Thirteen-week inhalation toxicity study of 1-methylnaphthalene in F344 rats.

Abstract

1-Methylnaphthalene is generally utilized in solvents, as an intermediate in organic synthesis, a dye carrier, in resins, and others. There are some toxicological studies of 1-methylnaphthalene; however, inhalation toxicity studies are rare. Each of 10 male and female F344 rats was exposed to vapors of 1-methylnaphthalene for 13weeks (6h a day, 5days per week) at concentrations of 0, 0.5, 4, and 30ppm in a whole-body inhalation chamber system. The exposure concentrations were 0.52 ± 0.05, 4.08 ± 0.25, and 30.83 ± 1.28ppm for the low-, middle-, and high-dose group, respectively. Body weight changes were not affected by exposure to 1-methylnaphthalene. Blood prothrombin time was delayed at 30ppm in male and female groups, and activated partial thromboplastin time was also delayed at 30ppm in the male group. Values of alanine aminotransferase in the serum were decreased and those of albumin were increased at 30ppm in the male group. Differential cell counts and levels of lactate dehydrogenase in the bronchoalveolar lavage fluid were not affected. However, mucous cell hyperplasia in the nasopharyngeal tissues was found and the severity was correlated to exposure concentrations. In conclusion, 1-methylnaphthalene mainly affects the upper respiratory system and the no-observed-adverse-effect levelis suggested to be 4ppm on the basis of histopathological findings.