Perspectives in Biology and Medicine

FLUORIDE, THE ENVIRONMENT, AND HUMAN HEALTH GEOFFREY E. SMITH* The success of water fluoridation and other forms of fluoride therapy in combating dental caries is well established and beyond dispute. Claims linking fluoridated water with mongolism, cancer mortality, mutagenic or birth effects, and sensitivity have either been unconfirmed or found lacking in substance [I]. However, the toxic properties of the fluoride ion have been known for more than a century, and the margin between a safe daily intake of fluoride and a potentially harmful one is impressively small [2]. When a substance can be both beneficial and, in excess, harmful , it is important to ensure that some individuals are not overexposed to that substance. Writing in Science, Leverett [3] has pointed out that "the widespread use of fluorides may have created a situation in which we are approaching a critical mass of fluoride in the environment, which is eliminating dental caries as a public health problem in the United States, and some other nations of the world." This statement summarises the paradoxical nature of fluoride. While tooth decay does not kill or cripple, it does cause a disproportionate amount of pain and misery across every age and social group in the developed countries of the world. Hence, the success of fluoride in reducing the incidence ofthis ubiquitous and costly disease is to be welcomed. On the other hand, the prospect of a "critical mass"—or more—of fluoride in the environment could have serious implications. Fluoride at very low concentrations is phytotoxic and harmful to livestock; and in man, excessive intakes of fluoride over many years may lead to a well-defined disorder, skeletal fluorosis, which can affect the teeth, skeletal tissues, and, secondarily, the nervous system [4]. While the scientific knowledge offluorides and their effects on human health is considerable, it is by no means complete, and most studies that comprehensively review the topic are able to identify areas in need of ?Address: 56 Surrey Road, South Yarra, Melbourne 3141, Victoria, Australia.©1986 by The University of Chicago. All rights reserved. 003 1 -5982/86/2904-0489$0 1 .00 560 I Geoffrey E. Smith ¦ Fluoride further research. For example, the pathogenesis of the osseous changes in skeletal fluorosis has yet to be elucidated [5], the question of the lower limit for a toxic fluoride content ofbone is still open [6], and the possible existence of preskeletal fluorosis in some individuals has not been adequately studied [7]. Furthermore, the precise mechanism by which dental fluorosis or "mottled enamel" is caused has not been established [8], and it has not yet been confirmed whether it is the incorporation of fluoride in the hydroxyapatite lattice of the enamel or the presence of fluoride in the fluid environment of teeth that is necessary for protection against caries [9]. Because fluoride is increasingly being used as a drug, and in view of the fact that several recent reports [7, 10, 11] have suggested that fluoride in the environment is increasing, a review of the subject may be in order. Fluoride in the Environment Fluorine constitutes 0.065 percent of the elements of the earth's crust and is a significant component of the total biogeochemical cycle in which life has evolved [12]. Man has always been exposed to fluorine in his environment; and fluorine (as fluoride) has always been a trace constituent of his diet and a component of his body fluids, tissues, and skeleton. Indeed, the ubiquitous occurrence of fluoride in nature means that it would be virtually impossible to prepare a diet entirely free of fluoride. However, while there are many natural sources of fluoride in the environment, a significant proportion of the fluoride that now enters the human body is from modern, man-made sources in the air, water, food, and forage. Consideration of multiple sources of fluoride intake is particularly relevant because there is an ever-increasing utilization of fluoride compounds by our technologically oriented society. Fluorine occurs in a combined form in a wide variety of natural materials , such as coal, clay, and mineral ores, and may be released when these are heated or burned. Thus, potential sources of fluoride emissions include industrial plants concerned with phosphoric acid...