural population
showing differences in their responses to fluoride.
Specific and varietal differences in susceptibility have been tabu-
lated by various researchers based on the following information: the
amount of injury induced by a given dose of fluoride; the dosage of flu-
oride required to reach the threshold for foliar markings; and the amount
of fluoride present in the leaves showing injury. These different means
of estimating susceptibility account at least in part for the anomalous
positions of several species in the tolerance ratings.
9.5.4 Effects on Vegetation
The effects of fluoride on vegetation depend on species and varietal
differences in susceptibility, the stage of development of the vegetation,
the concentration of fluoride in the air, the length of exposure, and
climatic factors.
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413
Excess fluoride may cause growth inhibition, tip and marginal necro-
sis of foliage (Figure 9.2), chlorosis, wilting, and eventual death of
the plant. Fruit quality and yield can be impaired. Inhibition of seed
germination may also occur. Fluoride causes these effects by altering
photosynthesis, carbohydrate metabolism, respiratory and oxidative proc-
esses, RNA metabolism, and calcium nutrition. The mechanisms involved
are complex and largely unresolved in vivo, but in vitro studies suggest
that many effects result from fluoride inhibition of essential enzymatic
reactions.
Excessive fluorides appear to exert mutagenic effects in some plants.
Chromosomal abnormalities, such as breakage, bridging, and stickiness of
mitotic cells, occur in a variety of plants after treatment with concen-
trations of gaseous hydrogen fluoride or aqueous sodium fluoride that are
too low to induce immediate visible injury. The mechanisms by which
fluorides induce chromosomal aberrations are not known.
ORNL PHOTO 5521-79
Figure 9.2. Apricot leaves showing various degrees of necrosis
caused by excessive levels of atmospheric fluoride.
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414
There are few data on possible synergistic effects on vegetation of
fluoride combined with other toxicants. Limited experiments with HF and
S0a indicate that the effects are additive in respect to reduction of
linear growth and leaf area on orange and mandarin trees. Experiments
also show that the inhibition of photosynthesis in alfalfa by N02 and HF
is additive. Inhibition of photosynthesis, with combined S02 and HF, is
somewhat more than additive.
When evaluating the effects of fluoride on a crop, consideration
should be given to the intended use of the crop. For example, Douglas
fir trees intended for lumber may exhibit needle tip burn but growth may
not be inhibited, and there is no known economic loss. The same kind of
trees grown as ornamentals, with the same symptoms of tip burn would be
aesthetically unacceptable and hence damaged. Gladiolus with fluoride-
induced markings on the leaves and flowers are unsalable, but if grown
for corm production there may be no reduction in either yield or quality.
In addition to recognition of the characteristic fluoride-induced
markings on crops in the field, there must also be recognition of similar
symptoms induced by other agents. Marginal and tip necrosis typical of
fluoride markings on leaves of many species may be similar to symptoms
of water stress, low temperature, overfertilization, and toxicity from
road salt. Fluoride-induced chlorotic patterns are mimicked by deficien-
cies of manganese, zinc, magnesium, calcium, boron, potassium, and iron;
by virus infection, genetic disorders, mite or leafhopper-induced stip-
pling; and herbicides. It is important to reinforce field observations
with fluoride analyses of vegetative materials.
Sampling and analysis of vegetative materials are usually done for
one or more of the following purposes: (1) to determine the amount and
distribution of airborne fluorides, (2) to determine the levels of fluo-
ride in and on vegetation to be utilized as animal feed, and (3) to deter-
mine the fluoride concentrations in vegetation that are harmful to the
plants. Although theory may dictate the sampling scheme and the location
of sampling sites, the biological or agronomic characteristics of the
vegetation should determine the amounts and types of samples to be taken.
Specific practices cannot be recommended for vegetation sampling and anal-
ysis unless the purpose of the sampling is identified. For any given
purpose, the methods of sampling and analyzing should be standardized.
9.6 DOMESTIC AND WILD ANIMALS
Animals normally ingest variable low-level amounts of fluoride with
no known adverse effects. It appears that trace amounts of fluoride are
essential to or at least enhance certain body functions such as optimum
tooth and bone development and mineralization. Growth and reproduction
in some laboratory animal species are reported to be improved by fluoride
ingestion at proper concentrations. Much of the published information,
however, describes the adverse effects of excessive fluoride ingestion.
9.6.1 Sources of Fluorides to Animals
Both terrestrial and aquatic animals are exposed to fluorides in
various forms and concentrations in their food, water, and air. Ingestion
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415
is the major mode of intake by most terrestrial mammals, birds, and lower
animal forms. Aquatic forms acquire fluorides from their food and their
environment. The most commonly encountered sources of excessive fluoride
for higher animals are the following: (1) forages which usually constitute
the major source of an animal's diet and that have been contaminated by
fluoride-laden industrial effluents or by wind-blown or rain-splashed soil
of high fluoride content; (2) water high in fluoride content because of
natural (usually geothermal) or industrial sources; (3) feed supplements
and mineral mixtures that have not been properly defluorinated; (4) for-
ages grown in soils high in fluoride content; and (5) a combination of
the various sources.
Many cases of fluoride toxicosis have resulted when airborne efflu-
ents, high in fluoride, have contaminated vegetation subsequently eaten
by animals. Some cases of fluoride toxicosis have been induced by animals
drinking waters with excessive fluorine from hot or warm springs, deep
wells, geysers, or waters accidentally contaminated. Phosphorus supple-
ments that have not been properly defluorinated have also caused toxicosis.
Soils usually contain relatively high amounts of fluoride without
translocation of excessive fluoride into the vegetation. However, animals
grazing such areas can ingest excessive fluoride from the soil, especially
if the pastures or ranges are overgrazed and the animals are forced to
eat the vegetation close to the ground or vegetation contaminated by wind
or rain splash.
9.6.2 Fluoride Toxicosis
Fluorides in animals are to some extent cumulative, but only in min-
eralizing tissues. When ingested in excessive amounts fluorides induce
characteristic lesions. The expression of severity of fluoride toxicosis
may be altered or influenced by several factors including: (1) amount of
fluoride ingested; (2) duration of fluoride ingestion period; (3) solubil-
ity (and thus relative toxicity) of ingested fluorides; (4) variations in
fluoride ingestion levels (intermittent exposure); (5) species of animal;
(6) age at time of ingestion; (7) level of nutrition; (8) exposure to other
toxic agents (synergism or alleviation of effects); (9) general state of
health of the animal; (10) stress factors; and (11) varied biologic re-
sponse by different individuals within a group.
