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

1 caused by cellular damage resulting from N0 2 exposure). The results from short-term exposures
2 indicate that rats experience no to minimal lung function impairment even at diesel exhaust
3 levels sufficiently high to cause histological and cytological changes in the lung. In subchronic
4 studies of durations of 4 weeks or more, frank adverse health effects are not readily apparent and
5 when found are mild and result from exposure to concentrations of about 6 mg/m 3 particulate
6 niatter and durations of exposures of20 hi day. There is ample evidence that subchronic
7 exposure to lower levels of diesel exhaust affects the lung, as indicated by accumulation of
8 particles, evidence of inflammatory response, AM aggregation and acc)llilulation near the
9 terminal bronchioles, Type II cell proliferation, and thickening of alveolar walls adjacent to AM
1 0 aggregates. Little evidence exists, however, that subchronic exposure to diesel exhaust impairs
11 lung function. Recent studies have implicated the organc fraction ofDPM in the induction of
12 resoiratory allergic disease.
13
14 5.1.2.3. Chronic Exposures
15 5.1.2.3.1. Effects on growth and longevity. Changes in growth, body weight, absolute or
16 relative organ weights, and longevity can be measurable indicators of chronic toxic effects. Such
17 effects have been observed in some but not all of the long-term studies conducted on laboratory
18 animals exposed to diesel exhaust. There was limited evidence for an effect on survival in the
19 published chronic animal stUdies; deaths occurred intermittently early in one study in female rats
20 exposed to 3.7 mg/m 3 partjculate niatter; however, the death rate began to decrease after 15 mo,
21 and the survival rate after 30 mo was slightly higher than that of the control group (Research
22 Committee for HERP Studies, 1988). Stu4ies of the effects of chronic exposure to diesel exhaust
23 on survival and body weight or growth are detailed in Table 5-3.
24 Increased lung weights and lung-to-body weight ratios have been reported in rats, mice,
25 and hamsters.· These data are summarized in Table 5-4. In rats exposed for up to 36 weeks to
26 0.25 or 1.5 mg/m 3 particulate matter, lung wet weights (normalized to body weight) were
27 significantly higher in the 1.5 mg/m 3 exposure group than control values after 12 weeks of
28 exposure (Misiorowski et al., 1980). Rats and Syrian hamsters were exposed for 2 years (five
29 16-h periods per week) to diesel exhaust diluted to achieve concentrations of0.7, 2.2, and 6.6
30 mg/m 3 particulate matter (Brightwell et al., 1986). At riecropsy, a significant increase in lung
31 weight was seen in both rats and hamsters exposed to diesel exhaust compared with controls.
32 This finding was more pronounced in the rats in which the increase was progressive with both
33 duration of exposure and particulate matter level. The increase was greatest at 30 mo (after the
34 . end of a 6-month observation period in the high-concentration male group where the lung weight
35 was 2.7 times the control and at 24 mQ in the high-concentration female group [3.9 times
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