Species Difference in Developmental Toxicity of an N‐Phenylimide Herbicide between Rats and Rabbits and Sensitive Period of the Toxicity to Rat Embryos

An N-phenylimide herbicide, S-53482, exhibited developmental toxicity in rats in the absence of maternal toxicity at a dose of 30 mg/kg. The developmental toxicities noted were embryolethality, teratogenicity (mainly ventricular septal defect [VSD] and wavy ribs) and growth retardation. In contrast to rats, the herbicide showed no developmental toxicity in rabbits even at a maternal toxic dose of 3,000 mg/kg. There was a remarkable species difference between rats and rabbits. A single dose of S-53482 was administered to pregnant rats on one of gestation days 11 through 15 (detection of plug = day 0). Day 12 of gestation was the most sensitive day for embryonic death, VSD, and decreased fetal body weight. It is likely that there is a common mechanism for the three types of developmental toxicity and that S-53482 does not produce VSD by its direct damage to embryonic heart tissue.