REPORT NO. 6
revised fallout
estimates for 1964-1965
and verification of the
1963 predictions
October 1964
Report of the
FEDERAL RADIATION COUNCIL
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REPORT NO. 6
revised fallout
estimates for 1964-1965
and verification of the
1963 predictions
October 1964
Report of the
FEDERAL RADIATION COUNCIL
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, B.C., 20402 - Price 25 cents
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CONTENTS
Page
List of Tables and Figures 1
Summary 2
Section I -- Introduction 4
Section II -- The Inventory of Long-lived
Radionuclides 5
Section III -- Radionuclides in the Diet and in
People 13
111
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LIST OF TABLES AND FIGURES
TABLE 1 Expected Annual Deposition of Strontiuni-90 in
the United States
TABLE 2 Global Strontium-90 in the Atmosphere
Month of January
TABLE 3 Comparison of Predicted and Observed Levels of
Radionuclides Deposited and in the U.S. Diet
in 1963
TABLE 4 Average Strontium-90 Content of Milk in the
U.S.
TABLE 5 Strontium-90 Content of Wheat and Flour in the
U.S.
TABLE 6 Average Strontium-90 Content of U.S. Total Diet
TABLE 7 Average Strontium-90 Content of Human Bone in
the U.S.
FIGURE 1 Strontium-90 Deposition over the United States
during 1963
FIGURE 2 Time History of Strontium-90 Surface Deposition
FIGURE 3 Mean Distribution of Strontium-90 in the
Atmosphere
FIGURE 4 Average Concentration of Radionuclides in Milk
Samples from Public Health Service Pasteurized
Milk Network
FIGURE 5 Strontium-90 Concentrations in Pasteurized Milk
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SUMMARY
On the basis of information available in June 1964, new
estimates of the levels of fallout expected in 1964 and
1965 from the atmospheric testing of nuclear weapons
conducted through 1962 have been made by the Federal
Radiation Council.
Based on the stratospheric inventory of strontium-90 in
January 1964, the predicted annual depositions in 1964
and 1965 have been increased by 50 percent over those
presented in FRC Report No. 4. This adjustment is well
within the expected uncertainty of the original estimate
and does not change the 30-year and 70-year dose estimates
made on the basis of the original predictions.
The inventory of long-lived fission products such as
strontium-90 and cesium-137 in the atmosphere by mid 1964
was reduced to one-half that in January 1963.
The deposition of fallout in the United States in 1963
was very close to the predicted values. The average
deposition in the "wet" areas was a little less than
predicted and that in the "dry" areas a little more.
The time of maximum deposition occurred about a month
later than it has in previous years.
Iodine-131 from the atmospheric testing of nuclear
weapons had disappeared by May 1963 and strontium-89 by
June 1964.
The observed levels in 1963 for strontium-89, strontium —
90, and cesium-137 in milk and dairy products, short-lived
nuclides leading to external exposure, and carbon-14 in
the atmosphere at ground level were all very close to the
values predicted in FRC Report No. 4. The observed values
of strontium-90 in the total diet and in new bone were
less than predicted for 1963. This discrepancy is
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considered to result from the fact that some non-dairy
products, particularly cereal grains, do not enter the
diet in significant quantities in the same year in which
they are grown.
New predictions for the strontium-90 and cesium-137 levels
in milk, and strontium-90 in cereal grains and the total
diet expected in 1964 and 1965 have been made to reflect
the adjusted annual fallout level and the lag time for
cereal grain products to enter the diet. These
predictions are that the levels of long-lived
radionuclides in milk in 1964 will be about the same as
they were in 1963. The strontium-90 concentrations in
the total diet in 1964 are expected to be higher than
they were in 1963 and to drop to 1963 levels in 1965.
Based on the predictions of dietary contamination levels
anticipated in 1963 and subsequent years, the Council
concluded in FRC Report No. 4 that the health risks from
radioactivity in food over the next several years are too
small to justify protective actions to limit the intake
of radionuclides by diet modifications or altering the
normal distribution and use of food, particularly milk
and dairy products. The present study has shown that the
predictions in FRC Report No. 4 were substantially correct,
and the conclusions in that report still apply.
