April 1973 (Volume 15, Issue 3, Pages 25-32)

Fluorides in the Air

by Michael J. Prival and Farley Fisher

MICHAEL J. PRIVAL and-FARLEY FISHER were research associates at the Center for Science in the Public Interest at the time this article was written.

WHEN A RANCHER sold 54 acres of his Garrison, Montana, land to the Rocky Mountain Phosphate Company it was a matter of civic pride. The new factory promised jobs and tax revenues for the industry-hungry region. Four years later, the Ponderosa pine and Douglas fir were turning brown, and the cattle on Garrison's ranches were so crippled they could not stand up. It took six years of vigorous and frustrating campaigning before the residents of Garrison succeeded in forcing the Rocky Mountain Phosphate Company to close permanently in January 1970.

The story of Garrison (1) is but one of many in which an industry and its neighbors have fought long and bitter battles over the damage caused by fluorides in the air. The federal government and many affected states have been slow to enact regulations to control fluoride air pollution. They have taken action only when public pressure has forced them to recognize an emergency, such as in the case of Garrison, where the people had to struggle to shut down an industry that threatened the very existence of their town. Unless more decisive steps are taken to control fluoride pollution, other American communities that successfully attract new industry may suffer as Garrison did.

Fluoride is released into the air in large quantities by aluminum reduction plants, phosphate processors, steel mills, coal burning operations, brick and tile manufacturers, and various less significant sources.(2)

It can cause adverse effects when ingested by domestic animals or absorbed by plants. There are also reports that fluoride air pollution can adversely effect human health, though these are less well documented than those concerning sensitive animals and plants.

Fluorides are released into the air in both a gaseous state (as hydrogen fluoride and silicon tetrafluoride) and in solid particles. The particles fall on, and the gases are absorbed by, vegetation near the polluting industry. If this vegetation includes forage crops which are fed to cattle, sheep, horses, or pigs, serious problems may ensue, since these animals, particularly the cattle, are vulnerable to fluoride. (3) In fact, according to the U.S. Department of Agriculture, "Airborne fluorides have caused more worldwide damage to domestic animals than any other air pollutant." (4)

Ninety-six percent of the ingested fluoride that accumulates in the bodies of animals is incorporated into the crystal structure of bone and tooth mineral.(5) When fluoride is ingested with food or water, most of that which is not deposited in the bones, teeth, and other calcified tissue is excreted in the urine within hours of ingestion.(6) Thus it is not surprising that fluoride mainly affects the bones and teeth.

Teeth are more markedly affected by ingested fluoride than are bones, but their high sensitivity is limited to the period of their formation. Thus a cow that has not been exposed to excessive fluoride before the age of two and one-half to three years will not develop the severe dental lesions which would occur in the same animal exposed at a younger age.(7) The developing tooth exposed to small amounts of fluoride may experience color variations ("mottling") that have little or no effect on the animal's ability to eat. Higher levels of fluoride result in more serious dental abnormalities, ranging from small, brittle, chalky areas on the tooth surface to pitting of enamel and easily eroded teeth.(3) Even more serious effects, including severe pain and the wearing down of the tooth right to the gum, can prevent the cattle from drinking cold water or eating.

Localized or generalized enlargement of certain bones in the legs (metacarpals and metatarsals) and the lower jaw (mandible) of cattle are common symptoms of excessive fluoride ingestion.(8) As highly abnormal bone tissue replaces normal bone, (9) overall enlargement occurs, and the normally smooth bone surfaces take on a chalky, white, irregular appearance.(3) Hard ground can cause fluorotic hoof (pedal) bones to fracture, resulting in severe lameness.(7) Cattle with advanced fluorosis may also be crippled by mineralization of ligaments, tendons, and the structures surrounding the joints.(10) Enlargement of the joints themselves may also contribute to lameness. Fluoride-induced tooth destruction, lameness, and stiff joints affect the animals ability to stand, eat, and graze, and all tend to lower the milk yield of dairy cattle or the weight of beef cattle.

Economic loss due to the crippling of animals by fluoride has been reported in widely scattered areas of the US The crippling of cattle in Garrison, Montana, was but one of many similar cases. The Cominco American Phosphate Company moved out of Douglas Creek, Montana, after being successfully sued for $250,000 in 1968.(11) Phosphate processing operations in Florida have affected both cattle and horses, (12) and crippling of cows has recently destroyed dairy operations near the Ormet Aluminum plant in Hannibal, Ohio. There have been complaints of damaged cattle teeth in the Massena, New York-Cornwall, Ontario area, where both the Reynolds Metals and Alcoa aluminum plants emit fluoride.(13) A farmer in Ferndale, Washington, recently won an $83,060 judgment against the Intalco Aluminum Company.(14) US Steel paid $4 million to cattle ranchers around its steel mill near Provo, Utah, before spending $9 million on fluoride-control devices.(15) The number of out-of-court settlements of claims of fluoride damage to animals and vegetation is impossible to determine, though it certainly exceeds the number of court-ordered payments.

