~ 5-6
the Nevada test site amounts to 90 thousand man rads, the latter is
1 per cent of the total genetically effective dose from fallout.
The
total genetically effective dose from fallout is in turn estimated to be
1.66% of average background radiation for the same period.
Thus the
genetically effective dose to the population around the Nevada test site
from past testing is 1/6000 part of the natural dose that would normally
be received by the whole United States population.
In the over-all
increase in harmful mutations it is therefore an exceedingly small
fraction.
It remains to be considered whether the dose received by any individual
in the area of highest exposures warrants great concern.
It is estimated
that from 100 to 500 persons received whole body exposures of 5 to 6.0
rads during the seven years of testing in Nevada.
This is about ten times
the exposure from average natural background for the same period.
The
Committee on Genetic Effects of Atomic Radiation of the National Academy
of Sciences has recommended that no individual should receive more than
50r up to age 30. A small number of persons have thus received about 10%
of the permissible gonadal exposure for an individual.
These same few
persons have in six years received up to double the Federal Radiation
Council's "basic guide" for whole body radiation.
Another way of regarding the probable genetic effect of the maximum doses
received by the small group of individual is to consider them in relation
to the present load of tangible genetic defects occurring normally without
relation to any added radiation.
The United Nations Scientific Committee
on the Effects of Atomic Radiation estimated that about 4% of all children
born have at least one defect on a genetic basis. It further appears that
there will be an approximately equal number of children that will exhibit
one or more defects of a non-hereditary nature. Thus, normally, 500
persons, one-half of whom are in their reproductive years, might be
expected to produce eventually about 350 children among whom there might
be 28 with some degree of congenital defect. - From considerations of the
doubling dose and the general genetic behavior of developmental mutants,
it follows that an additional 5 rad exposure to these 500 individuals
would have about 1 chance in 10 of producing 1 additional case of tangible
defect in their children; i.e., 29 cases instead of 28.
The medical implications of these findings must necessarily be expressed
in general terms.
Our scientific information is as yet much too incomplete
to permit reliable quantitative predictions.
We feel that the important
point to stress is that these exposures of persons to fallout radiation
both internally and externally must be considered in the perspective of
natural situations in which substantial numbers of people have lived for
periods of time extending to many centuries at background radiation levels
several orders of magnitude greater than those under consideration.