9.6.3 Signs and Lesions
Fluoride toxicosis may be either acute or chronic. Fortunately,
acute fluoride toxicosis is relatively rare and most often results from
accidental inclusion of toxic fluoride compounds such as sodium fluorosil-
icate or sodium fluoride in the diet of domestic animals. The rapidity
with which signs appear and the exact nature of the signs depend mainly
on the amount and type of fluoride ingested. Clinical signs may include
restlessness, stiffness, anorexia, excess salivation, nausea, vomiting,
incontinence of urine and feces, reduced milk production in lactating
animals, convulsions, weakness, severe depression, and cardiac failure.
Chemical analyses of blood and urine from affected animals reveal high
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416
fluoride content. Necropsy findings are usually limited to mucosal
necrosis of the digestive tract.
The much more common chronic fluoride toxicosis in animals develops
gradually and is usually insidious in nature. Time intervals of months
or even years may pass between the beginning of excess fluoride ingestion
and the manifestation of readily observable clinical signs. Some manifes-
tations of fluoride toxicosis may be confused with other toxicoses or
certain debilitating or degenerative diseases such as malnutrition or
arthrosis.
9.6.3.1 Dental Fluorosis The most distinctive and obvious primary
lesions of chronic fluoride toxicosis appear in developing permanent teeth
and bones. Developing teeth are extremely sensitive to excessive fluoride.
Once the teeth have formed, mineralized, and erupted, fluoride ingestion
will have little or no discernible effect on them. Thus, immature animals
are most susceptible to dental fluorosis. Severely affected teeth are
discolored (chalky white or creamy yellow to brownish black); they may
also have hypoplasia, pitting, and loss of enamel with exposure of the
dentine and are more susceptible to increased attrition.
Classification or evaluation of clinical dental fluorosis is usually
recorded as numerical values (Figure 9.3). The most widely used classi-
fication system includes a range from 0 (normal) to 5 (severe fluoride
effects). The incisor teeth are evaluated for enamel quality, defects,
ORNL PHOTO 6626-79
Figure 9.3. Classification of representative incisor teeth from
cattle from 0 to 5 reading left to right in A and B. A is with direct
light. B is with transmitted light. Source: Shupe et al., 1962.
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417
and abrasion pattern (Figure 9.4). The more difficult to examine cheek
(premolar and molar) teeth are classified 0 to 5 based on attrition
patterns only.
ORNL PHOTO 5524-79
Figure 9.4. Permanent bovine incisor teeth. Note chalkiness and
discoloration of enamel, hypoplasia, and excessive bilateral abrasion.
Dental lesions should be carefully examined and the incisor and
cheek tooth lesions correlated for their bilateral nature and chronolog-
ically similar lesions relating to the animal's age at the time of forma-
tion and mineralization of the individual teeth.
9.6.3.2 Osteofluorosis Fluoride toxicosis is also manifested by
gross, hyperostotic chalky white bone lesions if fluorides are ingested
at high enough levels for a prolonged period (Figures 9.5 and 9.6). These
lesions can be induced at any time during an animal's life. Severe oste-
ofluorosis has been reported in animals with normal permanent teeth, thus
accenting the significance of the age-effect factor in relation to induced
lesions.
Fluoride-induced bone lesions are generally bilateral and somewhat
symmetrical. The severity of the bone lesions is related to the struc-
ture and function of the bones involved and to the amount of stress and
strain placed on specific areas in the bones. Affected bones usually are
chalky white and have a roughened irregular periosteal surface. They may
also be larger in diameter and heavier than normal. The major bone changes
are located on the periosteal surface. In some advanced cases, endosteal
proliferation may occur with encroachment of bone and the marrow cavity
of some bones. If the lesions are severe and of long enough duration,
some secondary periarticular and intraarticular changes may occur. The
severity and exact nature of the fluoride-induced bone changes varies,
and one or more of the following conditions may occur: osteosclerosis,
osteoporosis, hyperostosis, osteophytosis, or osteomalacia. The above
listed changes such as increased density, porosity, hyperostosis, or
osteophytosis may be demonstrated radiographically as well as grossly.
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418
ORNL PHOTO 5522-79
Figure 9.5. Metatarsal bones from two cows of the same breed, size,
and age: left normal bone; right severe osteofluorosls.
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419
OR ML PHOTO 5526-79
Figure 9.6. Cross sections of the two metatarsal bones shown in
Figure 9.5. Bone from points of arrows outward is fluoride-induced
abnormal bone.
Osteones formed under the influence of excessive fluorides frequently
vary in size and shape with osteocytes often clumped or irregularly located
near the periphery of the osteone rather than evenly distributed throughout
the osteone. Abnormal canaliculi are associated with the clumped abnormal
osteocytes. Porous areas with excessive bone resorption or accelerated
remodeling occur with failure of bone growth and remodeling to keep a
proper balance between bone destruction and formation.
The precise pathogenesis of osteofluorosis is not fully understood.
There appear to be three phases associated with osteofluorosis: (1) ele-
vated fluoride levels in the bone without detectable structural changes;
(2) microscopic and radiographic bone changes without known alteration of
function; and (3) sequential and progressive structural bone changes that
result in abnormal bone structure and function with resultant alteration
of mechanical properties.
9.6.3.3 Other Signs Animals with moderate to severe osteofluoro-
sis sometimes exhibit an intermittent, nonspecific, atypical lameness or
stiffness that may be associated with calcification of periarticular struc-
tures and tendon insertions. This lameness or stiffness is often transi-
tory and intermittent in nature and limits grazing or feeding time, thereby
impairing animal performance. The type of lameness or stiffness seen is
not diagnostically specific for fluoride toxicosis. Other general nonspe-
cific signs sometimes associated with chronic fluoride toxicosis include
unthriftiness, thickened dry unpliable skin, and signs of poor performance.
9.6.3.4 Tissue Analyses Locations from which samples are taken
should be standardized and consistent. Fluoride content of bones normally
Increases with age (Table 9.1) even if the animal is on a lifelong low
fluoride Intake level. Usually 96% or more of the fluoride in an animal's
body is located in the bones and teeth.
