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National Research Council of Canada
NRC Associate Committee on Scientific Criteria for Environmental Quality

Environmental Fluoride 1977

by Dyson Rose & John R. Marier
National Research Council of Canada

NRCC NO. 16081
ISSN 0316-0114

The Associate Committee on Scientific Criteria for Environmental Quality was established by the National Research Council of Canada in response to a mandate provided by the Federal Government to develop scientific guidelines for defining the quality of the environment. The concern of the NRC Associate Committee is strictly with scientific criteria. Pollution standards and objectives are the responsibility of the regulatory authorities and are set for the purpose of pollution control. These may be based on scientific criteria starting point but they also take into account the optimal socioeconomic impact of proposed measures as well as the state of existing technology.

The Associate Committee's program includes the evaluation of available information on the probability of effects of contaminants on receptors together with the related fundamental principles and scientific knowledge. In this work particular attention is directed to receptors and contaminants (and their interactions) important to Canada. This Canadian approach is necessary because evaluations made in other countries or regions will not always be applicable to the particular circumstances prevailing in Canada.

Members of the Associate Committee, its Subcommittees and Expert Panels, serve voluntarily and are selected for their individual competence and relevant experience with due consideration for a balance among all sectors in Canada. Responsibility for the quality of study documents rests with the Associate Committee. Each report is carefully reviewed according to a multi-stage procedure established and monitored by the National Research Council of Canada in order to preserve objectivity in presentation of the scientific knowledge. Publication and distribution of the report are undertaken only after completion of this review process.

Comments on Associate Committee documents are welcome and will be carefully reviewed by the Expert Panels. It is foreseen that these scientific criteria may be revised from time to time, as new knowledge becomes available.

All documents published by the Associate Committee are published in both French and English.

FOREWORD

This report was requested by the Management Subcommittee of NRC's Associate Committee on Scientific Criteria for Environmental Quality. Dr. Dyson Rose (retired), formerly of the National Research Council's Division of Biological Sciences, undertook the task of preparing this report, with assistance from J.R. Marier of NRC's Environmental Secretariat

The report emphasizes Cause/Effect interrelations of environmental fluoride, and also attempts to identify deficiencies in the current scientific knowledge. The compilation covers the scientific literature that came to the authors' attention prior to June 30, 1977.

The report has been reviewed by the members of the Management Subcommittee of NRC's ACSCEQ, and by the following individuals:

Dr. J. Franke, Orthopedics Clinic, Martin Luther University, Halle, Wittenburg, DDR;

Drs. C.C. Gordon and P.C. Tourangeau, Environmental Studies Laboratory, University of Montana, Missoula, U.S.A.;

Dr. E. Groth, Environmental Studies Board, National Research Council, Washington, D.C., U.S.A.;

Dr. R.J. Hall, Analytical Chemistry Department, U.K. Ministry of Agriculture, Fisheries, and Foods, Newcastle-upon-Tyne, England;

Dr. S.S. Sidhu, Newfoundland Forest Research Centre, Canadian Forestry Service, Environment Canada, St. John's, Newfoundland, Canada.

The authors wish to express their thanks to the members of the Management Subcommittee, and to the other reviewers, for the valuable comments received. However, we must emphasize that the viewpoints expressed in this report represent our own assessment of the environmental fluoride situation.

The authors also wish to express their gratitude to Miss Lynda Boucher and Miss Pat Moss, for their sustained cooperation in typing this report.

Dyson Rose and J.R. Marier
October 4, 1977

TABLE OF CONTENTS

LIST OF TABLES
LIST OF FIGURES

INTRODUCTION

1.0 SOURCES AND DISTRIBUTION OF FLUORIDE POLLUTION

1.1 SOURCES

1.1.1 Atmospheric Emissions
1.1.2 Aqueous Discharges
1.1.3 Solid Wastes

1.2 DISTRIBUTION OF FLUORIDE

1.2.1 Airborne Fluoride
1.2.2 Water-borne Fluoride

2.0 EFFECTS OF FLUORIDE POLLUTION ON THE ENVIRONMENT, AND ON AGRICULTURE AND FORESTRY

2.1 EFFECTS ON VEGETATION

2.1.1 Aquatic Vegetation
2.1.2 Terrestrial Vegetation
2.1.2.1 Ecological Effects
2.1.2.2 Fluoride-Induced Effects on Agricultural and Forest Crops
2.1.3 Criteria for Crop Injury

2.2 EFFECTS ON ANIMALS

2.2.1 Aquatic Species
2.2.2 Insects
2.2.3 Wildlife
2.2.4 Livestock

3.0 PHYSIOLOGICAL EFFECTS OF FLUORIDE ON ANIMALS AND MAN

3.1 BLOOD

3.1.1 Fluoride Content of Blood
3.1.2 Effect of Fluoride on Blood Components

3.2 URINE

3.2.1 Fluoride Content of Urine
3.2.2 Effect of Fluoride on Urine Components

3.3 FLUORIDE-INDUCED CHANGES IN ENZYMES AND METABOLITES IN SOFT TISSUES

3.4 BONE

3.4.1 Fluoride Content of Bone
3.4.2 Fluoride Induced Changes in Bone

3.5 MUTAGENIC AND RELATED EFFECTS OF FLUORIDE

4.0 ORGANIC FLUORIINE COMPOUNDS

4.1 METHOXYFLURANE
4.2 OTHER ORGANOHALIDE ANASTHETICS
4.3 MISCELLANEOUS ORGANIC FLUORINE COMPOUNDS

5.0 FLUORIDE AND HUMAN ILLNESS

5.1 FLUORIDE INTAKE BY HUMANS

5.1.1 Intake From Foods and Beverages
5.1.2 Intake From Air

5.2 CARCINOGENIC IMPLICATIONS
5.3 OCCUPATIONAL FLUOROSIS
5.4 NEIGHBORHOOD FLUOROSIS
5.5 ENDEMIC FLUOROSIS (HYDROFLUOROSIS)
5.6 DIETARY-NUTRITIONAL DEFICIENCIES OR IMBALANCES AND FLUOROSIS
5.7 THYROID FUNCTION
5.8 KIDNEY RELATED PROBLEMS
5.9 ATTEMPTS TO ESTIMATE CRITERIA FOR HUMAN INTAKE OF FLUORIDE

5.9.1 Criteria Based on Bone Fluoride and Plasma F-
5.9.2 Assessment of Fluoride Intake From Air

6.0 OVERVIEW AND RECOMMENDED RESEARCH

REFERENCES

LIST OF TABLES (back to top)

1 - Total Fluoride Emissions to the Atmosphere by Canadian Industrial Sources in 1972
2 - Estimated Soluble Fluoride Emission Rates and Total Emissions for U.S. Industries, 1968 or 1970 Data
3 - Fluoride Emission Rates Collected from Various Reports on the Aluminum Industry
4 - Comparison of Fluoride Emission Rates in the Primary Aluminum Industry in Canada and the U.S.
5 - Fluoride Emissions from Phosphate Fertilizer Plants
6 - Volumes and Fluoride Contents of Some Industrial Waste Waters
7 - Fluoride Content of Water from the East Gallatin River, Montana
8 - Influence of Domestic and Industrial Sewage on the Fluoride Content of Rhine and Ham River Water
9 - Regression Equations Relating Airborne Fluoride Concentration to Plant Response
10 - Fluoride Content of Insects from Polluted and NonPolluted Areas of Montana
11 - Fluoride Content of Bones of Animals Collected in Non-polluted Areas of Montana
12 - Fluoride Levels in the Bones of Wild Birds from Non-polluted Areas
13 - Regression Equations Relating Plasma Ionic Fluoride Levels to Age in Adult Humans
14 - Mean Plasma Ionic Fluoride Levels for Humans Residing in Non-fluoridated and Fluoridated Communities
15 - Effect of Fluoride on the Levels of Various Blood Components in Experimental Animals
16 - Effect of Fluoride on the Levels of Various Blood Components in Humans
17 - Effect of Fluoride on Levels of Metabolites in, and Physiological Activities of, Animal Soft-Tissue Organs
18 - Effect of Fluoride on Some Physical Parameters of Animal Bones
19 - Recent Data Illustrating the Effects of Environmental Factors on the Range of Fluoride in Some Foods
20 - Recent Data on the Daily Intake of Fluoride by Children
21 - Recent Data on the Daily Intake of Fluoride by Adults
22 - The Percentage Contribution of Water and of Various Foods to the Fluoride Ingested by Humans
23 - Health Problems Among Residents Near Fluoride-Emitting Sources
24 - Symptoms Common to Both Fluoride Intoxication and Magnesium Deficiency
25 - Fluorosis in Persons Who Have the Diabetes Insipidus Syndrome

