Enhancement of mutagenicity of 1-nitropyrene by water as a diluent.

The mutagenicity of 1-nitropyrene was strongly enhanced in the Salmonella mutagenicity test with the preincubation modification when it was dissolved in dimethylsulfoxide and diluted with water. The enhancement of mutagenicity was not found in the plate incorporation method and seemed to be common to chemicals which have low solubilities in water. The indications were that the effectiveness of preincubation modification was due to the increased absorption of test chemicals by the Salmonella cells, and that the absorption depends primarily on the solubility of test chemicals in the assay mixture.