RADIATION STANDARDS, INCLUDING FALLOUT
95
(Statement by Dr. Cyril L. Comarfollows :)
STATEMENT oF Dr. C. L. Comar, CoRNELL UNIVERSITY
It is a privilege to appear before this committee and to acknowledge publicly
the wholehearted support of our work by numerous Federal agencies, especially
the Atomic Energy Commission, Public Health Service, and Departments of
Defense and Agriculture. Tribute is also due to many colleagues whose names
are well knownin the scientific literature.
Contamination of food and water represents the primary pathway by means
of which the human population is exposed to radiation from worldwide fallout.
The principles governing the movement of fallout radio-contaminants through
the food chain have been described fully in the 1959 hearings of the Special Subcommittee on Radiation, and in the literature. Recent developments have provided some refinement, but the basic principles as previously set forth have been
supported and arestill valid.
There has been much confusion regarding the comparative wholesomeness of
various constituents of our diet, a confusion that could be dispelled easily by
an understanding of a few basic facts. This report is an attempt to reemphasize
in as simple and blunt a way as possible a few of the most important principles
in relation to present day matters of public concern; such concern seems to revolve about the undertaking of individual action to reduce the dietary intake
of radioactivity and the prediction of future levels of dietary radioactivity. For
clarity, it has been desirable to oversimplify, but it should be noted that extensive research by many scientists and in many fields has been necessary in order
to single out these few important factors and present a simple but realistic
pattern of events.
Attention is here given primarily to iodine 131 and strontium 90, since these
two nuclides are the ones likely to produce the largest radiation exposure. It
should be pointed out, however, that intensive research is being carried out on
all aspects of fission product metabolism that may conceivably have any bearing
on radiation exposure.
IODINE 131
Iodine 131 is produced by nuclear weapons in relatively large amounts, has
a half-life of about 8 days, is transmitted efficiently through food chains, and
is deposited within the body in a small gland, the thyroid. Because of its 8-day
half-life, I'" is of significance only within weeks of the time of its production,
and thus comes primarily from tropospheric fallout. The I'’* injected into the
stratosphere disappears by radioactive decay almost entirely before it can be
returned to earth. It is likewise true that the I’ reaching the soil will disappear by radioactive decay before it can be taken up through the roots of growing plants and thereby be transmitted to the food of man.
Chart 1 shows the route of F™ through the food chain. There are two primary pathways. The radioiodine is deposited from the atmosphere on the surface of vegetation which is grazed by dairy animals, and the ingested radio-
nuclide secreted into milk.
Man also inhales I™ that is present in the air.
Ex-
posure of man to Icould also occur by consumption of fresh fruits and vege-
tables; however, such consumption is minor since it normally represents a very
small surface area of plant compared to that grazed by an animal, and most
often the surface contamination of fresh fruits and vegetables is removed by
washing or skinning before consumption. As supported by recent work of Eisenbud and coworkers, there seems little question but that fresh milk is the main
contributor of I to the human diet. As indicated on the chart, for example,
individuals in New York City in October 1961 who had from 300 to 700 picocuries (micromicrocuries) of I’ in the thyroid are estimated to have received
only about 20 picocuries by inhalation.
If the need should ever arise, there are several factors that simplify the
reduction of exposure to radioiodine: (1) Only one item of the diet, fresh milk,
is an important source of contamination; (2) the half-life is short enough so
that substitution of processed milk or dairy products for fresh milk effectively
reduces the level of contamination in the diet; (3) measurements are relatively
simple and rapid because of the radiation characteristies; (4) the time periods
during which I’ could be of importance can be predicted from knowledge of
the detonation of nuclear devices.
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