& Engineering News
25 August 2003
concerns surface once again
Research linking fluoride in drinking water to health problems could
lead to regulatory changes
decades of adding fluoride to drinking water to protect teeth from
decay, there are growing concerns about the efficacy and the safety
of this practice. Spurred by new research on fluoride's health effects
and at the request of the Environmental Protection Agency, the National
Academies' National Research Council (NRC) has begun another review
of the problems of water fluoridation.
Aug. 12, NRC held a public meeting to review EPA's standards for
fluoride in drinking water. Several witnesses defended the current
standards and the practice of adding fluoride to drinking water
to protect teeth. But some argued that the maximum contaminant level
(MCL) of 4 mg of fluoride per liter allowed by EPA in drinking water
presents health risks to the population and provides little, if
any, benefit to teeth. They claimed, in particular, that EPA's MCL
presents risks to bones and other organ systems.
1986, EPA set an MCL of 4 mg per L and a secondary MCL of 2 mg per
L for fluoride in drinking water. A secondary standard is a goal
that water systems should try to reach, but they cannot be fined
if they fail to do so. In 1993, the NRC Board on Environmental Studies
& Toxicology reviewed those standards and found them acceptable.
Last year, EPA asked NRC to once again review the toxicological
and exposure data on fluoride, especially new research, and determine
whether the standards can still be considered acceptable for protecting
the public from potential adverse effects of fluoride.
its 1993 review, the NRC panel found inconsistencies in the fluoride
database and gaps in knowledge. It recommended further research
on fluoride intake, dental fluorosis (mottling of the teeth caused
by excessive fluoride intake during tooth development), bone fractures
related to fluoride accumulation, and carcinogenicity. It also advised
that EPA's standards be reviewed when results of new research became
available. Since 1993, many studies have been published on fluoride's
effects on the nervous system and bone.
FORMAL CHARGE for the new NRC review is to examine the toxicological,
epidemiological, clinical, and exposure data published on fluoride
since 1993. At the recent public meeting held by NRC, Joyce M. Donohue,
toxicologist in EPA's Office of Water, pointed out that the enforceable
MCL of 4 mg per L was set to protect against crippling skeletal
fluorosis, while the nonenforceable secondary MCL for fluoride was
set at 2 mg per L to prevent dental fluorosis. "At 2 mg per
L, the incidence of moderate dental fluorosis ranges from 0 to 15%,"
she said, "and there are distinct increases in severe dental
fluorosis at levels above 2.5 mg per L." Teeth with severe
fluorosis are heavily stained and pitted and susceptible to fracture,
those with mild fluorosis have white opaque patches on small areas
of the teeth, and those with moderate fluorosis have yellow or tan
explained that if people consume a minimum of 20 mg of fluoride
per day for 20 years, they can contract crippling skeletal fluorosis.
To calculate the MCL, she said, 20 mg per day was divided by the
average water intake of 2 L per day to get 10 mg per L, and this
figure was divided by a safety factor of 2.5 to yield 4 mg per L.
"I do not know the origin of the 2.5 safety factor. Now, EPA
uses safety factors of 1, 3, and 10, not 2.5," she said. Safety
factors establish a margin of safety to account for individual variability
and species differences when extrapolating from animal to human
calculating the fluoride standards, Donohue explained, EPA assumed
that all fluoride exposure comes from drinking water, when in fact
it also originates from food processed with fluoridated water, personal
care products, food fertilized or treated with fluoride compounds,
and supplements. "In setting standards for all other drinking
water contaminants except barium, EPA has considered exposure from
many different sources, not just water," she said.
the NRC review in 1993, research indicates that over the past decade
people have had greater exposure to fluoride through personal care
products and that the prevalence of dental fluorosis may have increased,
Donohue said. Also, studies have raised questions about whether
topical exposure to fluoride may prove much more important than
systemic exposure in preventing dental caries, she said. (If the
primary action of fluoride is topical, drinking fluoridated water
would probably not be as important as fluoridated toothpaste in
preventing tooth decay.) In addition, new research suggests that
low levels of fluoride have developmental effects and effects on
the brain, she said.
the NRC panel's formal charge does not include an examination of
the benefits of fluoride, William R. Maas, director of the division
of oral health at the Centers for Disease Control & Prevention,
spoke for nearly an hour, defending water fluoridation. He attributed
the sharp decline in dental caries experienced in the U.S. since
the late 1940s to fluoridation and called it "an important
public health achievement." In the U.S., 162 million people,
or about 55% of the population, are drinking fluoridated water,
yet only 1.3% of school children experience moderate or severe dental
fluorosis, he said. Altogether, 22% of children have some degree
of fluorosis, he explained.
