The unexpected positive results from the National Toxicology Program’s (NTP) rodent study of fluoride carcinogenicity will make it difficult for the Environmental Protection Agency (EPA) not to classify fluoride a carcinogen, thereby terminating 40 years of public-water fluoridation in the United States.

Validated pathology results officially released by the NTP showed that, among male rats, four osteosarcomas occurred in the high-dose group of 80, one in the mid-dose group of 50, and none in the low dose (50) or control (80) groups. Additionally, among female rats, the NTP reported three oral squamous carcinomas in the high-dose group of 80 and none in the mid- and low-dose groups, though one occurred in the control group of 80. Among male rats, the incidence of oral squamous carcinoma was one out of 80 in the high-dose group, one out of 50 in the mid-dose group, and zero in the low-dose and control groups. (No frank malignant neoplasms were reported in mice, nor were any osteosarcomas reported in female rats.)

The high dose for fluoride was 79 ppm; the medium dose, 45 ppm; the low dose, 11 ppm. By comparison, the EPA permits up to 4 ppm of fluoride in drinking water.

‘Will Have Considerable Weight’

The NTP’s official interpretation of these findings should be available next month, and, following peer review by its board of scientific counselors in mid-April, its study will at last be complete – almost 14 years after Congress ordered it in 1977. Meanwhile, last month the EPA officially announced it was opening a review of its 1986 fluoride drinking-water standard, in which the agency will be considering new evidence of possible adverse health effects. The battleground then, is prepared for what may prove to be the last of the fluoridation crusades, with the NTP study as presiding deity.

Said Joseph Cotruvo, Ph.D., director of the EPA’s Office of Drinking Water: “NTP studies are very highly quality-controlled and reviewed and are the best studies we know of for animal carcinogenicity data. This is certainly an important study, and will have considerable weight in our evaluations.”

How much weight will depend, first of all, on how the NTP categorizes the strength of its evidence. According to NTP officials, the agency has five levels of evidence: “none,” “equivocal,” “some,” “clear,” and “inadequate study.” They declined to speculate on how their study will finally be tagged but conceded privately that a designation of “none” or “inadequate study” seemed remote.

Therefore, the study may be expected to arrive at the EPA labeled “equivocal” or “some” evidence. The EPA will then do its own weight-of-the-evidence evaluation, according to Dr. Cotruvo, “in which the NTP study will be considered in the context of the total body of data, including other carcinogenicity bioassays, mechanistic factors, and epidemiological studies.” (The EPA, of course, will also evaluate new evidence on the other possible adverse health effects of fluoride, which have been obscured by the recent focus on carcinogenicity.)

If the NTP study alone manages to run reviewer gauntlets with its significance intact, however, the EPA may find it difficult not to regulate fluoride as a carcinogen. As this article was being written, edicts from above constrained federal scientists from discussing the impact of the NTP study, but several were willing to provide off-the-record background. “It is difficult to see how EPA can fail to regulate fluoride as a carcinogen in light of what NTP has found,” observed one. “Osteosarcomas are an extremely unusual result in rat carcinogenicity tests. Toxicologists tell me that the only other substance that has produced this is radium. Even uranium, which is also deposited in bone, failed to do it.”

‘Further Implicates Fluoride’

“The fact that this highly atypical form of cancer occurred in the organ where fluoride is stored – bone – further implicates fluoride as the cause,” this scientist continued. “Also, the osteosarcomas appeared to be dose-related, and none occurred in controls, making it a clean study. If these results hold up, EPA can’t ignore them, despite the fact that they occurred in only one sex of one species. And the incidence of oral cancers in both male and female rats also seems suggestive. I think they’ll have to classify fluoride as a carcinogen.”

“EPA can’t ignore this,” agreed one of the agency’s scientists. “If we could regulate trichloroethylene as a carcinogen when only 2-4% of the test animals had problems, how can we discount these fluoride results?”

Under the Safe Water Act, a carcinogenic classification would require the EPA to set a maximum-contaminant-level goal of zero for fluoride in drinking water, because of the “no threshold” assumption that governs regulation of carcinogens by public-health agencies.

“The weight of current scientific evidence indicates it is likely that any substance found to be carcinogenic in lab animals is also likely to be carcinogenic in humans and that even the smallest amounts of this substance may cause a correspondingly small increase in the risk of cancer,” explained Robert Carton, Ph.D., an EPA environmental scientist. (He is president of EPA Local 2050 of the National Federation of of Federal Employees, which has been opposing what it views as the politicization of science at the EPA, using fluoride as a case in point.) “Since this is what the scientific evidence says, public-health agencies are ethically compelled to act on it.”

Impact? Can’t Even Guess

“The ‘no threshold’ concept cannot be proved and is the subject of scientific debate,” noted Dr. Cotruvo. “But it is the policy assumption that guides our regulation of carcinogens.” If the EPA tags fluoride a carcinogen, it will mean the end of public-water fluoridation in the United States.

“A new fluoride standard is going to happen – EPA has already set up a work group,” another agency scientist related. “Even if the NTP evidence is termed “equivocal,” they’ll regulate, because EPA determines risk as a function of toxicity times exposure, and the exposure population for fluoride in drinking water is over 140 million.Lead is the only substance with a larger exposure.”

Dr. Cotruvo, however, stated that “it is too early to speculate or even guess as to what the impact of NTP’s study will be on EPA’s fluoride standard.”