would face a number of scientific challenges. Major concerns are related to ensuring adequate testing of metabolites and the potential difficulties of evaluating novel chemicals, such as nanomaterials and biotechnology products with in vitro tests. Those challenges require maintenance of some whole-animal tests into the foreseeable future, as indicated in Option III, which includes specific in vivo studies to assess formation of metabolites and some mechanistic studies of target-organ responses to environmental agents and leaves open the possibility that more extensive in vivo toxicity evaluations of new classes of agents will be needed. Like Option IV, Option III emphasizes the development and application of new in vitro assays for biologic perturbations of toxicity pathways. Thus, although the committee notes that Option IV embodies the ultimate goal for toxicity testing, the committee’s vision for the next 10-20 years is defined by Option III.

The committee is mindful of the methodologic developments that will be required to orchestrate the transition from current practices toward its vision. During the transition period, there will be a need to continue the use of many current test procedures, including whole-animal tests, as the tools needed to implement the committee’s vision fully are developed. The steps that need to be taken to achieve the committee’s vision are discussed further in Chapter 5.

The committee notes that European approaches to improve toxicity testing emphasize the replacement of animal tests with in vitro methods (Gennari et al. 2004). However, a major goal of the European approaches is to develop in vitro batteries that can predict the outcome of high-dose testing in animals. The committee distinguishes those in vitro tests from the ones noted in Options III and IV. In vitro studies promise to provide more mechanistic information and to allow more extensive and more rapid determinations of biologic perturbations that are directly relevant to human biology and exposures.

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