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TABLE 9.1. GUIDE TO DIAGNOSIS AND EVALUATION OF FLUORIDE EFFECTS IN DAIRY CATTLE''
Parameter
Fluoride in moisture-free
diet, ppm
Degree of fluoride effects
on incisors
Degree of wear on molarsc
Fluoride in bone, ppm on
a dry, fat-free basis
Fluoride in urine, ppm
Fluoride in milk, ppm
Fluoride in blood, ppm
Fluoride in soft tissue.
ppm
Per ioa teal hyperostosis
j
Secondary changes
Age
(years)
2
4
6
2
4
6
2
4
6
2
4_
6
2
4
6
2
4
6
2
4
6
2
4
6
2
4
6
All
Normal
conditions
Up to 15
Up to 15
Up to 15
0-1
0-1
0-1
0-1
0-1
0-1
401-714
706-1138
653-1221
2.27-3.78
3.54-5.3
3.51-6.03
Up to 0.12
Up to 0.12
Up to 0.12
Up to 0.30
Up to 0.30
Up to 0.30
Up to 1.20
Up to 1.20
Up to 1.20
0
0
0
Absent
No adverse
effects
15-30
15-30
15-30
0-2
0-2
0-2
0-1
0-1
0-1
714-1605
1138-2379
1221-2794
3.78-8.04
5.3-10.32
6.03-11.29
Up to 0.12
Up to 0.12
Up to 0.12
Up to 0.30
Up to 0.30
Up to 0.30
Up to 1.20
Up to 1.20
Up to 1.20
0-1
0-1
0-1
Absent
Chronic fluoride toxicosis
Threshold
30-40
30-40
30-40
2-3
2-3
2-3
0-1
0-1
1-2
1605-2130
2379-3138
2794-3788
8.04-10.54
10.32-13.31
11.29-14.78
0.12-0.15
0.12-0.15
0.12-0.15
0.30-0.40
0.30-0.40
0.30-0.40
Up to 1.20
Up to 1.20
Up to 1.20
0-1
0-1
0-2
Occasionally
noticed
Moderate
40-60
40-60
40-60
3-4
3-4
3-4
0-1
1-2
1-3
2130-3027
3138-4504
3788-5622
10.54-14.71
13.31-18.49
14.78-20.96
0.15-0.25
0.15-0.25
0.15-0.25
0.40-0.50
0.40-0.50
0.40-0.50
Up to 1.20
Up to 1.20
Up to 1.20
0-2
0-3
0-4
Present
Severe
60-109
60-109
60-109
4-5
4-5
4-5
0-3
1-4
1-5
3027-4206
4504-6620
5622-8676
14.71-19.86
18.49-25.63
20.96-30.09
0.25 and above
0.25 and above
0.25 and above
0.50 and above
0.50 and above
0.50 and above
Up to 1.20
Up to 1.20
Up to 1.20
0-3
0-4
0-5
Present
Acute
fluoride
toxicosis*'
Over 250
Over 250
Over 250
aData based on controlled experiments ranging from 1.5 to 7.5 years and have been correlated with 855 fluoride-affected
field,cases that were necropsied and evaluated.
"Characterized by: excitement, high-fluorine content of blood and urine, stiffness, anorexia, reduced milk production,
excessive salivation, nausea, vomiting, incontinence of urine and feces, clonic convulsions, necrosis of mucosa of digestive
tract, weakness, severe depression in some cases, and cardiac failure.
°0 - normal, 1 - questionable, 2 - slight, 3 - moderate, 4 - marked, and 5 - severe.
"Stiffness and lameness, loss of body weight, reduced feed intake, rough hair coat, unpliable skin, and reduced milk
production.
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421
Fluorides do not normally accumulate in visceral organs or soft tis-
sues in sufficient quantities to provide reliable, accurate, and consist-
ent diagnostic information. Neither have fluorides been shown to induce
consistent demonstrable changes in the visceral organs or soft tissues.
Therefore, meat from fluoride-affected animals is safe for human consump-
tion and will usually contribute only negligible amounts to the total
human intake. Edible marine animals, particularly crustaceans, growing
in an environment that is usually quite high in fluorides will accumulate
more fluorides in both edible tissues and exoskeletons than will many
terrestrial dwellers. Even the larger amounts of fluoride that these
edible tissues will contribute to some human diets is not great enough
to cause any concern unless there are also other significant fluoride
sources. Milk from dairy animals consuming high fluoride levels will
have a fluoride content only slightly above normal, and the milk is safe
for human consumption (Table 9.1). The mammary gland is not a major ex-
cretor of fluorides. Some fluoride does cross the placental barrier to
the fetus but usually in only small amounts. No experimental evidence
has indicated any discernible fluoride-induced damage to fetuses of mam-
mals on a relatively high fluoride intake. Fluoride buildup in the food
chain of higher animals has not been detected.
9.6.3.5 Urine For domestic animals, urine samples, if properly
collected and analyzed for fluoride, can provide supportive data assisting
in the diagnosis and evaluation of chronic fluoride toxicosis. Individual
random samples may be too variable to provide reliable information.
In mammals, urine serves as one of the major means of fluoride elim-
ination from the body. On a low-level fluoride diet the urinary fluoride
content from animals rises slightly as animals age and the fluoride con-
tent of bone increases. Table 9.1 depicts the relationship of age and
level of fluoride ingestion to fluoride content in bone, urine, milk,
blood, soft tissues, and fluoride-induced lesions. Urinary levels of
fluoride may remain elevated for some time after animals are changed from
a high to a low fluoride intake. Under most circumstances, urine values
for cattle of less than 6 ppm fluoride are considered normal.
9.6.3.6 Necropsy Findings If clinical examinations and chemical
analyses indicate the need for more specific information, necropsies
should be performed on selected representative animals. For economic
reasons, some domestic animals may be sacrificed at a commercial abattoir
and after recommended tissues are taken for detailed study and evaluation,
the carcasses could be safely used for meat.
9.6.4 Diagnosis
Results of clinical examinations should be compared with necropsy
findings. Chemical analyses, especially of bones, reflect past exposure
to fluoride. All feed sources, including mineral supplements, should be
analyzed for fluoride content. Likewise all drinking water supplies should
be tested so that the cause(s) of fluoride toxicosis may be elucidated.
