humans are born with some identifiable mutation. This one percent is distributed over a
thousand or more traits, making the measurement of a small increase in the mutation of
any one trait an impossible task.
d. The estimate of the genetic risk of radiation is made extremely difficult by the
above situation. Therefore, the Committee on the Biological Effects of Ionizing
Radiation (BEIR) estimated the dose required to double the natural incidence of
mutations, considering that background radiation was responsible for all known
mutations. Radiation, of course, is not responsible for all natural mutations, but this
position represents an error in the direction of safety. This "doubling dose" forms the
basis for present day risk estimation. The current estimates of the "doubling dose" for
the categories of mutations listed above are based upon animal data. These estimates
lie between 50 and 250 rems.
2-13. JOINT COMMITTEE ON ATOMIC ENERGY
a. In the meantime, concern over weapons testing continued to increase. The
public pressure for "action" was so great that, in 1957, the Joint Committee on Atomic
Energy undertook the first of its renowned series of hearings on radiation protection
matters. It started initially with problems of fallout, but soon moved into other areas
which, except for weaponology, really had more important significance to the population
as a whole. These hearings, which began in 1957 and continued at least until 1970,
have compiled one of the finest records of the development of radiation protection
practice that exists.
b. In part because its earlier philosophy was not completely stated and in part
because of misunderstanding of the linear dose-effect nonthreshold concept, as brought
out in the joint committee hearings, the NCRPM appointed a special committee in 1959
to examine just this one point. This committee, including radiobiologists, physicists, and
physicians, studied the problem intensively for a year. It concluded that while it was not
possible to demonstrate or prove any relationship between dose and somatic effects in
the low-dose region, it would be prudent and in the conservative direction to assume that
there is a single linear dose-effect relationship and that there was no threshold below
which no effect would occur. This only confirmed the earlier position of the NCRPM, the
ICRUM, the National Academy of Sciences, and others.
c. However, the report and its discussion made it very clear that these were
statements of assumption and not statements of established fact. It is the lack of
distinction between the two that has caused no end of misinterpretation and trouble
during the past decade.
d. The NCRPM and other experienced groups have restudied the question
intensively over the last decade and still no basis for changing the position has been
found. On the other hand, it is becoming more and more evident that there are
important deviations from the assumed linear relationships between dose and effect,
depending upon the rate at which the dose is delivered. There is even the possibility