Micronucleus formation in 3-day mouse embryos associated with maternal exposure to chlorpyrifos during the early preimplantation period.

Chlorpyrifos, an organophosphate pesticide, was evaluated for its ability to induce cytogenetic damage in preimplantation embryos after maternal exposure. Pregnant female mice were intraperitoneally (i.p.) administered a single dose of chlorpyrifos (40 or 80 mg/kg) at 10:00 h on Day 0 of pregnancy. On Day 3 of gestation, blastocysts were collected and evaluated for gross morphology, micronucleus (MN) frequency, and cell number. A significant increase in MN frequency indicating cytogenetic damage was observed in the treatment groups in comparison to control. The MN frequency revealed a clear dose-dependent increase. There was also a significant decrease in the embryo cell number in the 80 mg/kg treated group. A simultaneous decrease in the cell number and increase in MN frequency may reflect an embryonic developmental disadvantage resulting from maternal treatment with chlorpyrifos.