October 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
the hypothesis (6) that fresh surfaces of all liquids evaporate at the maximum theoretical rate. LITERATURE CITED
(1) Alty, T., Phil. Mag., 15, 82 (1933). (2) Alty, T., and Nicoll, F. H., Can. J . Research, 4, 547 (1931). (3) Baranaev, M., J . Phys. Chern. (U.S.S.R.), 13, 1635 (1939). (4) Hickman, K. C. D., IND.ENG.CHEM.,to be submitted. (5) Hickman, K. C. D., and Trevoy, D. J., Ibid., 44, 1882 (1952). (6) Knudsen, M., Ann. Physik, 47, 697 (1916).
2369
(7) Langmuir, I., Phys. Rea., 2, 329 (1913). (8) Loeb, L. B., “Kinetic Theory of Gases,” p. 88, New York, McGraw-Hill Book Co., 1927. (9) Priiger, W., 2. Physik, 115, 202 (1940). (10) Rideal, E. K., J. Phys. Chem., 29, 1585 (1925). (11) Stedman, D. F., Trans. Faraday Soc., 24, 296 (1928). (12) Trevoy, D. J., Anal. Chem., 24, 1382 (1952). (13) Wyllie, G., Proc. Roy. Soc. (London), 197A,383 (1949). RECEIVED for review December 17, 1952. ACCEPTED June 24, 1953. Communication 1531 from the Kodak Research Laboratoriefi.
CORRESPONDEN,CE P
Effectiveness and Safety of Fluoridation of Public Water Supplies SIR: Before undertaking to advise the public in regard to the desirability of fluoridating a local water supply, a chemist should become familiar with the researches t h a t demonstrated that the dental health of a community is, t o a large degree, dependent upon the concentration of the fluoride ion in its water supply. These are to be found in two symposia arranged by the American Association for the Advancement of Science and published in two small volumes (1). RELATION O F FLUORIDE CONCENTRATlON I N A WATER SUPPLY T O DENTAL HEALTH
*
-1
During the first decades of this century a few dentists noted the high incidence of stained and mottled teeth in certain communities in the Rocky Mountain and Texas areas and their absence in other nearby towns. In the affected communities, the abnormality was encountered among only those persons who had lived there during the period in early life (up t o about the %ge of 12) in which the dentine and enamel of their permanent teeth were being formed. This distribution suggested that the condition was due to some water-borne cause. Proof of this came in 1931 when it was found that the water of St. David, Ariz., a town where mottling was prevalent, when concentrated t o one tenth its volume and fed t o rats, induced a somewhat similar defect in their teeth. Fluoride was found present in the water from the wells of this town in concentrations ranging from 3.1 to 7.1 parts per million. The fluoride content of public water supplies in the United States varies from traces t o 7 or 8 p.p.m., and in one town it is 15 p.p.m. The incidence and severity of mottled enamel have been shown by extensive dental surveys t o increase with the fluoride content of the water. The threshold concentration that induces mottling of a degree detectable only on careful examination by a dentist trained in its recognition is, in the North Central States, about 1 t o 1.5 p.p.m. Beginning at about 2 p.p.m., a n increasing proportion of the children have mottling of a grade t h a t is easily apparent, and, a t still higher concentrations, the affected areas of the teeth tend to assume a brown stain. I n hot areas in the South where the water intake is greater, the threshold for barely detectable mottling may be so low as 0.5 t o 0.7 p.p.m. Over a million persons in 500 communities use water t h a t contains naturally more than 1.5 p.p.m. Fluoride occur8 normally in the teeth and bones of all persons. Most of it comes from the water used, the food furnishing only about 0.2 to 0.3 mg. daily, a n amount insufficient to affect the dental health materially. As early as 1916, Frederick S. McKay, a Colorado dentist, noted t h a t mottled teeth seemed less subject t o decay than normal ones, an observation t h a t soon found confirmation by others in both this and other countries. Beginning in 1938, H. Trendley
Dean, United States Public Health Service, undertook a systematic epidemiologic study of the relation between the inciden. e of dental caries and the fluoride content of water supplies, which showed clearly t h a t quantities of fluoride too small to cause cosmetic damage are capable of conferring resistance to caries. I n some 21 cities in Indiana, Illinois, Colorado, and Ohio the caries rates calculated from the numbers of decayed, filled, and missing teeth, when plotted against the fluoride content fell on a smooth curve, the rates decreasing from 1037 in Michigan City with 0.1 p.p.m. to 236 in Galesburg, Ill., with 1.9 p.p.m. By plotting a similar curve for the incidence of mottling on the same graph, it became apparent t h a t the concentration of 1.0 to 1.2 p.p.m. is optimal for dental health, the teeth being cosmetically attractive and freer from decay than those in areas with lesser fluoride concentrations. I n recognition of their leadership in the painstaking research which established this relationship, McKay and Dean were jointly given a Lasker Award of the Bmerican Public Health Association. TESTING O F FLUORIDATION
