The effect of dimethylsulfoxide on the mutagenicity of the hair dye p-phenylenediamine.

Published data on the mutagenicity of the oxidative hair dye intermediate p-phenylenediamine in the Ames test are conflicting. The work reported here resolves the discrepancies, showing that the activity of p-phenylenediamine in the Ames Salmonella/microsome test is markedly influenced by the use of dimethylsulfoxide as solvent, and by the age of the solution prior to plating. Thus, aqueous solutions of p-phenylenediamine are non-mutagenic; fresh solutions in DMSO are equally non-mutagenic, but become highly active on standing at room temperature for 4 hr. These results suggest the need for caution in the choice of solvents and tight controls in the execution of the test.