PRINCIPLES OF TOXICOLOGY

18 Risk Assessment
RISK ASSESSMENT
ROBERT C. JAMES, D. ALAN WARREN, N. CHRISTINE HALMES, and
STEPHEN M. ROBERTS
Risk assessment is an ever-evolving process whereby scientific information on the hazardous properties
of chemicals and the extent of exposure results in a statement as to the probability that exposed
populations will be harmed. The probability of harm can be expressed either qualitatively or quantitatively,
depending on the nature of the scientific information available and the intent of the risk
assessment. Risk assessment is not research per se, but rather a process of collecting and evaluating
existing data. As such, risk assessment draws heavily on the disciplines of toxicology, epidemiology,
pathology, molecular biology, biochemistry, mathematical modeling, industrial hygiene, analytical
chemistry, and biostatistics. The certainty with which risks can be accurately assessed, therefore,
depends on the conduct and publication of basic and applied research relevant to risk issues. While
firmly based on scientific considerations, risk assessment is often an uncertain process requiring
considerable judgment and assumptions on the part of the risk assessor. Ultimately, the results of risk
assessments are integrated with information on the consequences of various regulatory options in order
to make decisions about the need for, method of, and extent of risk reduction.
It is clear that society is willing to accept some risks in exchange for the benefits and conveniences
afforded by chemical use. After all, we knowingly apply pesticides to increase food yield, drive
pollutant-emitting automobiles, and generate radioactive wastes in the maintenance of our national
defense. We legally discharge the byproducts of manufacturing into the air we breathe, the water we
drink, and the land on which our children play. In addition, we have a history of improper waste
disposal, the legacy of which is thousands of uncontrolled hazardous-waste sites. To ensure that the
risks posed by such activities are not unacceptably large, it is necessary to determine safe exposure
levels in the workplace and environment. Decisions must also be made on where to locate industrial
complexes, on remediation options for hazardous-waste sites, tolerance levels for pesticides in foods,
safe drinking-water standards, air pollution limits, and the use of one chemical in favor of another.
Risk assessment provides the tools to make such determinations.
This chapter provides an overview of the risk assessment process, and discusses
• the basic steps of risk assessment
• how risk assessments are performed in a regulatory context
• differences between human health and ecological risk assessments
• differences in the estimation of cancer and non-cancer risks
• differences between deterministic and probabilistic risk assessments
• issues associated with estimating risks from chemical mixtures
• comparisons of risks from chemical exposure with other health risks
• risk communication from chemical exposure with other health risks
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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