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SECTION I
INTRODUCTION
1.1 In FRC Report No. 4, issued May 1963, the
Federal Radiation Council evaluated the levels of fallout
that might be anticipated in the United States in 1963
and subsequent years following the programs of atmospheric
nuclear weapons testing conducted through 1962. The
report forecast a substantial increase in the probable
levels of radionuclides from fallout during 1963 with
decreasing quantities in subsequent years.
1.2 On the basis of the radiation doses associated
with these levels, it was concluded that the health risk
from radioactivity in foods anticipated over the next
several years would be too small to justify protective
actions to limit the intake of these radionuclides by
altering the normal production, processing, and
distribution of food, particularly milk and dairy products
1.3 The purposes of the present report are to: (1)
compare the predictions made as to the levels of fallout
anticipated in 1963 with the experience based on
surveillance measurements, (2) make more precise estimates
of the levels anticipated in 1964 and 1965, and (3)
evaluate the validity of the prediction procedures when
they are applied to a changing fallout situation such as
now exists. The study is based on information available
through June 1964. Although the probable average levels
for 1964 can be projected directly from currently
available surveillance information, new estimates of the
anticipated average levels of radionuclides in food in
1964 and 1965 utilize the stratospheric inventory data
and the cumulative levels in soil as of January 1964.
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SECTION II
THE INVENTORY OF LONG-LIVEERADIONUCLIDES
Verification of Predicted 1963 Fallout
2.1 As an aid in presenting the predictions
contained in FRC Report No. 4, the regions in the United
States were divided into "wet"and "dry" areas depending
on average annual rainfall (roughly separated by the 20"
rainfall isoline). The deposition of strontiuni-90 in
1963 was expected to average 50 me/mi2 (millicuries per
square mile) in the wetter regions and 20 me/mi2 in the
drier regions. A considerable range of variability
within each climatic area was expected due to rainfall
and other differences (depositions in the "wet" areas
were expected in the range of 30-60 me/mi2 and those in
the "dry" areas, 10-30 me/mi2).
2.2 The verification of the 1963 strontium-90
fallout over the United States appears on the large map
shown in Figure 1. The shading in Figure 1, taken from
FRC Report No. 4, separates the "wet"(heavy shading)
from the "dry" (unshaded) areas. The light shading in
the midwestern United States denotes areas with slightly
less than 20 inches of annual precipitation while the
lighter shading over the state of Florida indicates an
expected lesser fallout compared with the "wet" eastern
United States because of its sub-tropical location.
2.3 The fallout in "wet" areas generally lies
in the 30-60 me/mi2 range. No station reported a value
in excess of 60 me/mi2. The average derived from the
isolines in the "wet" areas is about 45 me/mi2 or within
about 10 percent of the predicted average. Fallout in
the drier regions of the United States was expected to
be about four-tenths as large as that in the "wet"
regions. Except for a few areas, deposition values were
below the predicted upper value of 30 me/mi2. The
observed mean value derived from the isolines is about
25 me/mi2, which is about 25 percent greater than the
prediction of fallout in the "dry" area.
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2.4 It should be noted that the prediction of
fallout for the year 1963 contained the possibility that
it might be in error by a factor of two. Thus, the 10
and 25 percent discrepancies fall well within the
uncertainty in the prediction. The north central United
States appears to have received higher fallout and the
south central and southwestern United States lower
fallout than expected.
2.5 The 1963 fallout data and a reexamination
of the results from earlier years suggest that the
designation of the "wet"and "dry" areas be modified to
conform with observed fallout data. The redefined areas
are shown in the inset in Figure 1.
