Isobutyraldehyde administered by inhalation (whole body exposure) for up to thirteen weeks or two years was a respiratory tract toxicant but was not carcinogenic in F344/N rats and B6C3F1 mice.

Isobutyraldehyde (a chemical structurally related to formaldehyde and used as a flavoring agent) was studied for toxicity and carcinogenicity by exposing male and female F344/N rats and B6C3F1 mice. Animals were exposed to isobutyraldehyde vapors 6 h per day, 5 days per week for up to 13 weeks or 2 years. In the 13-week studies, groups of 10 male and 10 female F344/N rats and B6C3F1 mice were exposed to concentrations of 0, 500, 1000, 2000, 4000, or 8000 ppm. Chemical-related body weight depression and deaths occurred in rats and mice exposed to 4000 and 8000 ppm. Necrosis of the epithelium accompanied with acute inflammatory reaction was observed in the nasal turbinate, larynx, and trachea of rats exposed to 8000 ppm. Exposure of rats to 4000 ppm resulted in metaplasia of the nasal respiratory epithelium, inflammation, degeneration of the olfactory epithelium, and osteodystrophy of the nasal turbinate bone. In the 13-week mouse study, exposure to 8000 ppm or 4000 ppm resulted in necrosis of the epithelium lining of the nasal turbinates. Osteodystrophy of the nasal turbinate bone and squamous metaplasia of the nasal respiratory epithelium were noted in mice exposed 4000 ppm. Degeneration of the olfactory epithelium was noted in males exposed 2000 ppm and in females exposed to 4000 ppm. In the 2-year studies, groups of 50 male and 50 male F344/N rats and B6C3F1 were exposed to concentrations isobutyraldehyde vapors of 0, 500, 1000, or 2000 ppm 6 h per day, 5 days per week. There were no differences in survival rates or mean body weights between exposed groups and control rats. Survival of male mice exposed to 2000 ppm and mean body weights of female mice exposed to 1000 or 2000 ppm were lower than those of the of the controls. No increase in neoplasm incidence was observed in rats and mice in the 2-year studies that could be attributed to isobutyraldehyde exposure. Chemical-related nonneoplastic lesions were limited to the nose of rats and mice. They included squamous metaplasia of the respiratory epithelium (rats), suppurative inflammation (rats), and olfactory epithelial degeneration (rats and mice) at 1000 and 2000 ppm.