Abbreviations: MR, mutation rate; DMSO, dimethyl sulfoxide; NPD, 4-nitro-1,2-phenylenediamine; SAZ, sodium azide; 9AA, 9-aminoacridine; MMS, methyl methanesulfonate; 2AA, 2-aminoanthracene. Remarks: DMSO was applied as vehicle of the test item and the positive control substances: NPD, 9AA, and 2AA. Ultrapure water was applied as vehicle for the positive control substances: SAZ and MMS. The mutation rates of the test item, untreated control, NPD, 9AA, and 2AA are given referring to DMSO. The mutation rates of the SAZ and MMS positive controls are given referring to the ultrapure water.