2.6 It should also be noted that the seasonal
variation in the deposition of strontium-90 during 1963
differed from that in previous years. Figure 2 presents
the time history of fallout in each hemisphere. Fallout
in the United States closely follows that of the
northern hemisphere. From 1958 through 1962 the peak
northern hemisphere fallout occurred in March, April, or
May. On the average, about 70 percent of the annual
fallout is deposited in the first six months of each
calendar year. However, in 1963 the peak concentration
extended into July and it took seven, rather than six,
months for 70 percent of the annual fallout to be
deposited.
Predictions of Future Fallout
2.7 The procedures used to predict the fallout
anticipated in the future are the same as those described
in FRC Report No. 4, and are based on measurements of
the stratospheric inventory of strontium-90 as it existed
in January 1964.
2.8 To reflect the stratospheric inventory as
of January 1964, the predictions of the fallout expected
in 1964 appearing in Table 1 have been increased by 50
percent over the prediction made for the same year in
FRC Report No. 4 (1963). This increase lies well within
the expected uncertainty of a factor of two or more
attributed to the forecast for 1964 made in that report.
The forecast for 1964 given in the present report is
expected to be verified well within a factor of two.
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2.9 Table 1 also contains a prediction of 1965
fallout. This forecast has also been increased by 50
percent over that previously reported. The uncertainty
in the present 1965 prediction is greater than a factor
of two. If the predictions are in error, there is more
likely to be an overestimation of the 1965 fallout than
an underestimation.
2.10 Table 2 lists the partition of strontium-
90 in various parts of the atmosphere (to 100,000 feet)
from 1963 to 1965. Figure 3 and Table 2 emphasize the
presence of greatest concentrations in the northern
hemisphere. It is likely that in a few years there will
be a tendency for equality between hemispheres as
suggested in Table 2. Thus, after the 1964 and 1965
fallout has been deposited, roughly one-half of the
remaining stratospheric inventory, about one megacurie,
should be in the stratosphere of the northern
hemisphere. It may therefore be anticipated that in the
years following 1965 the total additional strontium-90
deposition will be about 10 and 25 me/mi2 in the "dry"
and "wet"United States respectively.
2.11 The total inventory of strontium-90 on the
ground will increase until the fraction lost each year
by radioactive decay equals the annual deposit. On the
basis of present information it is anticipated that this
condition will have been reached by 1967. The total
inventory of strontium-90 on the earth's surface will
then continue to decrease in subsequent years.
2.12 The increase in carbon-I4 in the
atmosphere at ground level predicted in FRC Report No. 4
has been verified by observations made in 1963, and
original predictions in that report are considered to
be substantially correct.
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FIGURE 1
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FIGURE 2
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Sr-90 Megacuries/Month
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TABLE 1
Expected Annual Deposition of Strontium - 90 in the
United States
(millicuries per square mile)
Variability
Most Probable Value within area
Accumulated Deposition to January 1, 1964
"Wet" area 150 120-190
"Dry" area 65 40-85
Expected Deposition during 1964
"Wet" area 30 15-60
"Dry" area 12 5-20
Expected Deposition during 1965
"Wet" area 15 5_25
"Dry" area 6 2-10
Expected Total Deposition after January 1, 1966
"Wet" area 25 10-50
"Dry" area 10 5-20
In each year, it is expected that about 70% of the annual
fallout will occur in the first 6 months of the year.
Note: Designation of "wet"and "dry" areas have been
modified slightly since FRC Report No. 4
(see Figure 1)
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TABLE 2
Global Strontium - 90 in the Atmosphere
Month of January (megacuries)
1963 1964 Predicted 1965
NorthernHemi sphere
Stratosphere 5.7 3.4 2.1
Troposphere 0-3 0.2 0.1
Total Observed 6.0 3.6 2.2
Southern Hemisphere
Stratosphere 0.5 0.6 0.6
Trosposphere 0.1 0.1 0.1
Total Observed 0.6 0.7 0.7
Total Observe.d
(both hemispheres) 6.6 4.3 2.9
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ALTITUDE (thousands of feet)
MILLIBARS
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SECTION III
RADIONUCLIDES IN THE DIET AND IN PEOPLE
General Considerations
3.1 This section is concerned with that part of
the fallout which enters the food chain of man.
