Nasal Olfactory Epithelial Lesions in F344 and SD Rats Following 1- and 5-Day Inhalation Exposure to Naphthalene Vapor

The exposure–response relationship and threshold for nasal epithelial effects of naphthalene (NP) vapor in F344 and SD rats were investigated in 1-day (6 hours) and 5-day (6 h/d) studies at concentration ranges of 0 to 30 ppm. Lesions related to 1-day exposure were predominately necrosis of the olfactory epithelium (OE). The severity of OE lesions was concentration dependent and ranged from minimal (≤1 ppm) to marked (10-30 ppm). In the 5-day study, degeneration of OE was observed in both strains, both sexes, with increasing incidence and severity that correlated with concentration. The epithelial degeneration lesion was minimal to moderate in severity. At 0.1 ppm, minimal OE lesions were observed in female SD rats only (20% incidence). Animals exposed to 10 ppm NP followed by 14 days without exposure also had OE lesions, but of lower severity, showing evidence of good recovery. In both studies, differences between sex or strain were not remarkable.