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

1 Approximately 20,000 miners are employed, but not all of them are currently working in the
2 mines. Diesel engines were introduced in the metal mines in the early to mid-1960s. Although
3 all these miries use diesel equipment, it is difficult to estimate how many of these miners were
4 actually exposed.to diesel fumes.
5 Diesel engines were introduced in coal mines atan even later date, and their use is still
6 quite limited. In 1983, approximately 1 ,000 diesel units were in place in underground coal
7 mines, up from about 200 units in 1977 (Daniel, 1984). The number of units per mine varies
8 greatly; one mine may account for more than 100 units.
9 Even if it were possible to estimate how many miners (metal and coal) were exposed to
1 0 diesel exhaust, it would be very difficult to separate out the confounding effects of other potential
11 pulmonary carcinogens, such as radon decay products, heavy metals (such as arsenic,
12 chromium), etc. Furthermore, the relatively short latency period limits the usefulness of these
13 cohorts of miners.
14
15 8.5.1. The Cohort Mortality Studies
16 The cohort studies mainly demonstrated an increase in lung cancer. Studies of bus
17 company workers by Waller (1981), Rushton et al. (1983), and Edling et al. (1987) failed to
18 demonstrate any statistically significant excess risk of lung cancer, but these studies have certain
19 methodological problems, such as small sample sizes, short follow-up periods Gust 6 years in the
20 Rushton et al. study), lack of information on confounding variables, and lack of analysis by
21 duration of exposure, duration of employment, or latency that preclude their use in determining
22 the carcinogenicity of diesel exhaust. Although the Waller (1981) study had a 25-year follow-up
23 period, the cohort was restricted to employees (ages 45 to 64) currently in service. Employees
24 who left the job earlier, as well as those who were still employed after age 64 and who may have
25 .died from cancer, were excluded.
26 Wong et al. (1985) conducted a mortality study of heavy equipment operators that
27 demonstrated a significant increased risk of liver cancer in total and in various subcohorts. The
28 same analysis also showed statistically significant deficits in cancers of the large intestine and
29 rectum. Metastases from the cancers of the large intestine and rectum in the liver probably were
30 misclassified as primary liver cancer, which led to an observed excess risk. This study did
31 demonstrate a nonsignificant positive trend for cancer of the lung With length of membership and
32 latency. Analysis of deceased retirees showed a significant excess oflung cancer. Individuals
33 without work histories who started work prior to 1967, when records were not kept, may have
34 been in the same jobs for the longest period oftime. Workers without job histories included
35 those who had the same job before and after 1967 arid thus may have worked about 12 to 14
2/1/98 8-60 DRAFT --DO NOT CITE OR QUOTE