A teratological study was carried out on the
plasticizer tri-n-butyl phosphate (
TBP). Pregnant Wistar rats were treated orally on days 7-17 of gestation with
TBP at 0, 100, 200, 400 or 800 mg/kg/day in the dose-finding study and 0, 62.5, 125, 250 or 500 mg/kg/day in the subsequent teratological study.
Caesarean sections were performed on day 20 of gestation. In the dose-finding study, all of the pregnant rats were killed by the treatment with
TBP at 800 mg/kg/day. In the teratological study, salivation and depression of
body weight gain, adjusted
body weight gain and food consumption were observed at the higher doses of
TBP. There were no significant differences between the groups in the incidence of dead or resorbed foetuses, the number of living foetuses and the
body weights of living foetuses of both sexes. The incidence of rudimentary lumbar rib increased significantly at 500 mg/kg/day. There were two cases of malformation: a foetus with
deformity of fore- and hind-limbs at 400 mg/kg/day in the dose-finding study and
conjoined twins exhibiting three fore-limbs and four hind-limbs
at 125 mg/kg/day in the teratological study. These malformations were rare in the background data of teratology, and the incidence of foetuses with malformations was not increased significantly. Therefore,
TBP was considered not to be teratogenic in this study.