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

1 years longer; these workers exhibited significant excess risks of lung cancer and stomach cancer.
2 Ifthis assumption about duration of jobs is correct, then. these site-specific causes can be linked
3 to diesel exhaust exposure. One of the methodological limitations of this study is that most of
4 these men worked outdoors; thus, this cohort might have had relatively low exposure to diesel
5 exhaust. The authors did not present any environmental measurement data either. Because of
6 the absence of detailed work histories for 30% of the cohort and the availability of only partial
7 work histories for the remaining 70%, jobs were classified and ranked according to presumed
8 diesel exposure. Information is lacking regarding duration of employll).ent in the job categories
9 (used for surrogate of exposure) and other confounding factors (alcohol consumption, cigarette
10 smoking, etc.). Thus, this study cannot be used to support a causal association or to refute the
11 same between exposure to diesel exhaust and lung cancer.
12 A 2-year mortality analysis by Boffetta and Stellman (1988) of the American Cancer
13 Society's prospective study, after controlling for age and smoking, demonstrated an excess risk
14 ·of lung cancer in certain occupations with potential exposure to diesel exhaust. These excesses
15 were statistically significant among miners (RR = 2.67, 95% CI = 1.63, 4.37) and heavy
16 equipment operators (RR = 2.6, 95% CI = 1.12, 6.06). The elevated risks were nonsignificant in
17 railroad workers (RR = 1.59) and truck drivers (RR = 1.24). A dose response was also observed
18 for truck drivers. With the exception of miners, exposure to diesel exhaust occurred in the three
19 other occupations showing an increase in the risk of lung cancer. Despite methodologic
20 limitations, such as the lack ofrepresentiveness of the study population (composed of volunteers
21 only, who were probably healthier than the general population), leading to an underestimation of
22 the risk and the questionable reliability of exposure data based on self-administered
23 questionnaires that were not validated, this study is suggestive of a causal association between
24 exposure to diesel exhaust and excess risk of lung cancer.
25 Two mortality studies were conducted by Gustavssoil et al. (1990) and Hansen (1993)
26 among bus garage workers (Stockholm, Sweden) and truck drivers, respectively. An SMR of
27 122 was found among bus garage workers based on 17 cases. A nested case-control study was
28 also conducted in this cohort. Detailed exposure matrices based on job tasks were assembled·for
29 both diesel exhaust and asbestos exposures. Statistically significant increasing lung cancer
30 relative risks of 1.34, 1.81, and 2.43 were observed for diesel exhaust indices of 10 to 20, 20 to
31 30, and >30, respectively, using 0 to 10 as a comparison group. Adju.stment for asbestos
32 exposure did not change the results. The main strength of this study is the detailed exposure
33 matrices; some of the limitations are lack of smoking histories and low power (small cohort).
34 Hansen (1993), on the other hand, fpund statistically significant SMR of 160 due to
35 cancer of bronchus and lung. No dose response was observed, although the excesses were
2/1/98 8-61 DRAFT--DO NOT CITE OR QUOTE