Fluoride in Drinking Water A Scientific Review of EPA's Standards (2006) / Chapter Skim
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11 Drinking Water Standards for Fluoride
11 Drinking Water Standards for Fluoride
Pages 340-353
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From page 340... ...
First, an overview of current procedures for establishing exposure standards is provided, and risk assessment issues that have developed since the original MCLG and SMCL for fluoride were established are discussed. Current methods For setting standards For drinking Water To establish MCLGs for drinking water, EPA reviews studies of health effects of individual contaminants and uses the information to calculate an exposure level at which no known or anticipated adverse health effects would occur with an adequate margin of safety.
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From page 341... ...
DRINKING WATER STANDARDS FOR FLUORIDE 341 (including susceptible subpopulations) that is likely to have no appreciable risk of deleterious health effects during a lifetime.
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From page 342... ...
. Below, a few specific issues relevant to the committee's review of the drinking water standards for fluoride are discussed, including advances in carcinogenicity assessment, relative source contribution, special considerations for children, and explicit treatment of uncertainty and variability.
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From page 343... ...
In the drinking water program, the MCLG cannot account for more than 80% or for less than 20% of the reference dose (EPA 2000d)
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From page 344... ...
344 FLUORIDE IN DRINKING WATER sources of exposure other than drinking water were subtracted from the reference dose. In EPA's Methodology for Deriing Ambient Water Quality Criteria for the Protection of Human Health, a process called the exposure decision tree (Figure 11-1)
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From page 345... ...
DRINKING WATER STANDARDS FOR FLUORIDE 34 contributions (EPA 2000d)
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From page 346... ...
Despite their disagreement on characterization of the condition, these two members concurred with the committee's conclusion that the MCLG should prevent the occurrence of this unwanted condition. Strong evidence exits that the prevalence of severe enamel fluorosis is nearly zero at water fluoride concentrations to below 2 mg/L.
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From page 347... ...
Thus, before any conclusions can be drawn, more research is needed to clarify the relationship between fluoride ingestion, fluoride concentrations in bone, and stage of skeletal fluorosis. Bone Fractures The database on fluoride's effects on bone fractures has expanded since the earlier National Research Council (NRC)
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From page 348... ...
. Because serum fluoride concentrations may not be a good measure of bone fluoride concentrations or long-term exposure, the ability to show an association might have been diminished.
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From page 349... ...
The SMCL was selected to prevent objectionable enamel fluorosis in a significant portion of the population. EPA reviewed data on the prevalence of moderate and severe enamel fluorosis and found that, at a fluoride concentration of 2 mg/L in drinking water, the prevalence of moderate fluorosis ranged from 4% to 15% and that severe cases were observed at concentrations above 2.5 mg/L.
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From page 350... ...
. A comparison of the bone concentrations indicates that lifetime exposure at the SMCL could lead to bone fluoride concentrations that historically have been associated with stage II skeletal fluorosis.
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From page 351... ...
Relative Source Contribution At the time the MCLG was established for fluoride, a reference dose was not available and the MCLG was calculated directly from available data rather than as an apportioned part of the reference dose. In Chapter 2, the committee shows that at 4 mg/L, drinking water is the primary contributor to total fluoride exposure, ranging from 72% to 94% for average-waterintake individuals and from 92% to 98% for high-water-intake individuals.
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From page 352... ...
Secondary Maximum Contaminant Level The prevalence of severe enamel fluorosis is very low (near zero) at fluoride concentrations below 2 mg/L.
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From page 353... ...
DRINKING WATER STANDARDS FOR FLUORIDE 33 1 mg/L. These studies should focus on moderate and severe enamel fluorosis in relation to caries and in relation to psychological, be havioral, and social effects among affected children, among their parents, and among affected children after they become adults.
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