home edit2 whole TSD November 2002 PDF format - OEHHA

the shop workers, and found the results changed very little. The exclusion of shop workers simplifies
the analysis in that lung burden calculations are not needed because the exposures of other exposed
workers, namely train workers, are sufficiently low that lung burden may be assumed essentially
proportional to atmospheric exposures. Exposure measurements for 1982-83 (Woskie et al. 1988a),
just after the end of the follow-up period, show that train workers considered here all experienced
approximately the same average concentration of diesel exhaust (for example, 50 µg/m 3 , rounded, for
use in determining unit risk in this work). The present work uses years with any month of exposure
time, excluding the four years previous to each year of observation as the average lag time from
carcinogenesis to death. This calculation of exposure time starts in 1952 and continues yearly through
1980, the end of follow-up. It extends 7 years back from 1959, the start of follow-up, to account on
the average for the assumed linear rise of exposure from 1945 to 1959. The unexposed workers are
assigned zero exposure time throughout.
The OEHHA analysis uses two programs in the EPICURE software package, which is designed for
several standard kinds of epidemiological analysis. The first program, DATAB, reduces the individual
data to cells with each desired variable having a single value for the cell. The cells are designated by a
set of numbers, one for each categorical variable to determine the category number of that variable.
The second program, AMFIT, determines parameters of a model to provide a best fit of the data using
Poisson regression, a maximum likelihood procedure (Breslow and Day, 1987). The calculation
approach is described in more detail for the closely related calculations using general models, in
Appendix D of the diesel exhaust TAC document (OEHHA, 1998).
The assumptions not otherwise specified here are essentially those of Garshick et al. (1988). For
example, all years of the study are included, and their rather irregular boundary points on years of
exposure are used.
The OEHHA analysis explored the fit and other characteristics of a number of forms of a general model.
The model that appeared to be most satisfactory is the one with linear and quadratic continuous
covariates, age and calendar year. The slope calculated for relative risk (relative hazard) per year of
exposure is 0.015 (95% CI: 0.0086 to 0.022) year -1 . The slope divided by the intermittency correction
(0.33) and the assumed constant concentration (e.g., 50 µg/m 3 for 29 years) and multiplied by attained
age provides the excess relative hazard to determine the increase of lung cancer rates for the lifetable
calculation of the unit risk. The resulting unit risks are presented in Point II in Table 4, and closely
parallel the results for the case-control study (Point I). The highest values in that set are for the
assumption that workers on trains have a ramp (1,50) pattern of exposure. For the ramp pattern the
result is a 95% UCL of 1.8 × 10 -3 (µg/m 3 ) -1 and a MLE of 1.3 × 10 -3 (µg/m 3 ) -1 . For the roof (3,50)
pattern of exposure, the procedure is similar, but the exposure scale is increased by the ratio 65/29,
representing the ratio of area under the EF of the roof to the area under the EF of the ramp. The result
is a 95% UCL of 8.2 × 10 -4 (µg/m 3 ) -1 and a MLE of 5.7 × 10 -4 (µg/m 3 ) -1 . The lowest values in the set
are for the roof (10,50) pattern of exposure. Using a similar approach, multiplying the exposure scale
by the AUC ratio of 191/29, the 95% UCL for lifetime unit risk is 2.8 × 10 -4 (µg/m 3 ) -1 , with an MLE
of, 1.9 × 10 -4 (µg/m 3 ) -1 .
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