Effects on Plants

When the Anaconda Company opened its aluminum reduction plant in Columbia Falls, Montana, in 1955, company officials insisted that damage to animals and vegetation from fluoride emissions would be negligible. By 1969, following several expansions of the plant, dead and dying trees were observed over the entire west face of Teakettle Mountain, which stands between the reduction plant and Glacier National Park.(16) Trees on 2,000 acres of US Forest Service land have been destroyed (17) and fluoride has damaged lodgepole, white, and Ponderosa pines, and Douglas firs in Glacier National Park, eight miles from the plant.(16) As the data accumulate, the destruction of these unique national resources continues unabated. There are also documented reports of damage to trees and crops from fluoride emissions in Oregon, Washington, Idaho, and New York.(18)

Airborne fluoride can damage either the foliage or the fruit of a wide range of plants, and the amount of fluoride necessary for this depends on the species involved. The most characteristic type of lesion is "tip burn," in which the tips and edges of leaves turn brown in a characteristic pattern. The dead tissue may separate from the rest of the leaf and fall off, (19) decreasing the rate at which the whole plant grows. In the case of ornamental plants, of course, tip burn adversely affects the aesthetic and economic value of the plant, regardless of its effects on overall growth. For example, airborne fluorides from the intensive phosphate processing done in central Florida have damaged a major local gladiolus industry.

Plants with foliage particularly susceptible to fluoride damage include: apricots, grapes, plums, corn, sorghum, Jerusalem cherry, gladiolus, iris, St. John's wort, tulips, Douglas fir, western larch, and many species of pine.(20) Many other plants, including citrus trees, have suffered significant leaf damage from fluoride pollution but are not quite as sensitive as the above species.

In some plants it is the fruit which is effected by fluoride, while the leaves may be either sensitive or resistant. Peaches, for example, get soft suture disease or "suture red spot," in which the region of the peach along the seam near the tip ripens before the rest of the fruit. Thus, if the peach is picked and eaten when the rest of the fruit is ripe, this region is already over-ripe and soft, and often the fruit is split under the skin.(19) Fluoride causes "snub nose" or "shrivel tip" in cherries. The tip ripens and shrivels prematurely.(19) Fluoride from aluminum manufacture has been found to cause similar damage to apricots and pears growing near the Rhone River in Switzerland.(21) Economic loss to farmers, not to mention the loss of pleasure to consumers, can easily result from such crop damage.

Occupational Exposure

The effects of airborne fluorides on human beings were studied in great detail by Kaj Roholm, who reported in 1937 on the effects upon Danish workers of inhaling and swallowing large quantities of dust from fluoride-rich cryolite rock.(22) He discovered that fluoride intake and accumulation result in changes in bone structure, detected in the early stages as an increase in the density of bones to X rays. Such irreversible skeletal changes have now been studied in great detail and are part of the well characterized condition known as "skeletal fluorosis."

Roholm also discovered many nonskeletal symptoms among the cryolite workers, including gastrointestinal complaints, loss of appetite, shortness of breath, localized rheumatic pains, and susceptibility to colds. It is hard to distinguish which of the symptoms recorded by Roholm resulted from fluoride exposure and which were due to other working conditions and the physical nature of the inhaled dusts. Most American and Western European investigators now maintain that the only effect of occupational fluoride intake is skeletal fluorosis, which is harmful only in the advanced stages.

Investigators in certain other countries have reported both skeletal and non-skeletal effects of industrial exposure to fluorides. A recent report from the Soviet Union on the health of cryolite workers resembles Roholm's in that a whole array of symptoms were found, including inflammation of the upper respiratory passages, gastrointestinal disorders, and bone pain.(23). According to one report, workers in a Japanese aluminum factory may have suffered lung damage due to inhalation of fluorides.(24)

Few studies have been published on the effects of airborne fluorides on the health of American workers. In one such study, workers exposed to fluorides in a Tennessee Valley Authority (TVA) phosphate plant showed some signs of skeletal fluorosis.(25) They also had significantly more respiratory disease than their unexposed co-workers. Workers exposed to fluoride in Alcoa's relatively "clean" Massena, New York, aluminum plant also had some increase in the rate of upper respiratory infections, although the difference in this study was not statistically significant.(26)

An increased rate of respiratory symptoms might be due to the highly irritating-acid hydrogen fluoride gas in the air of the workplaces of these factories. Neither of the published American studies have reported the large array of nonskeletal effects described by Roholm in Denmark.

