Toxicity Testing Strategies to Determine Needs and Priorities (1984) / Chapter Skim
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EXECUTIVE SUMMARY
EXECUTIVE SUMMARY
Pages 1-18
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The development of a strategy for obtaining appropriate information requires an estimation of the quantity and quality of available toxicity data applicable to the assessment of human health hazard, as well as knowledge of the number of substances on which necessary experimental data are not yet available. A characterization of the magnitude of needed testing would be valuable to those who allocate resources for such testing.
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The study, titled "Identification of Toxic ana Potentially Toxic Chemicals for Consideration by the National Toxicology Program, " was established in the Board on Toxicology and Environmental Health Hazards of the NRC Commission on Life Sciences. In this report, the Committee on Sampling Strategies and the Committee on Toxicity Data Elements describe in detail the criteria and procedures they used to determine the nature and extent of toxicity testing and their collective judgment on the testing needs for a "select universe" of chemical substances.
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Statistical adjustment for duplications indicated that the select universe contained about 53,500 distinct entities. The Committee on Toxicity Data Elements and the Committee on Sampling Strategies regarded the contents of the select universe as closely approximating the expected universe of interest to NTP.
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'Thus, selection of substances that have already had some testing aoes not necessarily constitute random sampling of al1 possible substances in the select universe . The Committee on Toxicity Data Elements developed a well-structured, stepwise approach to the determination of toxicity-testing needs for substances in the select universe.
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The findings of the Committee on Sampling Strategies and the Committee on Toxicity Data Elements are based on analyses of the sample of 675 substances randomly chosen from the select universe and the subsample of 100 randomly chosen from the sample that had at least what the latter committee defined as prescribed minimal toxicity information. Some specific analyses are derived solely from the sample or the 6
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At the same time, it rejected the concept that every substance in the select universe required the adequate performance of a complete battery of toxicity tests for a human-health hazard assessment, even if that were practical. Thus, other criteria, including data from human exposures, were also used for judgments about testing adequacy.
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Some test types (acute oral administration in rodents, acute dermal application, acute eye irritation and corrosivity, guinea pig skin sensitization, and subchronic dermal application for 90 days) were deemed not to require repetition in most cases where they had been conducted.
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Occasionally, the committee recommended that these studies not be repeated, either because toxicity was sufficiently well established or because more information would be of slight value. TOX ICITY-TEST ING NEEDS For pesticides and inert ingredients of pesticide formulations, the Committee on Toxicity Data Elements considered 18 test types to be necessary according to the standards it adopted.
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The estimates of percentages for health-hazard assessment combine data obtained from the sample of 675 substances used to measure the existence of minimal toxicity information and the 100 with minimal toxicity information that were examined for the quality of test protocols. Results of this analysis indicate not only the percentage of substances in each of the seven categories in which sufficient data of adequate quality are available for a heath-hazard assessment when judged against the current standards for protocols, but also the percentage that would require additional testing if an assessment were to be performed.
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In these two categories, 36% and 39% of substances met the requirements for minimal toxicity information, respectively. The Committee on Toxicity Data Elements judged it possible to make at least a partial health-hazaru assessment for 94% and 92% of the substances with minimal toxicity information in each of these categories, respectively.
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~ A:::::: /// ...... 10 8 1 78 76 1 82 Complete Health Hazard Assessment Possible Partial Health Hazard Assessment Possible Minimal Toxicity I nformation Available Some Toxicity I Information Available (But below Minimal)
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Development of analytic methods; systems for monitoring ambient air, water, soil, ana togas; personal monitoring systems; and highly sensitive and selective instrumentation for the evaluation of human exposure should be integral parts of this effort. APPROACHES TO PRIORITY-SETTI NG Part 1 of this report shows that, of tens of thousands of commercially important chemicals, only a few have been sub~ectea to extensive toxicity testing and most have scarcely been tested at all.
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The priority-setting system and the testing program form a continuum whose overall objective is to yield information of maximal value about the overall hazards of chemicals. In examining traditional approaches, including expert judgment and mechanical priority-setting systems, the committee found some common themes that can be considered conventional wisdom and with which it agrees: · Long lists of candidate chemicals need to be reduced to short lists through screening, which yields increasing amounts of information on decreasing numbers of chemicals and possible tests.
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In particular, the concept of the value of information is an important contribution to systematic priority-setting. In brief, this concept asserts that the value of any information-gathering activity, such as toxicity testing or searching for information on human exposure to chemicals, lies in the value of the resulting information in guiding decisions.
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With these broad kinds of improvement in mind, the Committee on Priority Mechanisms decided to outline an illustrative system that would incorporate the stated goal and general features, building on the experience of previous priority-setting procedures, but trying to make them more systematic, defensible, and robust. The committee recognized that its own resources were inadequate to develop a fully operational priority-setting system with all the desirable features, but it hoped to provide NTP with sufficient guidance and examples to enable it to improve its current selection system while adhering to its institutional operating principles.
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· Expert judgment is essential for operation of the system beyond the earliest stage, where judgment enters into the design but not into the operation. Simply put, not enough is known about chemical hazards to specify a purely mechanical system, and humans need to integrate diverse data into judgments about the degrees of exposure and suspected toxicity.
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However, the implementation of these concepts in the illustrative system or one of similar scope would require adjustments in the established patterns of thinking about testing priorities. Specifically, full application of the proposed analytic techniques will require that each information-gathering procedure be described quantitatively with respect to its ability to identify and to characterize potentially toxic chemicals.
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