Their work made it seem possible t h a t by adjusting the fluoride content of water supplies t o that optimal for dental health, progress could be made in reducing the prevalence of caries or mottling throughout the country. It was soon found possible t o reduce the incidence of mottling in such towns as Bauxite, Ark., where the water had the grossly excessive content of 14 p.p.m., by changing the source of the water to a more nearly fluoride-free well. Although it seemed possible that the larger number of communities whose water was deficient in fluoride might be benefited by the addition of fluoride to their water supplies, i t was thought unwise t o recommend this until it had been shown in a few selected communities that it is technologically feasible when fluoride is added to maintain the desired concentration within narrovi limits and t h a t the incidence of caries could in practice be reduced to the extent predicted from the epidemiological studies. Accordingly, in 1945, carefully supervised fluoridation was begun in Grand Rapids, Mich., and Newburgh, N. Y. Muskegon, Mich., and Kingston, N. Y., were selected as control cities and agreed t o continue t o use their fluoride-free water sources. Each year, the teeth of thousands of school children in all four cities were examined by teams of skilled dentists. Since the children born after the start of fluoridation did not enter school until they reached the age of 5 or 6 years, examinations made during the earlier years of the test necessarily included children who had not had the benefits of fluoridation from birth. It was believed, therefore, t h a t the test would have t o be continued for a t least 10 years in order t o learn the maximum benefit obtainable by fluoridation. These tests have now been in progress for more than 8 years and
2370
Vol. 45, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
the results of examinations made after the seventh year have shown t h a t fluoridation is capable of reducing dental decay by about 60%. The caries rates in the control cities have shown little or no change, and the people of these cities have protested against being deprived of the benefits of fluoridation in order that the tests may be continued for their full scheduled period. Similar tests begun somewhat later in other communities (Brantford, Ont., Lewiston, Idaho, Marshall, Tex., and Sheboygan, ViTis.) are also yielding favorable results. On April 24, 1951, Leonard A. Scheele, Surgeon General of the U. S. Public Health Service, stated, in testifying before the Senate Subcommittee on Appropriations ( S ) , “During the past year our studies progressed to the point where we could announce an unqualified endorsement of the fluoridation of public water supplies as a mass procedure for reducing tooth decay by two thiids.” The benefits would be expected to be less in communities whose water is initially only slightly deficient in fluoride content and no one would suggest fluoiidation for communities n here the water already contains 1 p.p.m. or more. It is not offered as a panacea for the complete elimination of dental decay and it will not lessen the need for the continuance of the nutritional and oral hygienic measures that have hitherto been recommended. It provides a trace element in the amounts needed for the formation of sound teeth t h a t throughout life will tend to resist the inroads of caries, whatever its cause or causes. Since it does not cure caries once it has invaded the teeth, it is not “mass medication.” Blthough only a small part of the fluoride added to the water of a city is drunk by children during the period of tooth formation, fluoridation is nevertheless economical in view of the savings in dental bills it affords. Forsythe (4)has stated that “for every dollar spent for water fluoridation, $60 to 870 will be saved in terms of needed dental care.” No other method that has been proposed for providing fluoride is free from serious objections. There are too f e v dentists to make the method of topical application available to any large segment of an urban population. SAFETY OF FLUORIDATION
Persons unfamiliar with the toxicologic aspects of nutrition have been active in creating widespread alarm wherever fluoridation is under consideration. They seem unaware that it is now generally known that small amounts of such toxic elements as copper, zinc, and manganese are essential in the nutrition of both plants and animals. The continued ingestion of overdoses of certain of the vitamins, particularly the fat-soluble ones, has led to intoxication, which in some cases has been fatal. Water is the natural source of the fluorides needed for the formation of sound teeth. Careful studies have shown that chronic poisoning does not result from the use of water with 1 p.p.m. The characteristics of chronic fluorosis in man and animals are well known. I