The fluoride-exposed workers at a TVA phosphate fertilizer plant had, however, in addition to bone changes and respiratory symptoms, a higher rate of kidney abnormalities, as shown by the excretion of albumin in the urine.(25) People with skeletal fluorosis in India (27) and in Aden (28) also had alterations in kidney function, indicated by urea clearance tests or by excretion of albumin. While excretion of albumin is not always a sign of kidney disease, it may indicate that high levels of fluoride exposure have the potential to cause some kidney damage. A fluoride-exposed industrial worker, especially if he has a preexisting kidney condition, may be in danger from excessive fluoride ingestion.

A firm determination of the potential for low and moderate levels of airborne fluorides to effect the respiratory, gastrointestinal, and other non-skeletal systems is very important. American industries, such as steel and aluminum manufacturers and phosphate processors, in which workers are subjected to varying doses of fluorides, have accumulated a great deal of information on the health of these workers. Only one American company, Alcoa, has chosen to release any of this information to the public.(26) If more of these industrial studies were published in the open literature, the relationship between airborne fluorides and various skeletal and nonskeletal conditions could be better evaluated.

The American Conference of Governmental Industrial Hygienists has set a "threshold limit value" of 3 parts per million (ppm) for hydrogen fluoride gas in industrial workplaces.(29) The threshold limit value is supposed to be the concentration of gas that nearly all workers can inhale for eight hours a day, five days a week, with no adverse effects. The threshold limit value for fluoride-containing dusts is 2.5 milligrams fluoride per cubic meter, which is very close to the threshold limit value for hydrogen fluoride gas, with regard to fluoride concentration.

These threshold limit values appear to be set to protect employers from costly compensation suits rather than to ensure that the exposed workers have real health protection. For example, 2.5 milligrams fluoride per cubic meter could easily induce detectable, irreversible skeletal changes in workers. Drs. H. C. Hodge and F. A Smith of the University of Rochester state that daily fluoride intake should be kept below 5 to 8 milligrams per day to avoid the possibility of increased X-ray density of bones.(30) Thus at the accepted limit of 2.5 milligrams fluoride per cubic meter, in eight hours a man might inhale eight to ten cubic meters of air containing a total of 20 to 25 milligrams of fluoride. Hodge and Smith justify the existing standard by assuming that a man's lungs will only absorb 25 percent of the fluoride inhaled. There is, however, no evidence to support this low estimated absorption value. The absorption of gaseous hydrogen fluoride has been reported to be close to 100 percent, (31) and solid fluorides can be absorbed with about the same high efficiency as gaseous fluorides. (32) Thus, to ensure that daily intake is kept below 7 or 8 milligrams per day, the air concentration would have to average below about 0.8 milligram per cubic meter, not just below the 2.S milligrams now accepted.

Calculating Total Intake

The calculation of Hodge and Smith given above corresponds to a situation in which either particulate fluoride or hydrogen fluoride gas are present at the accepted threshold limit value concentration. If both are present simultaneously, then the amount of fluoride intake would be approximately doubled. Furthermore, the gas silicon tetrafluoride (SiF4), a major airborne form of fluoride in industry, is not taken into account by any occupational health standards. It too can contribute to total fluoride intake in factories. Thus, the threshold limit value for fluorides should not be restricted to particulates alone but should include all airborne forms of fluoride simultaneously.

We have still, however, neglected the fact that people ingest fluoride from many sources, including food and water. If the drinking water used by a worker is artificially fluoridated, his daily fluoride intake from food and water alone could easily exceed 3 or even 4 milligrams per day, especially if his job were physically demanding, resulting in high fluid consumption. In a region with naturally high-fluoride water, his intake might be still higher. If he eats vegetables that are grown in the vicinity of the industry, he may increase his fluoride intake even more, since local vegetation is likely to have been subjected to fluoride air pollution. High-fluoride dusts which settle on food eaten inside the factory can also be a significant source of ingested fluoride. (33)

It has been claimed by some that fluoride-induced, irreversible structural changes in bone which result in increased density to X-rays may weaken the bone, make it more brittle, or help induce or aggravate such conditions as osteoarthritis. In the absence of good experimental data concerning the relationships between bone fluoride content, mechanical properties, and osteoarthritis, it is only prudent to conclude that industrial workers should not be subjected to fluoride levels that result in detectable increases in bone density to X rays.

