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

1 pattern of adverse effects on respiratory morbidity; the majority of studies offer, at best,
2 equivocal evidence for an exposure-response relationship. The environmental contaminants have
3 frequently been below perinissible workplace exposure limits; in those few cases where health
4 effects have been reported, the authors have failed to identify conclusively the individual or
5 collective causative agents in the diesel exhaust.
6 Chronic effects of diesel exhaust exposure have been evaluated in epidemiologic studies
7 of occupationally exposed workers (metal and nonmetal miners, railroad yard workers,
8 stevedores, and bus garage mechanics). Most of the epidemiologic datfi indicate an absence of an
9 excess risk of chronic respiratory disease associated with exposure to diesel exhaust. In a few
1 0 studies, a higher prevalence of respiratory symptoms, primarily cough, phlegm, or chronic
11 bronchitis, was observed among the exposed. These increased symptoms, however, were usually
12 not accompanied by significant changes in pulmonary. function. Reductions in FEV 1 and FV C
13 and, to a lesser extent, FEF 50 and FEF 75 , also have been reported. Two studies detected
14 statistically significant decrements in baseline pulmonary function consistent with obstructive
15 airway disease. One study of stevedores had a limited sample size of 17 exposed and 11
16 controls. The second study in coal miners showed that both underground and surface workers at
17 diesel-use mines had somewhat lower pulmonary performance than their matched controls. The
18 proportion of workers in or at diesel-use mines, however, showed equivalent evidence of
19 obstructive airway disease and for this reason the authors of the second paper felt that factors
20 other than diesel exposure might have been responsible. A doubling of minor restrictive airway
21 disease was also observed in workers in or at diesel-use mines. These two studies, coupled with
22 other reported nonsignificant trends in respiratory flow-volume measurements, suggest that
23 exposure to diesel exhaust may impair pulmonary function among occupational populations.
24 Epidemiologic studies of the effects of diesel exhaust on organ systems other than the pulmonary
25 system are scant. Whereas a preliminary study of the association of cardiovascular mortality and
26 exposure to diesel exhaust found a fourfold higher risk ratio, a more .comprehensive
27 epidemiologic study by the same investigators found no significant difference between the
28 observed and expected number of deaths caused by cardiovascular disease.
29 Caution is warranted in the interpretation of results from the epidemiologic studies that
30 have addressed noncarcinogenic health effects from exposure to diesel exhaust. These
31 investigations suffer from myriad methodological problems, including (1) incomplete
32 information on the extent of exposure to diesel exhaust, necessitating in some studies estimations
33 of exposures from job titles and resultant misclassification; (2) the presence of confounding
34 variables such as smoking or occupational exposures to other toxic substances (e.g., mine dusts);
35 and (3) the short duration and low intensity of exposure. These limitations restrict drawing
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