Inhalation Developmental Toxicity Study of Propylene Oxide in Fischer 344 Rats

The developmental toxicity potential of propylene oxide (PO)was evaluated in Fischer 344 rats following inhalation exposure.Four groups of 25 mated female rats were exposed to 0, 100,300, and 500 ppm of PO for 6 hr per day on Gestation Days 6through 15, inclusive. Cesarean sections were performed on allfemales on Gestation Day 20 and the fetuses removed for morphologicalevaluation. Exposure to propylene oxide did not adversely affectsurvival, appearance, or behavior at any of the exposure levelstested. Maternal body weight gain and food consumption werereduced significantly among the females at the 500 ppm levelduring the exposure period. No exposure-related effects werenoted with respect to maternal water consumption, organ weights,cesarean section, or fetal morphological observations with thesole exception of increased frequency of seventh cervical ribsin fetuses at the maternally toxic exposure level of 500 ppm.In summation, the no-observable-adverse-effect level (NOAEL)of propylene oxide. when administered to Fischer 344 rats viawhole-body inhalation exposure, was considered to be 300 ppm.