The Ecological Aspect of Fluoride

by J. R. Marier
From the Environmental Secretariat, Biology Division, National Research Council, Ottawa, Ontario, Canada.

Presented at the 4th Annual Conference of I. S. F. R., The Hague, 10/24-27/71.

It is a great honor to be asked to present the Opening Address at this, the 4th meeting of the International Society for Fluoride Research. I chose "The Ecological Aspect of Fluoride", because I believe that such an appraisal is mandatory.

Ecology can be defined as "the influence of the environment on living things". Thus, there are two considerations: the environment and living things. During the journey of an all-pervasive pollutant (such as fluoride) from its source to its eventual targets, the word "environment" can mean many things. For instance, air, soil, and water can all serve as environments for fluoride. However, they also serve as modes of transport for fluoride's entry into vegetation. Similarly, vegetation can be an environment for fluoride, but it also serves as one of the modes of transport for fluoride uptake by other forms of life. In this manner, biological transfers occur, and food chains are built up, increasing in diversity all along a pollutant's journey. As if this were not complicated enough, man can complicate it further by recourse to fluoride-containing fertilizers, insecticides and mineral supplements for livestock.

As concerns his own environment, man can increase the fluoride burden from sources such as food and beverage processing, and widespread use of fluoride-containing aerosols and pharmaceuticals. Such sources include exposure to organic forms of fluoride, some of which are subject to biotransformation with consequent formation of toxic metabolites. And so, the assessment of the total environmental impact of fluoride is a complicated procedure, especially if one is trying to keep track of the multiple factors involved in cause-and-effect rela tionships.

Today, whether one is talking about fluoride or some other pollutant, it does not suffice to limit the discussion to the presence of a given substance in air, or water, or vegetation, or whatever. On the contrary, what is required is an integrated "tracking down" of a pollutant where ever it may exist in the ecosystem or in man's own environment. Also there is the consideration that fluoride is only one of many pollutants attempting to co-exist in our technological environment.

In view of the foregoing, it is obvious that a multidisciplinary approach is needed for a comprehensive evaluation, in which inputs from all the scientific specialties contribute to the total mosaic of knowledge. This is why I have always looked forward to the meetings of the ISFR, because this society brings together the geologist, meteorologist, the industrial researcher, analytical chemist, botanist, veterinarian, toxicologist, clinician. In other words, it creates an opportunity for dialogue between the various scientific specialties.

My purpose is not to dwell on things already familiar to everyone, but to present an insight into things I have wondered about during the preparation of a soon-to-be published article devoted to the topic "Environmental Eluoride". Everyone is familiar with the types of fluoric materials utilized in many industrial processes, how they give rise to fluoride emissions, the various forms of these fluoride emissions, as well as the problems they can create. In what follows, I will give examples of something that, in my opinion, will assume increasing importance in studies of man's environment. I refer to synergisms.

In the past many researchers, who have conducted field studies on polluted vegetation, have shown that fluoride tends to be the major atmospheric pollutant involved in a situation that also involves sulfur dioxide. This is true even though the concentration of airborne sulfur dioxide may greatly exceed that of fluoride. It emphasizes the fact that fluoride is much more phytotoxic. However, some researchers have wondered about a possible synergism involving both fluoride and sulfur dioxide. Thus, in 1952, Adams et al. had stated:

"...the possible synergistic effects of subdamage concentrations of sulfur dioxide in admixture with gaseous fluorine compounds must be thoroughly investigated... " (1).

Much later, in 1968, Van Raay reported:

" ... it is not unreasonable to presume that, for instance, apple trees may be more sensitive to SO2 contamination if HF pollution is also present" (2).

Then, in January 1971, the International joint Commission of the United States and Canada (charged with the study of ecological parameters in the Great Lakes basin) issued a report in which atmospheric fluoride measurements were included in the survey. The report contains the following statement:

"Continuous exposure to a combination of pollutants in low concentrations... may cause an increase in the damage that a (particular) pollutant can inflict" (3).

