1 presents some of the average radioisotope values
for milk in the United States for the years 1957 and
1958. In the early part of 1959, values for strontium-90 in milk from various locations in the United
States all averaged well under 30 micromicrocuries
(uuc) per liter. These values are below the recommended maximum permissible limits for lifetime
exposure to specifie radioisotopes in water. Discus-
sion of maximum permissible levels is beyond the
scope of this paper. It is urged, however, that sci-
entists and laymen should develop a clear understanding of what is implied by figures given as
maximum permissible levels and howthese figures
are derived.'
Dietary levels of strontium-90, which are ex-
pressed as micromicrocuries of strontium-90 per
gram of calcium, have been estimated at approximately 0.4, 2, 4, 5, and 7 for each year from 1953
to 1957 respectively. It is estimated that the maxi-
mum levels from tests to date will occur from 1962
to 1965 and that the average maximum level in the
diet of persons living in the United States at that
time may reach about 24 uuc of strontium-90 per
gram of calcium. Recent considerations indicate
that much of the present strontium-90 in milk may
not have come through the soil but found its way
into the plant by foliar absorption or other processes. This has important implications: (@) if there
is no further testing, the levels may fall fairly
rapidly, (b) the contamination of food when only
the soi] route is operative should be much lower
than at present, and (c) this would explain why
levels in non-milk foods are not greatly lower
than in milk foods as is expected because of the
dairy cow’s preferential use of calcium.
Milk from numerous areas has been analyzed to
determine the local variation in dietary levels of
strontium-90. The highest values observed were
about five times the mean value, while milk from
cows fed on vegetation grown in low-calcium soils
were approximately twice the mean value. There
appears to be less variation in the levels found in
the human population, presumably because the
individual consumes food that originates from many
areas. It is not yet possible, however, to express
variability in precise statistical terms.
The most direct and important evidence comes
from analvsis: of tissue samples from the human
population. Tvpical values, calculated and expressed
in terms of radiation dosage rather than concentra-
tion of radioisotopes, are given in table 1. A scale
of values to indicate expected response of man to
radiation is presented in table 2. It can be noted
that present and anticipated levels of radioactivity
in man, based onthe effects of nucleartests to date,
are below those known to produce any observable
effects. However, indiscriminate testing of nuclear
weapons, either by manynations or at higherrates,
could lead to levels of strontium-90 in the food
chain that would be of definite concern. The most
difficult issue, particularly because of its moral
overtones, is whether present levels (also of carbon14) * will produce absolutely no incidence or will
produce only finite incidences of genetic or somatic
harm in the world population. This is a complex
and controversial matter relating to linearity of
response and patterns of threshold versus nonthreshold behavior at lowlevels.
Low-level monitoring, which detects excess radi-
ation before health hazard levels are reached, will
become important as a public health function to
give advance warning of any peacetime operational
difficulties. Public reassurance will be provided
by monitoring at natural radiation levels before
and after nuclear installations are placed in operation.
Summary
Although at the present time there is no indication for a change in our dietary habits, broad-scale
research on the problem of radioactivity in foods
Tape 2.~Effects of Radiation on Man
Radiation Dose,
rad
Seuree and Conditions
(bsery ations
3,000-6,000 2020. .60.- $6oee radiuny or xX-racdi-
Rone sareoma
BOO Lee
Minnoal nondeleterous
ation to skeleton
eee tha geo pitediumnar
ca eee eee OD we radium
bone changes
Necobservable effects
DOE ee eee (stizeested as levels that
weuld double leukemi:
incidence)
TAS wee eee Natural baekgeround
Wee
eee
No observable etic ts
Creconnmended upper limit
ot radiation from any
Tatterade souree)
O20 Lee
OM ee
testimated dosage from
strontinnege trom tests
to Gime of writin)
Cestimated dosage tron
cesiwm 137 trom tests te
time ol writing)
and its implications must continue for future pub-
lic welfare. Even if testing of nuclear weapons is
halted, peacetime applications of atomic energy
will release some radioactive materials into the
environment. Therefore, close supervision of the
dietary levels of radioisotopes and understanding
of possible effects on man are necessary for evalua-
tion of atomic energy benefits versus biological
cost.
t
References
1. Report or United Nations Scientific Committee on El-
fects of Atomic Radiation, General Assembly, Official Records: Thirteenth Session, Supplement No. 17 (A/3838),
1958. Environmental Contamination from Weapon Tests,
HASL-42, United States Atomic Energy Commission, Technical Information Service, Oak Ridge, Tenn., Oct., 1958.
Nature of Radioactive Fall-out and its Effects on Man, Parts
1 and 2, Hearmys before Special Subcommittee on Radiation
of Joint Committee on Atomic Energy, Congress of United
States, United States Government Printing Office, May 27-29,
June 3-7, 1957.
2. Russell, R. S., and Ellis, F. B.: Movement of Stronti-
um “° Through Food Chains, Soils and Fertilizers 212269-
273 (Oct.) 1958. Comar, C. L.; Russell, R. S.; and Wasserman, R. H.:; Strontium-Calcium Movement from Soil to Man,
Science 1263485-492 (Sept. 13) 1957.
3. Totter, J. R.; Zelle, M. R.; and Hollister, H.: Hazard to
Man of Carbon-14, Science 128:1490-1495 (Dec. 12) 1958.