Evaluating the Health Risk
of Air Pollutants
some areas of the world, the air quality is so poor that mountains and hills that used to
be visible almost every day can hardly be seen anymore. For example, when I first moved to
a small town near Sacramento, California, you could see the glorious Sierra Madre
mountains every day, even though they were about a hundred miles distant. When I left the
area in the 1990s, the mountains were no longer visible except on a few days a year. We
have come to take air pollution, like noise pollution, sea, stream, and lake pollution,
and other forms of pollution for granted.
Scientists, however, need to
quantify pollution of different kinds and determine what pollution is a serious health
problem and what pollution is a minor nuisance. To do this, scientists define pollution in
1. emissions refers to the amount of a pollutant that actually
enters the environment
2. exposure refers to the amount of a
substance that people are actually exposed to.
A good example of the difference in
emissions and exposure is the chemical benzene, a volatile liquid that is used in enormous
quantities in industry and is emitted in automobile exhaust also. It is well documented
that exposure to benzene can cause leukemia, a form of blood cancer.
Emissions of benzene: Approximately 50 percent of all the benzene
released in the air comes from automobiles. However, the concentration of benzene in the
air we breathe is very low because the benzene is diluted into an enormous quantity of air
in the atmosphere.
Exposure to benzene: Cigarettes emit a
relatively tiny amount of benzene, but at least 50 percent of peoples' exposure to benzene
comes from cigarette smoke. Even non-smokers get most of their exposure to benzene, not
from breathing emissions from automobiles, but from second hand cigarette smoke.
Another example is exposure to chloroform, another volatile
solvent that can cause cancer. The major sources of chloroform come from sewage treatment
plants where chloroform is used to sterilize sewage. Tons of chloroform are released into
the atmosphere every year. However, the major source of exposure to chloroform is from
shower and bath water. Most potable water in the United States is treated with small
amounts of chlorine to kill harmful microorganisms that might be present in the water. A
tiny amount of the chlorine is converted to chloroform and, because we take so many
showers and baths, most of our exposure to chloroform comes from these sources. If you are
concerned about exposure to chloroform in household water, you can purchase filters that
will eliminate it in drinking water and bath water.
Written by Gordon Edlin, Ph.D.