LUNG-TUMOR INDUCTION BY INHALATION EXPOSURE TO MOLYBDENUM TRIOXIDE INRATS AND MICE

Inhalation studies of molybdenum trioxide (MoO3) were conducted becaus e of its wide use in industry, human exposure, and lack of data on car cinogenicity. Groups of 50 male and 50 female F344/N rats and B6C3F1 m ice were exposed to MoO3 by inhalation at 0, 10, 30, or 100 mg/m(3), 6 h/day, 5 days/week, for 2 years. In both rats and mice, survival and mean body weights of exposed groups of males and females were similar to those of their respective controls. There were significant exposure -dependent increases in blood molybdenum concentration in exposed rats and mice. There were no toxicological differences in bone density or curvature between exposed animals and their respective controls. In ra ts, dose-dependent increases in incidence of hyaline degeneration in t he nasal olfactory epithelium and squamous metaplasia of the epitheliu m lining the base of the epiglottis were observed. The incidence of al veolar/bronchiolar adenoma or carcinoma (combined) was marginally incr eased in males but not in females compared with controls. In mice, the incidences of squamous metaplasia of the epithelium lining the base o f the epiglottis, hyperplasia of the laryngeal epithelium, and metapla sia of the alveolar epithelium were significantly increased in all exp osed males and females compared with controls. The incidence of alveol ar/bronchiolar adenoma or carcinoma (combined) in exposed groups of ma les and females was significantly greater than that in the control gro ups. (C) 1998 Society of Toxicology.