Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
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1 For example, in a recent meta-analysis of 34 studies by the State of Cali<strong>for</strong>nia (Cal-EPA, 1997a)<br />
2 relative risk ratios ranging from 1.12 to 1.43 were derived, depending on the model used and<br />
3 whether or not they were corrected <strong>for</strong> smoking.<br />
4 Exposure estimation is a notable uncertainty in the risk estimates derived from the railroad<br />
5 worker case control study. However, according to Woskie et al. (1988), the 125 j.lg/m 3 estimate<br />
6 was probably reasonable as an average exposure near the end of the study period. The EPA risk<br />
7 estimate of 200 x 1 o- 5 per j.lg/m 3 defines the high end of a range of plausible upper-bound<br />
8 estimates <strong>for</strong> DE cancer risk, while 3 xi0- 5 j.lg/m 3 defines the lowest en4 of the human data range.<br />
9 The MLEs ofthe two exposure scenarios define a tighter range of30-100 x I0- 5 per j.lg/m 3 .<br />
10<br />
11 12.3.3.2.2. Assessing risk using a biomarker. A second approach using human data is the use of<br />
12 a biomarker as a dosimeter. Pike and Henderson (1981) related the concentration of<br />
13 benzo[a]pyrene (B[a]P) to smokers, British gas workers, U.S. coke oven workers, U.S. hot pitch<br />
14 workers, and residents of rural and urban locations and fotind good agreement in predicting lung<br />
15 cancer risk. They concluded that while B[a]P is not the only carcinogen present in DE, and<br />
16 perhaps not even the most important, it is a reasonably accurate dosimeter <strong>for</strong> assessing risk from<br />
. .<br />
17 combustion. or pyrolysis of petroleum products or tobacco and could there<strong>for</strong>e be appropriately<br />
18 used <strong>for</strong> DE risk assessment. Based on Pike and Henderson's estimated lung cancer risk o.f<br />
19 1/1,500 per ng/m 3 B[a]P and a reported B[a]P concentration of 3.9 ng per j.lg of diesel particulate<br />
20 · matter in exhaust from a Volkswagen engine (Heinrich et al., 1995), a maximum likelihood<br />
21 estimate of lung cancer risk of 2.6 x 1 o- 6 per !J.g/m 3 of diesel particulate matter can be derived.<br />
22 The 95% upper bound ofthis value, while not calculated by the authors, is near 1 x I0- 5 per<br />
23 j.lg/m 3 •<br />
24 A strength of the biomarker approach is its moderately good accuracy in estimating cancer<br />
25 risk from exposure to a number of combustion/pyrolysis pollutants using B[a]P as a dosimeter.<br />
26 However, while most of the combustion products assessed in the study contain organics similar to<br />
27 DE, unlike DE they have little or no insoluble. particulate matter. Although this approach, like the<br />
28 comparative potency method, fails to account <strong>for</strong> the carcinogenic effect of the particle itself or<br />
29 <strong>for</strong> modifications in potency because of the association of the organic component with particles,<br />
30 the human exposures of interest presumably don't have particle-driven effects either. Of course,<br />
31 the B[a]P concentration might also vary in diesel samples because of different types and sizes of<br />
32 engines being run under varying conditions and using different' fuels.<br />
33<br />
34 12.33.2.3. Assessing risk using anima1 studies. Previous EPA attempts to quantitatively<br />
35 estimate cancer risk based upon chronic rat bioassays used some <strong>for</strong>m of a linearized model to<br />
2/1198 12-22 DRAFT--DO NOT CITE OR QUOTE