Fingernail fluoride: A method for monitoring fluoride exposure

This work was based on the hypothesis that fingernail clippings can be used as a biomarker for the subchronic exposure to fluoride. The results provid e data on fac tors that may affect the concentration of fluoride in fingern ail clippings as determined with the electrode following HMDS-facilitated d iffusion. The following variables had only minor or no effects on the conce ntrations: (1) the surface area of the clippings (intact, minced or filed i nto powder) that were placed into the diffusion dishes; (2) soaking in deio nized water for up to 6 h; (3) soaking in fluoridated water (1.0 ppm) for 2 h, and (4) removal of the organic material of nails by dry ashing, Fingern ail fluoride concentrations were approx imately 50% higher than those in to enails. A 1-month period of increased fluoride intake by one of the authors resulted in significant increases in fingernail fluoride concentrations af ter a lag time of approximately 3.5 months. The fluoride concentrations in fingernail clippings obtained from three groups of Brazilian children were directly related to the concentrations in the drinking water (0.1, 1.6 or 2 .3 ppm). The results indicate that: (1) HMDS-facilitated diffusion complete ly separates fluoride from intact nail clippings, so the need for ashing or other preparative methods is obviated; (2) fingernail fluoride is derived mainly from the systemic circulation, and (3) fluoride intake is reflected by the concentrations in fingernails.