In the panel discussion and in the presentations, we heard many speakers say that rodent bioassays may not be as valuable as we once assumed because they tell us less about human toxicity than was believed. We also need physiological models to connect the in vitro data to the in vivo data in order to validate the observations observed in rodents and to use this information to predict responses in humans. Some speakers commented that if we know mechanism, risk assessment will become chemical-specific, i.e., each chemical entity will require a specific risk assessment approach. I don't think that this is true. However, I do believe that if we know a certain mechanism and we know which chemicals act via that mechanism, we will be able to do risk assessment on mechanistically identified groups of chemicals.
Professional judgment is needed.
The difference is that we now know that dose cannot be defined as the exposure dose but must be re-defined as the dose delivered to the target site. Hazard identification may eventually be based upon biomarkers of exposure. We are not there yet but in vitro studies are pointing us in the right direction. It was said that it is important to have an understanding of the dose-response relationship in humans. I heard that in vitro studies using human cells will help provide the basis for that understanding and thus may provide and understanding of which biomarkers to use.