Inhalation of radioactive materials and external sources
from fallout are not discussed in this report. Both
strontium-90 and cesium-137 have been measured in the
total diet and various diet components. Quantitative
relationships attempting to relate the radionuclide
levels in the total diet and diet components to the
quantity of fallout deposited, however, have been studied
much more extensively in regard to strontium-90.
3.2 The predictions have been made by a special
ad hoc group of technical representatives of all
interested agencies in the Federal Government. The
detailed methodology has been reported in the hearings of
the Joint Committee on Atomic Energy, "Fallout, Radiation
Standards, and Countermeasures," June 3, 4, and 6, 1963,
and in technical reports of the Health and Safety
Laboratory, U.S. Atomic Energy Commission.
3.3 These prediction procedures have been
developed to describe the general situations as found in
the conterminous United States. Special situations, such
as the lichen-caribou-manfood chain in Alaska require
different procedures to adequately describe them. The
factors concerned in this food chain are the subject of
studies being conducted by the Atomic Energy Commission
and the Public Health Service.
3.4 The general considerations related to
estimates of the strontium-90 content of the total diet
and diet components were outlined in FRC Report No. 4.
Milk, fresh fruits, and fresh vegetables are distributed
regionally or locally. Therefore, these items in the
diet tend to reflect the local levels of fallout.
Differences in the strontium-90 to calcium ratio of the
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total diet in different localities should be related
primarily to the strontium-90 in these dietary items.
Nationally distributed processed foods tend to lead to a
contribution of strontium-90 that is about the same in
all parts of the country. The delayed marketing and
consumption of such nationally distributed foods
introduces a lag between the time of fallout deposition
and the appearance of strontium-90 in the total diet.
3.5 Predictions of the anticipated levels of
strontium-90 in the diet and diet components may be made
by one or both of two general procedures: (1) Prediction
of the contamination levels expected in different dietary
components as a function of the fallout rate and
cumulative levels of strontium-90 in the soil, and the
calculation of total diet levels on the basis of the
contribution each component makes to the total diet; or
(2) multiplying the strontium-90 value for milk by an
empirically developed factor related to the fractional
contribution of milk to the strontium-90 and calcium
intake in the total diet. This factor changes when the
rate of fallout deposition changes.
3.6 The predictions for strontium-90 in the
total diet and milk as presented in both FRC Report No. 4
and the present report are Lased on estimates made for
New York City as representative of the "wef'areas and
for San Francisco as representative of the "dry" areas.
This practice has been adopted because the numerical
constants relating the fallout rate and the cumulative
levels of strontium-90 in soil to the respective dietary
contamination levels in these cities are the best
estimates available for these factors and also because
bone sampling in these areas is correlated with the diet
sampling. Strontium-90 and cesium-137 levels in milk and
the total diet have been measured in many localities
throughout the country under programs sponsored by the
Food and Drug Administration, the U.S. Public Health
Service, and the Atomic Energy Commission. Averages
computed from these data for the "wet"and "dry" areas,
as described in Figure 1, indicate that the averages for
"wef'and "dry" regions as a whole will usually be
comparable to the values predicted for New York and
San Francisco respectively.
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Verification of 1963 Estimates
3.7 Based on the information available in early
1963, estimates of the anticipated levels of strontium-90,
strontium-89, cesium-137, and iodine-131 in the diet and
some diet components were made in FRC Report No. 4. The
evaluation of iodine-131 data observed in 1963 was
incorporated in FRC Report No. 4. It was also estimated
that the annual average strontium-89 concentration in
milk would be about the same in 1963 as it had been in
1962, and that this nuclide would be reduced to
negligible levels in 1964. The observed average
concentrations of iodine-131, strontium-89, strontium-90,
and cesium-137 in milk from the middle of 1961 through
June 1964 are shown in Figure 4. This figure illustrates
the general trends. The network average is plotted
instead of the separate values for the "wet"and "dry"
areas. It can be seen that iodine-131 was essentially
gone by May 1963 and strontium-89by June 1964.