In order to ensure, with a small margin of safety, that the bones of the workers will not undergo detectable fluoride-induced changes, fluoride intake from the air at the workplace would have to be below 2 milligrams per day. The air itself thus would have to average below about 0.25 milligram (2SO micrograms) per cubic meter in total fluoride. This is equal to one-tenth of the currently accepted industrial standard for particulate fluorides alone.

In addition to its contribution to total fluoride intake, hydrogen fluoride has other effects. The accepted threshold limit value of 3 PPM for hydrogen fluoride gas is supposed to protect workers from damage to lungs, eyes, and other sensitive tissue. When hydrogen fluoride comes in contact with water (as on the surface of moist tissue) it forms an extremely strong and reactive acid called hydrofluoric acid. In an experiment in the Soviet Union, hydrogen fluoride concentrations as low as 0.036 PPM caused the subjects' eyes to become more sensitive to light.(34) This concentration is less than one-eightieth of the accepted threshold limit value supposed to protect the health of fluoride-exposed workers in the US

In other experiments, performed in the U. S.,(13) gaseous hydrogen fluoride concentrations averaging 3.5 PPM caused irritation and peeling of the skin as well as nose, and eye irritation. These experiments involved exposure for six hours a day and lasted only a few weeks. Workmen exposed to similar concentrations for eight or more hours a day over many years might be expected to suffer far more serious damage. But the accepted threshold limit value for hydrogen fluoride (3 PPM) is very close to the average concentrations (3.5 PPM) which caused these symptoms in a very short-term experiment.

Industrial fluoride pollution has been reported to have effects on the health of people living near polluting industries. Early in December 1930, thousands of people became sick and 60 died when a heavy mist settled into the Meuse Valley in Belgium. The official investigation of the incident concluded that sulfur dioxide and sulfuric acid mists were probably chiefly responsible for 3 the effects, Others, including Roholm, (35) believed that fluorides were the real culprits. A similar dispute over the possible role of fluorides grew out of the deaths of 20 people in Donora and Webster, Pennsylvania, during an air pollution episode in 1948.(36) Since no reliable measurements were made of the pollutant concentrations in either case, it is certainly impossible now to make any firm judgments, but the possibility that hydrogen fluoride mists contributed to the acute respiratory distress which resulted in the deaths certainly cannot be ruled out. Fatalities from high-level, acute hydrogen fluoride exposures have certainly taken place in industry.(33)

The question of possible effects of chronic exposure is, however, more relevant to the levels of fluorides usually found in the air surrounding polluting industries. Here, again, the available information is not conclusive in implicating fluorides, since fluorides are often accompanied by other airborne pollutants. For example, an aluminum smelter in Bratislava, Czechoslovakia, and aluminum and phosphate manufacturers in the Soviet Union emit large quantities of fluorides into the air. Pollution from these industries have been implicated in high rates of bronchitis, pneumonia, tuberculosis, and other upper respiratory infections in the surrounding areas.(37) The other air pollutants, including sulfur dioxide, "tar products," and particulates released by these plants, make it impossible to attribute the health effects observed to fluorides alone. The possible role of hydrogen fluoride certainly cannot, however, be discounted completely.

Of the many claims of damage to health from fluoride air pollution which have been made, only one has been upheld in US courts. In a highly controversial decision in 1955, a family was awarded $38,823 for various health effects attributed to emissions from the Reynolds Metals aluminum plant in Troutdale, Oregon.(38) The merits of the case are still disputed by those familiar with it.

Most areas of the US do not have significant fluoride air pollution problems. In a 1966-1967 national survey, over 7,700, 24-hour air samples taken at numerous locations across the US were analyzed for total water soluble fluorides. Ninety-seven percent of the nonurban and 87 percent of the urban samples had less than 0.04 parts per billion (ppb) fluoride (the lower limit of detection). Only 13 (0.2 percent) of the urban samples contained more than 0.8 ppb fluoride, the highest of these being 1.5 ppb. The highest concentration found in a non-urban location was 0. 13 ppb.(39)

The fluoride concentration in the air in Bratislava, Czechoslovakia, which contains an aluminum smelter as discussed above, often averages well over 100 ppb. By contrast, the airborne fluoride levels at the center of the most concentrated cluster of fluoride-emitting industries in the US, the phosphate processing plants of Polk County, Florida, rarely exceed 10 ppb and average less than 2 ppb, (40) because these industries are strictly regulated by the state. Residents of other states, with less vigorous enforcement programs, may be subjected to higher fluoride levels, even though the emitting sources may be much smaller. At the fluoride concentrations which exist in Polk County, it would be quite impossible for a person to inhale enough air to result in a fluoride intake of even 0.1 milligram per day. In contrast, for example, artificial fluoridation of public water supplies results in an average total fluoride intake of 2 to 5 milligrams per day.(41)

