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

1 The potency of the other diesel emission samples was not estimated directly because of
2 the weak response in the skin tumor initiation test. Instead, their potency relative to the Nissan
3 engine was estimated as the arithnietic mean of their potency relative to the Nissan in the
4 Salmonella assay in strain TA98, the sister chromatid exchange assay in Chinesehamster ovary
5 cells, and the mutation assay in mouse lymphoma cells. The estimated lifetime cancer risk per
6 microgram per cubic meter of extractable organic matter for extracts from these engines are as
7 follows: Volkswagen, 1.3 x 10- 4 ; Oldsmobile 1.2 x 10- 4 ; and Caterpillar, 6.6 x 10- 6 •
8 To convert these values to a lifetime risk per microgram per cupic meter of total DPM,
9 the results were multiplied by the fraction of extractable organic matter in the particles. This
1 0 conversion was based on the assumption that the carcinogenic effects were caused solely by the
11· organic fraction. These fractions were as follows: Nissan, 0.08; Volkswagen, 0.18; Oldsmobile,
12 0.17; and Caterpillar, 0.27. After this adjustment, the resulting estimated potencies per
13 microgram per cubic meter of inhaled DPM varied from 3.5 X 1 o-s for theNissan to 1.8 X 1 o- 6 for
14 the Caterpillar.
15 Harris (1983) developed comparative potency estimates for the same four engines used by
16 Albert et al. (1983) but used only two epidemiology-based potency estimates: those for coke .
17 oven emissions and for roofing tar. He employedpre1iminary data from three ofthe same assays
18 used by Albert et al. (1983)--the Sencar mouse skin tumor initiation assay, enhancement of viral
19 transformation in Syrian hamster embryo cells, and the L5178 mouse lymphoma test. The mouse
20 lymphoma test was used both with and without metabolic activation, whereas the Salmonella
21 assay was not used.
22 The diesel cancer potency estimates by Harris (1983) were then derived by multiplying
23 the epidemiology-based cancer potency estimates for both coke oven emissions and roofing tar
24 by the ratio of their potencies compared with DE particles in each of the four bioassays. For
25 example, the epidemiology-based relative risk of exposure to 1 J.tg/m 3 of coke oven emissions
26 was estimated to equal 4.4 x 10- 4 • In the skin tumor initiation test, 2.1 papillomas per mouse
27 were reported for the coke oven sample, compared with 0.53 for the Nissan engine extract. The
28 benzene-extractable fraction was assumed to equal 0.06 (slightly less than that in the Albert et
29 al., 1983, studies). The diesel potency estimate using this comparison is then equal to (0.53/2.1)
30 x 0.06 x 4.4 x 10- 4 /J.tg/m 3 , or 6.6 x 10- 6 /J.tg/m 3 DPM. A total of eight comparisons were made for
31 each engine, four bioassays times two epidemiology-based potency estimates.
32 · The Harris (1983) estimates are not comparable to those of Albert et al. (1983) without
33 adjustment. The unit risk estimates of Albert and co-workers are based on absolute risk during
34 lifetime exposure, whereas Harris reported his values in terms of relative risk per year of
35 exposure. To adjust this to lifetime risk for continuous exposure, it is necessary to multiply
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