In this chapter, the committee characterizes testing strategies used by federal and international agencies to gather the data used to identify and evaluate human health hazards and risks. Several examples of testing strategies that are currently used or have been proposed are presented. The testing strategies identified are not meant to be exhaustive but to illustrate the array of toxicity tests that may be required under different circumstances. Furthermore, presentation of the examples in this chapter is not meant to be a committee endorsement of any given strategy. The chapter concludes with committee observations on the current or proposed strategies.

TYPES OF TOXICITY-TESTING STRATEGIES

In practice, testing strategies vary considerably, although they can often be described by three basic testing approaches: battery, tiered, and tailored. A battery is a specific set of toxicity tests applied to all chemicals in a group. Testing batteries are sometimes intended to provide the minimal dataset necessary for risk-informed regulation or risk management.

In tiered testing, the results of a specific set of toxicity tests and risk-management needs are used to guide decisions about the nature and extent of further testing. Often, a substance is first assigned to categories (for example, based on structure or exposure) that guide testing sequences. The chemical then moves through a series of tests sequentially with the data from each test informing the next step in the process.

In tailored testing, information on exposure circumstances, suspected adverse effects, and knowledge of mechanism of action is used to determine the scope of tests to be conducted on a given chemical or class of chemicals. The strategies are thus tailored to the nature of the substance under consideration, its likely use or the likely exposure to it, and the extent of the information available and information needed. Tailored testing strategies may start with a flexible test battery and evolve to different tiers or types of testing in an iterative manner based on scientific judgment.

Characterizing an overall testing strategy as a battery, tiered, or tailored approach is often not possible, because testing strategies are typically combinations of these three basic elements. The examples that follow illustrate that point and demonstrate that testing strategies differ based on the concerns that they were meant to address. The examples address three applications: testing for registration of pesticides and food



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