2006 US National Research Council Quotes (exposure)


The following quotes are from the 2006 US National Research Council report Fluoride in Drinking Water: A Scientific Review of EPA’s Standards, which is the most comprehensive review of fluoride toxicity to date. I have read the report in full, and the quotes are my own selection. They are intended to highlight some key points, not provide a complete summary. The page numbers are from the PDF, and do not match those of the version which can be read online. References have been omitted here, and may be found in the original document. Quotes from the report relating to biological effects can be found here.

Fluoridation chemicals
p 19 “In practice, most fluorine added to drinking water is in the form of fluosilicic acid (fluorosilicic acid, H2SiF6) or the sodium salt (sodium fluosilicate, Na2SiF6), collectively referred to as fluorosilicates; for some small water systems, fluoride is added as sodium fluoride (NaF).”

Exposures in subpopulations
p 3 “Some subpopulations consume much greater quantities of water than the 2 L per day that EPA assumes for adults, including outdoor workers, athletes, and people with certain medical conditions, such as diabetes insipidus. On a per-body-weight basis, infants and young children have approximately 3 to 4 times greater exposure than do adults. Dental-care products are also a special consideration for children, because many tend to use more toothpaste than is advised, their swallowing control is not as well developed as that of adults, and many children under the care of a dentist undergo fluoride treatments.”
p 48/9 “Other groups of people [apart from habitual tea drinkers] who are expected to have exposures higher than those calculated here include infants given fluoride toothpaste before age 1, anyone who uses toothpaste more than twice per day or who swallows excessive amounts of toothpaste, children inappropriately given fluoride supplements in a fluoridated area, children in an area with high fluoride concentrations in soil, and children with pica who consume large amounts of soil.”

p 68 “A number of researchers have pointed out both the importance of evaluating individual fluoride intake from all sources and the difficulties associated with doing so, given the variability of fluoride content in various foods and beverages and the variability of individual intakes of the specific items”
p 71 “Fluoride should be included in nationwide biomonitoring surveys and nutritional studies (e.g., CDC’s National Health and Nutrition Examination Survey and affiliated studies). In particular, analysis of fluoride in blood and urine samples taken in these surveys would be valuable.”
p 71/72 “Probabilistic analysis should be performed for the uncertainty in estimates of individual and group exposures and for population distributions of exposure (e.g., variability with respect to long-term water consumption). This would permit estimation of the number of people exposed at various concentrations, identification of population subgroups at unusual risk for high exposures, identification or confirmation of those fluoride sources with the greatest impact on individual population exposures, and identification or characterisation of fluoride sources that are significant contributors to total exposure for certain population subgroups.
To assist in estimating individual fluoride exposure from ingestion, manufacturers and producers should provide information on the fluoride content of commercial foods and beverages.
To permit better characterisation of current exposures from airborne fluorides, ambient concentrations of airborne hydrogen fluoride and particulates should be reported on national and regional scales, especially for areas of known air pollution or known sources of airborne fluorides. Additional information on fluoride concentrations in soils in residential and recreational areas near industrial fluoride sources also should be obtained.
Additional studies on the relationship between individual fluoride exposures and measurements of fluoride in tissues (especially bone and nails) and bodily fluids (especially serum and urine) should be conducted. Such studies should determine both absolute intakes (mg/day) and body-weight normalised intakes (mg/kg/day).
Assumptions about the influence of environmental factors, particularly temperature, on water consumption should be re-evaluated in light of current lifestyle practices (e.g., greater availability of air conditioning, participation in indoor sports).
Better characterisation of exposure to fluoride is needed in epidemiology studies investigating potential effects. Important exposure aspects of such studies would include the following:
– collecting data on general dietary status and dietary factors that could influence exposure or effects, such as calcium, iodine, and aluminium intakes
– characterising and grouping individuals by estimated (total) exposure, rather than by source of exposure, location of residence, fluoride concentration in drinking water, or other surrogates
– reporting intakes or exposures with and without normalisation for body weight (e.g., mg/day and mg/kg/day)
– addressing uncertainties associated with exposure, including uncertainties in measurements of fluoride concentrations in bodily fluids and tissues
– reporting data in terms of individual correlations between intake and effect, differences in subgroups, and differences in percentages of individuals showing an effect and not just differences in group or population means.
Further analysis should be done of the concentrations of fluoride in various fluoride species or complexes (especially fluorosilicates and aluminofluorides) present in tap water, using a range of water samples (e.g., of different hardness and mineral content). Research also should include characterising any changes in speciation that occurs when tap water is used for various purposes – for example, to make acidic beverages.
The possibility of biological effects of [hexafluorosilicate], as opposed to free fluoride ion, should be examined.
The biological effects of aluminofluoride complexes should be researched further, including the conditions (exposure conditions and physiological conditions) under which the complexes can be expected to occur and to have biological effects.”
p 83 “More work is needed on the potential for release of fluoride by the metabolism of organofluorines [e.g. pharmaceuticals].”

p 27 “Measured fluoride in samples of human breast milk is very low. Dabeka et al. (1986) found detectable concentrations in only 92 of 210 samples (44%) obtained in Canada, with fluoride ranging from <0.004 to 0.097 mg/L. The mean concentration in milk from mothers in fluoridated communities (1 mg/L in the water) was 0.0098 mg/L; in nonfluoridated communities, the mean was 0.0044 mg/L). Fluoride concentrations were correlated with the presence of fluoride in the mother’s drinking water.”
p 30 “even at very high fluoride intakes by mothers, breast milk still contains very low concentrations of fluoride compared with other dietary fluoride sources.…
Cows’ milk likewise contains very low fluoride concentrations, compared with other dietary sources such as drinking water.”

p 44 “given the expected presence of fluoride ion (from any fluoridation source) and silica (native to the water) in any fluoridated tap water, it would be useful to examine what happens when that tap water is used to make acidic beverages or products (commercially or in homes), especially fruit juice from concentrate, tea, and soft drinks. Although neither Urbansky (2002) nor Morris (2004) discusses such beverages, both indicate that at pH < 5, [fluorosilicate] would be present, so it seems reasonable to expect that some [fluorosilicate] would be present in acidic beverages but not in the tap water used to prepare the beverages.”

2006 US National Research Council Quotes (pharmacokinetics and health effects)


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