Outside the Factory

Those who live around fluoride-emitting industries inhale fluorides directly and eat them in food contaminated by the polluted air. In terms of quantity, the inhaled fluoride is usually far less than the total eaten fluoride. For example, a person who ate one-half pound of heavily contaminated food every day might add 1 milligram to his or her daily intake of fluoride. It is improbable, however, that anyone would habitually consume this much highly contaminated food over long periods of time, and thus it is unlikely that fluoride contamination of food from industrial pollution would have a direct adverse effect on the health of most people. In such cases, though, in which people are exposed to fluoride at work or live in areas with excessively fluoridated water, food contamination must be considered as part of total environmental exposure, and then it might well be significant in terms of health.

In one report, for example, fluoride emissions from a Soviet superphosphate Plant were correlated with both dental fluorosis (mottling of teeth) and a low rate of tooth decay among nearby children.(42) Other studies have concluded that emissions from aluminum smelters in Kitakata, Japan, and from a brickyard in Graz, Austria, resulted in increased fluoride levels in the urine of local residents.(43) The fluoride emissions in Kitakata are also reported to have slightly affected the rate of skeletal development of nearby children.(44) It is probable that the high level of fluoride found in the typical Japanese diet (in tea, rice, and seafood (45) would make the average Japanese person more susceptible to adverse effects of increased fluoride intake than the average American would be. But the fact that some Americans have very atypical diets (for Americans) must be taken into account when the effects of fluoride air pollution on human health are considered.

The concentration of airborne fluorides inside a polluting factory may be on the order of 100 to 1,000 times that found outside the factory. The threshold limit value for hydrogen fluoride in industrial situations has been set at 3 PPM (3,000 ppb), though even this inadequate limit may be exceeded in real industrial situations. By contrast, as mentioned before, the air fluoride levels in many polluted areas of the US rarely exceed 10 ppb if emissions are controlled.

Thus the effects of hydrogen fluoride and other fluorides on the surrounding populations would generally be far less than those on the workers inside the plant. But a person outside the plant may have a preexisting disabling respiratory disease which can make him more susceptible to lung injury than a worker in the factory. In comparing occupational to general population exposure to an air pollutant, it must also be kept in mind that occupational exposure lasts about 8 hours a day, 5 days a week; nearby residents may breathe polluted air 24 hours a day, 7 days a week.

Either a person living near an industrial source of fluorides or a worker inside the industry may be subjected to other airborne pollutants as well. The possible interactions between fluorides and other air contaminants in causing respiratory damage has not been adequately investigated, but such interactions (synergism) have been demonstrated for more thoroughly studied pollutants.

Major sources of airborne fluoride in the US are steel manufacturers, phosphate processors, brick and tile products manufacturers, aluminum reduction plants, and coal burning operations. Fluoride emissions from steel mills originate from the use of fluorspar (which is 49 percent fluorine) as a flux to help remove impurities from the molten metal. In some cases, fluoride emissions may also result from fluoride impurities contained in the iron ore.(46) At high temperatures the fluorides are converted to gaseous and particulate forms which are released into the air. Steel plants are not generally equipped with devices specifically designed to control airborne fluorides, but those which control other emissions may simultaneously inadvertently reduce the amount of fluoride released. Of the two basic methods used to control air pollution, wet scrubbers are far more effective than electrostatic precipitators in capturing fluorides.(47) Wet scrubbers wash particles of solids and liquids and the soluble gases out of the outgoing air, while electrostatic precipitators can recover the particulates but not the gases. The less efficient electrostatic precipitators are, however, more common than wet scrubbers in the steel industry, and about one-third of the steel-producing capacity of the US has no provision for air pollution control at all.

With few exceptions, (48) fluoride has not been singled out as a major pollutant from steel mills, because the ill effects of the other emissions from these operations have been much more obvious. But if future control of air pollutants does not utilize techniques which capture fluorides, the steel industry may find that after installing expensive control devices, it will be plagued by a new set of complaints from nearby citizens due to the now unmasked fluorides it releases into the air.

Primary aluminum reduction plants have had long experience with the fluoride pollution problem, since fluoride is the principal offending emission from many of them. Wet scrubbing of the gases from these plants, followed by treatment of the scrubbing water with lime to recover the valuable fluoride, has been common. But plant and animal damage, and subsequent lawsuits, have persisted in spite of these control techniques. Recently, procedures for recycling the gaseous fluoride by reacting it directly with the alumina used to make aluminum have been developed.(49) This recycling method has the advantage of being more efficient than wet scrubbing as well as actually making money for the company by saving on purchases of expensive, fluorine-rich cryolite.

