Toxicity and carcinogenicity study in F344 rats following 2 years of whole-body exposure to naphthalene vapors

The toxicologic and carcinogenic potential of naphthalene was studied by ex posing groups of 49 male and 49 female F344 rats to atmospheres containing 0, 10, 30, or 60 ppm of the chemical for 6 h daily, 5 days/wk for 2 yr. Mea n body weights of exposed groups of male rats were less than for the contro l group throughout most of the study. Mean body weights of exposed female r ats were generally similar to those of controls. Survival of exposed and co ntrol rats was similar. Under the conditions of this 2-yr inhalation study, naphthalene was carcinogenic to male and female F344/N rats, causing incre ased incidences of respiratory epithelial adenoma ( males: control, 0%; low dose, 12%, mid dose, 17%; high dose, 31%; females: 0%; 0%; 8%; 4%) and olf actory epithelial neuroblastoma ( males: control, 0%; low dose, 0%; mid dos e, 8%; high dose, 6%; females: 0; 4%; 6%; 24%) of the nose. In both sexes o f rats, exposure to naphthalene also caused significant increases in the in cidences of nasal lesions including hyperplasia, atrophy, chronic inflammat ion, and hyaline degeneration of the olfactory epithelium and hyperplasia; squamous metaplasia, hyaline degeneration, and goblet-cell hyperplasia of t he respiratory epithelium; and glandular hyperplasia and squamous metaplasi a.