Fluoride in Drinking Water A Scientific Review of EPA's Standards (2006) / Chapter Skim
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3 Pharmacokinetics of Fluoride
3 Pharmacokinetics of Fluoride
Pages 89-102
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From page 89... ...
oVerVieW oF Fluoride Chemistry, units, and measurement Fluoride is the ionic form of fluorine, the most electronegative element. Water in the United States is typically fluoridated with fluorosilicates or sodium fluoride.
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From page 90... ...
of fluoride in bone ash is equivalent to about 560 mg/kg wet weight. Fluoride concentrations in body fluids typically are measured with a fluoride-specific electrode, an instrument that cannot reliably measure concentrations below about 0.019 mg/L and tends to overpredict at lower concentrations.
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From page 91... ...
. Fluoride concentrations in plasma, extracellular fluid, and intracellular fluid are in approximate equilibrium.
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. Bone fluoride concentrations were predicted to increase approximately linearly as a function of water concentration, at least up to 4 mg/L.
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predicting bone concentrations in people after lifetime exposures to assumed water concentrations or other exposure scenarios, and (2) comparing plasma and bone fluoride concentrations in rats and humans with the same exposure.
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concluded that average bone fluoride concentrations were linearly related to water concentration. (As discussed in Appendix C, this analysis is fully ecologic)
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Even TABLE 3-3 Multiple Regression Results for Zipkin Data Coefficient 95% CI P value Intercept -556 mg/kg (-1,512, 401) 0.25 Water fluoride 1,527 (1,224, 1,831)
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For 16, fluoride concentrations were measured in the water sources (2.6 ± 1.4 mg/L) ; bone concentrations were 4,910 ± 2,250 mg/kg ash.
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Because the pharmacokinetics of fluoride are nonlinear, we would not necessarily expect people with the same cumulative exposure to have the same bone fluoride concentrations. Indeed, the model may overpredict bone concentrations for long-term exposure to lower fluoride concentrations via water.
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Species age at different rates, and age affects pharmacokinetics, especially bone development and kidney function. Evidence suggests that rats require higher chronic exposure than humans to achieve the same plasma and bone fluoride concentrations.
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. FaCtors modiFying PharmaCokinetiCs and their imPliCations For Potentially susCePtiBle PoPulations Changes in chronic exposure to fluoride will tend to alter plasma and bone fluoride concentrations.
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From page 100... ...
in two patients with reduced renal function and exposure to drinking water with fluoride at 1.7 and 2.6 mg/L. Four renal patients with severe skeletal changes or bone pain had elevated serum and bone fluoride concentrations; the bone concentrations ranged from about 5,500 to 11,000 mg/kg (Johnson et al.
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Findings · Bone fluoride concentrations increase with both magnitude and length of exposure. Empirical data suggest substantial variations in bone fluoride concentrations at any given water concentration.
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102 FLUORIDE IN DRINKING WATER ments of fluoride in soft tissues are based on short-term exposures and some atypically high values have been reported. Thus, more studies are needed on fluoride concentrations in soft tissues (e.g., brain, thyroid, kidney)
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