Thus, it can be appreciated that such a consideration is not only of long standing, but remains uncertain. The only criterion I have found concerning the simultaneous presence of both HF and S02 in the same atmosphere is that proposed in 1968 by Lindberg in the Soviet Union (4). In this approach, the level of HF and S02 is expressed as an arithmetic fraction of whatever "maximum permissible" concentrations are selected for a given exposure-time; and, when the sum of these two fractions exceeds a total of 1, an undesirable situation is deemed to exist. Thus, if the air contains 3/4 of the permissible level for HF and also for S02, the sum is 1.5 - and therefore - unacceptable. However, this calculation implies a simple additive effect of airborne HF and S02, and would underestimate the condition if a synergism magnifies the combined effect of these two pollutants.

The "co-existence" of airborne fluoride and sulfur dioxide is a very realistic consideration. Even the activities that entail considerable atmospheric fluoride emission utilize fossil fuels as an energy source. A recent Canadian study has demonstrated (5) that there is a close parallel between the concentration of atmospheric fluoride and sulfur dioxide originating from coal-burning. One can only wonder about the effects of any inherent synergism on all forms of biological targets.

Another example of a synergism involves the magnitude of fluoride uptake in vegetation, arising from the use of fluoride-containing phosphate fertilizers. In 1969, Bovay (6) described how phosphate fertilizers containing 1.1% of potassium fluoroborate greatly enhanced uptake of fluoride, with consequent damage to vegetation. Hydrophonic studies by Collet et al (7) revealed that the cause was not the fluoroborate as such, but rather the simultaneous presence of unbound borate. It was shown that mildly acidic conditions (pH 5.6) favored hydrolytic cleavage of fluoroborate, and that the presence of only 10-5M of available boron (i. e. 0. 11 mg/1) would double the uptake of fluoride via the root-system of vegetation. Collet et al. attributed this phenomenon to a synergistic effect of unbound boron on fluoride uptake.

Such findings may have implications regarding the use of fluoride-containing fertilizers, even when such fertilizers do not contain boron. Certain soils, as attested to by a recent survey in California (8), are known as "high boron soils", and can contain as much as 64 ppm of boron. Remembering that only 0. 11 ppm of available boron were required to double fluoride uptake by vegetation, and that mildly acidic conditions increased the availability of boron, one wonders about the use of fluoride-containing fertilizers, particularly in acidic high-boron soils.

I have now given two examples of synergisms: one in air, and one in soil. Next, I want to deal with a condition in the 3rd major component of the ecosystem: water. This too, will be related to the topic of synergism. It revolves around man's propensity to utilize the world's waterways as a "catch all" for unwanted materials. Today, all over the civilized world, one can see (and often, smell) the consequences of such a practice. Also, I realize that - in the field of "pollution control" - abatement of airborne emissions is often achieved by resorting to spray towers and scrubbing devices; in this way, the problem can be transferred from air to water. On Canada's East coast, we recently had a situation in which 22,800 pounds of fluoride per day was discharged into a relatively small harbor inlet (approximately 13 square miles) for more than 4 months (9). As a result of this incident, I became interested in uptake of fluoride by aquatic vegetation, although I have found only one report on this topic. A study at the French Atomic Energy Centre in Pierrelatte has shown (10) that exposure of aquatic vegetation to 100 ppm of waterborne fluoride for 5 days increased the vegetation's fluoride content 50 fold, whereas exposure to 20 ppm for 14 days increased it 38 fold. Unfortunately, the report does not provide information concerning exposure to lower levels of waterborne fluoride for longer periods of time.

This is of interest, not only because it relates to the aquatic food chain, but also because of another possibility that deserves serious consideration. Within the past few years, Miller and his co-workers have awakened the world to the possiblity that vegetation exposed to fluoric air-pollution possesses the ability to convert inorganic fluoride to the much more toxic fluoroacetate and fluorocitrate forms (11). This is a finding of a great importance. All past surveys of fluoride pollution have used inorganic fluoride as a "guideline" for mammalian symptomatology and toxicity. However, if vegetation-borne compounds such as fluoroacetate contribute to the symptomological pattern, this would require some serious reappraisals. While there is no information on the topic, one cannot help but wonder about such an inorganic-to-organic mechanism in aquatic vegetation. After all, it is in an aquatic environment that mercury was found to convert to more toxic organic forms.