3.8 The estimates for the longer-lived nuclides
in the diet and in people were presented in the form of
the expected annual average for the "wet"and "dry" areas
as described in Figure 1. These estimates were based on
the most probable value of the annual fallout deposit,
the expected distribution of this annual increment by
month, and the cumulative deposit on the ground at the
beginning of 1963.
3.9 Table 3 compares the observed levels of
strontium-89, strontium-90, and cesium-137in the 1963
diet and strontium-90 in the bone with the anticipated
annual averages for the "wet"and "dry" areas. The
observed values reported are based on all surveillance
data available. Figure 5 shows isolines of the annual
average concentrations of strontium-90 in milk based on
the Pasteurized Milk Network of the U.S. Public Health
Service. The computed averages are 27 and 16 picocuries
strontium-90 per liter for the "wef'and "dry" areas
respectively. The agreement between the predicted and
observed values is quite good in all categories except
for the strontium-90 to calcium ratio in the total diet
and new bone. The diet values, which represent the
predictions for the final step in the chain of this
radionuclide transmitted through the environment to man,
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were overestimated by a factor of 1.7 for the "wef'areas
and 3.5 for the "dry" areas.
3.10 The predictions in FRC Report No. 4 for
strontium-90 in the diet were made before most of the
1963 fallout occurred and before some crops were grown.
The predictions were not expected to differ from the
observed values by more than a factor or two. The
discrepancy between the predicted and observed value for
the total diet is larger than expected. It is now
apparent from detailed studies that non-milk products
contributed less to strontium-90 content of the total
diet in 1963 than would be calculated by the past
prediction procedures used in relating fallout rate to
the strontium-90 content of the total diet. Adjustments
in the prediction procedures will be discussed in
connection with the new estimates. (Par. 3.23)
3.11 Table 3 shows two values for the strontium-90
to calcium ratio in bone. The ratio in new bone being
formed is one-fourth that in the average diet because the
body selectively discriminates against strontium. The
observed value for new bone is based on a few
measurements on infants less than 1 year old. The
observed value for the average of the 0-4 year age group
is less because, in the older children, the concentration
of strontium-90 is diluted more by the calcium already
present.
3.12 The 1963 predictions of 50 and 35 picocuries
strontium-90 per gram calcium as the expected values for
the total diet in the "wet"and "dry" areas respectively
led to predicted concentrations of 12 and 9 picocuries
strontium-90 per gram calcium in new bone formed in 1963.
The observed values of 7 and 2 picocuries strontium-90
per gram calcium for new bone and 5 and 3 picocuries
strontium-90 per gram calcium in the 0-4 age group are in
good agreement with the observed ratios in the total
diets in 1963. However, they are lower than the values
of 12 and 9 picocuries strontium-90 per gram calcium
reported in FRC Report No. 4 as the values expected to
result from fallout anticipated in 1963.
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Predictions of Future Levels
3.13 After the termination of atmospheric
testing, iodine-131 essentially disappeared from the
environment by May 1963 and strontium-89by June 1964.
New predictions will be made for only the long-lived
nuclides strontium-90 and cesium-137.
Milk
3.14 The radionuclide concentrations in fresh
milk follow closely the radionuclide content of the cow's
fodder. In many parts of the country, the dairy cows are
put on pasture in the spring, and during the months while
the cows are on pasture the radionuclide concentration in
milk varies with the fallout rate. As indicated in
Section II, a maximum in the fallout rate is usually
reached in April, May, or June. Strontium-90 and
cesium-137 concentrations in milk usually increase to a
maximum in these months, followed by steadily diminishing
concentrations during the summer and early fall. This
decrease reflects the lower fallout rate during these
seasons plus the loss of surface deposits through
weathering, new growth replacing the contaminated grass,
and normal changes of feeding practices during the
season. When the cows are shifted to stored fodder the
radionuclide concentration in milk then reflects the
content of the fodder. The slight perturbation in the
pattern of fallout deposited by month in 1963 as compared
to previous years did not have much effect on the annual
average concentrations in milk possibly because dairy
cattle were on pasture in many parts of the country
during the whole period of interest.
