Concentration dependence of the embryotoxic effects of benzene inhalation in CFY rats.

CFY rats were exposed to continuous benzene inhalation 24 h/day from day 7 to day 14 of gestation at 150, 450, 1500, or 3000 mg/m3 (50, 150, 500, or 1000 ppm) atmospheric concentrations. None of the benzene concentrations used proved to be teratogenic. There was no increase in the incidence of external, visceral, or skeletal malformations. Benzene inhalation at a 150 mg/m3 concentration brought about a slight toxic effect at a 450 mg/m3 concentration a more pronounced effect on both mothers and fetuses. The toxic effects were manifest as an increase in maternal mortality, circulatory damage, decreased gain in body weight, decrease in the weight of the placenta in the mothers and an increase in mortality (early and late), retardation of development (weight and skeleton) in the fetuses. No further change in the parameters was seen with further increases in benzene concentration. Avoidance of the risks of benzene exposure seems desirable before the commencement of planned pregnancy in the human.