Inhalation teratology study on monochlorobenzene in rats and rabbits

The embryotoxic and teratogenic potential of inhaled monochlorobenzene (MCB) was evaluated in rats and rabbits. Bred Fischer 344 rats and inseminated New Zealand White rabbits were exposed to 0, 75, 210, or 590 ppm of MCB via inhalation for 6 hr/day during the period of major organogenesis. Exposure to 590 ppm caused elevated liver weights in both species and decreased body weight gain and feed consumption in rats. Inhalation of MCB vapors during gestation was not embryotoxic or teratogenic in rats. In rabbits, a few MCB-exposed fetuses exhibited visceral malformations which were not observed among concurrent controls, though no dose-related increase in malformations occurred. To further evaluate the effects of MCB in rabbits, additional groups were exposed to 0, 10, 30, 75, or 590 ppm. This subsequent study did not result in any increase in malformations in the MCB-exposed groups. Fetal effects were limited to a slight delay in skeletal development which occurred only in rats exposed to 590 ppm, a maternally toxic concentration.