Management of Commercially Generated Radioactive Waste - U.S. ...

E.6
support the RSS position (Brown 1976). The EPA, in its formal review of the RSS study, disagreed
with several aspects of the RSS health effects model, including the 0.2 dose rate
effectiveness factor, and concluded that the RSS central estimate of late somatic effects
"may be underestimated by a factor of 2 to 10" (EPA 1976).
Finally, the RSS acknowledges in its lower-bound estimate the possibility that a
threshold for cancer induction may exist. While a threshold for primary radiation effects
at the molecular level is considered unlikely on theoretical grounds, the mechanisms by
which such effects become expressed as cancers are not understood, and available data in no
way preclude the possibility of a threshold for these expressed effects. The RSS calculates
its lower-bound estimate assuming a 10- or 25-rem threshold dose, either of which is larger
than most doses predicted to occur to an individual from CWM activities.
The most recent and most thoroughly documented estimates of cancer risk from radiation
exposure are those contained in the 1977 UNSCEAR Report. These values are listed in
Table E.1.1. The UNSCEAR Report cautions that these values are". . . derived essentially
from mortalities induced at doses in excess of 100 rad. The value appropriate to the much
lower dose levels involved in occupational exposure, and even more so in environmental expo-
sures to radiation, may well be substantially less; . . ." (p. 414). Also shown in
Table E.1.1 are the risk estimates adopted in the 1977 Recommendations of the International
Commission on Radiological Protection (ICRP 1977), which were based primarily on the UNSCEAR
Report.