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Nitric oxide (NO') is a physiological messenger formed by several cell types. Reaction with 02 forms oxides that nitrosate amines at pH values near 7. We now report experiments in which NO' was added to intact human cells and to aerobic solutions of DNA, RNA, guanine, or adenine. TK6 human lymphoblastoid cells were mutated 15-to 18-fold above background levels at both the HPRT and TK gene loci. Xan-

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The human cell mutagenicity of Los Angeles airborne fine particulate matter is examined via bioassay-directed chemical analysis. A 1993 composite fine particle sample is separated via liquid chromatography into fractions containing organic compounds of varying polarity. Samples are analyzed by the h1A1v2 human cell mutagenicity assay to identify those fractions that contain human cell mutagens and by GC/MS to identify the chemical character of those mutagens. Those subfractions that contain unsubstituted polycyclic aromatic compounds (PAC) are responsible for a considerable portion of the mutagenic potency of the whole atmospheric sample. Six unsubstituted PAC (cyclopenta[cd]pyrene, benzo[a]pyrene, benzo[ghi]perylene, benzo[b]fluoranthene, indeno[1,2,3-cd]pyrene, and benzo[k]fluoranthene) account for most of the mutagenic potency that can be assigned to specific compounds within the atmospheric samples. Important semipolar mutagens that are quantified include 2-nitrofluoranthene and 6Hbenzo[cd]pyren-6-one. A large number of other aromatic organics are identified as candidates for future testing as pure compounds in the human cell assay, at which time it should be possible to account for more of the mutagenic potency of the atmospheric samples.