n sheep and cattle, it occurs in certain regions where volcanic ash or fluoride-bearing dusts derived from phosphate deposits contaminate their forage. I n man, it occurs among workers in the Danish cryolite industry, where it results from the inhalation of fluoride-bearing dusts. A monograph by Roholm ( 7 ) offers a complete description of the manifestations of chronic fluoride intoxication. Evidence as to the threshold daily intake t h a t induces it has been provided b y animal experimentation, human metabolic studies, observations on industrially exposed workers, and medical examinations of persons living in communities where the water contains excessive amounts. This has been summarized elsewhere ( 5 ) . The first indication of a slightly excessive daily intake appears in the teeth as mottling. I n the absence of mottling of a disfiguring degree, no harm has ever been found t o occur in any other part of the body. Most of the fluoride absorbed by the body from water is eliminated in the urine and sweat, only a very small fraction of it being stored in the teeth and bones. The urinary concentration agrees well with that in the drinking water
over the range of 0.2 to 8 p.p.m. The skeleton can retain fairly large amounts of fluoride without any evident harm, although if the amounts stored are large enough, x-ray photographs may show their shadows to have an increased density. This observation, made in the course of routine chest x-ray examinations of the Danish cryolite workers, stimulated much of the extensive experimental work that has been done on chronic fluorosis. When very large amounts of fluoride are stored in the bones, periosteal outgrou ths appear, and in the vertebral column new bone formation may lessen motility. Only when the daily intake is very great are any of the vital organs affected. I n our laboratory, 65 mg. of fluoride \$-asgiven daily to each of two litter-mate dogs, while a third served as control. This intake was maintained for over 5 years, when the control dog died. The daily dosage was of the order of 3 to 5 mg. for each kilogram of body weight; one dog was given its fluoride as the sodium salt and the other was given fluoride as cryolite. During life no changes could be detected radiographically in their bones, although after they were Idled, the ash of the bones of the dog given sodium fluoride contained ten times the amount of fluoride found in the case of the dog used as control. No noteworthy changes in the organs of these animals were found on microscopic examination. Hodges (6) found no evidence of skeletal fluorosis in x-rays of 31 persons mho had lived for 18 to 68 years a t Bureau, Ill., where the water has 2.5 p.p.m., or in those of 86 persons a t Kempton, Ill., There the content has varied between 1.3 and 3 p.p.m. A radiologic survey of 114 persons n h o had lived for a t least 15 years a t Bartlett, Tex., wherc the content is 8 p.p.m., revealed minimal evidence of an increase in the density of the bones of only 12% of those examined, but in no case was there any interference n i t h the use of the bones or joints. Medical examinations. which included urinalysis and blood counts, revealed no evidence that the residents of Bartlett were less healthy than mere those of nearby Cameron, where the water contained only 0.3 p.p.m. ( 2 ) . Comparisons of the mortality rates from nephritis, heart disease, or cancer in high- and low-fluoride areas have failed to show any association of these diseases .cvith the fluoride content of the water. Although pejoratively written, the final report of the Delaney Committee admitted that “the major portion of scientific opinion is that fluoridation of drinking water in amounts up t o 1 p.p.m. presents no hazard to the public health,” and that “such highly qualified and reputable organizations as the American Medical Association, the Kational Research Council, the American Public Health Association, the American Dental Association, and the A4ssociation of State and Territorial Health Officers have endorsed the program of fluoridating the public drinking vater supply.” LITERATURE CITED
(1) American -4ssociation for the Advancement of Science, Washing-
ton, D. C., “Fluorine and Dental Health,” 1942; “Dental Caries and Fluorine,” 1946. (2) brnold, F. A,, Jr., testimony at Hearings before House Select Committee to Investigate the Use of Chemicals in Food Products, p. 1055 of Record. (3) Forsythe, B. D., statement a t Hearings before House Select Committee to Investigate the Use of Chemicals in Food Products, p. 1483 of Record. (4) Ibid., p. 1485. ( 5 ) Heyroth, F. F., Am. J . Pub. Health, 42,1508 (1952). (6) Hodges, P. C., Fareed, 0 . J.. Ruggy, G.. and Chudnoff, J. 9 . J . Am. Med. Assoc., 117, 1938 (1941). (7) Roholm, K., “Fluorine Intoxication,” London, €1. K. Lewis &Co., Ltd., 1937. FRANCIS F. HEYI~OTH, 11.D. KETTERING LABORATORY DEPARTMENT OF PREVENTIVE MEDICINE A N D IXDCSTRIAL HEALTH, OF MEDICINE, UNIVERSITY O F CINCIXSATI, COLLEGE CIICINIATI, OHIO
