Comparison of Fluoride Metabolism When Administered as NaF or Silicofluorides to Rats

Drinking water is fluoridated using NaF, fluorosilicic acid (HFS) or sodium fluorosilicate (SFS). Critics of the use of silicofluorides claim that they are metabolized differently from NaF and could cause higher tissue F concentrations. Objective: To compare the general features of fluoride metabolism when administered as NaF, HFS or SFS to rats. Methods: Weanling, female SD rats (8/group) were given free access to AIN-76A food (0.7 ppm F) and deionized water containing 24-ppm F added as NaF or commercial grades of HFS or SFS for five months. While housed in pairs, five 48-h metabolic balance studies were done during the 4th and 5th months. Food and water intake and the output of urine and feces were determined gravimetrically. Water and urine F concentrations were determined with the electrode after buffering with TISAB; plasma, food and fecal concentrations were determined after HMDS-facilitated diffusion. Results: There were no significant differences among the groups for body weight gains during the study, plasma F concentrations, nor for the intake of food or water. The balance data (mean ± SE, µg/48-h) are shown in the table. There were no significant differences among the groups for any of the six variables.