Sampling and analytical techniques should be standardized and recorded to
insure reliable and reproducible data.
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422
In regard to forage crop sampling, extensive efforts should be made
to accurately sample the forage the involved animals have actually been
ingesting.
There is considerable experimental information on the tolerance of
livestock to fluoride in feed when animals are housed and managed under
ideal experimental conditions. There is a paucity of information on tol-
erances of animals under field conditions when they may not be ideally
fed and properly sheltered or managed. Information on tolerances of some
animals to waterborne fluoride is also limited. Response of animals to
waterborne fluoride varies as ambient air temperature influences the amount
of water consumed. Figure 9.7 illustrates the relation of ambient air
temperature and water intake by beef cattle as related to dietary dry
matter intake.
100
80
60
ORNL-DWG 79-20896
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423
For wildlife the diagnosis, treatment, or prevention of fluoride
toxicosis is much more difficult and in many cases it is impossible to
follow and utilize the procedures used for domestic animals.
9.6.5 Treatment
There is no known successful treatment for chronic fluoride toxico-
sis. Supportive and symptomatic treatment may be given. Complete recovery
from moderate to severe lesions induced by excessive fluoride ingestion
does not occur. If dental lesions are present, they are irreversible. In
fact, if lesions are severe enough to hasten dental abrasion, the acceler-
ated wear will continue, especially if rough abrasive feeds are utilized.
Osteofluorotic lesions may be prevented by reducing to normal the
total fluoride intake. Animals with extensive bone lesions do not live
long enough to have the bone remodeled to normal. After animals stop
ingesting excessive fluoride levels, normal bone is laid down over pre-
viously induced osteofluorotic bone.
Animals adversely affected by fluoride toxicosis may be aided by
providing good nutrition and by avoiding all possible stresses. The diet
should be nutritionally well balanced, of good quality, and in sufficient
amounts to promote desirable performance and growth.
If economic or logistic feasibilities dictate the animals may not be
removed from toxic sources of fluorides, some preventive relief may be
obtained by feeding alleviating compounds. Beneficial effects have been
observed by feeding adequate mineral supplements and adding calcium carbo-
nate, magnesium, or aluminum compounds to the diet. Inclusion of some
aluminum (most often aluminum sulfate) or calcium (calcium carbonate)
compounds in the diet has lessened the effects of a given amount of fluo-
ride. A nutritional balance of other minerals, particularly phosphorus,
should be maintained to obtain maximum benefits from aluminum and calcium
additions.
9.6.6 Species Tolerances
Tolerance levels for various livestock species have been determined.
Where applicable, different levels for long-term production/reproduction
animals as compared to short-term fattening/slaughter animals have been
calculated and can be found in Table 9.2. The values given are for sodium
fluoride or for compounds of similar solubility (toxicity) in the total
dietary intake. Less soluble fluoride compounds, such as calcium fluoride,
are less toxic on a given parts-per-million fluoride basis.
Fluorides in water, particularly those occurring naturally, are often
dissolved inorganic forms that are biologically available. Fluorides in
water are often relatively more toxic than equivalent amounts in the die-
tary dry matter. Many fluoroorganic compounds have the fluorine ionically
bound and biologically unavailable. These variations in biologic avail-
ability and relative toxicity of fluoride forms and sources present must
also be taken into consideration when evaluating fluoride toxicosis.
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TABLE 9.2. FLUORIDE TOLERANCE LEVELS IN FEED AND
WATER FOR DOMESTIC ANIMALS BASED ON
CLINICAL SIGNS AND LESIONSa
Species
Cattle
Dairy and beef heifers
Dairy, mature
Beef, mature
Finishing
Sheep, breeding
Lambs, feeder
Horses
Swine, growing
Turkeys , growing
Chickens , growing
Dogs, growing
Feed2*
(mg/kg)
30
40
50
100
60
150
60
70
100
150
50
Water0
(mg/liter)
2.5-4.0
3-6
4-8
12-15
5-8
12-15
4-8
5-8
10-12
10-13
3-8
'Values should be reduced proportionally
when both water and feed contain appreciable
amounts of fluorides.
&A suggested guide when fluoride in the feed
is essentially the sole source of fluoride, tol-
erances based on sodium fluoride or other fluorides
of similar toxiclty.
cThe average ambient air temperatures and the
physical and biological activity of the animals
Influence the amount of water consumed and hence
the wide range of tolerance levels suggested. For
active animals In a warm climate, the lower values
should be used as critical level Indicators.
Fluoride tolerance levels for other mammalian species and for lower
animal species are generally less well documented or nonexistent and often
more variable than those reported here. The effects of waterborne fluo-
rides on fish have been studied somewhat. Hatching time of fish eggs is
extended in high fluoride waters. Effects of fluorides on growing fish
varied with species, size at exposure time, water temperature, and calcium
and chloride levels in the water. The above factors, plus water pH and
the presence of other contaminants, influence the tolerance and overall
effects of fluorides on aquatic animals. Some reports indicate that
aquatic animals can usually tolerate fluoride levels up to 1.5 ppm in the
water. The effects of higher fluoride levels are variable. Low levels
appear to stimulate growth rates, but higher levels slow egg hatching and
growth and are also otherwise toxic in some species. Edible tissues in
aquatic animals, particularly crustaceans, will accumulate much greater
fluoride levels than will terrestrial mammals up to 50 ppm have been
reported in some studies. Reversal of fluoride storage or accumulation
in aquatic animals occurs much more rapidly than in terrestrial dwellers.
Most reports cite return to normal levels in approximately the same length
of time as it took the high levels to accumulate after the animals' water
supply returned to a low fluoride level. Tolerance levels for some animal
species are difficult to establish because of the many variables involved
and the limited research conducted.
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425
Effects of fluorides on insect species are highly variable. Levels
of sodium fluoride (0.01%) mixed in flour have been shown to stimulate
egg production in one type of beetle (Triboliwn sp.) often found in cereal
products, while 0.1% of the same compounds will inhibit egg production.
One organic fluoride compound (perfluorobutene-2) mixed with air in a 1:9
ratio and used as an air source for fruit flies (Droeophila sp.) increased
mutations in the offspring. The close ionic bonding of such compounds,
however, limits the likelihood of the fluorine alone being the chief toxic
principle. Reports of fluoride toxicosis in honeybees have been published.
