home edit2 whole TSD November 2002 PDF format - OEHHA

q 1 * =
Excess relative risk × CA lifetime lung cancer risk.
Air concentration × exposure factor × intermittency factors × duration of
exposure/lifetime
= 0.57 × 0.025
(5 or 500 µg/m 3 ) × 10 m 3 /shift/20m 3 /d × 5d/7d × 48wk/52wk × 45 yrs/70yrs
Therefore, the results of the meta-analysis bracket lung cancer risks up to approximately 1.3 × 10 -4
(µg/m 3 ) -1 (assuming all the worker populations in the meta-analysis were exposed to 5 µg/m 3 ) to 1.3 ×
10 -2 (µg/m 3 ) -1 (assuming all the workers populations in the meta-analysis were exposed to 500 µg/m 3 ).
As these assumptions establish the extreme bounds of probable exposures, and such calculations based
upon a meta-analysis are novel and subject to further possible refinements, these results are not
incorporated into the range of risks. However, these results do bracket the carcinogenic potencies
which would be consistent with the results of the meta-analysis and the broadest range of exposure
estimates.
A more plausible range can be estimated by determining the 90% confidence interval (CI) of the range
of risks. For the meta-analysis the range of concentrations thought to be plausible by Hammond
(personal communication) was 5 to 500 µg/m³ with a mean of about 200 µg/m³, which corresponds to a
unit risk of 3.3 × 10 -4 (µg/m³) -1 . Using that concentration range as the 98% CI for a shifted lognormal
distribution fixes the geometric standard deviation at 1.22 with a shift of the origin of the distribution by
330 µg/m³. The 90% CI for this distribution of concentration is [52.5 to 356.5 µg/m³], corresponding
to a 90% CI for the distribution of unit risk of [1.6 × 10 -4 to 1.2 × 10 -3 (µg/m³) -1 ].
Railroad Worker Study-Derived Cancer Unit Risks
Quantitative relationships were also developed between lung cancer risk and exposure to diesel exhaust
for two nation-wide studies of lung cancer rates in U. S. railroad workers. These relationships provided
additional values for the range of risk to the general California population. The first, Garshick et al.
(1987a), is a case-control study. Using a logistic regression, that study determined the coefficient of the
logistic relationship of the odds of lung cancer for duration of the workers’ exposure to diesel exhaust.
The coefficient determined in that study was used to estimate lifetime unit risks for exposure of the
general population. The second study, Garshick et al. (1988), is a cohort study. Using a proportional
hazards model, that study calculated the relative hazard of lung cancer for increasing duration of worker
exposure. However, those numerical results have not been supported by Garshick (1991); so instead
of using them to derive lifetime unit risks for the general population, new analyses were performed with
the individual data, upon which that study is based, to determine a linear relationship of lung cancer
hazard for worker exposure to diesel exhaust.
The term hazard was used for a prediction of incidence (cancers per year per population) resulting from
a model. Relative hazard is generally called relative risk in epidemiological model work, and the term,
relative risk, was used in the context of the epidemiology results. The lifetime inhalation unit risk, often
simply called unit risk, is defined as the probability of contracting lung cancer from a 70-year exposure
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