LIST OF FIGURES (back to top)

1 - An illustration of the atmospheric distribution of gaseous fluoride, in relation to elevation and distance from an industrial point source. (see figure)
2 - Influence of airborne gaseous fluoride on the yield of beans, strawberries, and oranges, as plotted from the data of several authors. (see figure)
3 - Influence of dietary fluoride on the weight-gain of young swine. (see figure)
4 - Interrelation between rib bone fluoride content, blood plasma F-, and fluoride intake from three daily meals. Data are for 55-year-old lifetime residents. (see figure)

INTRODUCTION (back to top)

"Environmental Fluoride" (Marier and Rose 1971) was largely completed before the National Research Council, Canada, Associate Committee on Scientific Criteria for Environmental Quality had become operational. The document thus differs somewhat in format from later Associate Committees' documents. The relevant Subcommittee therefore requested another document on this topic.

Comprehensive reviews on fluoride were published by the World Health Organization (WHO 1970), by the U.S. National Academy of Sciences (NAS 1971), and as "a non-experimental dissertation on a topic dealing with political aspects of public policy-making on scientific issues" (Groth 1973). These three documents differ from one another in intent, but all agree on the need for further research on the effect of environmental fluoride. Thus the WHO (1970) report states:

"Little is known about the in vivo effects of fluoride at the low levels occurring naturally in body-fluids and soft tissues on enzymes and the various facets of general metabolism in the living organism..."

"However, the indices of early intoxication are poorly defined and this has resulted in an element of speculation and confusion about the toxic potentialities of the fluoride ion".

Similar statements emphasizing the lack of precise knowledge are found elsewhere in the document.

Similarily, the National Academy of Sciences document (NAS 1971) states:

"The available information is insufficient in depth and scope to allow unequivocal statements to be made about the effects on plants of fluoride at low atmospheric concentrations. One reason for the lack of information is the paucity of experiments designed to relate air quality to effects on plants. A second is the lack of sufficient ambient-air monitoring in connection with field studies and surveys, due in part to the lack of accurate and precise methods for the separation and collection of particulate and gaseous fluorine compounds. A third reason is the inadequacy of present experimental techniques for long-term studies in which field conditions can be simulated".

"Unfortunately, many studies for a better evaluation of the effects of airborne fluoride on human health remain to be done. Not many authors have investigated the incidence and magnitude of effects on the thyroid gland, the hematopoietic system, the cardiovascular system, and the central nervous system. However, these systems respond readily to a number of stresses, not only to fluoride, and a causal relation to airborne fluoride has been established only poorly or not at all. More careful studies are required, with better attention being paid to the nature of the responses, the presence or absence of other medical or physical conditions that might contribute to the occurrence of the responses, and the proper control groups".

"The airborne fluorides to which subjects are exposed must be better evaluated with respect to amounts of fluoride-containing material, proportions of gaseous and particulate fractions, chemical and physical properties (including particle size) of the particulate fraction, and meteorologic conditions in the surrounding community when resident populations are being studied".

The third document (Groth 1973) presents the need for further research even more emphatically. Thus

"...there have been very few studies of potential non-lethal effects of chronic accumulation of fluoride on populations exposed to lifetime ingestion".

"Amounts of fluoride ingested by average adults are sufficient to produce chemical and structural changes in the mineral of the bones, and the long-term health significance of these changes is not known".

"In short, there are a great many unanswered questions in regard to long-term potential adverse effects of fluoridation, and a number of indications of potential harm which have not been shown yet to be unfounded. In view of the seriousness of some of the possible consequences if fluoridated water is in fact harmful to a fraction of the population, extensive, continuing research would seem imperative. However, there are no ongoing large-scale efforts being made to carry out such research".

During the seven year period (1970 to 1977) covered in the present document, there has been a voluminous output of literature related to fluoride pollution and fluoride toxicity to plants, animals and man. This has increased our general knowledge of the multiple effects of chronic exposure to fluoride, and has confirmed and possibly augmented the difficulties attending attempts to relate quantitatively exposure and time factors to effect. Nevertheless, a prime purpose of the present review is to identify criteria (dose-response relations) that may assist in establishing limits of exposure. A second purpose is to identify areas where additional research is urgent.

In environmental studies, it is often necessary or convenient to investigate individual sources of fluoride and to focus on the level of fluoride acting through a particular pathway. For example, the pathway involving airborne fluoride, forages, and domestic cattle has been studied extensively. However, it is essential to remember that living organisms respond to the total fluoride impact from all sources: plants are affected by fluorides in soil, water, and air; animals by fluorides in their forages, feed supplements and water; and man by fluorides in his foods, beverages, drugs and prophylactic agents, cigarettes, and air. Therefore a comprehensive assessment of the cumulative impact of fluorides on man's environment requires consideration of the total fluoride contributed by multiple sources.

A serious effort has been made to consider all papers published since 1970 that are relevant to environmental fluoride. Because of the voluminous literature on the dental aspects of fluoride and on the freon-ozone argument, these two areas have been intentionally left for others to summarize and develop criteria. Papers on fluoride therapy in humans have been included only because data on high-dose, short-term effects appear relevant to chronic exposure (low-dose, long-term) situations. Reports on pollution control technology are considered to be outside the scope of this review. Sampling and analytical methodology are discussed only in relation to the interpretation of environmental effects.

Undoubtedly we have overlooked valuable research papers particularly among those published in languages other than English and French; for this we apologize to the authors concerned. For conciseness and brevity, we have omitted specific reference to about half the papers we examined.

1.0 SOURCES AND DISTRIBUTION OF FLUORIDE POLLUTION (back to top)

1.1 SOURCES (back to top)

The sources of fluoride in man's environment have been discussed by numerous authors (e.g. Marier and Rose 1971; NAS 1971; Bittel and Vaubert 1971; Prival and Fisher 1974; Bojic et al.1975). Sources of fluoride include natural sources such as volcanic gases, and soluble fluorides in the earth's crust. However, the pre- ponderance of pollution problems have been caused by modern-day man-made sources which singly, or in combination, occasionally lead to the presence of harmful levels of fluoride compounds in air, water, food or forage. In this section, we present data on the amounts of fluoride discharged from major man-made sources, and attempt to indicate the extent of the geographical areas affected by the fluoride discharges.

Fluoride emission data from industrial sources are often circumscribed by industrial secrecy and by industries' ability to have environmentally-relevant data classified as proprietary to the industry. Also, governments have sometimes been loath to release data gathered at public expense as well as those submitted by industry. The rationale often given for this secrecy is that it allows decisions to be made in the absence of public clamor and emotionalism. Less rationally, it also denies the public's right to take part in decisions involving a balance of economic and environmental objectives. The secrecy situation in Great Britain has been discussed by Tinker (1972).

