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

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