3.15 Table 4 summarizes the data on the average
strontium-90 content of milk from 1959 through 1963 and
presents new predictions for 1964 and 1965. These
predictions reflect the new values for the annual
increment of fallout in 1964 and 1965, as shown in
Table 1, and the cumulative level of strontium—90 in the
soil at the beginning of 1964. Figure 4 shows the trends
in average concentrations of strontium-90 and cesium-137
in milk through June 1964. A breakdown of the data into
separate estimates for the "wet"and "dry" areas suggests
that the prediction for the average concentration of
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strontium-90 in milk of the "wet"areas in 1964 will
probably be very close to the observed value and that the
prediction for the "dry" areas may be less than the
observed value. This possible discrepancy is not
expected to exceed a factor of two.
3.16 The formulas used to relate cesium-137
concentrations in milk to the fallout rate and the
cumulative deposit of cesium-137 on the ground are more
uncertain than those for strontium-90. On the basis of
present information it is expected that the average
concentration of cesium-137 in milk in 1964 will be about
the same as it was in 1963 and will decrease in 1965.
The ratio of cesium-137 to strontium-90 is not expected
to remain constant with time because of the different
mechanisms involved in the movement of these nuclides
through the food chain to milk. In general, the
cesium-137 concentrations are expected to decrease faster
than the strontium-90 concentrations.
Wheat and Flour
3.17 The strontium-90 content of wheat and flour
in the United States from 1959 through 1961 was shown in
Table 8 of FRC Report No. 4. The analyses of the 1962
crop were not available at the time that report was
written, so the expected value in 1962 was estimated on
the basis of what was known about the fallout rate in
1962. The expected values of strontium-90 per kilogram
of wheat were given as 130 picocuries in 1962, 250
picocuries in 1963, and 100 picocuries in 1964.
3.18 Table 5 summarizes the average
concentrations of strontium-90 observed in wheat and
flour from 1959 through 1963 and makes new predictions
for 1964 and 1965. The observed value of strontium-90 in
1962 wheat was 40 percent less than the estimated value
used in preparing the estimates of FRC Report No. 4.
There is good agreement between the predicted and
observed values for the 1963 crop.
3.19 The contamination of cereal grains by
fallout appears to be far more sensitive to the fallout
rate between the time the grain has headed out and
harvest than to either the cumulative total in the soil
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or to the total annual increment of fallout. This
time-span is about 6 to 8 weeks for the most important
crops, and makes the relative levels of contamination
from year to year very sensitive to perturbations in the
fallout rate by month. Under these conditions it is not
surprising to find large variations in the same crops
grown in different areas, or different crops grown in the
same areas. The difference between the predicted and
observed values for 1962 may be attributable at least in
part to this cause.
3.20 The new estimates for 1964 and 1965 are
based on the adjusted figures for the annual increment of
fallout for those years as shown in Table 1 and the
cumulative level of strontium-90 in the soil at the
beginning of 1964. The formula used in making the
present predictions assumes that the level of
contamination in wheat is primarily determined by the
fallout rate in the month of June of each year.
Total Diet
3.21 The levels of cesium-137 in the total diet
in 1964 are expected to differ from those observed in
1963 by about the same percentage as strontium-90 in the
total diets for the same years. The factors entering the
prediction of the strontium-90 content of the total diet
have been discussed in paragraphs 3.1 - 3.6. Tabulated
predictions have been given for the strontium-90 levels
in milk and wheat. Wheat may be considered
representative of the cereal grains. In the past, these
two components have accounted for 60 to 70 percent of the
total strontium-90 intake and about 75 percent of the
total calcium intake in the United States diet. The
ratio of strontium-90 to calcium in the total diet should
be close to the ratio estimated from these two components.
The strontium-90 intake through fruits and vegetables is
subject to a considerable regional variation. This
source accounts for most of the remaining 30 percent of
strontium-90 and an additional 13 percent of calcium.
