Inhalation toxicity of acetaldehyde in rats. III. Carcinogenicity study.

Male and female Wistar rats were exposed to acetaldehyde vapour at nominal concentrations of 0, 750, 1500 or 3000/1000 ppm during 6 h/day, 5 days/week for up to 28 months. Major compound-related effects included increased mortality, growth retardation, nasal tumours, and non-neoplastic nasal changes in each of the test groups. The treatment-related nasal changes comprised: (1) degeneration, hyperplasia, metaplasia and adenocarcinomas of the olfactory epithelium at all exposure levels; (2) squamous metaplasia accompanied by slight to severe keratinisation and squamous cell carcinomas of the respiratory epithelium at the 2 highest exposure levels; and (3) slight to severe rhinitis and sinusitis in top-concentration rats. In the larynx hyperplasia and keratinized squamous metaplasia of the epithelium in the vocal cord region were seen in many rats of the mid- and top-concentration groups. One female rat of the 1500 ppm group had developed a laryngeal carcinoma in situ. It was concluded that under the conditions of the present study acetaldehyde is both cytotoxic and carcinogenic to the nasal mucosa of rats. The effects of acetaldehyde on the nose were compared to those of formaldehyde.