Radiation workers, however, are never under ten years
PHOTO
FROM
“MEDICINE”
MAGAZINE
old, nor often over seventy. By their relatively small num-
bers, they do not represent a fair sample of the diversity of
mankind. Just as there are some people who have been
found unusually sensitive to sunlight, so there must be some
who are more sensitive than others to radioactivity. For
such reasons it has been considered desirable to set the
tolerance dose for the entire population lower than that for
medically-controlled radiation workers. Typically, the
maximum “permissible’’ dese for occupationally exposed
people is reduced by a somewhat arbitrary factor of 10
to obtain the maximum “permissible” exposure for people
at large.
By such a standard, the general population ought not to
receive more than about 30 rads per lifetime. or roughly
four times the U.S. background radiation. This does not
mean that such a dose is guaranteed to be safe, or that it
will produce no damage. On the contrary. it implies accept-
ing as socially tolerable some genetic damage, which can
be estimated only very roughly because of our poor knowl-
edge of human genetics.
Estimates, nonetheless, have been made. The U.N. Scientific Committee on the Effects of Atomic Radiation, for
example, has attributed to one rad, from any source and
applied only once to a single generation of the world’s
entire population, the capability of causing ultimately 100
to 4000 defective births for each million of the population.
The percentages are small (between 0.01 per cent and
0.4 per cent} and the range is large (a tacit admission to
the inexactitude of our knowledge). But when applied to the
world’s population of about 214 billion people. half of
whom are assumedto be below the mean reproductive age.
the total number of defective births will range from 125.000 to 5 million,* spread out over scores or even hun-
dreds of generations. These defectives may not be discernible from among the much larger number of cases which
are a result of other unknownfactors.
Assessments can also be made for the somatic damage
induced by radiation. While there is common acceptance
of the inevitability of genetic damage, however, there is
no such agreement regarding somatic damage. Many
scientists believe that a radiation threshold exists for so-
matic effects, that we have not yet exceeded this value, and
therefore that no somatic damage (cancer, leukemia, short-
ening of the life span) can be attributed to the low levels
of radiation to which we have been exposed so far. Other
scientists hold to the view that biophysical distinctions
cannot be made between somatic and genetic effects and
that radiation which causes damage to reproductive cells
can also damage any other living cells. No one knows at
this time which view is correct.
INTERNAL RADIATION
In addition to the radiation received by the body from
without, at least three substances contribute their radiation
from within the body, and have done so since there first
*A conservative estimate, based on the assumption that the world
population will not increase.
“Hot spots” in thigh bone of a woman who worked with radium
some 30 years earlier show up dramatically in photograph taken
by means of intense radiations emanating from the honeitself
were men: potassium-40, carbon-14, and radium and_ its
radioactive decay products.
Carbon and potassium are necessary components of
life; they are fairly uniformly distributed within the body
and from person to person, so it seems not unrealistic to be
guided by the tolerancedose information developed in our
studies of external radiation. It is plain that potassium-40
(which contributes about 1.5 rad per 70 years) and carbon-14 (about 0.1 rad per 70 years) have not added much
to the natural background radiation.
But radium is another story. It plays no knownrole in
the life process; it is present because it is widely distributed
in the soil and rocks. It is ingested, or sometimes taken
into the lungs, and though it is present in very small
amounts, its activity can be more important than that of
potassium-40 or carbon-14.
Radium is not uniformly spread through the body. Because its chemical behavior closely resembles that of the
element calcium, constituent of all bone, radium concentrates in the bones. Furthermore, in large doses it does not
distribute itself uniformly even within the bones. The bone
grows most, of course, in youth. But even the mature bone
undergoes remodeling; its constituents are steadily being
taken up and laid down again. This means that where
radium lodges depends on just what part of the bone is
active when the radium enters, and on the whole complex
matter of bone formation, growth, and maintenance.
The energy emitted in the decay of radium is chiefly
carried by particles which cannot penetrate the whole body
to reach the outside. They spendall their energy in a distance of a thousandth of an inch; they deposit a thousand
times as much energyin crossing a cell as do the rays from
potassium-40. The variability of the site of radium also
implies its possible concentration in local “hot spots” be-
yond the average value (see photo above).
A hundred or so persons have been examined who
have held excessive amounts of radium in their bones for
CONSUMER REPORTS
105