PRINCIPLES OF TOXICOLOGY - Biology East Borneo

19 Example of Risk AssessmentApplicationsEXAMPLE OF RISK ASSESSMENT APPLICATIONSALAN C. NYE, GLENN C. MILLNER, JAY GANDY, and PHILLIP T. GOADAs described in the preceding chapter, human health risk assessment is a flexible, occasionallycomplex, often controversial process used to characterize the probability and types of adverse healtheffects that may result from chemical exposure. Historically, risk assessments have been criticized formany reasons, such as failing to quantitatively account for the effects of variability and uncertainty inthe characterization of human health risk. Despite these and other shortcomings, risk assessment is anaccepted decision-making tool for evaluating the adverse health effects resulting from environmentaland occupational chemical exposure.19.1 TIERED APPROACH TO RISK ASSESSMENTThe risk assessor is often confronted with practical concerns in assessing risks from chemicalexposures. 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 ofimmediate concern• Consideration of the varying physicochemical properties of the chemical and how these mayeffect exposure and toxicity• The toxic effects resulting from exposure to more than one chemical• The use of varying risk assessment methods by different regulatory agenciesOne 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 thatconservatively protects human health. The manner in which this is done is governed by the assessor’sability 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, firstlevel of analysis. Use of higher, more complex tiers of risk assessment is more costly. The decision touse more complex and costly risk assessment practices will depend on whether the results of simpleconservative screening risk assessment indicates the need for further study, whether additional studyor data will provide more accurate estimates of risk, and whether increased accuracy is worth theadditional 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.479