Embryotoxicity and fetotoxicity of orally administered chlorpyrifos in mice

Abstract Pregnant CF-1 mice were given 0, 1, 10, or 25 mg/kg/day of chlorpyrifos by gavage on Days 6 through 15 of gestation. Severe maternal toxicity was observed among pregnant mice given 25 mg/kg of the test compound. Plasma and erythrocyte cholinesterase levels were significantly reduced among maternal mice at all dosages. Fetotoxicity was noted among litters of mice given 25 mg/kg of chlorpyrifos as evidenced by decreased fetal body measurements and an increased incidence of minor skeletal variants. An increase in the incidence of exencephaly was observed among litters of mice at the lowest dosage, 1 mg/kg/day, but not at 10 or 25 mg/kg. Additional groups of mice were given 0, 0.1, 1, or 10 mg chlorpyrifos/kg/day on Days 6 through 15 of gestation. Plasma and erythrocyte cholinesterase levels were significantly decreased among maternal mice at 1 and 10 mg/kg but not at the lowest dosage, 0.1 mg/kg. No evidence of a teratogenic response was observed in these mice. Thus, since exencephaly was not repeatable and was not found at 10- and 25-fold higher dose levels in the original study, chlorpyrifos was not teratogenic in mice at dose levels up to 25 mg/kg/day.