Preparation of oils for bacterial mutagenicity testing

4 procedures used to prepare fossil-derived oils for bacterial mutagenicity testing have been examined. These are, (a) dewaxing by partitioning the oil between dimethyl sulfoxide (DMSO) and cyclohexane, (b) incorporating a surfactant to increase compatibility of the oil with the bioassay media, (c) directly slurrying the oil in DMSO, and (d) computing the mutagenicity of the oil by summing the contributions of individual chemical class fractions. DMSO slurries generally exhibit higher mutagenicities than computed by summing the contributions of chemical class fractions. Results of testing DMSO-slurries correlate (r = 0.87) well, however, with those obtained by summation. Mutagenicity results agree within a factor of two for the samples tested by 4 sample preparation procedures.