42 l © 2025 American Dental Association
Section 2: Safety
In light of the collective evidence on various health end points and total exposure to fluoride,
the committee concludes that the EPA’s MCLG of 4 mg/L should be lowered. Lowering the
MCLG will prevent children from developing severe enamel fluorosis and will reduce the lifetime
accumulation of fluoride into bone that the majority of the committee concludes is likely to put
individuals at increased risk of bone fracture and possibly skeletal fluorosis, which are particular
concerns for subpopulations that are prone to accumulating fluoride in their bones.26
To develop an MCLG that is protective against severe enamel fluorosis, clinical stage II skeletal
fluorosis, and bone fractures, the EPA should update the risk assessment of fluoride to include
new data on health risks and better estimates of total exposure (relative source contribution) for
individuals. The EPA should use current approaches for quantifying risk, considering susceptible
subpopulations, and characterizing uncertainties and variability.26
The 2006 NRC report26 contained one major recommendation related to the SMCL:
The prevalence of severe enamel fluorosis is very low (near zero) at fluoride concentrations
below 2 mg/L. From a cosmetic standpoint, the SMCL does not completely prevent the
occurrence of moderate enamel fluorosis. The EPA has indicated that the SMCL was intended to
reduce the severity and occurrence of the condition to 15% or less of the exposed population.
The available data indicate that fewer than 15% of children will experience moderate enamel
fluorosis of aesthetic concern (discoloration of the front teeth) at that concentration. However,
the degree to which moderate enamel fluorosis might go beyond a cosmetic effect to create an
adverse psychological effect or an adverse effect on social functioning is not known.26
Additionally, the subcommittee identified data gaps and made recommendations for future research
relevant to future revisions of the MCLG and SMCL for fluoride.26
It should be emphasized that the 2006 NRC report was not a review of fluoride as used in community
water fluoridation. In fact, the 2006 NRC Report in Brief 26 states: “The committee did not evaluate
the risks or benefits of the lower fluoride concentrations (0.7–1.2 mg/L) used in water fluoridation.
Therefore, the committee’s conclusions regarding the potential for adverse effects from fluoride at
2–4 mg/L in drinking water do not apply at the lower water fluoride levels commonly experienced by
most US citizens.”26
In response to the recommendations noted above from the NRC report, in 2011, the EPA completed
and peer-reviewed a quantitative dose-response assessment based on the available data for severe
dental fluorosis as recommended by the NRC.199 Additionally, the EPA completed and peer-reviewed
a document on the environmental exposure of children and adults to fluoride and the relative source
contribution for water that is needed to derive the MCLG from the dose-response assessment.199
These efforts were being undertaken during 6-Year Review 2, and therefore no action on fluoride
MCLG and SMCL levels was taken during the 6-Year Review 2.
In December 2016, the EPA announced the review results for its third 6-Year Review (called 6-Year
Review 3),200 in which the EPA completed a detailed review of 76 national primary drinking water
regulations. The regulation for naturally occurring fluoride in water was examined as part of this review
and is included among the list of regulated contaminants considered to be “Low priority and/or no
meaningful opportunity” under “Not Appropriate for Revision at this Time.”200
The announcement of the results of the 6-Year Review 3 in the Federal Register 201 indicated that,
with the reviews of fluoride conducted since the first 6-Year Review (including but not limited to the
2006 NRC report and the EPA Fluoride Risk Assessment and Relative Source Contribution) and noting
that other contaminants are of much greater concern, the EPA recommended that no further action
Section 2: Safety
In light of the collective evidence on various health end points and total exposure to fluoride,
the committee concludes that the EPA’s MCLG of 4 mg/L should be lowered. Lowering the
MCLG will prevent children from developing severe enamel fluorosis and will reduce the lifetime
accumulation of fluoride into bone that the majority of the committee concludes is likely to put
individuals at increased risk of bone fracture and possibly skeletal fluorosis, which are particular
concerns for subpopulations that are prone to accumulating fluoride in their bones.26
To develop an MCLG that is protective against severe enamel fluorosis, clinical stage II skeletal
fluorosis, and bone fractures, the EPA should update the risk assessment of fluoride to include
new data on health risks and better estimates of total exposure (relative source contribution) for
individuals. The EPA should use current approaches for quantifying risk, considering susceptible
subpopulations, and characterizing uncertainties and variability.26
The 2006 NRC report26 contained one major recommendation related to the SMCL:
The prevalence of severe enamel fluorosis is very low (near zero) at fluoride concentrations
below 2 mg/L. From a cosmetic standpoint, the SMCL does not completely prevent the
occurrence of moderate enamel fluorosis. The EPA has indicated that the SMCL was intended to
reduce the severity and occurrence of the condition to 15% or less of the exposed population.
The available data indicate that fewer than 15% of children will experience moderate enamel
fluorosis of aesthetic concern (discoloration of the front teeth) at that concentration. However,
the degree to which moderate enamel fluorosis might go beyond a cosmetic effect to create an
adverse psychological effect or an adverse effect on social functioning is not known.26
Additionally, the subcommittee identified data gaps and made recommendations for future research
relevant to future revisions of the MCLG and SMCL for fluoride.26
It should be emphasized that the 2006 NRC report was not a review of fluoride as used in community
water fluoridation. In fact, the 2006 NRC Report in Brief 26 states: “The committee did not evaluate
the risks or benefits of the lower fluoride concentrations (0.7–1.2 mg/L) used in water fluoridation.
Therefore, the committee’s conclusions regarding the potential for adverse effects from fluoride at
2–4 mg/L in drinking water do not apply at the lower water fluoride levels commonly experienced by
most US citizens.”26
In response to the recommendations noted above from the NRC report, in 2011, the EPA completed
and peer-reviewed a quantitative dose-response assessment based on the available data for severe
dental fluorosis as recommended by the NRC.199 Additionally, the EPA completed and peer-reviewed
a document on the environmental exposure of children and adults to fluoride and the relative source
contribution for water that is needed to derive the MCLG from the dose-response assessment.199
These efforts were being undertaken during 6-Year Review 2, and therefore no action on fluoride
MCLG and SMCL levels was taken during the 6-Year Review 2.
In December 2016, the EPA announced the review results for its third 6-Year Review (called 6-Year
Review 3),200 in which the EPA completed a detailed review of 76 national primary drinking water
regulations. The regulation for naturally occurring fluoride in water was examined as part of this review
and is included among the list of regulated contaminants considered to be “Low priority and/or no
meaningful opportunity” under “Not Appropriate for Revision at this Time.”200
The announcement of the results of the 6-Year Review 3 in the Federal Register 201 indicated that,
with the reviews of fluoride conducted since the first 6-Year Review (including but not limited to the
2006 NRC report and the EPA Fluoride Risk Assessment and Relative Source Contribution) and noting
that other contaminants are of much greater concern, the EPA recommended that no further action
