Determining Health Effects of Pollutants 85Determining Health Effects of Pollutants
LEARNING OBJECTIVES
- Describe how a dose–response curve is used to
determine the health effects of environmental
pollutants. - Describe the most common method of
determining whether a chemical causes cancer. - Distinguish among additive, synergistic, and
antagonistic interactions in chemical mixtures. - Explain why children are particularly susceptible
to toxicants.
W
e assess the toxicity of a pollutant by the dose
at which adverse effects are produced. A dose
of a toxicant is the amount that enters the
body of an exposed organism. Doses can be
measured in several ways, but all include a quantity (mass
or volume). A time component is important as well, since
a milligram of a chemical all at once can have very differ-
ent effects than the same milligram spread over a day or
week. Finally, it is useful to know the weight of the person
(or other organism) who is exposed: A large adult can
tolerate a much larger dose of a toxin than can an infant.
The response is the type and amount of damage that ex-
posure to a particular dose causes. A dose may cause death
(lethal dose) or harm but not death (sublethal dose). Lethal
doses, which are usually expressed in milligrams of toxicant
per kilogram of body weight, vary depending on the organ-
ism’s age, sex, health, and metabolism, as well as on how the
dose was administered (all at once or over a period of time).
The lethal doses, for humans, of many toxicants are known
through records of homicides and accidental poisonings.
One way to determine acute toxicity is to adminis-
ter different-sized doses to populations of laboratory
animals, measure the responses, and use these data to
predict the chemical effects on humans (Figure 4.11).
The dose that is lethal to 50 percent of a population of
test animals is called the lethal dose–50 percent, or LD 50.
It is usually reported in milligrams of chemical toxicant
per kilogram of body weight. An inverse relationship ex-
ists between the size of the LD 50 and the acute toxicity
of a chemical: The smaller the LD 50 , the more toxic the
chemical, and, conversely, the greater the LD 50 , the less
toxic the chemical (Table 4.3). The LD 50 is determined
for new synthetic chemicals—thousands are produced
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The results of chemicals eaten or inhaled by laboratory animals
are extrapolated to humans.
© Wolfgang Flamish/zefa/CorbisLD 50 values for selected chemicals (Josten and Wood
s Table 4.3
Chemical LD 50 (mg/kg)*
Aspirin 1750
Oxycodone 920
Morphine 600
Caffeine 200
Cocaine 93
Methyl mercury 30
Ethanol 14
Nicotine 9.5
Sodium Cyanide 6.4
Strychnine 0.96
*Administered orally to rats.
Interpreting Data
How much caffeine would an 80 kg (175 lb)
person have to ingest to reach the LD 50.