Reproductive-toxicologic Assessment of the Epoxides Ethylene Oxide, Propylene Oxide, Butylene Oxide, and Styrene Oxide

Ethylene oxide (CAS no 75-21-8), propylene oxide (CAS no 75-56-9), butylène oxide (CAS no 106-88-7), and styrene oxide (CAS no 96-09-3) were tested for teratogenic activity by inhalation exposure of rats and rabbits. Ethylene oxide and propylene oxide were tested at only one concentration in both species (150 ppm for ethylene oxide and 500 ppm for propylene oxide). Butylene oxide was tested at 250 and 1,000 ppm in both species, while styrene oxide was tested at 100 ppm in rats and 15 and 50 ppm in rabbits. For each of these four epoxides, the acute toxicity was similar for pregnant and nonpregnant rats. Styrene oxide was the most toxic in both species, and rabbits were more sensitive than rats. Rats exposed to propylene oxide for 7 h/d, 5 d/week for three weeks before breeding had a significant reduction in the number of corpora lutea. Fetal mortality was not increased, but significantly fewer mated rats were found pregnant following gestational exposure to styrene oxide, a finding suggesting preimplantation loss. In rabbits exposed to styrene oxide, the number of resorptions per litter was increased in a concentrationrelated manner, but differences were not statistically significant. Fetal examinations revealed evidence of fetotoxicity with all four epoxides. There was no overt teratogenic activity, but a number of minor morphologic aberrations were detected.