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Response
54
RADIOLOGICAL ISSUES
EPA contends that the risk factors attributed to the EPA in the second paragraph on
draft p. E.3 have been superseded by more recently derived numbers, and a more extensive
consideration of the various risk factors that have been suggested by the EPA, and by
others, could have been included. In any case, the more recent EPA numbers would not have
led to different conclusions with regard to the range of values employed in the Statement,
as summarized in draft Table E.2 (draft p. E.6).
Draft pp. E.3 and E.5
Issue
EPA's dissatisfaction with the health effects estimates in the Reactor Safety Study
(RSS) is documented in Reference 53, draft Appendix E. Recent literature has done nothing
to dispel our belief that the use of a dose rate reduction factor is ill-advised as is the
minimal plateau duration (30 years) used in the RSS.
The UNSCEAR 1977 Report suggests (except for leukemia) a 50-yr expression period unless
the period has been shown to be shorter or longer for a specific cancer (Reference 2, draft
Appendix E, par. 12, page 363).
In particular, the two major human cancers associated with radiation, lung and breast,
are considered to elevate risk for the duration of lifespan following exposure (C. E. Land,
and J. D. Norman, "The Latent Periods of Radiogenic Cancers Occurring Among Japanese A-Bomb
Survivors," Late Biological Effects of Ionizing Radiation, 1, IAEA, Vienna, pp. 29-47,
1978; V. E. Archer, E. P. Radford and 0. Axelson, "Radon Daughter Cancer in Man: Factors
in Exposure-Response Relationships," Health Physics Society Annual Meeting, June 1978).
The dose reduction factor in the RSS report appears to be derived from an analysis by
Mays, et al. considering ten sets of animal data from nine studies. If an additional two
studies (that happen to show a reverse effect) are included in the analysis, the dose reduc-
tion factor becomes 1.7 + 0.20 reported by Mays, et al. As UNSCEAR 1977 points out, most
of the existing animal carcinogenesis data comes from observations at doses above 50 rads
and that each tumor-model system has peculiarities which prevent generalization across mul-
tiple organ systems and cancers. See Reference 53 of this appendix for comments on the dose
reduction factor in the RSS.
As has been pointed out by Crump, et al. (K. S. Crump, D. G. Hoel, C. H. Langle, and
R. Peto, "Fundamental Carcinogenic Processes and Their Implications for Low Dose Risk Asses-
sment," Cancer Res., 36, pp. 2983-2979, 1976): "It is likely that the error in the accept-
able dose associated with a simple linear extrapolation will be made less than those
associated with species extrapolation to man from the laboratory animal data. The BEIR
Report (Reference 16) recommended linear extrapolation on pragmatic grounds. The theoret-
ical conclusions of the present paper are that linear extrapolation to low-dose levels is