Industrial and governmental secrecy has been detrimental to Canadian efforts to develop criteria relating the concentration of pollutants to their effects. Thus the studies of LeBlanc and his students (1971, 1972) on the effects of air-borne fluorides on epiphytes and bryophytes could not be related to existing but secret data on fluoride concentrations in the air. Similarly, the author of a report on pollution in the Shawinigan and other areas of Quebec (Pellissier 1973) repeatedly comments on the non-availability of results from related air-monitoring programs. Sidhu and Roberts (1976) encountered a parallel situation in Newfoundland.

1.1.1 Atmospheric Emissions (back to top)

In spite of the secrecy discussed above, some information on atmospheric fluoride emissions by industry has become available during recent years. Environment Canada (1976) published data on fluoride emissions to the atmosphere in Canada during 1972. A portion of the data is reproduced in Table 1 and shows that, with the exception of aluminum production, the fluoride emissions are preponderantly in gaseous form. The U.S. Environmental Protection Agency (EPA 1972) reported the corresponding U.S. data in considerable detail, and we present summarized data in Table 2.

Unfortunately, the data in Table 1 and 2 are not directly comparable. Fluoride emissions into the atmosphere occur in gaseous and particulate forms, and the particulates vary in solubility. The solubility of the particulate matter has a marked influence on its toxicity to plants and animals (NAS 1971). Thus, the "Total soluble fluoride emissions" as recorded in Table 2 are more directly relevant to environmental-impact criteria than are either the "total" or "percent gaseous" data of Table 1.

The primary aluminum reduction industry, which is the largest single-industry source of atmospheric fluoride pollution in Canada (Table 1), and the third largest in U.S., has been the subject of several studies. Data on the rates of fluoride emission (i.e. the amount of fluoride released to the atmosphere per unit of aluminum produced) are presented in Table 3. The low emission rates for recently constructed smelters are indicative of the progress being made in controlling atmospheric emissions by this industry.

An interesting comparison can be made between the emissions from U.S. primary smelters in 1970 and those of Canadian smelters in 1972 (Table 4). Effluent fluorides, (i.e. total fluoride at source, before passage through emission control units) per unit of aluminum produced, are similar for Canadian and U.S. reduction lines. However, the average amount of fluoride emitted to the atmosphere, per ton of aluminum produced, is markedly higher for Canadian than for U.S. smelters.

The steel industry, which is the major source of atmospheric fluorides in U.S. and third largest in Canada (Tables 1 and 2), does not appear to have been studied as intensively, regarding fluoride emissions, as the aluminum industry. In part, this is probably related to the presence of other pollutants besides fluoride in emissions from steel mills, and to the fact that attention has been primarily focussed on pollution by sulfur dioxide and particulate matter.

In relation to the phosphate industry, which is also a major source of fluoride emissions, Osag et al. (1976) have presented a comparison of "industry wide" and "best controlled" atmospheric emissions (Table 5). It is difficult to relate these data to the rate of emission (3.1 to 4.1 lb/ton of P205 equivalent) in Table 2, but it would appear that the data of Osag et al. refer only to specific steps in the process and not to overall emissions. They probably do not include emissions from the surface of gypsum ponds (King and Ferrell 1975).

In discussing the lesser sources of fluoride emissions shown in Table 1, the Environment Canada (1976) report notes that "It is not possible to rationalize" differences in the fluoride effluent data reported by the Canadian "clay products" industry and by the U.S. Environmental Protection Agency. Environment Canada's estimates of possible fluoride emissions by this source therefore vary from 274 to 2463 tons (249 to 2239 metric tons) in 1972 (Environment Canada 1976, their Table 7). The lower figure was used to calculate the "misc. sources" total shown in Table I .

Glass manufacturing firms in Canada are reported to have "almost totally phased out by 1972" the use of fluorspar as a flux. Fluoride emissions by this industry are therefore thought to be low, i.e. 5 tons (Environment Canada 1976, p. 14, 15).

The Environment Canada (1976) report on fluoride emissions by the petroleum industry (hydrofluoric acid alkylation process) indicates an "HF consumption" of 0.3 to 0.8 lb HF/barrel of alkylate. Available information does not enable us to relate "consumption" to emission. However, if we assume that emissions occur at the same rate as in U.S. plants (Table 2), the estimated total 1972 emissions in Canada of "less than one ton" (Environment Canada 1976, D. 19) indicates a Canadian production of alkylate of less than 37 barrels per day. Data published by Energy, Mines and Resources of Canada (EMR 1973) indicate that Canadian HF-alkylation capacity was 13,470 barrels per day in 1972, and had increased to 24,620 barrels per day in 1975 (EMR 1976).

Data on fluoride added to the atmosphere by domestic burning of coal in Canada are not available, but the amounts are probably small because of the extensive use of other fuels for domestic heating in Canada. The potential impact of domestic fuel burning on fluoride pollution should be considered if changes in fuel consumption patterns occur. Baum et al. (1972) report that 34 to 72% of the fluoride in coal, which varied from 0.0025 to 0.039% in the coals tested, was contained in the flue gases of an industrial type furnace. We have been unable to locate similar data for domestic-type furnaces.

1.1.2 Aqueous Discharges (back to top)

Data on the volumes and concentrations of fluoride wastes being discharged to rivers, lakes and oceans are not plentiful. All wet-scrubbing systems for control of atmospheric emissions probably contribute some fluoride to the aqueous discharge, but economic factors often favor recovery of fluoride from the scrubbers (e.g. as precipitated calcium fluoride) and re-use of the water. Effluents and overflows from limed settling-ponds contribute fluoride to the aqueous environment. General discussions of problems related to pollution of waterways have been published by McCaull (1972) and Cheremisinoff and Habib (1973).

Recent data on the volumes and fluoride contents of industrial waste waters (Table 6) make it evident that large quantities of fluoride are being discharged to waterways. For example, it can be calculated that if all North American plants discharge fluoride at the rate (14 kg/metric ton) reported by Teworte (1972), the total discharge by the aluminum industry would exceed 63,000 metric tons, or about 4-fold the amount discharged into the atmosphere.

The production of uranium tetra- and hexa-fluorides involves the discharge of significant quantities (625 to 1134 tons per year in U.S.) of hydrofluoric acid by way of aqueous sewage (EPA 1972).

Rak (1969) presented data on the discharge of fluoride in waste waters during production of some inorganic fluoride compounds. The reported discharges ranged from 5.7 kg per metric ton of product for aluminum fluoride, to 55 kg/metric ton of product for cryolite.

Pettyjohn (1975) has reported environmental damage caused by an unsuitable aqueous disposal method applied to steel industry "pickling wastes".

Dicalcium phosphate 0.14%
Triple superphosphate 1.87%
Diammonium phosphate 2.00%

Gordon (1970b) lists fluoride contents ranging from 0.58 to 2.34% for fertilizers sold in Montana.

1.2 DISTRIBUTION OF FLUORIDE (back to top)

Reviews on fluoride and fluoride effects (WHO 1970; NAS 1971) usually stress that "fluoride is well-nigh ubiquitous: detectable traces occur in almost all substances" (Hodge and Smith 1977). This can be said about a great number of pollutants; nevertheless, this fact is relevant to a discussion of fluoride for two reasons: (1) it emphasizes the need to consider total fluoride from all sources when investigating fluoride injury to plants, animals and man; and (2) it often makes estimation of the role played by industrial fluoride pollution more difficult. Manmade fluoride pollution nearly always arises from a small geographic area or point-source and is detectable above the natural or background fluoride over a definable area. Assessment of the distribution and extent of these man-made fluoride anomalies is considered in this section. Attention will, of course, be focussed on soluble fluoride as this is the most environmentally-relevant form (cf. p. 10).

