Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
1<br />
2<br />
3<br />
4<br />
5<br />
6<br />
7<br />
8<br />
9<br />
10<br />
11<br />
12<br />
13<br />
14<br />
15<br />
16<br />
17<br />
18<br />
19<br />
20<br />
21<br />
22<br />
23<br />
24<br />
25<br />
26<br />
27<br />
28<br />
29<br />
30<br />
31<br />
32<br />
33<br />
34<br />
35<br />
36<br />
37<br />
38<br />
39<br />
40<br />
41<br />
42<br />
43<br />
44<br />
•<br />
•<br />
•<br />
•<br />
et al., 1987; Benhamou et al., 1988; Hayes et al., 1989; Steenland et al., 1990;<br />
Gustavsson et al., 1990; Emmelin et al., 1993). Some ofthese studies did adjust <strong>for</strong><br />
the confounding effects of smoking, asbestos, and other exposures. Furthermore, a<br />
recent publication by HEI ( 1995) demonstrates this strength of association in graphic<br />
presentation (Figures 8-1 and 8-2). Although the studies had smaller increases in<br />
lung cancer risk and only some of the studies considered by HEI (1995) are<br />
considered in this chapter, it demonstrates the lung cancer excesses consistently all<br />
across the various populations.<br />
Consistency: Five cohort studies and nine (including one :q.ested case-control) case- ·<br />
control studies of lung cancer conducted in several populations in the United States<br />
and Europe consistently found the same effect (i.e., lung cancer).<br />
Specificity: All of the above-mentioned studies found the same specific effect (i.e.,<br />
lung cancer).<br />
Biological gradient: The biological gradient, which refers to the dose-response<br />
relationship, was observed in the cohorts of Canadian railway workers (Howe et al.,<br />
1983), heavy bulldozer operators (Wong et al., 1985), and truck drivers who had<br />
enrolled in the American Cancer Society's prospective mortality study (Boffetta and<br />
Stellman, 1988). In th,e case-control studies, a dose response was observed in railroad<br />
workers (Garshick et al., 1988; Hayes et al., 1989; Steenland et al., 1990). Although<br />
other studies failed to observe a dose response, these studies were methodologically<br />
limited due to confounding by other exposures and lack of either quantitative data on<br />
exposure or surrogate data on dose.<br />
Biological plausibility: Because diesel exhaust consists of a carbon core particle<br />
with surface layers of organics and gases, the tumorigenic activity may reside in one,<br />
some, or all of these components. As explained in Chapter 9, there is clear evidence<br />
that the organic constituents have the capacity to interact with DNA and give rise to<br />
mutations, chromosomal aberrations, and cell trans<strong>for</strong>mations, all well-established<br />
steps in the process of carcinogenesis. Furthermore, these organic chemicals include<br />
a variety of polycyclic aromatic hydrocarbons and nitroaromatics, many of which are<br />
known to be pulmonary carcinogens. Alternatively, Vostal (1986) suggests that<br />
"diesel" particles themselves induce lung cancer, most likely via an epigenetic<br />
mechanism, if they are present at sufficiently high doses: This makes a convincing<br />
argument <strong>for</strong> biological plausibility of lung cancer occurrence under some condition<br />
of exposure.<br />
When the same causal inference criteria were applied to the seven case-control<br />
studies in which risk of bladder cancer was assessed, the results were:<br />
2/1198<br />
• Temporality: There is temporality of exposure to diesel exhaust prior to the<br />
occurrence of bladder cancer.<br />
8-67 DRAFT--DO NOT CITE OR QUOTE