Another consideration about water: As is the case with air, it can abound with a multitude of pollutants. Recently, I have examined documents relating to water quality parameters, and was surprised to find that there are at least 75 of these. Permissible levels can be found for such elements as arsenic, barium, boron, cadmium, chromium, lead, manganese, mercury, selenium, as well as compounds such a cyanide, pesticides, weed-killers, sulfonates, phenols, and detergents. Although relatively low levels have been set for these, one wonders about the sum total of their cumulative effect and also about the possibility of synergisms, not only among the above-mentioned group, but including fluoride. Based on such considerations, a recent Canadian article advocates that 'Water should be considered a food and brought under the control of the Federal Food and Drug Directorate ... water would then have to be tested and approved in the same manner as food additives "(12). Some people in our Food & Drug Directorate would not welcome this proposal, primarily because they are already overworked in their attempt to keep up with the proliferation of additives, adulterants, and outright toxic substances in the galaxy of foods and drugs.

So far, I have given examples of potential synergisms as they apply to air, soil, and water. However, consideration of today's environment requires inclusion of the biological targets of pollutants. In this area, I have been interested in something that must be considered akin to a synergism, namely the intake of a pollutant in a biological organism beset by nutritional inadequacy. In many reports the "toxicity" of fluoride was assessed in mammalian species that, otherwise, were receiving an optimal diet. This is quire acceptable if the species in question is normally maintained on such a high dietary regime. But extrapolation of such findings to human populations is unwarranted, because the nutritional status of the human being seems to leave much to be desired. United States surveys indicate that more than half of the population have inadequate intakes of dietary components such as calcium and vitamin C (13) and a similar trend seems to prevail in regional surveys done in Canada (14). Recent reports by Reddy and co-workers (15) have described how dietary insufficiencies of either calcium, vitamin C, or protein, aggravate the toxic effects of fluoride in rhesus monkeys.

In all such situations, the things that worry me about fluoride, and about other pollutants, are not the things we know, but the things we do not know, or the things we have neglected.

I will now present a few final impressions. It is often stated that fluoride is only a "local" problem and yet, at a 1968 symposium in Wageningen, it was reported that fluoride-induced injury to coniferous forests could occur at a distance of 32 km from the emitting source, and the destruction of some species at a 13 km distance (16). It all depends on how one defines the word "local". Of course, it is possible to establish a low level baseline for fluoride in ambient air by avoiding all sectors likely to be contaminated by industrial emissions. And yet, the fact remains that many districts have more than their share of industrial activity, plus the emissions that such activities entail. The Wageningen symposium included a presentation in which it was estimated that 400,000 hectars of European forests had been destroyed by the action of atmospheric fluoride and sulfur dioxide (17). A recent report attests to the situation in the Montana region of the United States, and summarizes it as follows:

"Gaseous and particulate fluoride effluents ... have caused considerable environmental damage over a large geographical area. Herbaceous plants, shrubs, and trees showed foliar burn correlated with excessive fluoride accumulations... The occurrence of elevated fluorides in insects indicates accumulation through the food chain of the ecosystem. Foliar necrosis due to fluorides was found in Glacier National Park, representing an unwarranted intrusion by technology of man into one of the few remaining truly pristine habitats of the world" (18).

But, in spite of such occurrences, the question is often asked: 'What does it matter if some vegetation is destroyed?" To me, this represents the attitude that propelled mankind into what I call The Age of Pollution, and is tantamount to someone asking: "How much of Lake Erie (or Lake Balaton, or Lake Constance) can we destroy?" The ecosystem is an integrated and interactive organism, and, like it or not, we are part of that system.

Concerning fluoride emissions of various forms, wisdom dictates that every effort should be made to contain fluorides within the confines of the factory. There are now economic incentives for pursuing such a policy, because compounds such as cryolite and hydrofluoric acid can be synthesized from waste fluoric gases and particulates (19,20,21). Such recycling can benefit all industries involved in the utilization or emission of fluoric products. One thing is certain: It will undoubtedly benefit the ecosystem.

