Toxic effects of acute inhalation exposure to 1-methylnaphthalene and 2-methylnaphthalene in experimental animals

Neurotoxic and sensory respiratory irritation effects of 1-methylnaphthalene and 2-methylnaphthalene in male rats and male Balb/C mice were investigated under conditions of acute inhalation exposure. Rotarod performance and pain sensitivity behaviour were tested in rats exposed to 1-methylnaphthalene at concentrations of 152-407 mg/m3, and 2-methylnaphthalene at concentrations of 229-522 mg/m3 immediately after termination of a four-hour exposure. The respiratory rate was measured in mice by the whole body pletysmographic method in 6 min duration exposure to various concentrations of 1-methylnaphthalene and 2-methylnaphthalene. Exposure to both methylated naphthalene derivatives resulted in concentration-dependent decrease in pain sensitivity in rats and depression of respiratory rate and mice. At the concentrations applied no statistically significant disturbances in rotarod performance behaviour were observed. The concentrations depressing the respiratory rate to 50% (RD50) were 129 mg/m3 and 67 mg/m3, for 1-methylnaphthalene and 2-methylnaphthalene, respectively. As based on RD50 values, the MAC values of 4 mg/m3 for 1-methylnaphthalene, and of 2 mg/m3 for 2-methylnaphthalene are suggested.