The fact that efficient utilization of this method requires that each tank ("pot") of melted alumina be tightly sealed ("hooded") to capture the escaping gases also increases the protection of the workers in the plant. Some American plants are not yet fitted with hooded pots, and the acrid hydrogen fluoride fumes fill the whole working room. The fact that steel and aluminum manufacture require fluorides in their processes gives these industries a direct economic incentive to capture fluoride effluents and reuse them. Other fluoride-emitting industries are not in the same position. Fluoride is released from coal burning, brick and tile processing,cement manufacturing, and, most significantly, phosphate processing, solely because it exists as an impurity in the raw materials.

Most of the industrial uses of phosphate, including fertilizer, animal feed supplement, and phosphoric acid production, involve reaction of the phosphate with sulfuric acid at elevated temperatures. Gaseous hydrogen fluoride and silicon tetrafluoride are released during these "acidulation" steps. The gaseous fluorides may be controlled by wet scrubbing devices, and the fluorides which become dissolved in the scrubbing water removed with lime in nearby settling ponds. Uncontrollable volatile fluorides escape from these settling ponds, however, and may account for as much as 90 percent of the total airborne fluorides released during phosphoric acid manufacture.(2) In addition, inefficient recovery of fluorides from the ponds can result in pollution of local streams and rivers.(50)

While the fluorides recovered from phosphate processing operations serve no purpose in the industry itself, the sale of waste fluosilicic acid to the fluoride-hungry aluminum and steel industries can make emission control extremely profitable.(51) Recovered fluorides from phosphate processing are also used to fluoridate public water supplies for the prevention of dental decay.

Fluoride impurities in coal and in the clays used to manufacture brick, tile, and cement contribute significantly to the total fluoride air pollution problem. As with steel manufacture, the fluoride problem in these industries has been masked by other pollutants such as sulfur dioxide and particulates. The control of these emissions will simultaneously control the fluorides which are trapped in solid particles, but gaseous fluorides may escape. Since almost all of the fluoride released from cement manufacture combines with the lime in solid particles, enforcement of controls on particulates (52) should go a long way toward preventing any airborne fluoride problem from arising. It is not yet clear if the same reasoning can be applied to coal-burning power plants, which have also been subjected to control of particulate emissions.

Monitoring Airborne Fluorides

The need for nationwide control of airborne fluorides seems clear. The difficult question to answer is: what kind of federal standards should be set? It is the standard procedure of pollution control agencies to monitor air pollution by collecting samples of the pollutant in question directly from the air. Thus "ambient (surrounding) air" standards are usually set for airborne levels, averaged over various time intervals to account for fluctuating concentrations. It is generally agreed, however, that the fluoride concentration in a sensitive plant or in an animal's food is a far better indicator of potential damage than is the concentration in the air surrounding the plant or animal. The rate at which fluoride moves from the air into the sensitive organism is dependent on many factors besides the airborne concentration. For example, gaseous fluorides enter plants far more readily than do particulate fluorides. It is reported that a light rain or fog, by dissolving gaseous fluorides and bringing them in contact with leaves, tends to promote fluoride uptake. Heavy rain, on the other hand, tends to wash the fluorides away.(53) Attempts to correlate airborne fluoride levels with levels in, and damage to, vegetation have been notoriously unsuccessful.

Since simple monitoring of fluoride in ambient air is not likely to be adequate to protect plants and animals, the simultaneous control of levels of fluoride in the air and levels in sensitive plants, in food, and in forage should all be included in any set of standards. Permissible concentrations should be determined by field studies in areas where fluoride pollution is a problem. The greenhouse studies which have been done to correlate fluoride concentrations with plant damage are quite inadequate in that they do not take into account the important variables of temperature, moisture, and plant nutrition.(54) That fluoride accumulation can also increase susceptibility of a plant to diseases is another factor not considered by the greenhouse studies. These considerations indicate that fluoride standards to protect plants should be set well below the levels at which fluoride alone causes demonstrable harm under optimal conditions.

Limiting Fluoride in Forage

Similarly, the sensitivity of cattle to fluoride in forage is affected by such variables as level of nutrition, stress factors, the breeding of the cattle, and the supplementation of the animals' diet with forage from non-polluted areas and phosphate-containing feed supplements which themselves contain fluoride.