children who have lived in areas with fluoridated drinking water
all their lives have on average 1.6 fewer cavities than children
with no exposure to fluoridation, Maas said. Put another way, 12-year-old
children in fluoridated areas have an average of 4.25 decayed, missing,
or filled tooth surfaces out of a total of 128 surfaces, while 12-year-old
children in fluoridated areas have 2.81 cavities out of a possible
128. This represents a 39% reduction in decay from fluoridation,
Connett, a chemistry professor at St. Lawrence University, called
the 39% reduction a vagary of comparing small numbers--a difference
that may not be statistically significant. Connett noted that few
countries in Western Europe fluoridate their drinking water. Overall,
only 1 to 2% of Europe's population drinks fluoridated water, yet
all European Union nations have experienced tooth decay reductions
similar to those in the U.S. over the past 50 years. Therefore,
it is illogical to attribute the decline in tooth decay in the U.S.
to fluoridation, he said.
people who drink water that meets the EPA standard may have some
degree of skeletal fluorosis."
ARGUED that EPA's MCL of 4 mg per L, or 4 ppm, puts people at risk
for skeletal fluorosis. There are four stages of the disease, he
said, and the standard is designed to prevent only the most severe
stage. The first three stages are indistinguishable from arthritis
unless a doctor performs a bone biopsy to determine the fluoride
water with a 4-ppm fluoride content for 20 years yields bone fluoride
levels of more than 6,000 ppm," Connett said. People with clinical
phase I of skeletal fluorosis have been reported to have bone fluoride
contents of 6,000 to 7,000 ppm, he explained. Therefore, "many
people who drink water that meets the EPA standard may have some
degree of skeletal fluorosis," he said. Those who drink more
than the average of 2 L per day would be at particular risk, he
said it is likely that many people who live in communities with
moderate fluoride content in their water supplies (about 1 ppm,
for example) experience preclinical skeletal fluorosis. Some individuals
who have lived all their lives in areas with 1 ppm fluoride in the
water supply have been found to have elevated levels of fluoride
in their bone ash, he explained.
is evidence from both human and animal studies that cortical bone
with excessive levels of fluoride is more brittle and prone to fracture,
Connett said. With the exception of vertebrae, most bones in the
body are primarily cortical, including the femoral neck in the hip.
Consequently, people who accumulate excessive levels of fluoride
in their bones are probably more likely to experience a hip fracture,
11 clinical trials over the past decade, people were given fluoride
tablets (20 to 34 mg per day over 1 to 4 years) to treat osteoporosis,
Connett said. The effects were the opposite of what researchers
expected. In all of these studies, the group of patients who received
the tablets had higher hip fracture rates than the control group
patients, who were given a placebo.
people will experience cumulative fluoride doses over their lifetimes
from fluoridated water which exceed the cumulative doses that have
caused increased hip fractures in clinical trials," he said.
"For humans, exposure to 4 ppm fluoride in drinking water yields
an average of 6,400 ppm fluoride in bone," and several clinical
trials showed increased fracture rates when the bone concentration
is as low as 3,800 ppm, he explained.
is also new evidence that fluoride can have neurotoxic effects,
Connett said. Phyllis J. Mullenix, then a toxicologist at the Forsyth
Research Institute in Boston, examined the effect of sodium fluoride
on rat behavior. In utero fluoride exposure caused hyperactivity
in the rats, and those dosed after birth were hypoactive.
another study, one group of rats drank water containing 1 ppm sodium
fluoride, a second group drank water with 1 ppm aluminum fluoride,
and a control group drank distilled water. In both treated groups,
but not in the control group, the brains developed the type of b-amyloid
deposits associated with senile dementia in humans, Connett said.
review of fluoride has broader ramifications than the fluoridation
of water. It may influence EPA's decisions on the insecticide sulfuryl
fluoride (SO2F2), a substitute for stratospheric-ozone-depleting
methyl bromide. EPA is now in the process of deciding whether the
temporary tolerance it granted for the postharvest fumigation of
food with SO2F2 should be made permanent. SO2F2 leaves residues
on walnuts and raisins that are metabolized to inorganic fluoride.
the NRC committee has just commenced its review of fluoride, it
has not yet drawn any conclusions from the deliberations. It will
hold another public meeting in November and plans to complete its
review by November 2004.