Induction of rat mammary gland tumors by 1-nitropyrene, a recently recognized environmental mutagen

1-Nitropyrene, a direct-acting mutagenic component of extracts of diesel exhaust and ambient air particulates, is one of the major nitroarenes found in products of incomplete combustion. Injection of this compound into newborn Sprague-Dawley-derived CD rats at 100 mumol/kg body weight s.c. once a week for 8 weeks induced 32 and 28% sarcomas, primarily malignant fibrous histiocytomas, at the site of injection in male and female animals, respectively. Mammary tumors, most of which were adenocarcinomas, developed distant from the site of injection in 47% of the females. Similar but lesser responses were observed in animals given one-half this dose. This carcinogenic response is consistent with the systemic effects of structurally related aromatic amines. 4-Nitrobiphenyl, given at equimolar doses, was not tumorigenic in this study.