Comparative embryolethal effect of bromofenofos and dephosphate bromofenofos in rats.

Bromofenofos (BF) and dephosphate bromofenofos (DBF) were administered at equimolar doses to rats on day 10 of pregnancy. The dams were killed on day 21, and the fetuses were removed, weighted and examined by routine teratological methods. BF caused a significant increase in fetal resorptions at 58.2 mg/kg. Approximately 69% of the implants were resorbed at this dose level. In rats given DBF equimolar to 58.2 mg/kg BF, the resorption rate was 81.9%. Administration of BF resulted in a dose-dependent decrease in fetal body weights which was significant at 29.1 mg/kg or more. DBF caused a significant decrease in fetal body weights, beginning at 25.1 mg/kg equimolar to 29.1 mg/kg BF, and the decreased fetal body weights were almost the same between BF and DBF. BF at 58.2 mg/kg induced significant gross and skeletal malformations, with incidences of 35.6 and 27.6%, respectively. In rats given DBF equimolar to 58.2 mg/kg BF, gross and skeletal malformations were seen in 54.5 and 61.5% of the fetuses, respectively. There were similarities in the types of malformations observed between BF and DBF. Both compounds induced no significant internal malformations. It was concluded from these results that the embryolethal and teratogenic effects of BF is due to its metabolite, DBF, which cannot respond to cholinesterase inhibition.