Respiratory irritative effects of trimethylbenzenes: an experimental animal study.

Sensory respiratory irritation effects of trimethylbenzene isomers (TMBs) (hemimellitene, mesitylene and pseudocumene) in male Balb/C mice were investigated in conditions of acute exposure and in male Wistar rats in conditions of repeated 90-day inhalation exposure to pseudocumene. The pseudocumene, mesitylene and hemimellitene concentrations depressing the respiratory rate to 50% (RD50) were 578, 519, 541 ppm, respectively. Inhalation exposure to pseudocumene for 90 days increased the total number of cell macrophages, polymorphonuclear leukocytes and lymphocytes number at all three test concentrations compared with the controls. Total protein lactate dehydrogenase (LDH) and acid phosphatase activity in bronchoalveolar lavage (BAL) were significantly increased in all exposed groups. Based on the effects observed in the respiratory tract, the threshold limit value of at least 10 ppm should be considered for the occupational exposure to trimethylbenzene isomers.