Visualizing Environmental Science

94 CHAPTER 4

don’t know to avoid exposures, children are generally more

susceptible to chemicals. The potentially lethal dose for a child

is considerably less than the potentially lethal dose for an

adult. Air pollution restricts a child’s lung development. Also,

a child has a higher metabolic rate than an adult and therefore

breathes more air and more air pollutants into the lungs.

5

The Precautionary Principle 90

1. The precautionary principle is the ideal that new
   technologies, practices, or materials should not be adopted
   until there is strong evidence that they will not adversely
   affect human or environmental health.

4

Determining the Health Effects

of Pollutants 85

1. A dose–response curve is a graph that shows the effect of
   different doses on a population of test organisms. Scientists
   test the effects of high doses and work their way down to a
   threshold level, the maximum dose that has no measurable
   effect. It is assumed that doses lower than the threshold level
   will not have an effect on the organism and are safe.


2. A carcinogen is any substance (for example, chemical,
   radiation, virus) that causes cancer. The most common
   method of determining whether a chemical is carcinogenic is
   to expose laboratory animals such as rats to large doses of
   that chemical and see if they develop cancer. It is assumed
   that we can extrapolate from high doses of chemicals and the
   high rates of cancer they cause in rats to determine the rates
   of cancer expected in humans exposed to lower amounts of
   the same chemicals.


3. When a chemical mixture is additive, the effect is exactly
   what you would expect, given the combined individual effects
   of each component of the mixture. A chemical mixture that
   is synergistic has a greater combined effect than expected.
   An antagonistic interaction in a chemical mixture results in a
   smaller combined effect than expected.


4. Because they weigh less than adults, are growing, are
   more often exposed to toxicants in the environment, and Andy Levin/Science Source Images

Key Terms

acute toxicity 77
biological magnification 83
carcinogen 86
chronic toxicity 77

dose–response curve 86

epidemiology 77

pathogen 78

persistent organic pollutants (POPs) 84

precautionary principle 90

risk 74

risk assessment 75

toxicology 77

What is happening

in this picture?

James L. Amos/NG Images

Why do we use animal testing to determine whether a new
pesticide causes cancer?

This mouse developed cancer after exposure to high levels of a
toxicant. What uncertainties are associated with extrapolating
this result to low levels of exposure of that toxicant in humans?

Chemical manufacturers have sometimes paid human subjects
to be exposed to low doses of new chemicals, but the EPA
currently has a moratorium on such testing. Suggest a possible
reason for the moratorium. Do you consider such testing
ethical? Why or why not?