1.2.1 Airborne Fluoride (back to top)

The presence of fluoride in rainwater collected in areas remote from human settlements (Carpenter 1969) suggests that air which has not been contaminated by human activity does contain some fluoride. However, ambient-air fluoride is usually below the level of detection, which can be roughly defined as less than 0.05 ug F/m3 air (Thompson et al. 1971). Natural phenomena such as dust storms and forest fires can contribute small amounts of soluble fluoride to the atmosphere. Volcanic activity can contribute larger amounts. However, except for unusual circumstances (e.g. volcanic activity), all soluble fluoride found in the atmosphere in excess of 0.05 ug/m3 can be assumed to have originated from man-made sources.

From the above discussion, it miqht be concluded that the distribution and extent of abnormal fluoride concentrations arising from point-sources would be relatively easy to monitor. Unfortunately, however, man's activities are so widespread that background levels exceeding 0.05 ug/m3 are not rare, even in rural areas of industrialized countries. The spread of pollution from a major source often must be determined against a somewhat variable background level arising from multiple minor sources (e.g. domestic coal burning) and from distant major sources (Fischer and Brantner 1972). Thompson et al. (1971) reported data on 9,175 air samples collected in various non-industrial urban sites and 2,164 samples from non-urban sites. The distributions, as percentages found within the limits (ug/m3) shown, were: urban = 88% < 0.05; 12% between 0.05 and 1.0; 0.2% > 1.0; non-urban 98.5% < 0.05; 1.5% between 0.05 and 1.0; 0.14% > 1.0. Davison et al. (1973) reported that only a small percentage of urban air samples from Northumberland contained < 0.05 ug F/m3, and that the average fluoride level was 0.28 pg/m3. On the other hand, "most" air samples from rural sites contained < 0.05 ug F/m3 even though 19% of the samples exceeded the 0.1 ug/m3 level.

Data which have become available since 1970 confirm the presence of abnormally high airborne fluoride concentrations in association with many of the industries for which fluoride emissions are shown in Table 2. Peak fluoride concentrations within these high-fluoride zones are rarely available, because they occur over company-owned land. In a study of the effectiveness of potroom ventilization, Sutter (1973) recorded mean daily atmospheric concentrations (aluminum industry) of 540 to 3700 ug F/m3. In a study of fluoride emissions from an openhearth (steel smelter) furnace with an electrostatic precipitator, Brown et al. (1971) presented the data shown in Fig. 1. These data are no longer representative of this particular smelter, because the operating procedure has been changed (Schuldt 1977). They do, however, indicate the high concentrations and the atmospheric stratification that can occur within a few hundred feet of a point-source of fluoride emissions. The stratification was still apparent 12,000 feet (3.6 km) from the source (Fig. 1).

Data for airborne fluoride concentrations in areas surrounding fluoride-emitting factories have been presented in numerous reports. These include data gathered by static and dynamic air sampling devices (IJC 1971; Linzon 1971; Bourbon et al. 1971) and by analysis of vegetation (Linzon 1971; Gilbert 1971; Carlson 1972; Gordon 1970a, 1976; Keller 1975; Jacobson and Weinstein 1977; Sidhu 1977a).

The studies of C.C. Gordon and his co-workers at the University of Montana (Gordon and Tourangeau 1977; Tourangeau et al. 1977) are particularly important because of their contribution to our knowledge of "shielding" effects. These studies clearly demonstrate that vegetation tends to impede or intercept fluoride in air that is moving through the foliage, thus creating an adjacent down-wind area of lower airborne fluoride concentration. (Little or no effect of this sort was observed with sulfur dioxide). The effect is so marked with airborne fluoride that samples of needles taken from the upper, windward side of a pine tree exposed to atmospheric fluoride will consistently contain 2- to 4-fold more fluoride than found in equal-age needles from the lower, lee side of the same tree. The effect becomes even more marked when windward and leeward sides of a small grove are compared; also, groundcover vegetation under a stand of pines may contain little fluoride, even in areas that are obviously polluted. Terrain elevations that allow unimpeded impact by airborne fluoride result in an increased amount of fluoride in exposed vegetation (Note also the stratification effect illustrated in Fig. 1).

Sidhu (1977b) has similarly observed the effects of terrain elevation and shielding in a fluoride-polluted Canadian coniferous forest. However, to ensure consistency of sampling, he recommends collection of foliage samples from the windward side of the mid-crown, "because defoliation occurred in the upper crown". In a study of the fluoride content of lichens, Gilbert (1971) observed that even a boulder provided some shielding from fluoride carried by prevailing winds.

These observations make the siting of air-sampling devices and the collecting-points for vegetation extremely critical. Gordon and Tourangeau (1977) recommend that the sites for air-sampling devices for Maryland farmlands be "in the middle of open fields, ... one to two feet (0.3 to 0.6 m) above the height of corn crops and away from stands of hard woods which impede or intercept the fluoride-polluted winds". Samples of agricultural crops should be taken from parts of the field that are 50 ft (15 m) or more from hedgerows or other vegetation that is taller than the crops. In non-agricultural areas, sampling should be from near the top of windward slopes, at a height sufficient to be clear of any screening by vegetation.

The fluoride content of vegetation varies with the plant species and variety, and with the stage of development (Chang 1975; Weinstein 1977). It is also influenced by the plant tissue sampled (leaf, fruit, etc.), the age of individual leaves or needles (Chang 1975; Gordon 1976), the location of sampled foliage on the plant (Gordon 1976), and the season (Harris 1974). All these factors must be considered when sampling vegetation as a means of monitoring fluoride in air. [See Guderian and Schoenbeck (1971), Teulon (1971), and Sidhu (1977a) for a discussion of other aspects of the methodology.] Uptake from the soil must also be considered (Weinstein 1977).

When the above factors are taken into consideration in the planning of a study, reliable data on the extent, concentration and distribution of a man-made atmospheric fluoride anomaly can be determined with reasonable accuracy, even against an urban fluoride background. These factors are influenced by pollution loading, wind velocity and constancy, other meteorological conditions, and geographic factors. Some examples of airborne fluoride discharges are given herein. Preference has been given to Canadian data.

Gilbert (1971) studied fluoride levels around a small (20,000 tons per year) aluminum smelter in Scotland. On the basis of an average rate of emission for smelters in O.E.C.D. countries of 6.1 kg F per metric ton of aluminum (OECD 1972), the total discharge would have been only 123 metric tons (135 short tons) per year of total fluoride. The smelter was surrounded by a "bryophyte desert" about 0.5 mile (0.8 km) wide and extending about 1 mile (1.6 km) downwind and 0.7 mile (1.1 km) upwind. This, in turn, was surrounded by a further area of damage, and elevated fluoride levels in vegetation were observed 4.3 miles (6.9 km) downwind.

LeBlanc and co-workers (1971, 1972, 1975) studied epiphytes in the proximity of a Canadian aluminum smelter with an unspecified (proprietary company data) amount of atmospheric fluoride discharge. The area of vegetative disturbance, as indicated by an "Index of Atmospheric Purity" based on species frequencies, extended 10 km (6.2 miles) downwind.

Carlson and Dewey (1971), Carlson (1972), and Harris (1974) have reported extensively on the distribution of atmospheric fluoride discharged by an Anaconda aluminum smelter in Flathead County, Montana. In spite of assurances by the company that vegetation damage would not occur (Burk 1972), this smelter had a 10-year history of causing foliage injury in the surrounding territory. Nevertheless, the smelter capacity was greatly expanded between 1965 and 1970. By 1970, foliar material from various species contained fluoride levels in excess of background values (i.e. greater than 10 ppm, dry weight basis) over a 213,760 acre (86,570 hectare) area. Extensive injury, and foliar fluoride concentrations above 30 ppm, were observed over a 69,120 acre (27,994 ha) area. During 1970, this Anaconda plant installed fluoride emission control equipment that reportedly reduced emissions from 7,500 to 2,500 lb (3,410 to 1,136 kg) per day. A subsequent survey showed above-normal (> 10 ppm) fluoride in 1971 foliage over an area of 179,200 acres (72,575 ha) along with serious injury and > 30 ppm fluoride in foliage over 15,200 acres (6,156 ha).