These incidents usually involved errant pesticide applications with an
acute response and high mortality within two to three days of exposure.
Like many other reports, the amount of fluoride involved in bee fluoride
toxicosis is variable.
9.6.7 Prevention of Fluoride Toxicosis
Caution must be exercised by animal owners, animal-feed processors,
and industries to prevent the occurrence of fluoride toxicosis. All
sources of feed and water should not contain fluoride in excess of normal
recommended levels. It is very important to avoid overgrazing by live-
stock so that chances of ingesting high-fluoride soils are lessened.
Fluorine in any mineral or mineral mixture that is to be used directly
for the feeding of domestic animals should not exceed 0.20% for dairy and
breeding cattle, 0.30% for slaughter cattle, 0.30% for sheep, 0.30% for
horses, 0.35% for lambs, 0.45% for swine, and 0.60% for poultry. The total
intake is of major importance and when total fluoride intake is calculated,
it should include both feed and water intake as recommended in Table 9.2.
One must also be aware of potential industrial pollution from new
industries in an area or from long-established industries that change
processes or methods of operation. Another area of recent concern is the
rapid expansion of sprinkler irrigation with geothermal waters. Some
waters are safe for use in flood irrigation, but unpublished data indicate
a high fluoride content in forage sprinkled with water containing high
levels of fluoride (5 to 10 mg/liter).
Owners of domestic animals and wildlife managers should carefully
observe all phases of animal health and be aware of problems that may
occur with infectious agents, nutritional imbalances, and now, more than
ever, with toxicities of all kinds including fluoride toxicosis.
Measures should be taken to exclude domestic animals and wildlife
from as many sources of excessive fluoride as practical. Prevention and
control of fluoride toxicosis in animals can be achieved when the complex-
ity of the disease is realized, properly diagnosed, and the source(s) of
excessive fluorides is eliminated.
9.7 HUMANS
Proper amounts of ingested fluoride are beneficial to man. Dental
benefits are maximized when water containing approximately 1 ppm (1 mg/
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426
liter) fluoride is consumed during the years of tooth formation and con-
tinued throughout life. This conclusion is based on epidemiological stud-
ies conducted in areas where fluoride occurs naturally in the water and
in other areas where it has been added at the recommended level to public
culinary water supplies. Some fluoridation programs have been in opera-
tion since 1945 and have been successful in reducing and/or, in some
subjects, preventing dental caries.
Only when massive (e.g., 20 to 80 mg or more per day) dosages of
fluoride are taken in over long periods (10 to 20 years) are adverse
effects encountered. No adverse effects have been reported when water
containing 1 ppm of fluoride has been drunk during periods of 10 to 20
years. Fluoride-induced mottling of tooth enamel having only cosmetic
effects has been reported only when fluoride concentration in the water
exceeded 1.4 to 1.6 ppm, and it was minimal at such levels.
Research has established that people consuming water containing 1
ppm of fluoride experience no adverse effects on their kidneys, thyroid
glands, reproductive functions, growth, development, blood, urine, or
hearing. No cases of allergic reactions have been positively linked with
consumption of water fluoridated to the 1 ppm level.
Research has also provided evidence that suitable amounts of fluoride
may be helpful in preventing or alleviating bone diseases such as
osteoporosis.
Man is subject to similar tooth and bone effects from excessive
fluoride ingestion as are other higher animals. However, detrimental
effects are usually minimized by the nature of man's diet and habits and
by dilution of fluoride sources because food and water are obtained from
diversified sources.
Fluoride-containing compounds that are involved in human chronic
fluoride toxicosis are almost exclusively inorganic forms. The fluoride
is bound in compounds of varying solubility. Commonly encountered forms
include calcium fluoride, sodium aluminum fluoride, and sodium fluoride.
The adverse biological effects of a given compound are proportional to
the solubility of the compound.
Fluoroorganic compounds do not mimic the physiological effects of
inorganic fluorides. In most of the organic compounds the fluoride is
tightly bound. Compounds that do not readily yield free fluoride ions
in the body fluids have little or no toxicity that is due to their fluo-
ride content alone.
Most wells and community water supplies naturally range from 0.01
or less to 10 (or rarely more) ppm fluoride. In some parts of Africa,
brackish pothole waters must be used as culinary water supplies during
periods of extreme drouth, thus increasing fluoride intake to a serious
level.
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427
The amount of fluoride ingested with water is dependent on the fluo-
ride content of the water and the amount of water consumed. There is a
great variation in both of these factors. Age, physical activity, and
ambient air temperatures all affect water consumption rates.
Most human foods are minor sources of fluorine, even when grown in
high fluorine soils. Many factors can influence the fluoride content and
analytical results. Table 9.3 lists the fluoride content of some foods.
TABLE 9.3. FLUORIDE CONTENT OF VARIOUS FOODS
Food Content (ppm)
Meat 0.2-2.0
Fish (fresh and canned) 0.1-30.0
Hen eggs 0.5-1.5
Cow milk 0.05-0.25
Tea (dried leaves) 3.0-180
Citrus fruits 0.07-0.36
Noncltrus fruits 0.06-0.22
Cereals and cereal products (most) 0.1 or less-0.3
Vegetables and tubers 0.08-0.8
Many foods contain less than 0.3 ppm fluoride on a fresh-weight
basis, the exceptions being certain seafoods and tea. Most fluoride
occurring in food is in chemical forms that can be assimilated by the
body. An average American diet provides approximately 0.2 to 0.5 mg
of fluoride daily.
Cow milk and meat (skeletal muscle) normally contain very little
fluorine. High fluoride intake by the cow does not appreciably increase
the fluoride content of the cow's milk or meat (Table 9.1).
In addition to the fluorides ingested in foods, minute amounts may
also be ingested as fluoride supplement tablets, fluoride-vitamin and/or
mineral supplements, fluoride-containing dentifrices or mouthwashes, or
in fluoride-containing drugs. In the drugs, the fluoride is often con-
tained in organic forms and metabolically unavailable.
Estimates of fluoride ingestion with diets range from about 0.2 to
2.7 mg per day worldwide with little variation shown from country to coun-
try. Some studies on U.S. per capita ingestion range from 0.2 to 0.8 mg
of fluoride per day.
