Understanding the shape of the exposure–
response relationship and determining whether
there are safe thresholds are important for the
formulation of public health policies for pollution
control. Mortality studies suggest that the exposure–
response relationships for particulate-matter pollution
in the case of both short-term
15
and longterm
11
exposures are nearly linear, with no discernible
safe thresholds within relevant ranges of exposure.
Likewise, in the Children’s Health Study, the
exposure–response relationships appear to be nearly
linear, without discernible safe thresholds.
An issue with clinical implications concerns the
identification of groups that are most at risk or
that are most susceptible to the effects of pollution.
One evaluation of the literature
1
suggests that the
proportion of a given population that is at risk for
death, hospitalization, or life-threatening conditions
owing to short-term exposure to air pollution
is very small and limited to the elderly, infants,
and persons with chronic cardiopulmonary disease,
influenza, or asthma. There appears to be a much
broader susceptibility to small, transient changes
in lung function, low-grade pulmonary inflammation,
or other subclinical physiological changes in
response to short-term exposure.