Microbial detection of mutagenic nitro-organic compounds in filtrates of coal fly ash

The presence of mutagenic nitro-organic compounds on coal fly ash was indicated by the greatly reduced microbial mutagenicity of the ash filtrates with nitroreductase-deficient strains of Salmonella typhimurium compared to their corresponding parental strains. Addition of the liver S-9 microsomal enzyme preparation significantly increased the mutagenic activities of the ash extracts. Extracts of fly ash mutagens were prepared with horse serum, dimethyl sulfoxide, or azeotropic benzene/methanol mixture. The data were normalized to net revertants per 10(8) Salmonella typhimurium cells per milligram of ash used. This normalization procedure is essential for interpretation of comparative results. Both four-way and three-way analyses of variance were used to simultaneously evaluate the differences between solvent extracts, fly ash mutagen, S-9 activation, and nitroreductase-deficient strains and their parental strains. Of the three extraction systems tested, benzene/methanol azeotropic mixture was generally found to have the highest extraction power, and horse serum was the lowest. The results show that overall 87.5% (+/- 1.8 SE) of the mutagenic activity of the fly ash was associated with nitro-organic compounds.