Uncontaminated air normally contains only minute quantities of fluo-
ride that are measured in parts per billion (ppb). Results of fluoride
analyses of air samples collected in various U.S. cities during the 1950s
ranged from 0.04 to 1.8 ppb fluoride.
Hydrogen fluoride is the most widely encountered gaseous fluoride
compound in the environment. It is widely used in certain industrial
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428
processes. When exposure is to high levels and for long periods of time,
hydrogen fluoride may cause eye, skin, and respiratory system irritation.
Winds blowing over soils or rocks containing fluoride may move
excessive amounts into the air, onto edible vegetation, or into culinary
water supplies and consequently into the food chain. Many industrial
processes may also liberate fluoride-laden dusts or particulates into the
atmosphere. The biologic effects of the fluoride intake from dust or
particulate matter are much more closely related to ingestion of similar
quantities of sodium fluoride than to inhalation of comparable amounts
of gaseous hydrogen fluoride compounds.
Because elemental fluorine occurs only rarely, if ever, in nature,
human exposure occurs only in some industrial manufacturing processes or
in laboratories.
Aerosol propellants containing fluoroorganic compounds do not consti-
tute a health hazard solely because of their fluoride content. They are
a potential problem because of their possible reaction with the protective
ozone layer in the upper atmosphere.
From a health standpoint, except for rare industrial exposures, the
most significant exposures of man to atmospheric fluorides come not from
inhalation but ingestion of dust or particulate-contaminated food and/or
water. An average person breathing air containing 10 ppb fluoride, even
with 100% retention, would only have an intake of 0.16 mg fluoride per
day.
Ingested soluble fluoride compounds are rapidly absorbed in the gas-
trointestinal tract, primarily in the stomach. A high percentage of the
fluoride in an average diet is absorbed. Less soluble fluoride compounds
are absorbed to a lesser extent, with residual amounts being excreted in
the feces. Diets rich in calcium, magnesium, or aluminum compounds, or
low in fat, reduce absorption of fluorides. Soluble fluorides as gases
or vapors, or as fine particle-sized dust can be readily absorbed from
the respiratory tract. The absorption of hydrogen fluoride through the
skin has also been reported.
Absorbed fluorides are rapidly distributed throughout the body via
extracellular fluids. The level of fluoride in these circulating fluids
is stabilized either by excretion or by storage of fluoride in bones and
mineralizing tissue. Unless the body is absolutely overwhelmed by an
acute dosage, stabilization occurs rather rapidly.
The principal route of fluoride excretion is via urine although some
is excreted in sweat, especially from those who sweat profusely. After
absorption, quantities of fluoride appear rapidly in the urine. The amount
excreted is governed by many factors. Urinary fluoride concentrations can
vary from hour to hour, even in the same individual. Therefore, single
urine analyses may not accurately reflect a person's fluoride intake
status. When fluoride intake is at a relatively constant level, human
urinary fluoride concentrations are usually nearly equivalent to the
drinking water concentrations.
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429
The main portion of fluoride administered by any route, on entering
the extracellular fluids, is sequestered by the skeleton and/or developing
teeth and mineralizing tissue. Fluorine is the most exclusively bone-
seeking element known. Fluorine incorporated into bone increases the size
of the apatite crystals, or building blocks of bone, and decreases their
solubility. The bones of persons on long-term low-fluoride intake levels,
will gradually increase in fluoride content. Such low-level accumulations
occur with no demonstrable changes in either bone structure or function.
Skeletal tissues have a very high degree of physiological tolerance to the
slow accumulation of low levels of fluorides. In experimental animals on
fluoride-ingestion trials, the rate of fluoride uptake by bone decreases
with time as bone activity and growth rate slow with maturation and/or
aging. The bone crystal sites available for fluoride incorporation may
also be reduced following near saturation with fluoride.
Fluoride deposition in the skeleton of man is not an irreversible
process. If a person changes from an elevated to a low fluoride intake
level, fluorides will be removed from the bone and excreted in the urine
as normal bone remodeling proceeds.
In moderate amounts, fluorides tend to stimulate bone cells to produce
a bone matrix that is better mineralized. This harder bone counteracts
one of the most debilitating diseases of the elderly demineralization
of the skeleton or osteoporosis. It has been noted that osteoporosis in
the elderly is much more rare in populations consuming adequately fluori-
dated water (as high as 8 ppm fluoride) than in the general population.
Elevated fluoride-intake levels may disturb normal bone growth, develop-
ment, and remodeling with resultant osteofluorosis. Poor nutrition in-
creases the effects of a given fluoride intake level. Ligaments may
calcify, and there may be extra bone development. This fluoride-induced
bone may develop around joints and restrict movement, or develop as spur-
like projections or roughened surfaces on long bones. Gross bone lesions
only appear in humans who have had extreme chronic exposure to fluorides
or (much more commonly) where effects of high fluoride intake have been
modified or exaggerated by poor diet or malnutrition. Many residents of
India and China exhibit greater effects of fluoride ingestion than their
actual intakes predict that there should be, based on experimental studies
of uncomplicated chronic fluoride toxicosis.
Fluoride ingestion levels have a lifelong effect on the skeleton.
Bones are dynamic in that they constantly undergo growth, adaptive changes,
repair, and remodeling. A proper, but constant fluoride intake, coupled
with good nutrition, promotes a healthier skeletal system.
Developing teeth, particularly permanent teeth, are extremely sen-
sitive to fluorides. Epidemiological and experimental studies have ver-
ified the association of fluorides, particularly waterborne fluorides at
a concentration of approximately 1 ppm fluoride, with production of enamel
that has significant resistance to decay. Significantly higher levels of
fluoride have a converse effect. The enamel-forming cells (ameloblasts)
are stimulated to form a poor enamel matrix with subsequent poor mineral-
ization. How much ameliogenesis is affected depends on fluoride ingestion
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430
levels and other factors such as nutrition. Slight overexpoaure to fluo-
rides results only In slightly hypoplastic enamel which, while not aesthe-
tically pleasing, Is actually harder and more resistant to wear and decay
than normal enamel. Higher fluoride intake levels at the time of tooth
development cause hypoplastic and discolored enamel which may also be
softer than normal (Figure 9.8).
