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 ó
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
                          - 2 -

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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.
                            - 3 -

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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.
                          - 4  -

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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.


                           - 5 -

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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.

                          - 6 -

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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.
                          - 7  -

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FIGURE 1
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       FIGURE 2
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Sr-90 Megacuries/Month
           - 9 -

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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)
                          -  10 -

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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
                           -  11 -

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ALTITUDE (thousands of feet)
        MILLIBARS
           - 12 -

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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
                            -  13  -

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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.
                            -  14 -

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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,
                           - 15  -

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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.
                           -  16  -

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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 strontiumó90 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
                           - 17  -

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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
                           - 18  -

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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
                            -  19 -

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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
                            -  20 -

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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.
                            - 21  -

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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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 - 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 9ó15 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.
                         - 27  -

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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.
                      - 28  -

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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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