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THE EFFECT OF FLUORIDE ON LEAD SOLUBILITY
Citation:
METZ, D. H., M. R. SCHOCK, AND D. DIONYSIOU. THE EFFECT OF FLUORIDE ON LEAD SOLUBILITY. Presented at AWWA Annual Conference, San Antonio, TX, June 12, 2006.
Description:
Difficulties in predicting and controlling lead corrosion are encountered by hundreds of water systems across the country. Inorganic carbonate, sulfate, silicate, orthophosphate, pH, total organic carbon, temperature and the type/amount of chlorine residual are all known factors in determining human exposure to lead resulting from the corrosion of domestic plumbing. A recirculation system was used to determine the effect of two commonly used fluoridation chemicals in lead levels. Fifty-five gallon recirculation systems containing synthetically produced drinking water with 4-ft new lead pipe sections of 0.5-in ID were used to determine differences in lead solubilities and scale composition. The chemical constituents of the water were carefully controlled around target values. Two tanks were used as controls having no fluoride added, two contained sodium fluoride at a concentration of 1 mg/L as F and two tanks contained hydrofluosilic acid at a concentration of 1 mg/L as F. The fluoridation chemicals did not increase lead solubility. In fact, the tanks containing NaF had significantly lower lead levels than the controls. No definitive cause of lower lead levels in the NaF tanks has been determined. The scales had different appearances, but the chemical composition of the scales (by XRD analysis) was not significantly different.