Figure 9.8. Permanent human teeth of a 55-year-old man. Note
extensive discoloration and hypoplastic chalky white areas caused by
the ingestion of water with high fluoride content during the period of
tooth formation.
Once teeth have formed and erupted Into the oral cavity, effects of
excessive fluoride are minimal. After the ameloblasts have completed
their formative work, they are Incapable of reconstructive repair work,
and continued fluoride exposure cannot lead to further enamel defects.
Fluorides do not accumulate in human soft tissues or organs In any
appreciable amounts. Soft tissues are markedly unresponsive to an In-
creased fluoride Intake in terms of showing an elevation of fluoride
content or alteration of function.
Dental benefits from the ingestion of optimally fluoridated water
have been consistently reported through evaluatory surveys from 27 states
in the United States and 9 other countries. More than 100 of these stud-
ies cover surveys ranging from 10 to 22 years. The results consistently
show a marked reduction in the number of decayed, missing, and filled
teeth; a reduction in the size of cavities which occur; and a definite
increase in the number of carles-free children In those Individuals re-
ceiving near the optimum fluoride level during the period of tooth
formation.
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431
The recommended optimum concentration of fluoride in water (0.7 to
1.2 ppm according to locality) has shown no Impairment of, or adverse
effect on, the general health status of individuals. No systemic abnormal-
ities or abnormal laboratory findings have been noted that were associated
with fluoride Ingestlon at the recommended level. Only when relatively
large amounts of fluoride (8 to 20 mg or more per day) are Ingested over
periods of many years are any generalized adverse effects encountered.
9.8 RESEARCH NEEDS
Although extensive research has been conducted and voluminous liter-
ature compiled regarding the effects of fluorine and its compounds on
biological systems, some aspects still need clarification and additional
research.
9.8.1 Properties and Environmental Occurrences
There is a need for a better characterization of the amounts and the
chemical and physical nature of airborne fluorides in suburban, urban,
and especially the industrial atmospheres.
Research is needed to facilitate modeling the dispersion and fallout
of airborne fluorides from industrial sources. Such information would be
useful In predicting the accumulation of fluorides in vegetation, crops,
and pastureland in the vicinity of Industrial sources, as well as Indi-
cating human populations that might be exposed.
Currently employed methods for sampling and measurement of airborne
and partlculate fluorides alone or in combinations still leave much to
be desired. Better standardization of methods and definition of sampling
procedures would allow results to be more easily compared, extrapolated,
and Interpreted as to the total effect on the environment.
9.8.2 Environmental Interactions
Almost no information exists that describes possible Interactions
between gaseous and particulate fluorides or between fluoride and other
pollutants. Such data would be valuable in predicting the degree and
type of possible injury in various biological systems.
Some chemical combinations in biological materials interfere with
analyses for fluorine. Standardized methods of dealing with these inter-
fering factors need to be developed so that analytical results will be
more consistent among laboratories.. Ways to more effectively extrapolate
analytical values (particularly from air sampling) to potential biological
effects should be developed.
9.8.3 Mi croor^anisms
There is a paucity of basic understanding of effects of fluorides on
microorganisms. There is a wide array of microblal responses to fluoride
exposure, but the effects of various governing factors under varied condi-
tions and on different organisms need additional research.
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432
It is known that: (1) certain fluoride levels will inhibit some
enzymes; (2) certain bacteria can concentrate fluorides; (3) fluorides
cause some microbial metabolic alterations; (4) some bacteria develop a
resistance to fluoride effects; (5) there is potential for development
of a whole array of fluoride-containing antimicrobial agents with unique
powers of selective specificity; (6) some persistent fluorocarbons can
be chemically split and decomposed by some bacteria; and (7) many other
phenomena are known but the specific mode of action in these and many
other instances is not fully understood.
Though the role of fluoride incorporated into developing teeth is
known, the mechanism by which topical application of fluoride to teeth
acts as a cariostatic agent is not known. Similarly, interactions of
fluorides and other ions on the development of dental caries are not com-
pletely understood. Apparently fluorides alter the metabolism of oral
microbes, but the mechanism is not understood.
Answering some of the basic questions of fluoride effects on micro-
organisms may lead to better understanding of fluoride effects on other
life forms.
9.8.4 Vegetation
Additional understanding of the structural and physiological char-
acteristics of vegetation sensitivity to or tolerance for fluorides is
needed. Further studies could reveal the location of fluoride accumula-
tions in the cells and its relation to mineral nutrition and other
physiological reactions in vegetation.
Additional research is required in order to determine how various
forms of fluorides influence the different species and varieties of plants
grown under differing environmental conditions such as intermittent expo-
sure. More information is needed regarding the amount of fluoride uptake
by various plants, as compared to the concentrations of fluorides in the
soils. The information gained would make possible extrapolation of more
data from controlled experiments to practical field conditions. There is
presently a paucity of data related to the beneficial and harmful effects
of fluorides on the yield and quality of crops growing under field
conditions.
With increasing demands for energy there has been an increased re-
lease of geothermal waters containing high levels of fluoride and utilized
for crop production. In order to best manage the use of these and other
effluent waters, research on fluoride accumulation, translocation, and
injury to crops is needed. Of particular concern is the effect from use
of high-fluoride waters for sprinkler irrigated crops. Minimizing the
fluoride content of forage crops irrigated with such waters is of concern
to the livestock industry.
9.8.5 Domestic and Wild Animals
Much is now known about various aspects of fluoride toxicosis in
some animals, but our knowledge is far from complete.
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433
Reports of fluoride effects are most often based on studies of con-
fined experimental animals. Because of the many variables and factors
involved in fluoride toxicosis, extrapolation of such experimental data
to practical field situations is often difficult. Fluoride levels that
can be tolerated under different environmental conditions need to be
better defined.
There is a marked variation in tolerance levels reported in the lit-
erature for many lower animal forms, especially aquatic species. Much
additional research is needed, under standardized conditions, to decrease
the reported tolerance ranges.
The effects of interactions of fluorides with other possible toxi-
cants warrant substantial study in all species. These elements may occur
together naturally, yet little is known of their combined effects.
The effects of stress, whether from the environment, poor management
practices, or other factors such as nutritional inadequacies, need more
research.
