Journal of Environmental and Public Health Volume 2013 (2013), Article ID 439490, 13 pages http://dx.doi.org/10.1155/2013/439490 http://www.hindawi.com/journals/jeph/2013/439490/ Download full PDF
Physiologic Conditions Affect Toxicity of Ingested Industrial Fluoride
1Department of Chemistry, University of California, San Diego, La Jolla, CA 92037, USA
2STAR Tutoring Center, Palomar Community College, San Marcos, CA 92069, USA
Received 30 September 2012; Revised 13 March 2013; Accepted 3 April 2013
Academic Editor: Stephen Peckham
Copyright © 2013 Richard Sauerheber. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The effects of calcium ion and broad pH ranges on free fluoride ion aqueous concentrations were measured directly and computed theoretically. Solubility calculations indicate that blood fluoride concentrations that occur in lethal poisonings would decrease calcium below prevailing levels. Acute lethal poisoning and also many of the chronic effects of fluoride involve alterations in the chemical activity of calcium by the fluoride ion. Natural calcium fluoride with low solubility and toxicity from ingestion is distinct from fully soluble toxic industrial fluorides. The toxicity of fluoride is determined by environmental conditions and the positive cations present. At a pH typical of gastric juice, fluoride is largely protonated as hydrofluoric acid HF. Industrial fluoride ingested from treated water enters saliva at levels too low to affect dental caries. Blood levels during lifelong consumption can harm heart, bone, brain, and even developing teeth enamel. The widespread policy known as water fluoridation is discussed in light of these findings.
Synthetic industrial fluoride compounds lack calcium and are listed toxic substances (Buck , Gleason , Blakiston , The Merck Index ). Calcium fluoride is found in natural minerals and is not labeled a toxic compound because of the comparatively high lethal oral acute dose of the purified compound when tested in mammals (LD50 ~ 3,750 mg/kg). The fluoride compounds, sodium fluoride NaF and fluorosilicic acid H2SiF6, added into municipal water for human ingestion purposes are synthesized artificially by industrial reaction and have been used as rodenticides, insecticides, and pediculicides, with acute oral lethal doses in experimental animals comparable to arsenic and lead (LD50~ 125 mg/kg) (The Merck Index ) due to the fluoride at ~60–90 mg/kg.
Waters in the U.S. can contain natural calcium fluoride along with other calcium and magnesium salts (U.S. Centers for Disease Control (CDC) ), but pure pristine fresh drinking water does not contain fluoride. Fluoride is not a normal constituent of the mammalian bloodstream (Merck manual for Health Care Professionals ). It has no nutritive value  or physiologic function but has been believed by some to be useful for teeth based on an initial correlation with natural calcium fluoride in drinking water [1, 8]. The chief ingredient in normal teeth enamel is hydroxyapatite that contains calcium phosphate, not fluoride. After nearly 7 decades of adding industrial fluoride compounds into public water supplies in the U.S. and other countries that have agreed to this policy, the principal documented effects of ingested fluoride on teeth are to increase incidence of abnormal permanent enamel fluorosis during teeth development and to abnormally incorporate into underlying dentin bone (National Research Council (NRC) ). Fluorosis, unsightly at best, afflicts ~5 million U.S. teenagers aged 12–15 as of 2004 .
The reported adverse consequences of adding fluoride lacking calcium into public water supplies include effects on man, animals, and the environment [1, 8–12]. Ingested industrial fluoride incorporates chiefly into bone with an ion exchange process that is irreversible and thus not physiologic. Normal biochemical effects of nutrient minerals are saturable and readily reversible. Fluorine leads all elements in electronegativity and is extremely reactive and not found in nature. But fluoride is permanent because the ion has no electronegativity, cannot be reduced further, or oxidized by any known substance. Fluoride instead associates with positive charged ions in particular aluminum, calcium, and iron. Thus its toxicity depends on the environment in which it resides.
Soluble fluoride at 60 mg/kg single oral dose without calcium causes acute heart failure in research animals (CDC ) and caused lethal heart failure reported in a child after swallowing concentrated dental gel . Twenty-five ppm artificial fluoridated water leads to chronic heart failure in research animals  which compares with levels during accidental overfeeds where kidney dialysis patients died (Gessner et al. ). At lower concentrations (~1 ppm), artificially fluoridated water supplies are documented to have caused horses, frogs, chinchillas, and alligators to die prematurely that consumed treated water continuously for extended periods of time (Spittle ). Discharged fluoride into the Columbia River to ~0.3 ppm blocked salmon navigation upstream to spawn (Damkaer and Dey ). Even though natural fluoride at 1 ppm is in the world’s oceans with substantial calcium and magnesium salts, this arrangement is normal and harmless to aquatic species.
Natural calcium fluoride is considered insoluble (to 8–10 ppm fluoride maximum depending on water pH). But industrial synthetic fluorides are fully soluble and are all toxic calcium chelators. The degree of absorption of any fluoride compound after ingestion is correlated with its solubility (Goodman and Gilman ). Industrial fluorides are completely absorbed, but natural fluoride minerals cryolite (Na3AlF6) or fluorite (mineral fluorspar with CaF2) are poorly absorbed (see Endnote 1). The dietary cations calcium and iron retard absorption by forming complexes in the GI tract. Although large populations are reported to safely consume 1 ppm fluoride in water for long periods of time, this is when it exists naturally at this level.
In what was considered unthinkable, in Hooper Bay, Alaska, in 1994 an industrial fluoridation overfeed of calcium-deficient Yukon River drinking water caused fatal heart block in an otherwise healthy 41 year old male. This is the largest known poisoning in the U.S. from a fluoridated water supply. Approximately 300 people with severe gastrointestinal pain survived the incident (Gessner et al. ). Electronic feeding equipment is now employed to prevent overfeeds and acute poisoning. But chronic effects of industrial fluoridation of public water supplies on humans, animals, and the environment require further study if fluoridation of fresh water supplies continues. Many countries require great expenditures to remove endogenous natural fluoride from drinking water that causes skeletal and other pathology at 8–10 ppm even when water contains substantial antidote calcium to minimize assimilation of the ingested fluoride . The present study investigates conditions involved in acute and chronic fluoride toxicity and environmental effects of industrial fluorides added into public water.