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

1 the latter, 16 were classified as benign keratinizing cystic tumors, and 4 were classified as
2 carcinomas. No tumors were reported in 115 controls. The tumor incidence in this study was
3 comparable to that reported previously for the diesel exhaust-exposed animals.
4 The importance of DPM and of insoluble respirable particles in tumorigenic responses of
·. 5 nits was investigated and reported by Heinrich et al. ( 1995). In this chronic inhalation exposure
6 study, female Wistar rats were exposed to whole diesel exhaust (0.8, 2.5, or 7.0 mg/m 3 ), 18
7 h/day, 5 days/week for up to 24 mo. Groups ofrats were also exposed to ultrafine Ti0 2 particles
8 ( 10 mg/m 3 ) and car boD: black particles ( 11.6 mg/m 3 ) using the same exposure regimen, except
9 that after 4 mo the exposure concentrations ofTi0 2 and carbon black were increased to obtain
10 lung particle burdens similar to those observed in rats exposed to whole diesel exhaust. Controls
11 were exposed to clean air. Following exposure to the test atmospheres, the rats were maintained
12 in clean air atmospheres for an additional 6 mo.
13 In analyzing the studies of Heinrich et al. (1986a,b ), Heinrich (1990), Mohr et al. (1986),
14 and StOber (1986), it must be noted that the incidence of lung tumors occurring following
15 exposure to whole diesel exhaust, coal oven flue gas, or carbon black ( 15 .8%, 18.1 %, and 8% to
16 17%, respectively) was very similar. This occurred despite the fact that the PAH content of the
17 P AH -enriched pyrolyzed pitch was more than three orders of magnitude greater than that of
18 diesel exhaust; carbon black, on the other hand, had only traces of P AHs. Based on these
19 findings, the organic fraction is not the sole cause. of tumor induction by diesel exhaust. This
20 issue is discussed further in Chapter 10.
21 · In the Heinrich et al. ( 1995) report, the cumulative exposures for the rats in the various
22 treatments groups were 61.7, 21.8, and 7.4 g/m 3 x h for the high, medium, and low whole-
23 exhaust exposures and 102.2 and 88.1 g/m 3 x h for the carbon black and Ti0 2 groups,
24 respectively. For tumor incidence comparison (number of rats with tumors) among the diesel
25 exhaust exposure groups, significant increases were observed in the high (22/100;p