Several states have passed air pollution regulations that limit the amount of fluoride that may accumulate in forage used to feed cattle. Some of these state regulations are based on the "tentative proposal" offered by University of Wisconsin biochemist J. W. Suttie.(56) Suttie's proposal specifies that monthly samples of forage be analyzed for fluoride and that: (1) the yearly average fluoride content not exceed 40 PPM (dry weight); (2) the fluoride content not exceed 60 PPM for two consecutive months; and (3) the fluoride content not exceed 80 PPM in any month. It should be noted that alfalfa hay from unpolluted areas averages less than 4 PPM in fluoride and rarely exceeds 10 PPM(57)

According to Suttie, (56) animals receiving a diet containing about 50 PPM fluoride will be subject to lameness and have easily worn teeth. Some severely fluorotic teeth, which are more easily worn down than healthy teeth, are usually seen when the fluoride concentration in the diet exceeds 40 PPM(16) The fluoride research group at Utah State University, led by James LeGrande Shupe, found that milk production fell by 18 percent when cattle were maintained on rations containing 49 PPM fluoride.(58) Thus, the 40 PPM annual average suggested by Suttie is quite close to the levels shown to have adverse effects on otherwise well-managed dairy cattle.

It is important to recognize that the standards discussed above relate to forage fluoride only, and most well-managed milking cattle receive at least 30 percent of their dry matter as a feed concentrate rather than as forage.(56) This concentrate is usually low in fluoride and thus will effectively dilute the fluoride contained in the forage. Suttie took this dilution into account in setting a forage standard somewhat higher than the level which is desired in the total ration.

In some areas, however, commercial cow feeds often exceed 40 PPM in fluoride.(59) This fluoride is apparently contained in the phosphate salts added as mineral supplements to the feed. The Association of American Feed Control Officials limit for fluoride in cattle feeds is 90 PPM, though even this high standard is sometimes exceeded.(57) The fact that commercial dairy feed may average well above 40 PPM in some locations implies that it is not valid to set a standard of 40 PPM for forage with the expectation that the fluoride content of the total diet will remain below 40 PPM

In addition to the possibility of high-fluoride commercial feed concentrate, the use of standards which are close to demonstrably harmful levels has other dangers. Many cattle will be far more sensitive to the adverse effects of fluoride than are the well-managed animals used in university experiments. Factors that can increase susceptibility to fluorosis include sub-optimal nutrition, stress on the animal, and biological differences between individual animals.(60) Thus some cattle may suffer adverse effects even at fluoride levels below 40 PPM in their total diet.

Shupe (3) recommends that the total diets of milking cattle be kept below an average of 30 PPM fluoride. If commercial cattle feed in an area is high in fluoride, then forage fluoride levels might have to be kept at 25 PPM or less to meet this suggested standard.

It should be pointed out that the standards discussed above are set solely to protect farmers from economic loss. There are, however, marked effects on the cattle at fluoride levels well below those that induce experimentally demonstrable economic loss. These effects include abnormal enlargement of bones in the legs and wearing down of teeth.(61) To ensure protection of cattle from "non-economic" damage would require far more stringent standards than any of those that have been proposed or enacted.

Improving Standards

One stumbling block in the way of federal action on fluorides is the interpretation of section 109 of the Clean Air Act of 1970 which calls for the setting of "national ambient air quality standards" for air pollutants. Since it is desirable to control vegetation levels directly as well as through ambient air levels, vegetation concentrations could be used as indicators of the ambient air concentrations. The state of Maryland, for example, has interpreted its own ambient air quality legislation in this way to set fluoride standards for food, animal forage, and sensitive plants as well as the ambient air.

Limitations on the amount of a pollutant which new or expanded industrial operations may emit may be imposed by the Environmental Protection Agency in accordance with section 111 of the Clean Air Act. Of the industries which are significant fluoride emitters, only coal-burning power plants and Portland cement factories have thus far come under regulation. Although the control of fluorides from these industries was not included in the regulations, it was apparently assumed that the control of particulate emissions would result in the inadvertent limitation of fluorides as well.

Control of new steel manufacturing plants is expected in the near future. Since control devices which remove particulate matter and sulfur dioxide from the airborne waste may not effectively control the considerable amounts of gaseous fluorides present, any regulation of steel mills should include a separate pro- vision for fluorides. The fact that the more modern type of steel manufacture, the basic oxygen furnace, uses two to three times as much fluoride-containing fluorspar as the older open hearth process makes control of new sources even more urgent.

The Environmental Protection Agency has chosen some of the most serious threats to human health as the first targets for control under the Clean Air Act of 1970. It is now time to move on to include those pollutants, such as fluoride, whose severe impact on plant and animal life, and consequently on human welfare, is indisputable, although the danger they present to human health is still a matter of some debate (as will be discussed in the second article in this series).

