Health Assessment Document for Diesel Emissions - NSCEP | US ...

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et al., 1987; Benhamou et al., 1988; Hayes et al., 1989; Steenland et al., 1990;
Gustavsson et al., 1990; Emmelin et al., 1993). Some ofthese studies did adjust for
the confounding effects of smoking, asbestos, and other exposures. Furthermore, a
recent publication by HEI ( 1995) demonstrates this strength of association in graphic
presentation (Figures 8-1 and 8-2). Although the studies had smaller increases in
lung cancer risk and only some of the studies considered by HEI (1995) are
considered in this chapter, it demonstrates the lung cancer excesses consistently all
across the various populations.
Consistency: Five cohort studies and nine (including one :q.ested case-control) case- ·
control studies of lung cancer conducted in several populations in the United States
and Europe consistently found the same effect (i.e., lung cancer).
Specificity: All of the above-mentioned studies found the same specific effect (i.e.,
lung cancer).
Biological gradient: The biological gradient, which refers to the dose-response
relationship, was observed in the cohorts of Canadian railway workers (Howe et al.,
1983), heavy bulldozer operators (Wong et al., 1985), and truck drivers who had
enrolled in the American Cancer Society's prospective mortality study (Boffetta and
Stellman, 1988). In th,e case-control studies, a dose response was observed in railroad
workers (Garshick et al., 1988; Hayes et al., 1989; Steenland et al., 1990). Although
other studies failed to observe a dose response, these studies were methodologically
limited due to confounding by other exposures and lack of either quantitative data on
exposure or surrogate data on dose.
Biological plausibility: Because diesel exhaust consists of a carbon core particle
with surface layers of organics and gases, the tumorigenic activity may reside in one,
some, or all of these components. As explained in Chapter 9, there is clear evidence
that the organic constituents have the capacity to interact with DNA and give rise to
mutations, chromosomal aberrations, and cell transformations, all well-established
steps in the process of carcinogenesis. Furthermore, these organic chemicals include
a variety of polycyclic aromatic hydrocarbons and nitroaromatics, many of which are
known to be pulmonary carcinogens. Alternatively, Vostal (1986) suggests that
"diesel" particles themselves induce lung cancer, most likely via an epigenetic
mechanism, if they are present at sufficiently high doses: This makes a convincing
argument for biological plausibility of lung cancer occurrence under some condition
of exposure.
When the same causal inference criteria were applied to the seven case-control
studies in which risk of bladder cancer was assessed, the results were:
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• Temporality: There is temporality of exposure to diesel exhaust prior to the
occurrence of bladder cancer.
8-67 DRAFT--DO NOT CITE OR QUOTE