Sidhu and Roberts (1976) reported damage and high foliar fluoride concentrations in the vicinity of a Canadian phosphorus plant. The total area affected was 11,434 ha (28,242 acres), but fluoride emission data were "confidential to the industry". However, in a subsequent paper, Sidhu (1977a) reported airborne fluoride concentrations ranging from 0.8 to 20.8 ug/m3 at a 3 0.7 km distance from this factory, and concentrations of 0.06 to 0.34 ug/m at 18.7 km.

Preliminary data have also become available concerning fluoride distribution around an aluminum reduction site at Kitimat B.C. (Gordon 1976). At a production rate of 250,000 tons aluminum per year, and a reported emission rate of 5 to 7 lb F/ton Al, total fluoride emissions are estimated at 625 to 875 tons (568 to 795 metric tons) per year or 3,425 to 4,795 lb/day (1,556 to 2,180 kg/day). The data available are insufficient to define the totality of the area affected by these emissions, but "a twenty-plus square mile 'death band' of dead timber trees" (5,180 ha) is reported. Foliage collected from coniferous trees 5, 10, 11, and 20 miles north of the smelter contained higher fluoride levels than Gordon had observed at these distances around other aluminum plants.

Fischer and Brantner (1972) studied the fluoride content of beech (Fagus silvatica) leaves in Austrian urban areas of heavy and moderate air pollution, and in open country. Fluoride levels of less than 10 ppm were common in leaves from unpolluted areas. Fluoride levels in leaves from urban areas were up to 47 ppm. Even in wooded areas outside the city limits, fluoride levels well above 10 ppm were encountered at "fronts of collision which were caused by the particular meterological conditions" in the area.

1.2.2 Water-borne Fluoride (back to top)

The "average dissolved fluoride content of the major rivers of the world is fairly well defined at 0.01 to 0.02 ppm" (Carpenter 1969). Atmospheric dusts are thought to be the major sources of this "background" fluoride, although the source of a large portion of the fluoride-containing atmospheric dust is a subject of some dispute (Carpenter 1969, Bressan et al. 1974). Leaching of fluoride from rocks increases the fluoride content of ground waters, but under the conditions observed by Jacks (1973), this source contributed little fluoride to surface waters.

The contribution of domestic sewage from cities to the fluoride content of rivers was studied by Masudo (1964). The amount of fluoride found in effluent sewage, in excess of the amounts present in the cities' water supplies, were as follows:

Raw sewage ( 4 cities) 1.30 mg/l
After primary treatment (23 cities) 1.28 mg/l
After secondary treatment (29 cities) 0.39 mg/l

Fluoride is considered to be a "difficult to treat" industrial waste (Environment Canada 1975).

Soltero (1969) and Bahls (1973) reported fluoride concentrations in the East Gallatin river (Table 7). These data show that elevated fluoride caused by sewage discharge from the city of Bozeman was detectable for a distance of 4 km below the sewage outlet.

A study of fluoride input into Narragansett Bay, Rhode Island (reviewed by Groth 1975b) indicated that "36% of the fluoride entering the Bay was due to fluoridation of water supplies in five communities on rivers feeding into the estuary".

Data on the fluoride content of the Rhine (Teworte 1972) and Ham (Lee and Whang 1972) rivers (Table 8) also indicate that both domestic and industrial sewage contribute significantly to the total fluoride content. Seepage and leaching from solid and liquid waste disposal sites can also cause serious pollution of run-off and ground waters (Stepanek et al. 1972; Pettyjohn 1975).

The distribution of fluoride released into flowing bodies of water such as rivers is usually detectable on the basis of differentials between the fluoride content of samples taken above and below the known or suspected source of pollution. However, lakes, bays, and inlets can present a more difficult problem, although comparative analyses (i.e. in relation to input-sources) can provide meaningful information on the degree and extent of a contaminated zone. Ocean water has a nearly constant fluoride content of 1.35 to 1.4 mg total fluoride/litre, (Carpenter 1969; Bewers 1971), and a fluoride-to-chloride ratio of 6.71 0.07 x 10 5:1 (Warner and Jones 1975). Theoretically, inflow of fluoride-contaminated river water should be detectable as a change in the F:Cl ratio. However, if an ion-specific electrode is used to determine fluoride in brackish or ocean water, it is necessary to correct the observed fluoride ion activities for the complexing effect of magnesium (Thompson 1967; Brewer et al. 1970).

Use of the F:Cl ratio has provided considerable information showing fluoride pollution of estuaries and ocean-bays. For example, Kitano and Furukawa (1972) determined the fluoride-to-chloride ratio, to estimate fluoride pollution in Tokyo Bay. Fluoride concentrations in contaminated inflowing waters ranged from 0.15 to 1.07 mg/l, with F:Cl ratios of 1.4 x 10-4 to 3.6 X 10-2:1. Surface samples from the bay contained from 0.63 to 1.28 mg F/kg water, and the F:Cl ratio varied from normal (i.e. 6.71 X 10-5) up to 9.05 x 10-5:1. Values above 7.1 x 10-5 were encountered at 11 sampling points (mostly surface) in the western half of the Bay, but not at sampling points in the eastern half which is influenced by incoming seawater.

The distribution of waterborne fluoride discharged from the aluminum reduction plant at Kitimat, B.C., has led to abnormally-high F:Cl ratios throughout the surface waters of Kitimat Harbour (Harbo e,t al. 1974). Observed F.-Cl ratios ranged from 13 to 1,500 x 10-5 (av. 158 X 10-5) and fluoride concentrations ranged from 0.10 to 11.0 mg/l (av. 1.17). Occasional high F:Cl ratios were also encountered in subsurface waters at depths from 10 to 100 m (av. 7.61 x 10-5; range 6.64 to 15.0 X 10-5). Comparable samples taken from Howe Sound "where input of non-natural fluoride is not known to occur" had F:Cl ratios ranging from 7.8 to 66 X 10-5, av. 14.5 x 10-5 for surface samples; and from 6.55 to 7.42 x 10-5, av. 6.83 x 10-5 for subsurface samples. No investigation of the factors causing high F:Cl ratios in surface waters of Howe Sound was reported.

An interesting but incomplete study of water-borne fluoride has been reported for Tampa Bay, Fla. (Taft and Martin 1974). In July 1973, a phosphate plant was discharging an estimated 24,000 lbs (10,900 kg) of fluorine daily, along with quantities of phosphate and nitrate, into Tampa Bay. This resulted in deposition of solid calcium fluoride at the point of discharge and for about 1,000 ft. (300 m) into the bay. The precipitate accounted for only a small portion of the total fluoride in the discharge. Fluoride concentrations in samples of surface water above the fluorite deposit varied between 16.3 and 36.5 ppm. No data were presented for a more extended area of the Bay. Nevertheless, a severe thermal effect was generated at the fluorite:water interface, and this caused a significant increase in the temperature of the surface water. The authors also reported the absence of all living organisms in the afflicted area.

The effect of fluoride on aquatic life is discussed in Sections 2.1.1 and 2.2.1.

