4-Week inhalation toxicity of 2-methylnaphthalene in experimental animals.

This paper presents toxic effects of 2-MN in laboratory animals under conditions of 4-week inhalation exposure to 2-methylnaphthalene (2-MN) vapors. Male Wistar rats were exposed to 2-MN vapors at a nominal concentration of 0, 2, 10 or 50 mg/m(3) in dynamic inhalation chambers for 4 weeks (6 h/day, 5 days/week). After 4 weeks of inhalation exposure the animals were necropsied. Blood samples were collected and selected organs were weighted and prepared for histological examinations. The effects of the increased levels of exposure to 2-MN experienced by the experimental rats were as follows: a) increasing γ-glutamylotransferase activity, b) stimulation of the hematopoietic system, c) lower cholesterol concentrations, d) higher number of goblet cells in lobar bronchi, e) hyperplasia of hepatic bile ducts. Four-week exposure of the animals to 2-MN at 2 mg/m(3) proved to be the no-observed-adverse-effect-level (NOAEL), while 10 mg/m(3) appeared to represent the lowest-observed-adverse-effect-level (LOAEL).