3-Nitrobenzanthrone (3-nitro-7 H-benz [d, e] anthracen-7-one) was isolated from the organic extracts of both diesel exhaust and airborne particles and was identified as a new class of powerful direct mutagen. Its mutagenicity by Ames Salmonella assay is very high (208 000 revertants/nmol in Salmonella typhimurium TA98 and 6 290 000 revertants/nmol in YG1024) and compares with that of 1, 8-dinitropyrene, which is the direct mutagen of strongest ...