Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
Health Assessment Document for Diesel Emissions - NSCEP | US ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
1 Studies showing these effects are described in Chapter 5. Epidemiologic studies of people<br />
2 exposed in various occupations in which diesel engines are used provide suggestive evidence <strong>for</strong><br />
3 a respiratory effect. Although detailed in<strong>for</strong>mation describing the pathogenesis of respiratory<br />
4 effects in humans is lacking, the effects in human studies lend qualitative support to the findings<br />
5 in controlled ·animal studies.<br />
6 The weight of evidence from the available toxicological data on diesel exhaust indicates<br />
7 with high confidence that inhalation of diesel exhaust can be a respiratory hazard, based on<br />
8 findings in multiple controlled laboratory animal studies in several species with suggestive<br />
9 evidence from human occupational studies. The endpoints of concern include biochemical,<br />
1 0 histological, and functional changes in the pulmonary and tracheobronchial regions. There is<br />
11 also some evidence <strong>for</strong> effects on respiratory system-related immune function. Although there is<br />
12 some suggestive evidence of liver and kidney changes in animals exposed to diesel exhaust, as<br />
13 well as some indication of neurotoxic effects at high concentrations, these data are inadequate to<br />
14 indicate that a hazard exists <strong>for</strong> these endpoints. Studies of other endpoints, including<br />
15 reproductive and developmental toxicity, in controlled animal exposures have shown rio evidence<br />
16 of potential hazard.<br />
17<br />
18 6.3. APPROACH FOR DERIVATION OF THE INHALATION REFERENCE<br />
19- CONCENTRATION ·<br />
20 Twelve long-term(> 1 year) laboratory animal inhalation studies of diesel engine<br />
21 emissions have been conducted. The focus of these studies has been on the respiratory tract<br />
22 effects in the pulmonary region. Effects in the upper respiratory tract and in other organs were<br />
23 not found consistently in chronic animal exposures. The research programs on the toxicology of<br />
24 diesel emissions at the Inhalation Toxicology Research Institute (ITRI) and the Japanese <strong>Health</strong><br />
25 Effects Research Program (HERP) consisted of large-scale chronic exposures, with exposed<br />
26 animals being designated <strong>for</strong> the study of various endpoints and at various time points (Ishinishi<br />
27 et al., 1986, 1988; Mauderly et al., 1987a,b, 1988; Henderson et al., 1988; Wolff et al., 1987).<br />
28 Each research program is represented by multiple published accounts of results. These programs<br />
29 were selected as the principal basis <strong>for</strong> deriving the RfC because each contains studies that<br />
30 identify an LOAEL and an NOAEL <strong>for</strong> respiratory effects after chronic exposure (see Section<br />
31 5.2) as well as pulmonary histopathology.<br />
32 <strong>Diesel</strong> particulate matter is composed of an insoluble carbon core with a surface coating<br />
33 of relatively soluble organic constituents. Because macrophage accumulation, epithelial<br />
34 histopathology, and reduced clearance have been observed in rodents exposed to high<br />
35 concentrations of chemically inert particles (Morrow, 1992), it appears possible that the toxicity<br />
2/1/98 6-3 DRAFT--DO NOT CITE OR QUOTE