Page 137 - Fundamentals of Air Pollution

IV. Impact of Air Pollution on Humans 107

TABLE 7-1
Three Disciplinary Approaches for Obtaining Health Information
Discipline Population Strengths Weaknesses

Epidemiology Communities Natural exposure Difficulty of quantifying
exposure
Diseased groups No Many covariates
extrapolations
Susceptible Minimal dose-response
groups data
Long-term, low- Association vs. causation
level effects
Clinical studies Experimental Controlled Artificial exposure
exposure
Diseased subjects Few covariates Acute effects only
Vulnerable Hazards
persons
Cause-effect Public acceptance
Toxicology Animals Maximal dose- Realistic models of
response data human disease?
Cells Rapid acquisition Threshold of human
of data response?
Biochemical systems Cause-effect Extrapolation
Mechanism of
response

In general, clinical studies provide evidence on the effects of air pollutants
under reproducible laboratory conditions. The exposure level may be accu-
rately determined. The physiological effect may be quantified, and the
health status of the subject is well known. This type of study can determine
the presence or absence of various endpoints for a given sample group
exposed to short-term, low-level concentrations of various air pollutants.
The fact that the subjects are exposed to the actual pollutants existing in
their community is both the greatest strength and the greatest weakness
of epidemiological studies. The strength is the real-world condition of the
exposure and the subjects; the weakness is the difficulty in quantifying the
relationship between exposure and subsequent effects. In the future, the
development of biomarkers may provide a better indication of target dose.
The effects attributed to air pollutants range from mild eye irritation to
mortality. In most cases, the effect is to aggravate preexisting diseases or
to degrade the health status, making persons more susceptible to infection
or development of a chronic respiratory disease. Some of the effects associ-
ated with specific pollutants are listed in Table 7-2. Further information is
available in the U.S. Environmental Protection Agency criteria documents
summarized in Chapter 22.