Developmental Toxicity: Extrapolation Across Species

There is a pervasive lack of understanding about the definition of a developmental toxicant and the experimental design necessary to differentiate between maternal toxicants and those uniquely, i.e., selectively, hazardous to the conceptus. Thus, the acceptance of the adult-to-developmental (A/D) ratio and its ability to identify those compounds uniquely hazardous to the conceptus has been compromised, as has the extrapolation of hazard across species. The failure to establish a shared understanding is discussed, together with the role of an in vitro screen for determining the A/D ratio. The addition of an environmental exposure factor permitting the extrapolation of hazard assessment across species and the estimation of potential human developmental toxicity is detailed.