Health Effects of Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 603

airways (an asthma-associated phenotype) was still more common in the western city [209].
However, at least one study has raised the question that diagnostic bias, in part, may be playing a
role in the increased reported prevalence of atopic disease in the areas of former East Germany
[211]. Cross-sectional surveys of children were conducted in two formerly highly polluted areas
(combustion of brown coal with high sulfur content and heavy metal containing dust from smelt-
ers) and one area of minimal pollution in areas of former East Germany in 1992-1993 and
1995-1996. No changes were noted in the self-reported prevalence of asthma or atopic disease.
However, physician-diagnosed allergy increased without a concomitant change in the preva-
lence of speciic IgE to a variety of common aeroallergens. A decrease in physician-diagnosed
bronchitis was also observed. These results conlict with a study of similar design carried out in
Leipzig in 1991-1992 and 1995-1996 in which the prevalence of sensitization followed that of
reported symptoms [212]. Whether explanation of the differences is due to technical problems
with the skin testing device in Leipzig, as claimed by one set of investigators [211], or is due to
differences in air pollutant composition, population differences or chance cannot be determined
from the data. In aggregate, these studies point to the dificulty in linking human health out-
comes with the PM aerosol as would be expected from the data on mechanisms.
23.5.3.4 Cancer
As noted in Figure 23.20, PM aerosol has been associated with an increased risk of cancer. By
and large, this excess risk has been noted for cancer of the lung [189,192]. The speciic compo-
nents of PM that are responsible for this excess risk have not been elaborated fully. However,
several exhaustive reviews have been conducted related to the role of PM aerosol from diesel
engines in the induction of cancer [213,214]. EPA provided a model for the hypothetical path-
ways that may be involved in carcinogenesis (Figure 23.22) and is based on concepts presented
in Section 23.3. Most of the evidence to a carcinogenic potential in humans is derived from
occupational studies. EPA reviewed 22 such studies (Section 7.2 of Ref. [214]) and estimated the
pool relative risk at between 1.33 and 1.47. Given the much higher levels of exposure that occur
in occupational environments relative to ambient environments, it is dificult to assess the risk
beyond that which has been presented for lung cancer in the epidemiological studies cited previ-
ously. EPA has attempted to assess general population risk based on the conversion of exposures
observed in occupational settings, for which risk estimates are available, to those experienced
by the general population (Table 23.13). Based on a variety of assumptions related to the data
in Table 23.13 (see pp. 8-13 to 816 of Ref. [214]), EPA estimated that the lifetime risk of lung
cancer from exposure to ambient diesel PM could vary between 10 −6 and 10 −4 , although a zero
risk could occur due to an unmeasured threshold.
23.5.4 H ealtH e FFects a ssociated witH a cute and s ubacute e xPosures to PM
There is an enormous body of research that documents the association between short-term
changes, usually measured over the week before a deined health outcome, and health effects.
Effects on mortality, worsening of asthma and respiratory symptoms, and effects on lung func-
tion have been studied most widely. Perforce, this review is limited to a representative sample
of studies that have demonstrated health effects and some of the critiques that have been levied
against the validity of the associations. In addition, this section covers only the data related to
the associations between daily changes in air pollution and daily mortality for several reasons:
(1) mortality and years of life lost is an endpoint of major public health signiicance; and (2)
the most extensive analyses on the effects of study design and statistical analysis techniques on
estimates of effect have been carried out in relation to the mortality data. Excellent summaries
of the large database related to worsening of asthma and other acute respiratory illnesses can be
found in a number of the U.S. EPA references.