2.0 EFFECTS OF FLUORIDE POLLUTION ON THE ENVIRONMENT, AND ON AGRICULTURE AND FORESTRY (back to top)

The sources of man-made fluoride pollution discussed in Section I result in above-normal concentrations which impinge on terrestrial and aquatic flora and fauna, and on man. The exposure of living organisms to above-normal concentrations of fluoride, which induces fluoride accumulation by the organism, may result in an alteration of the organism's biochemistry and morphology. Directly or indirectly, such changes may restrict the organism's ability to maintain its ecological position. In the plant kingdom, an example of this has been provided by McLaughlin and Barnes (1975) who observed that fluoride accumulation in the foliage of some pines and hardwoods reduced photosynthesis and stimulated dark respiration, thus undoubtedly reducing the amount of carbohydrate available for growth and seed production. In the animal kingdom, Gerdes et al. (1971b) report that exposure of fruit flies to low levels of atmospheric fluoride significantly reduced the fecundity and egg hatchability of the descendants who were not themselves exposed to fluoride.

Some published data suggest that exposure to low levels of airborne fluoride can stimulate the growth of some plants (cf. Weinstein 1977). Bennett et al. (1974) suggest that a low level of fluoride and of ozone was the norm under which plants evolved, and that in tests on the effects of exposure to fluoride the "control" plants should not be grown in fluoride-free air. However, growth that occurs as a result of fluoride stimulation is often abnormal (Weinstein 1977). Even the growth stimulation that resulted in an increased fresh weight in bean plants (Pack 1971a) did not result in an increased yield of beans, and the ripened beans produced by exposed plants developed less vigorous seedlings than did beans from control plants (Pack 1971b). It is thus doubtful that the apparent growth stimulation occasionally observed on exposure of plants to low levels of atmospheric fluoride is of any evolutionary, ecological, or economic advantage.

2.1 EFFECTS ON VEGETATION (back to top)

2.1.1 Aquatic Vegetation (back to top)

Available data on the responses of aquatic vegetation to fluoride pollution have been briefly reviewed by Groth (1975a, b). The data are insufficient to allow firm conclusions to be drawn, but do indicate that levels as low as 2 ppm in water can decrease the growth of one species of Chlorella. The data also show that many aquatic plants accumulate fluoride to concentrations that may be many-fold higher than the external concentration.

Ishio and Makagawa (1971) report that Potphyxix tenaa, an alga, was killed by a 4-hour laboratory fumigation with fluoride (1.8 ppm in head space of growth chamber) and that the critical concentration appeared to be 0.9 ppm.

Kilham and Hecky (1973) have discussed possible ecological effects of relatively high natural fluoride levels in African lakes.

The accumulation of fluoride by aquatic plants and plankton is of interest because of its potential impact on animals that consume these organisms. In an unpolluted area of New Zealand, Stewart et al. (1974) observed fluoride levels from 31 to 209 ppm in the shells of species feeding on plankton, and from 1,425 to 1,882 in the skeleton of Blue cod that feed on crabs, shrimp, shell-fish, etc. The data suggest that, for the stages mentioned above, the food-chain concentration factor is at least 10:1. As noted by Groth (1975b), "we have very little knowledge of the sublethal effects of fluoride on behaviour or reproductive processes, or of the potential accumulation of the pollutant in aquatic foodchains. Yet such effects, should they occur, would probably be more important ecologically than the mortality which might result from very high, but short lived, pollution episodes".

2.1.2 Terrestrial Vegetation (back to top)

Dochinger (1971) dates the awareness of fluoride-induced damage caused in terrestrial vegetation back to German reports of the 1880's and states that "For the last 30 years, the injury to agriculture by fluorine compounds has intensified because of the expansion of industries ...." Bossavy (1971) has summarized estimates of the damage occurring primarily to forests, in European countries.

Literature on the biochemical and morphological changes caused by exposure of terrestrial vegetation to fluoride has been reviewed by McCune and Weinstein (1971), Chang (1975) and Weinstein (1977). For consideration of some other aspects of the effects of fluoride on plants, such as the uptake of fluoride from soils, the influence of environmental factors on the uptake of airborne fluoride, etc., the reader is referred to Marier and Rose (1971), NAS (1971), Treshow (1971), Miller and McBride (1975) and Weinstein (1977).

Terrestrial plants exposed to airborne fluoride frequently display foliar damage, sometimes grow less vigorously, and almost invariably accumulate significant amounts of fluoride in their foliage. These effects are all of aesthetic, economic or environmental significance. The interrelations among, and criteria for, each of these factors will therefore be considered with regard to airborne fluoride concentrations.

2.1.2.1 Ecological Effects (back to top)

As noted above, it can be assumed that many of the fluoride-induced changes occurring in vegetation will decrease the plant's ability to maintain its ecological position. However, studies of the actual ecological effects have rarely been undertaken. Coniferous trees seem to be the most seriously affected forest species in many situations (Gordon 1976; Tourangeau et al. 1977; Carlson and Dewey 1971). Moreover, fluoride-induced changes in relative species dominance have been confirmed by Sidhu (1977b), who also commented that:

"Preliminary results of a recent long-term study of the effects of fluoride on forest vegetation in Newfoundland showed that the softwood tree canopy (balsam fir, black spruce, larch) was being replaced by undergrowth of hardwoods (white birch, American ash). As the mortality of the original tree cover (softwoods) continued, the shrub layer showed a significant increase in raspberry, skunkcurrant, calamagrostis, and fireweed, underneath the hardwood tree species. Hardwood species (which defoliate every year) tend to accumulate fluorides at higher concentrations and at a faster rate than the softwoods. Therefore, it is suspected that the change from soft- to hardwood tree cover will result in the addition of higher amounts of fluoride to the soil. Also, the wildlife of the area feeding on the hardwoods will experience fluoride toxicity within a shorter period and over larger affected areas."

Although epiphytes and bryophytes are considered more tolerant to fluoride than conifer species (Sidhu 1977b), alterations in species frequency among these organisms have been observed (LeBlanc et al. 1971, 1972; Gilbert 1971). LeBlanc et al. (1972) report that a few species such as Frullania ebotrancensis, Lecanora impudens, and Physcia ciliata could not be found within a 12 km (7.5 miles) distance from a fluoride source, although they were prevalent in the surrounding territory. Even the species that were able to maintain themselves close to the source were up to five times more plentiful beyond the pollution zone. Gilbert (1971 also reported complete absence of a Lecanora species in a fluoride-polluted area.

It should also be noted that if fluoride is injurious to pollinating insects (see Section 2.2.2), this could result in an indirect, but potentially extensive, effect on some ecological communities.

2.1.2.2 Fluoride-induced Effects on Agricultural and Forest Crops (back to top)

Information on fluoride-induced injury to vegetation, which is often not directly applicable to the development of criteria, has appeared in numerous reports. This information is nevertheless important for an overall concept of fluoride phytotoxicity, and is therefore briefly reviewed.

Bennett and Hill (1973) exposed 4- to 8-week-old barley and alfalfa plants to hydrogen fluoride in fumigation chambers for a single 2-hour period, and measured carbon dioxide uptake as an index of photosynthesis. With this short exposure period, 50 ppb HF were required "before clearly measurable inhibition of the net carbon dioxide rates occurred". The percentage inhibition of apparent photosynthesis was linearly related to HF concentration throughout the range from 0 to 250 ppb, with no evidence of a no-effect threshold within the accuracy of the measurements. Poovaiah and Wiebe (1973) noted that fumigation of soybean plants with low (15 to 20 ppb) concentrations of HF for 1 to 4 hours caused stomatal closing, reduced transpiration, and increased leaf temperature. McLaughlin and Barnes (1975) report that trees which had accumulated 10 to 60 ug fluoride per g dry weight of leaf tissue (from sodium fluoride in an aqueous spray) had a reduced rate of photosynthesis and an increased rate of dark respiration.

