SODIUM-FLUORIDE IS A LESS EFFICIENT HUMAN CELL MUTAGEN AT LOW CONCENTRATIONS

Sodium fluoride was found to induce gene‐locus mutations at the thymidine kinase (tk) and hypoxanthine guanine phosphoribosyl transferase (hgprt) loci in human lymphoblastoid cells. A single, 28 hr exposure to up to 600 μg/ml sodium fluoride induced a concentrationdependent increase in mutant fraction at both gene loci and reduced cell survival to 12% relative to negative control cultures. When cells were exposed to sodium fluoride concentrations that were only minimally toxic using a 20 day treatment protocol, no detectable induction of mutation was ob‐served at the the hgprt locus, and induction of mutation was observed at the tk locus only for treatment with 65 μg/ml sodium fluoride; exposure to 50 and 35 μg/ml sodium fluoride did not induce detectable mutation. The assay protocol used was of sufficient statistical sensitivity to detect the level of mutation predicted based on a linear extrapolation of data obtained from a 28 hour exposure. The implications of these observations with regard to the extrapolability of mutagenicity data to low concentrations are discussed. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company