Teratogenesis associated with oxydemeton-methyl in the stage 12 chick embryo

The teratogenic potential of oxydemeton-methyl (ODM) was investigated using a stage specific localized topical method of application to the stage 12 chick embryo. A dose of 0.01, 0.05, 0.10, 0.50, 1.0, or 2.0 mg/embryo was applied to the vitelline membrane directly above the stage 12 embryo. The embryo was then returned to the incubator and monitored daily until stage 41 (15 day). At stage 41 the embryo was autopsied and examined for gross external and internal malformations, wet weight, and crown-rump length. Experimental data was compared to unopened and saline treated controls. At doses less than 0.50 mg/embryo, survival rates were high (> 80%) but when that dose was exceeded, the survival rate fell significantly (P < 0.001). A dose-dependent increase in malformation rate was seen in all treatment groups with 0.10 mg/embryo, producing a maximum malformation rate (19/33) with minimum mortality (3/36). Crown-rump lengths and wet weights were significantly less than controls in all treatment groups (P < 0.001). Anomalies were primarily seen in the musculoskeletal (ventral midline, limb, and neck) and cardiovascular (ventricular septum and aortic arches) systems. Thoracogastroschisis and ventricular septal defects were the most common combination of malformations. Our data suggest that ODM is teratogenic when topically applied to the stage 12 chick embryo.