Bale and Hart (1973a, b) exposed seedling roots of barley (Hordeum vulgare) to solutions containing 1 x 10-2, 1 x 10-4 and 1 x 10-6 M (190, 1.9 and 0.019 ppm) fluoride (as NaF or HF) for 12 to 72 hours and examined dividing cells for chromosomal aberrations. They concluded that "it is clear that each of the concentrations of sodium fluoride and hydrofluoric acid used in these experiments is capable of inducing chromosomal abnormalities and of producing mitotic inhibition in the meristematic region of roots".

Pack (1971a, b) grew beans from seedling to maturity in the presence of 0.58 to 10.5 ug fluoride/m3 air, then grew a second generation, without exposure to fluoride, from the seeds of these plants. Exposure of the first generation to as little as 2.1 ug F/m3 caused the development of less vigorous second-generation seedlings. Vins and Mrkva (1973) report a decrease of 30 to 70% in the diameter growth of pine trees at pollution levels that caused no otherwise-visible injury. These authors relate the decreased growth primarily to sulfur dioxide pollution, but there is an interesting relation between increasing fluoride emissions between 1960 and 1967 (their Fig. 1) and the rapid decline in annual diameter increments (their Fig. 5) during this same period. (NOTE: See also Carlson, C.E., and Hammar, W.P. 1976. Impact of fluorides and insects on radial growth of lodgepole pine. Proc. Montana Acad. Sci. 35: 39.)

Facteau et al. (1973) reported that the growth of pollen tubes in the styles of cherry blossoms was decreased by fumigation with hydrogen fluoride either before or after pollination. Pollen tube length, expressed as a percent of style length 72 hours after fumigation, decreased linearly as a function of the product of exposure-time and atmospheric fluoride level. A somewhat similar result was obtained in studies with apricot flowers (Facteau and Rowe 1977). Fluoride-induced reduction in pollen germination and tube growth has also been observed in tomato and cucumber plants (Sulzbach and Pack 1972) while inhibited seed production or fruiting has been reported, with soybean, bell-pepper, sweet corn, and cucumber being more susceptible than pea, grain sorghum, or wheat (Pack and Sulzbach 1976).

Conover and Poole (1971) found that cuttings of Cordyline terminalis var "Baby Doll", a horticultural foliage plant, suffered serious (approaching 50%) leaf necrosis when set for rooting in water containing 0.5 ppm fluoride.

"Soft-suture" of peaches is the "best known example of fluoride injury to fruit" (NAS 1971). Facteau and Rowe (1976) were able to induce this injury in Elberta peaches by spraying the trees at weekly intervals with 0.025% ammonium fluoride solution.

Maclean et ae. (1976) conclude that hydrogen fluoride (0, 5.0 and 9.7 ug F/m3 for 7 days) was more phytotoxic to tomato plants grown in magnesium-deficient media than to those grown in complete media. Similarly, Pack and Sulzback (1976) have demonstrated how calcium nutrition can influence the response of plants to airborne gaseous fluoride. Pilet and Bejaoui (1975) report that fluoride added to the culture medium for Rubus hispidus tissues markedly reduced oxygen absorption by the tissues, particularly in media deficient in calcium and magnesium. Increased levels of calcium and magnesium had a protective action, in that they lessened the degree of fluoride inhibition of oxygen absorption.

The concept that vegetation may be stressed by pollutants present at levels that induce relatively minor injury, or even at levels that do not induce detectable injury in normal healthy plants, requires further study. The importance of this concept relates to the possible summing of stresses from various sources, with the total stress inducing an injury that cannot be easily related to any one cause. Evidence of such stress-induced injuries resulting from multiple causes is difficult to establish experimentally, but the effect of magnesium deficiency discussed above (MacLean et al. 1976) is probably a dual-stress phenomenon. However, in foliage, there can also be an in situ effect of fluoride on magnesium. In a study of air pollution, Garrec et al. (1977) observed that fluoride accumulation led to a depletion in the magnesium content of pine needles; in addition, there was a similar depletion in foliar manganese content.

Probably the most striking example of multi-stress effects is to be found in studies of the relation between atmospheric pollution and insect infestations of forest species. The host-parasite relation is complex, and as noted by Heagle (1973), the presence of an atmospheric pollutant may act to either the advantage or disadvantage of the insect.

However, studies of forest species under field conditions have demonstrated that the stress placed on trees by pollutants can increase the degree of infestation by insects. Heagle (1973) states that "A common finding is that trees injured and weakened by pollutants are more likely to be attacked by insects that normally require weakened trees for successful reproduction". Jensen (1975) notes that "Some evidence has been provided that air-pollution stress can initiate and/or aggravate insect infestation and microbial infection of woody plants". Hay (1975) states that "Insects and mites have been implicated as a stress factor on trees being influenced by pollutant emissions".

Most of the above statements have been made relative to pollutants in general, but the work of Carlson et al. (1971, 1974) and of Carlson and Hammer (1974) shows that atmospheric fluoride induces an insect-favouring stress in forest trees. Failure to recognize this stress-factor led prior investigators to incorrectly diagnose a combined fluoride injury and insect attack in the "death-band area" near Kitimat, B.C. (Gordon 1976).

When pollutants act in combination, each exerts its own stress, and each can influence a different metabolic function. Thus, the effects of exposure to sulfur dioxide and gaseous fluoride mixtures induced additive effects on citrus species, but may have induced greater-than-additive effects on Zea mays and Hordium vutgare (Reinert et al. 1975).

In apricot orchards, trees that were stressed by competition from weeds showed more leaf damage from airborne fluoride than did trees from well-tended plots (Oelschlager and Moser 1969).

Fluoride-induced stresses undoubtedly affect vegetation in diverse ways, depending on the species and conditions. One possible mode of action in coniferous trees has been noted by Bligny et al. (1973) who report that exposure to fluoride delayed the formation of epicuticular waxes on the lower surfaces of Abus alba needles. This could increase water loss from the needles, and also increase their susceptibility to invasion by parasitic organisms. Keller and Schwager (1971) have attempted to relate fluoride-induced stress to an increased activity of an enzyme (peroxidase). Yee-Meiler (1974) has shown an increased phenolic content of Norway spruce subjected to "physiologischen Schadigungen" by fluoride (0.257 mg F/dm2 per 30 days).

Fluoride concentrations expressed in ug/dm2 per day or month refer to data collected by exposing lime-filter papers to ambient air for the started time. Marier and Rose (1971), using the greenhouse data of Adams (1961), suggested conversion by the equation:

Airborne F(ug/m3) = 0.006 x lime-paper (ug F/dm2 per month).

Israel (1974a) has compared results based on field trials, and suggested the equation:

Airborne F(ug/m3) = 0.003 x lime-paper (ug F/dm2 per month).

Israel's estimate of the accuracy of the conversion is + 50%.

The difference in conversion factors (0.006 vs 0.003) may relate to differences in air velocity across the lime-paper (Israel 1974a).

More recent, Sidhu (1977a) has also conducted a field-study intercomparison, and has proposed an equation that can be expressed as follows:

Airborne F(ug/m3) = 0.0076 x lime-paper (ug F/dm2 per month),

which yields values 2 1/2 times higher than Israel's, but only about 25% higher than the Adams equation proposed by Marier and Rose (1971). Furthermore, Sidhu (1977a) concludes that "In the absence of a more reliable and accurate regression equation, Adams' equation can be used to convert the fluoridation plate data to the ug F/m3."

2.1.3 Criteria for Crop Injury (back to top)

Regression equations calculated from data presented in recent papers and which indicate mathematical relations between yield and airborne fluoride; or yield and foliar fluoride; or foliar fluoride, airborne fluoride and exposure time, are presented in Table 9. The yield vs airborne fluoride data are also presented in Fig. 2. Because of the small number of data-points available, some of these regressions do not achieve statistical significance. However, taken as a group, they reveal a consistent pattern of increasingly harmful effects with increasing exposure of vegetation to fluoride.

