Inhalation toxicity of acetaldehyde in rats. II. Carcinogenicity study: interim results after 15 months.

Male and female Wistar rats were exposed to acetaldehyde vapour at concentrations of 0, 750, 1500 and 3000/1000 ppm during 6 h/day, 5 days/week for up to 27 months. The present paper deals with the results obtained during the first 15 months of the study, including interim kills after 13, 26 and 52 weeks. Major compound-related lesions occurred in the nose and larynx. The nasal lesions comprised: (1) degenerative changes of the olfactory epithelium at all dose levels, frequently accompanied by focal hyperplasia of basal cells and thickening of the submucosa with loss of Bowman's glands and nerve bundles in the dorsomedial region, (2) stratified squamous metaplasia of the respiratory epithelium lining the caudoventral part of the nasal septum and the inner aspect of the ventral endoturbinates often accompanied by severe keratinisation and occasionally by papillomatous hyperplasia, almost exclusively observed at the top-dose level, and (3) malignant tumours (squamous cell carcinomas and adenocarcinomas) at all dose levels. Hyperplasia and keratinised stratified squamous metaplasia of the laryngeal epithelium were seen at the 2 highest dose levels.