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

1 Studies showing these effects are described in Chapter 5. Epidemiologic studies of people
2 exposed in various occupations in which diesel engines are used provide suggestive evidence for
3 a respiratory effect. Although detailed information describing the pathogenesis of respiratory
4 effects in humans is lacking, the effects in human studies lend qualitative support to the findings
5 in controlled ·animal studies.
6 The weight of evidence from the available toxicological data on diesel exhaust indicates
7 with high confidence that inhalation of diesel exhaust can be a respiratory hazard, based on
8 findings in multiple controlled laboratory animal studies in several species with suggestive
9 evidence from human occupational studies. The endpoints of concern include biochemical,
1 0 histological, and functional changes in the pulmonary and tracheobronchial regions. There is
11 also some evidence for effects on respiratory system-related immune function. Although there is
12 some suggestive evidence of liver and kidney changes in animals exposed to diesel exhaust, as
13 well as some indication of neurotoxic effects at high concentrations, these data are inadequate to
14 indicate that a hazard exists for these endpoints. Studies of other endpoints, including
15 reproductive and developmental toxicity, in controlled animal exposures have shown rio evidence
16 of potential hazard.
17
18 6.3. APPROACH FOR DERIVATION OF THE INHALATION REFERENCE
19- CONCENTRATION ·
20 Twelve long-term(> 1 year) laboratory animal inhalation studies of diesel engine
21 emissions have been conducted. The focus of these studies has been on the respiratory tract
22 effects in the pulmonary region. Effects in the upper respiratory tract and in other organs were
23 not found consistently in chronic animal exposures. The research programs on the toxicology of
24 diesel emissions at the Inhalation Toxicology Research Institute (ITRI) and the Japanese Health
25 Effects Research Program (HERP) consisted of large-scale chronic exposures, with exposed
26 animals being designated for the study of various endpoints and at various time points (Ishinishi
27 et al., 1986, 1988; Mauderly et al., 1987a,b, 1988; Henderson et al., 1988; Wolff et al., 1987).
28 Each research program is represented by multiple published accounts of results. These programs
29 were selected as the principal basis for deriving the RfC because each contains studies that
30 identify an LOAEL and an NOAEL for respiratory effects after chronic exposure (see Section
31 5.2) as well as pulmonary histopathology.
32 Diesel particulate matter is composed of an insoluble carbon core with a surface coating
33 of relatively soluble organic constituents. Because macrophage accumulation, epithelial
34 histopathology, and reduced clearance have been observed in rodents exposed to high
35 concentrations of chemically inert particles (Morrow, 1992), it appears possible that the toxicity
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