PRINCIPLES OF TOXICOLOGY

ecommended that substantially dissimilar risks (e.g., risk of cancer versus risk of losing money in the
stock market) not be compared since the relative magnitudes of such risks are difficult to comprehend.
Also, research on risk perception has suggested that directly comparing voluntary and involuntary risks
or natural and technologic risks does not always improve a lay person’s understanding of an
environmental risk. However, the risk comparisons described in list items 2, 3, and 4 above are thought
to be of considerable communicative value.
There are no shortages of data available for risk comparisons, since we all incur risks by virtue of
our continuous exposure to chemicals at work and at home. Indeed, the potentially hazardous chemicals
in the food we eat, the water we drink, and the air we breathe are numerous and the list continues to
growth as new studies are published. In addition, some medications carry a risk of cancer, and because
the dosages of these chemicals are high relative to those chemicals found in the environment,
over-the-counter medications and prescription drugs may carry significant theoretical risks even when
used as intended. The following tables of risk comparisons have been provided to illustrate some
different types of risk comparisons that can be made. Tables 18.4a and 18.4b illustrate the risks
projected for volatile organic chemicals and pesticides measured in homes during the USEPA study
of residential environments (a type 3 risk comparison). Table 18.5 illustrates the theoretical risks
associated with taking a daily dose of 12 different drugs (again, a type 3 risk comparison). Table 18.6
shows risk in a slightly different manner. In this table, risks for various activities, diseases, or lifestyle
choices are compared by the number of days each is believed to decreases one’s life expectancy (a
comparison mixing categories 5, 6, and 7). Table 18.7 compares many different activities, all of
which carry the same one-in-a-million level of risk (a type 8 risk comparison that combines aspects
of types 5, 6, and 7).
TABLE 18.4a Cancer Risks for Indoor Air Exposures to VOCs (TEAM Studies)
Chemical
Indoor Exposure Levels
(µg/m 3 ) Potency, (µg/m 3 ) –1 × 10 –6
Lifetime Cancer Risk
(× 10 –6 )
Benzene
Air15 8 120
Smokers 90 8 720
Vinylidene chloride 6.5 50 320
Chloroform
Air 3 23 70
Showers (inhalation) 2 23 50
Water 30 2.3 70
Food and beverages 30 2.3 70
p-Dichlorobenzene 22 4 90
1,2-Dibromoethane 0.05 510 25
Methylene chloride 6 4 24
Carbon tetrachloride 1 15 15
Tetrachloroethylene 15 0.6 9
Trichloroethylene 7 1.3 9
Styrene
Air 1 0.3 0.3
Smoker s 6 0.3 2
1,2-Dichloroethane 0.5 7 4
1,1,1-Trichloroethane 30 0.003 0.1
Source: Adapted from Wallace (1991).
18.8 COMPARATIVE RISK ANALYSIS 469