(Read the National Research Council of Canada's 1977 report "Environmental Fluoride", co-authored by John Marier.)

Bibliography

1. Adams, G.F., et al.: Atmospheric Pollution in the Ponderosa Pine Blight Area. Industr. Eng. Chem. 44:1356, 1952.

2. Van Raay, A.: The use of Indicator Plants to Estimate Air Pollution by S02 and HF. in "Air Pollution". Proceedings of the First European Congress on the Influence of Air Pollution on Plants and Animals. Wageningen, April 22-27, 1968, p. 319.

3. Joint Air Pollution Study of St. Clair-Detroit River Areas, for International Joint Commission: Canada and the United States. Ottawa and Washington, January, 1971, p. 2-63.

4. Lindberg, Z.Y.: Maximum Permissible Individual Concentrations of S02 and HF when both are Present in the Atmosphere. Materilayi Dokladov Nauchrisa Sessii. Rizhskogo Meditsinkogo Instituta, 15th, 1968, p. 42.

5. Cooke, N. E.: Air Surveys Linked with Mathematical Model to Protect Environment. Water and Pollution Control, May 1971, p. 59.

6. Bovay, E.: Fluoride Accumulation in Leaves Due to Boron-Containing Fertilizer. Fluoride 2: 222, 1969.

7. Collet, G. F., et al.: Role de la Composition Chimique des sels Fluore's dans leur Penetration Accumulation et Action Biologique Chez les Vegetaux. Schweiz. Landwirtsch. Forsch. 8:65, 1969.

8. Bingham, F. T., et al.: Characteristics of High Boron Soils. Hilgardia 40: 193, 1970.

9. Idler, D. R.: Coexistence of a Fishery and a Major Industry. Chemistry in Canada. December 1969, p. 16.

10. Teulon, F.: Choix de Detecteurs Biologiques Pour la Contamination des Eaux par le Fluor et lluranium. (Commissariat a Venergie atomique, Pierrelatte). Societe francaise de Radioprotection. Congres International sur la Radioprotection du Milieu, Toulouse, March 1967, p. 597.

11. Yu, M. H., and Miller, G. W.: Gas Chromatographic Identification of Fluoroorganic Acids. Environm. Sci. Technol. 4:492, 1970.

12. Davey, T., and Douloff, N.: A Report on Corrosion Inhibitors in Drinking Water. Canad. Consult. Eng., March 1971, p. 32.

13. National Dairy Council of Canada: Bulletin Service. No. 198, Dec. 1, 1969.

14. Caron-Lahaie, L., and Mongeau, E.: Etude sur le Rejime Alimentaire d'un Groupe. d'adolescentes. Canad. Dietetic Assoc. J., Dec, 1968, p. 182..

15. Reddy, G. S., et al.: Effect of Dietary Calcium, Vitamin C and Protein. Metabolism 20: 642-650, 1971.

16. Robak, H.: Aluminum Plants and Conifers in Norway. Proceedings of the First European Congress on the Influence of Air Pollution on Plants and Animals. Wageningen, April. 22-27, 1968, p. 27.

17. Bossavy, J.: Informations sur les Dommages causes par la Pollution de l'air aux Plantes et aux Animaux dans les Pays Europeens. Proceedings of the First European Congress on the Influence of Air Pollution on Plants and Animals. Wageningen, Apr. 22-27, 19680 p, 15.

18. Carlson, C. E., and Dewey, J. E.: Environmental Contamination by Airborne Fluorides in Montana. Phytopathology 61:887, 1971.

19. Ju Seong Lee, et. aL: Synthesis of Cryolite. Kungnip Kongop Yonguso Pogo (Korea), 17:71, 1967.

20. Nayar, K. P.A.: Fluorine Recovery for Synthetic Cryolite. Chem. and Process Eng. 50:117, 1969.

21. Barber, J. C. and Farr, T. D. : Fluoride Recovery from Phosphorus Production. Chem. Eng. Progress, 66:56, 1970.

To learn more about fluoride pollution, see www.fluoridealert.org/f-pollution.htm