PRINCIPLES OF TOXICOLOGY

19 Example of Risk Assessment
Applications
EXAMPLE OF RISK ASSESSMENT APPLICATIONS
ALAN C. NYE, GLENN C. MILLNER, JAY GANDY, and PHILLIP T. GOAD
As described in the preceding chapter, human health risk assessment is a flexible, occasionally
complex, often controversial process used to characterize the probability and types of adverse health
effects that may result from chemical exposure. Historically, risk assessments have been criticized for
many reasons, such as failing to quantitatively account for the effects of variability and uncertainty in
the characterization of human health risk. Despite these and other shortcomings, risk assessment is an
accepted decision-making tool for evaluating the adverse health effects resulting from environmental
and occupational chemical exposure.
19.1 TIERED APPROACH TO RISK ASSESSMENT
The risk assessor is often confronted with practical concerns in assessing risks from chemical
exposures. These include, but are certainly not limited to
• The lack of toxicity and dose-response information in humans or inadequate data in animals
• Lack of identification of the most sensitive individual
• Extrapolation of toxicity data from one route of exposure to another
• Extrapolation of toxicity data from high doses in animals to much lower doses in humans
• Quantifying uncertainty and variability in the risk assessment
• Accounting for all sources of chemical exposure and not just the source of exposure of
immediate concern
• Consideration of the varying physicochemical properties of the chemical and how these may
effect exposure and toxicity
• The toxic effects resulting from exposure to more than one chemical
• The use of varying risk assessment methods by different regulatory agencies
One way of dealing with several of these problems is a tiered, or iterative, approach to risk assessment.
In every risk assessment, the risk assessor is expected to assess these problems in a manner that
conservatively protects human health. The manner in which this is done is governed by the assessor’s
ability to obtain exposure and toxicity information. In discussing the tiered approach to risk assessment,
the NRC (National Research Council) indicates that a risk assessment includes a conservative, first
level of analysis. Use of higher, more complex tiers of risk assessment is more costly. The decision to
use more complex and costly risk assessment practices will depend on whether the results of simple
conservative screening risk assessment indicates the need for further study, whether additional study
or data will provide more accurate estimates of risk, and whether increased accuracy is worth the
additional cost.
Principles of Toxicology: Environmental and Industrial Applications, Second Edition, Edited by Phillip L. Williams,
Robert C. James, and Stephen M. Roberts.
ISBN 0-471-29321-0 © 2000 John Wiley & Sons, Inc.
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