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TRIBUNE : Caries Preventative Already Has One Rap Against
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MEDICAL TRIBUNE
February 22, 1990
Caries Preventative Already Has One Rap Against It
by Joel Griffiths
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."
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