While it is recognized that some substances, particularly certain
aluminum and calcium compounds, will alleviate symptoms of fluoride tox-
icosis under confined experimental conditions, the practice has not been
thoroughly tested under field conditions. More studies of the amounts
and effects of the total fluoride intake from all combined sources under
field conditions are needed. Likewise, the biological availability of
various types of fluorides from different sources needs to be further
ascertained.
More effort needs to be directed toward determining the mechanism
and pathogenesis of fluoride effects. The mode of action of fluoroorganic
pesticides needs additional study. Is fluorine itself the active agent
or is some other substance in the pesticide involved?
Additional information on the effects of intermittent ingestion of
fluorides, particularly seasonal variations in intake of high-fluoride
content feed and water, is needed. Geothermal energy developments may
release waters having high fluoride contents that may be consumed by ani-
mals or that aquatic species may be exposed to. The relation of this
potentially toxic water to total animal fluoride exposure should be
determined.
Fluorides combine in bone to form fluoroapatite crystals that are
larger and less soluble than normal. What effect does this type of bone
have in animals whose productive efficiency is related to their ability
to periodically mobilize large amounts of calcium from their bodies?
Heavily lactating dairy cows and laying hens must utilize some of their
own body stores of minerals to attain a high level of productive perform-
ance. The effect of high fluoride content in bone on such performance
needs further study.
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434
9.8.6 Humans
There are many worthwhile topics for research relating to the effects
of fluorides on humans. Basic studies on some lower-life forms, if ade-
quately planned and properly extrapolated, may give further insight into
some aspects of the effects of fluorides. Accurate current data on fluo-
ride consumption from food, water, and beverages in different geographic
areas, under various economic and cultural circumstances are needed. Stud-
ies using a systematic approach based on a dose-response plan should be
made on basic growth effects of fluoride on cells. The effects of fluo-
rides on cell membrane permeability should be studied. Additional research
is needed regarding long-term effects of fluoride-induced bone changes and
the influence of nutrition, especially relative to fluorides' interaction
with other trace elements. The role of various physiological stresses on
the expression of fluoride-induced lesions needs further study. Some fluo-
rine compounds have been used therapeutically. The mechanisms by which
they supposedly aid wound healing should continually be evaluated. Addi-
tional information is needed regarding causes that may mimic the effects
of fluoride on teeth. Studies relating to the effects of fluoride on
biological systems should utilize levels that approximate those normally
found in the environment or those that can be realistically extrapolated.
9.9 CONCLUSIONS
Fluorine is a highly reactive element that readily combines with
other elements to form fluorides. Fluorides are ubiquitous in the envi-
ronment and are found in substantial quantities in some minerals and rock
formations. They are economically important to many industries and their
usage is increasing.
Fluorides are found in all biological systems. Various factors in-
fluence biological responses of vegetation, animals, and humans to fluo-
ride. In proper amounts they are known to be beneficial to humans, some
other animals, and vegetation. In excessive amounts they are toxic to
biological systems. Effects of lifelong ingestion of optimal levels of
fluoride in humans include increased resistance to dental caries and, in
bone, an increase in the size of the apatite crystals that are less solu-
ble. The signs and lesions associated with excessive fluoride intake vary
in magnitude and are dependent on the interactions of the factors that
influence fluoride toxicosis.
The principal sources of fluoride for humans are water and food,
with air usually providing only minimal amounts. Forages contaminated
by some industrial effluents, dust, water, and inadequately defluorinated
mineral supplements are the major fluoride sources for animals. Major
sources of fluoride to vegetation include: gaseous or particulate efflu-
ents from some industrial operations, wind-blown or rain-splashed soil,
and sprinkler irrigation with water of high fluoride content. Fluorides
may be incorporated within the vegetation or may be only surface contam-
inants. Some vegetation may accumulate large amounts of fluoride without
showing any visible effects. Other vegetation is more susceptible to
fluorides.
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435
Vegetation normally contains, and animals and humans normally ingest,
trace amounts of fluorides with no known detrimental effects. Fluoride
intake standards and comprehensive guides have been developed for use in
diagnosing and evaluating biological effects of fluorides.
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436
SECTION 9
REFERENCES
These references are not intended to be all inclusive. Only a few
of those that are most pertinent to this chapter are listed. There was
no intent to slight or disregard other publications that could have been
chosen.
1. Association of American Feed Control Officials, Inc. 1979. Official
Publication. Baton Rouge, La. p. 56.
2. Baylink, D. J., and D. S. Bernstein. 1967. The Effects of Fluoride
Therapy on Metabolic Bone Disease A Histologic Study. Clin. Orthop.
55:51-85.
3. Benedict, H. M., J. M. Ross, and R. H. Wade. 1964. The Disposition
of Atmospheric Fluorides by Vegetation. Int. J. Air Water Pollut.
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23. Leone, N. C., M. B. Shimkin, F. A. Arnold, C. A. Stevenson, E. R.
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ft U.S. GOVERNMENT PRINTING OFFICE: 1980-640-245/247
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/1-78-050
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Reviews of the Environmental Effects of Pollutants:
IX. Fluoride
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7.AUTHOR(s) John s> Drury> j. T< Ensminger, Anna S.
Hammons, James W. Holleman, Eric B Lewis, Elizabeth
L. Preston, Carole R. Shriner, and Leigh E.
8. PERFORMING ORGANIZATION REPORT NO.
ORNL/EIS-85
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Information Center Complex, Information Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
10. PROGRAM ELEMENT NO.
1HA616
11. CONTRACT/GRANT NO.
IAG D5-0403
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory, Cincinnati, Ohio
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati. Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final December 1979
14. SPONSORING AGENCY CODE
EPA/600/10
16. SUPPLEMENTARY NOTES
16. ABSTRACT
This document is a review of the scientific literature on the biological and
environmental effects of fluoride. Included in the review are a general summary
and a comprehensive discussion of the following topics as related to fluoride and
specific fluorine-containing compounds: physical and chemical properties; occur-
rence; synthesis and use; analytical methodology; biological aspects in microorga-
nisms, plants, wild and domestic animals, and humans; and distribution, mobility,
and persistence in the environment. The document also contains an evaluation of
potential hazards resulting from fluoride contamination of the environment and
suggests current research needs. More than 1000 references are cited.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
cos AT I Field/Group
*Pollutants
Toxicology
Fluoride
Health Effects
06
06
8. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (ThisReport)'
Unclassified
21. NO. OF PAGES
472
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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