A Perspective on Risks 75PROCESS DIAGRAM
Agricultural workers have a greater than average
exposure to chemicals such as pesticides.(^1) Hazard identification
Can exposure to a substance cause adverse health effects
such as cancer or brain defects?
(^2) Dose-response assessment
What is the relationship
between the amount of
exposure (dose) and the
severity of the adverse health
effects (response)? Very low
doses may have no effect or
delayed effects, while higher
doses may have delayed
effects, immediate effects, or
both.
(^3) Exposure assessment
How much, how long, and
how often are individuals
exposed to the substances in
question? Exposure
assessment requires
understanding where people
live, what they eat or drink, as
well as how different
substances travel in air, water,
and food.
(^4) Risk characterization
Information about dose-response and exposures is
combined to provide a detailed description of the
likelihood and extent of adverse health effects. Risk
characterization indicates that Mexican Americans, who
make up a disproportionate fraction of agricultural
workers in the United States, are at higher risk from
pesticides than are other groups (see graph).
Risk management
Once risks have been characterized, this information can
help inform decisions about risk. Importantly, the process
of assessing and managing risks does not just go in one
direction, from hazard identification to assessment to
management. Rather, each step feeds back information
to the others. For example, managers may find that a risk
characterization does not describe the risks most
important to them, or may identify a new risk needing
further analysis.
General
population
Mexican
Americans
Blood level of DDT (ng/g) 200
300
400
500
600
700
0
Sisse Brimberg/NG Images
Science and Judgment in Risk Assessment Committee on Risk Assessment
of Hazardous Air Pollutants National Research Council NATIONAL
ACADEMY PRESS Washington, D.C. 1994
The four steps involved in risk assessment for adverse
health effects are summarized in Figure 4.2. For example,
we might learn that a chemical is a hazard—that is, it can
harm human health. Next, we assess what sort of harm
the chemical can do, how potent it is, and how
much of it people are exposed to. We use these
data to characterize the risk—that is, how much
risk it poses, to which people, and how it can
be reduced. Finally, we can use this characteriza-
tion to guide our management choices—that is,
what we do (if anything) to reduce the risk. Once
a risk assessment is performed, its results are combined with
relevant political, social, and economic considerations to
determine how we can best avoid, reduce, or eliminate a
particular risk and, if so, what we should do. This evaluation
includes the development and implementation
of laws to regulate hazardous substances.
Risk assessment estimates the probability
that an event will occur and lets us set priori-
ties and manage risks in an appropriate way. As
an example, consider a person who smokes a
pack of cigarettes a day and drinks well water
risk assessment
The quantitative
and qualitative
characterization of risks
so that they can be
compared, contrasted,
and managed.
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Interpreting Data
What is the ratio of the DDT blood
level for Mexican Americans to
that of the rest of the population
of the United States?