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

1 The corresponding odds ratios for petrol exhausts were 0.6 (95% Cl = 0.3, 1.3), 1.4 (95% CI =
2 .0.5, 3.7), and 3.9 (95% CI = 0.4, 35.5). Restricting the analysis to only moderate or high annual
3 doses of exposure adjusted for year of birth and smoking showed a sevenfold increased risk for·
4 subjects exposed to both diesel and petrol exhausts (OR= 7.1, 95% CI = 0.9, 58.8). For
· 5 exposure to diesel (OR= 1.1) and petrol (OR= 1.0) exhausts alone, no excess risk was detected
6 in this analysis. Odds ratios were calculated for low, moderate, and high exposure to benzene,
7 with rates of 1.7 (95% CI = 0.6, 5.1) for low annual doses, 1.1 (95% CI = 0.3, 4.5) for moderate
8 annual doses, and 3.0 (95% CI = 1.0, 8.7) for high annual doses.
9 The authors discuss misclassification and confounding as sources of bias in this study.
10 To examine misclassification they compared hygienist-assessed exposure and self-reported
11 exposure for printing ink and found a higher relative risk and fewer exposed subjects for
12 hygienist-assessed exposure, indicating that specificity was a problem for self-reported exposure.
13 It is not known to what extent this may have affected the risk estimates for diesel exhausts since
14 data on self-reported exposure to diesel are not presented. They also mention the possibility of
15 exposure misclassification from using an average annual dose in which a person exposed to an
16 agent at a high level for a few working days and a person exposed to a low level for many days
17 are both rated as exposed to low annual doses. Although statistically nonsignificant elevated
18 odds ratios of 1.3, 2.3, and 2.9 were derived for low, moderate, and high levels of diesel
19 exposure, the authors state that some of their subjects may have later worked in jobs with
20 benzene exposure, and because an elevated risk was detected for benzene exposure, this
21 ·confounding effect may explain some of the excess risk. An almost statistically significant
22 interaction was observed for exposure to combined diesel and petrol exhausts (OR =·7.1, 95% CI
23 = 0.9, 58.8), which changed to 5.1 (95% CI = 0.6, 43.3) after adjustment for benzene exposure,
24 again providing evidence for the confounding role of benzene exposure in explaining some of the
25 observed results.
26 Table 8-3 summarizes the bladder cancer case-control studies.
27
28 8.5. DISCUSSION AND SUMMARY
29 Certain extracts of diesel exhaust have been demonstrated to be both mutagenic and
30 carcinogenic in animals and in humans. Animal data suggest that diesel exhaust is a pulmonary
31 carcinogen among rodents exposed by inhalation to high doses over long periods of time.
32 Because large working populations are currently exposed to diesel exhaust and because
33 nonoccupational ambient exposures currently are of concern as well, the possibility that exposure
34 to this complex mixture may be carcinogenic to humans has become an importantpublic health
35 issue.
2/1/98 8-54 DRAFT--DO NOT CITE OR QUOTE