There can be little serious debate, however, over the need to improve the occupational health standards for hydrogen fluoride and other airborne fluorides. Any devices used to control emissions of fluoride from polluting industries can, and should, be designed to minimize exposure of the people who work within the industry. Conversely, when steps are taken to protect the health of the workers, the contaminated air should not simply be moved out of the factory more quickly. Only those control techniques which minimize both internal and external pollution by recovering the valuable, but potentially dangerous, fluorides will be adequate to protect both human health and human welfare.

NOTES

1. Garrison Conference, Garrison, Montana, Intrastate Air Pollution Abatement Conference, held at Deer Lodge, Montana by the National Center for Air Pollution Control, US Dept. of Health, Education, and Welfare, Aug. 16, 1967. Merson, B., "The Town that Refused to Die," Good Hskpng., Jan. 1969, p. 80.

2. Stein, L., "Environmental Sources and Forms of Fluoride," Biologic Effects of Atmospheric Pollutants - Fluorides, National Academy of Sciences-National Research Council, Washington, D.C., N.A.S., 1971, pp. 5-28.

3. Shupe, J. L., "Fluorosis of Livestock," Air Quality Monograph No. 69-4, American Petroleum Institute, New York, 1969.

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32. Collings, G. H., Jr., R. B. L. Fleming, and R. May, A.M.A. Arch. Ind. Hith., 4:585, 1951.

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35. Roholm, K., J. Ind. Hyg. Toxicol., 19:126, 1937.

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38. National Emission Standards Study, Report of the Secretary of Health, Education, and Welfare to the U.S. Congress, U.S. Senate Document no. 91-63, Mar. 1970.

39. Yunghans, R. S., and T. B. McMullen, Fluoride, 3:143, 1970.

40. Huffstutler, K. K., "Fluoride Concentrations in Various Receptors near Phosphate Industries," paper presented at 63rd annual meeting of the Air Pollution Control Assn., St. Louis, Mo., June 1970.

41. San Filippo, F. A., and G. C. Battistone, Clin. Chim. Acta, 31:453, 1970.

42. Khnygin, V. L., and R. A. Shamsutdinova, Gig. I Sanit., 35(10)-.85, 1970.

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45. Minoguchi, G., "Japanese Studies on Water and Food Fluoride and General and Dental Health," Fluoride and Human Health, World Health Organization monograph no. 59, Geneva, WHO, pp. 294-304.

46. Purvance, loc. cit.

47. Kirkendall, E., letter from E. Kirkendall, vice president, American Iron and Steel Institute, to J. L. McGinnity, National Air Pollution Control Admin., Sept. 14, 1970.

48. "Giant Fume Catcher Stops Fluoride Emission," Chemical Engineering, loc. cit.

49. Cook, C. C., G. R. Swany, and J. W. Coipitts, J. Air Poll. Cont. Assn., 21:479, 1971.

50. Toler, L. G., "Fluoride In Water in the Alafia and Peace River Basins, Florida," Florida State Board of Conservation, Division of Geology, Florida Geological Survey, Report of Investigations, no. 46, 1967.

51. "Cleanup Pays off for Fertilizer Plant," Environmental Science and Technology, 6(5):400, 1972.

52. "Standards of Performance for New Stationary Sources," Federal Register, Dec. 23, 1971,p.24876.

53. Bolay and Bovay, Phytopath. Z., loc. cit.

54. Treshow. M,, Ann. Rev. Phytopath., 9:21, 1971.

55. Treshow and Dean, loc. cit.

56. Suttie, J. W., J. Air Poll. Cont. Assn., 19:239, 1969.

57. Suttie, J. W., J. Agri. Food Chem., 17:1350, 1969.

58. Stoddard, G. E., G. Q. Bateman, L. E. Harris, J. L. Shupe, and 0. A. Greenwood, J. Dairy Sci., 46.720, 1963.

59. Suttie, J. W., J. Agri. Food Chem., loc. cit. Eastalco Survey, report of the fluoride monitoring program, Eastalco Aluminum Plant, Buckeystown, Maryland, Sept.-Dec., 1971.

60. Shupe, J. L., "Diagnosis of Fluorosis In Cattle," Publikation der Iv. Internationalen Tagung der Weltgesellschaft f~r Buiatrik. 4. bis 9. August 1966 in ZGrich, pp. 1-17.

61. Shupe, "Fluorosis in Livestock," loc. cit. Suttle, J. Air Poll. Cont. Assn., loc. cit. Hobbes and Merriman, loc. cit.