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

1 occupations. The observed absence of an association for exposure to asbestos, a well-established
2 lung carcinogen, may be explained by the misclassification errors in exposure status or by
3 sample size constraints (not enough power). Likewise, the association for diesel exhaust
4 reported by only 7 cases and 17 controls also may have gone undetected because of low power.
5· In conclusion, there is insufficient evidence from this study to confirm or refute an association
6 between lung cancer and diesel exhaust exposure.
7
8 8.3.5. Gars hick et al. (1987): A Case-Control Study of Lung Cant;er and Diesel Exhaust
9 Exposure in Railroad Workers
1 0 An earlier pilot study of the mortality of railroad workers by the same investigators
11· (Schenker et al., 1984) found a moderately high risk of lung cancer among the workers who were
12 exposed to diesel exhaust as compared to those who were not. This study was designed to
13 evaluate the feasibility of conducting a large retrospective cohort study. On the basis of these
14 findings the·investigators conducted a case-control study of lung cancer in the same population.
15 The population base for this case-control study was approximately 650,000 active and retired
16 male U.S. railroad workers· with 1 0 years or more of railroad service who were born in 1900 or
17 later. The U.S. Railroad Retirement Board· (RRB ), which operates the retirement system, is
18 separate from the Social Security System, and to qualify for the retirement or survivor benefits
19 the workers had to acquire 1 0 years or more _of service. Information on deaths that occurred
20 between March 1, 1981, and February 28, 1982, was obtained from the RRB. For 75% ofthe
21 deceased population, death certificates were obtained from the RRB, and, for the remaining 25%,
22 they were obtained from the appropriate state departments of health. Cause of death was coded
23 according to the eighth revision of the lCD. The cases were selected from deaths with primary
24 lung cancer, which was the underlying causeof death in most cases. Each case was matched to·
25 two deceased-controls whose dates of birth were within 2.5 years of the date of birth of the case
26 and whose dates of death were within 31 days of the date of death noted in the case. Controls
27 were then selected randomly from workers who did not have cancer noted anywhere on their
28 death certificates and who did not die of suicide or of accidental or Unknown causes.
29 Each subject's work history was determined from a yearly job report filed by his
30 employer with the RRB from 1959 until death or retirement. The year 1959 was chosen as the
31 effective start of diesel exhaust exposure for this study, since by this time 95% of the
32 locomotives in the United States were diesel powered. Investigators acknowledge that because
33 the transition to diesel-powered engines took place in the early 1950s, some workers had
34 additional exposure prior to 1959; however, if a worker had died or retired prior to 1959, he was
35 considered unexposed. Exposure to diesel exhaust was considered to be dichotomous for this
2/1/98 8-28 DRAFT--DO NOT CITE OR QUOTE