Dermal developmental toxicity of N-phenylimide herbicides in rats

S-53482 and S-23121 are N-phenylimide herbicides and produced embryolethality, teratogenicity (mainly ventricular septal defects and wavy ribs), and growth retardation in rats in conventional oral developmental toxicity studies. Our objective in this study was to investigate whether the compounds induce developmental toxicity via the dermal route, which is more relevant to occupational exposure, hence better addressing human health risks.

S-53482 was administered dermally to rats at 30, 100, and 300 mg/kg during organogenesis, and S-23121 was administered at 200, 400, and 800 mg/kg (the maximum applicable dose level). Fetuses were obtained by a Cesarean section and examined for external, visceral, and skeletal alterations.

Dermal exposure of rats to S-53482 at 300 mg/kg produced patterns of developmental toxicity similar to those resulting from oral exposure. Toxicity included embryolethality, teratogenicity, and growth retardation. Dermal administration of S-23121 at 800 mg/kg resulted in an increased incidence of embryonic death and ventricular septal defect, but retarded fetal growth was not observed as it was following oral exposure to S-23121.

Based on the results, S-53482 and S-23121 were teratogenic when administered dermally to pregnant rats as were the compounds administered orally. Thus, investigation of the mechanism and its human relevancy become more important.