(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

Table 8.13. (cont.)
Notes:
Cancer Margin of Safety [MOS] = Point of Departure / Lifetime Average Daily Dose
Lifetime average daily doses are calculated from values presented in Table 7.53, and
are time-weighted based on the exposure duration over a 70-yr lifespan.
Point of departure is presented in Table 8.3.
Values are rounded to two significant figures.
a Values represent cancer risk estimates associated with an infant ingesting human milk
from a mother who is occupationally exposed to benzene, in addition to other applicable
background exposures.
Table 8.14. Indoor air comparison (in-home):
Table 8.14. cancer margins of safety
Results of cancer margin of safety analysis for exposures to indoor air.
Cancer Margin of Safety
(unitless)
Female Male
In-Home Indoor Air
Typical a
210 200
High End a
45 43
Alaska 25 24
Notes:
Margin of Safety [MOS] = Point of Departure / Lifetime Average Daily Dose
Points of departure are presented in Table 8.3.
Lifetime average daily doses are calculated from values presented in Table 7.53,
and are time-weighted based on the exposure duration over a 70-yr lifespan.
Values are rounded to two significant figures.
a Typical and high-end values for the continental United States.
8.4 Risk Characterization Summary
The EPA default (linear) approach of calculating HQs and excess cancer risks contains, as
EPA’s acknowledges, has a significant degree of conservatism. The use of a single value for
the HQ and/or CSF inappropriately conveys a level of confidence or certainty about the risk
estimates, when in fact the HQ and excess risk predicted using a single point estimate contain a
large degree of uncertainty, and usually reflect, as with EPA’s benzene IRIS values, the upper
end of the conservative range of uncertainty. Rounding to one significant figure does not
alleviate this problem. Providing a range of risk estimates though, with some discussion and
transparency about the uncertainty involved in the “high” and “low” guidance values (e.g.,
Benzene VCCEP Submission
March 2006
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