3.22 Observations of the strontium-90 to calcium
ratio in the total diet compared to that in milk have
generally fluctuated between 1 and 2 for the past several
years. The most logical explanation for this variability
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appears to be that the lower values of the total diet to
milk ratio occur during the periods of increased fallout
deposition when the strontium-90 in milk, fresh fruits,
and fresh vegetables is increasing; other non-milk
components reflect the strontium-90 to calcium ratio of
products grown before the fallout deposition started
increasing. Following a period of relatively high
fallout deposition and when the deposition rate is
decreasing, the strontium-90 to calcium ratio in milk
decreases. However, relatively high ratios of
strontium-90 to calcium may be found in the total diet
because the non-milk components will reflect the
strontium-90 to calcium ratio of products grown during
the time of the higher fallout deposition rate. It has
been assumed that the strontium-90 to calcium ratio of
the total diet will be 1.5 times the predicted value for
milk for purposes of long-term prediction. However,
this ratio (1.5) cannot be considered reliable for
developing short-term predictions especially when the
annual rate of fallout deposition changes such as it has
done since 1962.
3.23 The predictions in FRC Report No. 4 utilized
both the diet to milk ratio method and the procedure of
directly predicting the anticipated strontium-90 levels
in different dietary components. For the direct
estimates it was assumed that the time lag between the
production of all dietary components and the entry of the
produce into the market is less than one year. In the
present report, it is assumed that milk products and
fruits and vegetables are consumed in the same year in
which the products are produced. However, for the cereal
grains it is assumed that 25 percent comes from the crop
grown during the year of interest while 75 percent comes
from the crop grown during the previous year. New
predictions for the strontium-90 to calcium ratio of the
total diet are shown in Table 6. These predictions
reflect the adjusted estimates of the fallout deposition
rates for 1964 and 1965 as shown in Table 1.
3.24 When the adjusted assumptions are applied to
the 1963 figures, the "predicted" values would be 40 and
20 picocuries strontium-90 per gram calcium for the total
diets of the "wefand "dry" areas respectively. Although
these values are closer to the observed values of 30 and
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10 picocuries strontium-90 per gram calcium than the
original predictions of 50 and 35 picocuries strontium-90
per gram calcium, the adjusted assumptions would still
overestimate the strontium-90 contamination of the total
diet as it existed in 1963. However, the new predictions
of 40 and 20 picocuries strontium-90 per gram calcium for
the total diet in the "wet" and "dry" areas respectively
in 1964 may be closer to the observed annual averages
since 1964 is the second successive year of relatively
high fallout deposition.
3.25 The ratios of strontium-90 per gram calcium
in bone observed in the past and predicted for the future
are shown in Table 7. The numerical values for 1964 and
1965 are one-fourth the predicted ratio of strontium-90
to calcium in the total diet shown in Table 6. The
difference between the strontium-90 concentrations in new
bone being formed and the average level in the 0-4 year
age group (illustrated in Table 3) is expected to
decrease with time.
Dose Estimates
3.26 The estimates made in FRC Report No. 4 for
the expected 30-year and 70-year doses are not altered by
the revised estimates of radioactive nuclides in the
diet. The doses estimated for external exposure from
short-lived nuclides and for strontium-89 correspond to
the observed values for these nuclides in 1963. The
shift of one year in the time of the maximum value of
strontium-90 expected in the diet has very little effect
on the estimated 70-year dose from strontium-90.
3.27 During the past three years a whole body
counter has been used to measure the cesium-137body
burdens of the inhabitants of several villages in artic
Alaska chosen to evaluate environmental factors and
dietary patterns unique to that region. Estimates of
doses to individuals in 1964 based on these measurements
range up to about 400 millirems. Depending upon the
further fallout expected and the long-term retention in
the food chain, this might correspond to 30-year doses
ranging up to several rems.