Significant correlations between airborne fluoride levels and foliar fluoride concentrations ("C" and 'T' in Table 9) are difficult to attain under field conditions. However, if close attention is paid to the location of sampling sites and to the selection of foliage of uniform age from specific species and varieties, such correlations can be achieved. The correlation coefficient for Linzon's (1971) data (Table 9) is 0.48. In controlled greenhouse studies, the concentration of fluoride and the age of foliage are usually controllable factors; under these conditions, the time of exposure can be included as a component of the regression equation [data of McCune and Hitchcock (1971) and MacLean and Schneider (1973) in Table 9].

The data on the yield of oranqes (Leonard and Graves 1970, 1972) shown in Table 9 and Fig. 2, were for trees exposed for 28 months in field shelters with low ambient levels of fluoride pollution (i.e. 0.1 to 0.4 ug/m3). Data for beans (Pack 1971a) were from a 70-day greenhouse study at high levels of airborne fluoride. Both indicate a severe loss of yield with increasing fluoride levels, i.e. approximately 19% per 0.1 ug/m3 for oranges, and 3% per ug/m 3 (approximately 1.2 ppb) for beans. The data on strawberries (Pack 1972) are from a 5-month greenhouse study, and indicate about a 5% loss in weight of individual fruits per ug/m3 increase in airborne fluoride. This loss in yield (fruit set does not appear to have been affected) was accompanied by a statistically significant decline in fruit quality, as indicated by the "development rating" assigned by the original author.

Yield of oranges in field shelters was also related to the fluoride content of the foliage (Leonard and Graves 1972), declining by about 5% for each 100 ppm increase in fluoride in 10-month-old leaves.

In field tests, Israel (1974b) observed a highly significant multiple regression between the fluoride content of forage and of air-plus-soil. This was expressed as:

F(foliage) = 11.4 F(air) + 0.0085 F(soil),

where fluoride content of foliage and soil is expressed in ppm and of air in ug/dm2 per day absorbed by lime-paper.

In a recent survey of a Newfoundland region in Canada, Sidhu (1977a) concluded that "The safe levels of fluoride in air for forest species appear to be between 0.17 to 0.23 ug/m3." This is very close to the lower limit given by the estimates of Marier and Rose (1971), i.e. "The average gaseous fluoride level in ambient air should be below 0.4 ug/m3 and might have to be as low as 0.2 ug/m3."

2.2 EFFECTS ON ANIMALS (back to top)

2.2.1 Aquatic Species (back to top)

The ecological significance of the exposure of aquatic animals to fluoride has been studied to a limited extent, but much more research is required before broad conclusions can be drawn. The following paragraphs summarize the available recent information.

A large number of species have been shown to suffer injury from exposure to fluoride (Groth 1975a). The response of fish to fluoride is influenced by a number of factors such as species and strain, concentration of calcium and chloride in the water, temperature, and the size or age of fish used in the study (Sigler and Neuhold 1972). The response of other species to fluoride is probably influenced by at least some of these factors, but few data are available.

Fish and other aquatic species tend to accumulate fluoride from the environment, primarily in the skeleton (including the gills) and exoskeleton. Groth (1975a) has tabulated the accumulation of fluoride by a number of species. Stewart et al. (1974) analyzed specimens from an uncontaminated estuarine-coastal area of New Zealand. They report fluoride levels from 509 to 2885 ppm (ash basis) in the skeleton, and from 31 to 209 ppm in the exoskeletons, of different species. Wright and Davison (1975) also report "background" fluoride levels for a number of species, but give the data only as ug/g fresh weight. These authors also report data from controlled experiments that clearly demonstrate accumulation of fluoride in the exoskeleton of shore crab (Carcinus maenas ). Blue crab (Callinectus sapiduz), exposed to 20 ppm fluoride in water, accumulated fluoride in the exoskeleton and suffered a 4.5% reduction in growth increment per molt (Moore 1971). Moore estimates that this would result in a 52% reduction in the final size of an average crab.

Wright (1977) reported a whole-body fluoride concentration of 10 ppm, wet weight basis, in fry of Brown trout exposed to 5 ppm fluoride in tap water for 200 hours. These fry suffered increased mortality, as compared to fry in a control tank, but mortality appeared to occur only in a susceptible portion of the total population.

Hemens and Warwick (1972) and Hemens, et al. (1975) studied the potential environmental effects of the "scrub water" from an aluminum smelter in South Africa. Brown mussels (Perma perma) were the most sensitive of the organisms tested. In this species, mortality occurred at fluoride levels from 1.4 to 7.2 mg/l in sea water after exposure for 15 days, but lack of food during the test-period may have enhanced toxicity. All species tested had accumulated fluoride extensively (wholebody fluoride to water-borne external fluoride ratios varied from 25:1 to 149:1) after exposure for 72 days at 52 ppm fluoride. The authors interpret some of their data as being indicative of a greater fluoride accumulation during deposition of new skeletal material.

Lubinski and Sparks (1975) attempted to assess the total toxicity to Bluegills of several pollutants present in the Illinois river by expressing the contribution of each pollutant as "Bluegill toxicity units". They found that fluoride was one of six major contributors to the total toxicity of the river water. Taft and Martin (1974) have reported the absence of all living organisms in a fluoride-polluted zone of Tampa Bay.

2.2.2 Insects (back to top)

Data on the effects of exposure of insects to fluoride are limited. Lillie (1970) has reviewed the literature on the toxicity of fluoride to honeybees and concluded that 4 to 5 ug of accumulated fluoride per bee may be the lethal level. Assuming an average dry weight per bee of 30 m , this corresponds to 130 to 170 ppm (dry weight). Trautwein et al. (1972) reported that the average total-body fluoride content of winter-killed bees ranged from 0.63 to 4.81 ug per bee (21 to 160 ppm dry weight basis). The highest levels were found in bees from hives located near sources of fluoride pollution.

Carlson and Dewey (1971) report data from the analysis of a number of insect species captured in non-polluted and polluted areas of Montana (Table 10). All insects were presumably collected live, but the honeybees with an average fluoride content of 221 ppm probably would not overwinter successfully. Other insects, such as bumblebees at 406 ppm and sphinx moth at 394 ppm fluoride, must be considered endangered, even in the absence of further evidence.

Mohamed (1971) reported evidence that exposure to fluoride caused chromosome damage and mutagenesis in fruit flies (Drosophila metanogaster). In a continuation of these studies, Gerdes et al. (1971a, exposed four strains of fruit flies at airborne gaseous HF levels of 0, 1.3, 2.9, 4.2 and 5.5 ppm for periods of up to 6 weeks. All flies were killed within 3 days at 5.5 ppm. All strains suffered at least 25% mortality in 6 weeks, even at the lowest level (1.3 ppm) of exposure, but the relation between mortality and fluoride concentration was non-linear, especially for the two "wild type" strains. In these two strains, about 65% of the population appeared to be resistant to fluoride, even at the 4.2 ppm level.

The offspring of the surviving flies from the 0, 1.3, and 2.9 ppm fluoride levels of the above experiment were also studied (Gerdes et 1971b). Statistically significant declines in fecundity and egg hatchability with increasing parental exposures were observed. Gerdes et al. concluded that the exposure to fluoride caused genetic damage. The dose-response plots for vegetation (Section 2.l.3) and swine (see Section 2.2.4) do not appear to indicate the existence of a no-effect threshold for fluoride. If the genetic effects in insects respond to dose in a similar manner, the cumulative genetic, evolutionary, and ecological effects of exposure to low levels of environmental fluoride could become manifest with continued exposure of successive generations.