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OCR for page 295
6
CONCLUSIONS AND RECOMMENDATIONS
Far more chemicals are in the human environment than can be evaluated
for potential toxicity with available methods and resources. Therefore,
some chemicals have to be selected for testing for their potential impact
on public health, and that requires a priority-setting process. The
selection of chemicals for testing is made difficult by the existence of
many possible health effects to test for and many possible tests and
combinations of tests to choose from.
Much of the information needed to set priorities for testing is
fragmentary or lacking; little if any toxicity information is available
on most chemicals, and the information on human exposure to or potential
toxicity of only a few is more than minimal. Moreover, many of the data
that do exist are not easily retrievable or are not in a form that makes
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. . .
them readily usable or veritable. An essential function or any
priorityffetting system must be to serve as a guide to strategies for
improving the available data through the most rapid and effective
combinations and sequences of information-gathering procedures.
On the basis of its review of existing priority-setting systems, the
Committee on Priority Mechanisms has concluded that such systems must be
logically and scientifically defensible, open to peer review, practical,
and explicit about their underlying assumptions. Such analytic
techniques as systems analysis and decision theory appear to permit
design approaches with those characteristics. Application of these
analytic techniques requires, however, that each information-gathering or
testing procedure be described quantitatively with respect to its ability
to identify potentially toxic chemicals; and the current art of toxicity
testing and priority-setting does not readily permit such quantitative
descriptions with great precision. Efforts toward further quantification
of performance characteristics of toxicologic methods are essential to
the development of an optimal priority-setting system.
In addition to information on the accuracy of testing procedures, the
design of a priority-setting system involves the number and types of
chemicals to be considered by the system, the accuracy of selection
procedures, the availability of testing resources, penalties for
misclassifying chemicals, costs of selection and testing, and adequacy of
information on exposure to and the potential health effects of the
chemicals to be considered.
Priority-setting systems must also be flexible, so that they can be
applied by users with different missions. No system can anticipate and
address all possible contingencies, and a given system should be
adjustable to suit specific needs. Testing may be undertaken for a
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variety of reasons--e.g., to provide special scientific insights or to
improve knowledge of testing procedures. At times, policy considerations
may dictate testing of substances that would otherwise receive lower
priorities. A priority-setting system should be able to respond to
changes that result from advances in science and changes in the perceived
relative importance of various toxicity and exposure problems.
There is no evidence that any priority-setting system can remedy the
basic problem of insufficient data. In the light of that impediment, the
following may be considered as characteristics of a system that would
advance the state of the art of priority-setting:
· Use of explicit, detailed, and formal decision-making procedures
in selecting and ranking chemicals for testing, such as are illustrated
in the approach described in this report, which is based on principles of
systems analysis and decision theory.
· Validation and quantification of the performance characteristics
of all tests and other information-gathering procedures used in the
testing programe
· Development of relevant data bases, including those related to the
production and use of chemicals, to the potential for human exposure, to
structure-activity relationships, and to toxic activity.
· Characterization of the universe of chemicals to be tested.
· Estimation of the prevalence of substances that can cause
different types of toxicity.
· Development of systematic procedures to ensure that the
priority-setting process corrects and refines itself on the basis of
experience.
· Inclusion of a procedure for systematic screening of the entire
select universe of chemicals as defined in this report, as a basis for
nominating substances to be tested.
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Representative terms from entire chapter:
testing procedures