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3.28 On the basis of present information, the
estimates made in FRC Report No. 4, regarding the
maximum concentrations of radionuclides to be expected
from fallout, the projected doses from these nuclides,
and the evaluation of the possible risks were essentially
correct. However, the time of the maximum contamination
of the total diet is now expected to occur in 1964
instead of 1963. It is concluded that the predictions
made in FRC Report No. 4 were substantially correct and
the conclusions in that report still apply.
- 22 -
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FIGURE 4
200-
180-
160-
T 140H
0)
AVERAGE CONCENTRATION OF RADIONUCLIDES
IN MILK SAMPLES FROM PUBLIC HEALTH SERVICE
PASTEURIZED MILK NETWORK (pc/liter)
Cesium-137
./
1961
1962
1963
1964
- 23 -
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TABLE 3
Comparison of Predicted and Observed Levels
of Radionuclides Deposited and in the U.S. Diet in 1963*
"Wet" "Dry"
Pred. Obs. Pred. Obs.
Deposition (me Sr90/mi2)
Range 30-60 10-30
Most Probable Value 50 45 20 25
Milk
Sr90 (pc/liter) 30 25 10 15
Sr89 (pc/liter) 55 50 40 40
Cs137 (pc/liter) 140 125 ~ 85
Wheat (pc Sr90/kg wheat) 250 220
Flour (pc Sr90/gm Ca) 40 40
Total Diet (pc Sr90/gm Ca) 50 30 35 10
New Bone (pc Sr90/gm Ca) 12 7 92
Age 0-4Bone (pc Sr90/gm Ca) 5** 5 3** 2
*Except for bone, both predicted and observed values have
been rounded to the nearest 5 units for purposes of com-
parison since this is considered to be more in keeping
with the reliability of the estimates.
**Calculated from the observed strontium-90 calcium ratio
in the diet.
- 24 -
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FIGURE 5
ro
CD
Q
W
W
H
CO
£
i—r
CO
O
H
ffj
w
U
£
O
U
H
&
O
OJ
H
CO
- 25 -
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TABLE 4
Average Strontium-90 Content of Milk in the U.S.*
(picocuries strontium - 90 per liter of milk)
Observed
New York
1959
1960
1961
1962
1963
1964
1965
10
10
10
15
30
30
25
"Wet" Areas San Francisco
15
10 5
10 5
15 5
25 10
Predicted
10
5
"Drv"Areas
10
5
5
10
15
--
*Predicted and observed values have been rounded to the
nearest 5 units for purposes of comparison since this is
considered more in keeping with the reliability of the
estimates.
- 26 -
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TABLE 5
Strontium-90 Content of Wheat and Flour in the U.S.*
(picocuries per kilogram)
Average from 9—15 States
weighted for production
Observed
Year of
Harvest Wheat Flour
1959 50 10
1960 25 5
1961 25 10
1962 85 15
1963 220 40
Predicted
1964 140 20
1965 80 10
*Predicted and observed values have been rounded to the
nearest 5 units for purposes of comparison since this is
considered more in keeping with the reliability of the
estimates.
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TABLE 6
Average Strontium-90 Content of U.S. Total Diet*
(picocuries strontium-90 per gram calcium)
Observed
N.Y.C. ("Wet" Area) S.F. ("Dry"Area)
1959 15 10
1960 10 5
1961 5 5
1962 10 5
1963 30 10
Predicted
1964 40 20
1965 30 15
*Predicted and observed values have been rounded to the
nearest 5 units for purposes of comparison since this is
considered more in keeping with the reliability of the
estimates.
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TABLE 7
Average Strontium-90 Content of Human Bone in the U.S.
(picocuries strontium-90 per gram calcium)
Bone *
Observed (0-4 years old")
"Wef'Areas "Drv"Areas
1958 2.0 2.0
1959 2.7 2.2
I960 2.4 1.8
1961 2.6 0.9
1962 3.1 1.1
1963 5.0 1.9
Predicted (new bone 0-4 yr old)
1964 10 5
1965 8 4
*See paragraph 3.25
- 29 -
* U.S. GOVERNMENT PRINTING OFFICE : 1964 O - 752-504 (67)
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