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

1 uncertainties below). Based on the Mauderly et al. (1987) study, the risks associated with
2 continuous exposure to 1 J-Lg/m 3 of diesel emissions calculated by two different models are
3 summarized below:
4
5
Lung Tumor Data Used
Malignant tumors
Total tumors
Alternative Model
MLE
8.16E-6
N.A.
95% u.b.
1.65E-5
N.A.
LMSModel
95% u.b.
1.74E-5
3.44E-5
(taken from Chapter 11)
1 2. The model suggests that populations with higher expected background rate (e.g., smokers)
2 may be subjected to higher lung cancer risk than the populations with lower background rate.
3 It is noted that U.S. females have about the same background lung cancer rates as the
4 Fischer-344 rats (about 1 to 2%), whereas U.S. males have a background rate of 6%.
5 However, because most oflung cancers are smokers, the risk to nonsmokers (males or
6 · females) should be about the same. The use of the unit risk estimate provided in Chapter 11
7 may somewhat underestimate risk to smokers (or other respiratory-impaired persons) unless
8 adjustment on lung burden is made. Table B-6 provides an example of such adjustment.
9
10 B.S. DISCUSSIONS ABOUT UNCERTAINTIES OF RISK ESTIMATES
11 · Although, it is interesting to note that risk estimates by the LMS model are comparable to
1 2 those calculated by the alternative model, there are uncertainties about low-dose extrapolation by
13 the alternative (as well as by the LMS) model: first, the model parameters are estimated
14 statistically, not measured in the laboratory; and second, the model parameters are estimated