Increased cytotoxicity and mutagenicity of diesel fuel after reaction with NO2.

Gas chromatography/mass spectrometry (GC/MS) of diesel fuel aromatics detected polynuclear aromatic hydrocarbons from naphthalenes to phenanthrenes, but no four- or five-ring aromatics. This aromatic fraction treated with NO2 was found to contain nitro-aromatics, but only the naphthalene and biphenyl nitro-aromatics were detectable by direct GC/MS. By reduction of the nitro groups to amines, diazotization and reduction to yield aryl-iodides, it was possible to demonstrate that nitro-derivatives of most of the starting aromatics were present after NO2-treatment. Diesel fuel was separated into aliphatic and aromatic fractions by extraction with diethyl sulfoxide. These fractions were devoid of mutagenic activity in the Ames bioassay and exhibited low cytotoxicity to CHO cells in culture. However, after reaction with NO2, the products contained frameshift mutagens which did not require activation by S-9 microsomal enzymes. The biological activity of the NO2-treated aromatic fraction from fuel was more than 40 times greater in Salmonella TA100 than fuel aliphatics treated with NO2. The LC50 to CHO cells in culture increased more than fivefold for aromatics and more than tenfold for aliphatics. Similar to the diesel exhaust particulate extract, the cytotoxicity of the nitrated fractions was decreased by serum and glutathione. Reaction of fuel aromatics with NO2 may be one mechanism which contributes to the formation of cytotoxic and mutagenic activities in diesel exhaust.