REPORT NO. 7
     background material
     for the development
             of  radiation
     protection standards
  protective action guides
                      for
strontium-89,  strotium-90
         and  cesium-137
                  MAY 1965

             Staff Report of the
   FEDERAL RADIATION COUNCIL

-------
   REPORT NO. 7
   BACKGROUND MATERIAL
   FOR THE DEVELOPMENT
   OF  RADIATION
   PROTECTION  STANDARDS
    PROTECTIVE ACTION GUIDES
    FOR
    STRONTIUM- 89,  STRONTIUM- 90
    AND CESIUM- 137
   MAY 1965
   Staff Report  of the
   FEDERAL RADIATION COUNCIL
For sale by the Superintendent of Documents, U.S. Government Printing Office
        Washington, B.C., 20402 - Price 30 cents

-------
                     FEDERAL RADIATION COUNCIL
                                   MEMBERS


SECRETARY OF  HEALTH,  EDUCATION,  AND WELFARE (CHAIRMAN)
SECRETARY OF  AGRICULTURE
SECRETARY OF  COMMERCE
SECRETARY OF  DEFENSE
SECRETARY OF  LABOR
CHAIRMAN,  ATOMIC  ENERGY  COMMISSION
SPECIAL ASSISTANT TO  THE PRESIDENT FOR  SCIENCE AND  TECHNOLOGY (ADVISER)

                                    STAFF
                     P. C.   TOMPKINS,
                     C. C.  PALMITER.
EXECUTIVE  DIRECTOR
 SPECIAL   ASSISTANT
                               WORKING GROUP
    F. A.  TODD
    H.O. WYCKOFF
    G. L.  HEKHUIS
    J. G.  TERRILL,  JR.

    J. P.  O'NEILL
    F. WESTERN
DEPARTMENT  OF AGRICULTURE
DEPARTMENT  OF COMMERCE
DEPARTMENT  OF DEFENSE
DEPARTMENT  OF HEALTH,  EDUCATION,

DEPARTMENT  OF LABOR
ATOMIC  ENERGY COMMISSION
AND  WELFARE
NATIONAL ACADEMY OF SCIENCES - NATIONAL RESEARCH COUNCIL
   ADVISORY COMMITTEE TO THE  FEDERAL RADIATION COUNCIL
    A.C. UPTON (CHAIRMAN)
    H. L.  ANDREWS
    V. P.  BOND
    C. L.  COMAR
    J. F. CROW
    S. P.   HICKS
    E.  MACMAHON
    J. E. RALL
    W. L.  RUSSELL
    E. L.  SAENGER
    SHIELDS WARREN
OAK RIDGE NATIONAL  LABORATORY
NATIONAL  INSTITUTES  OF  HEALTH
BROOKHAVEN  NATIONAL  LABORATORY
CORNELL  UNIVERSITY
UNIVERSITY OF WISCONSIN
UNIVERSITY OF MICHIGAN
HARVARD SCHOOL OF  PUBLIC  HEALTH
NATIONAL  INSTITUTES  OF  HEALTH
OAK RIDGE NATIONAL  LABORATORY
UNIVERSITY OF CINCINNATI
NEW ENGLAND DEACONESS HOSPITAL
            AD HOC PANEL ON ENVIRONMENTAL FACTORS
    A. H.  WOLFF  (CHAIRMAN)
    B. R.  BRUCKNER
    J. J.  DAVIS
    G. F.   FRIES
    W. C. HANSON
    J. HARLEY
    F. P.  HUNGATE
    F. W.  LENGEMANN
    T. F.  MC CRAW
    J. RIVERA
    D. G.  WATSON
U.S.  PUBLIC  HEALTH  SERVICE
U.S.  PUBLIC  HEALTH  SERVICE
ATOMIC  ENERGY COMMISSION
DEPARTMENT  OF AGRICULTURE
BATTELLE-NORTHWEST  LABORATORY
HEALTH  AND  SAFETY LABORATORY (AEC)
BATTELLE-NORTHWEST  LABORATORY
CORNELL  UNIVERSITY
ATOMIC  ENERGY COMMISSION
HEALTH  AND  SAFETY LABORATORY (AEC)
BATTELLE-NORTHWEST  LABORATORY
                       AD HOC DOSIMETRY PANEL
    W. S. SNYDER  (CHAIRMAN)
    C. W.  MAYS
    W. P.  NORRIS
    J. RIVERA
    H.Q. WOODARD
OAK RIDGE NATIONAL LABORATORY
UNIVERSITY OF  UTAH
ARGONNE  NATIONAL LABORATORY
HEALTH  AND SAFETY LABORATORY (AEC)
SLOAN-KETTERING   INSTITUTE

-------
                           TABLE OF CONTENTS


                                                                   Page  No.

List  of Figures and Tables	      iv

Summary	       1

Section  I  Introduction   ..........       5

Section  n General Considerations	       9

Section  IE The Acute Localized Contaminating
            Event	      30

Section  IV  Worldwide  Contamination  from
              Stratospheric Fallout	      40
                                    in

-------
                   LIST OF FIGURES AND TABLES
FIGURE 1   Important  Steps in the  Transmission  of Radioactive
            Material  Through  the  Food  Chain  to Man

FIGURE 2   The  Relative  Concentration  of  Radionuclides  in
            Milk  Following  a  Single Deposition  on  Pasture

TABLE 1    Constants  for  Equation   (1)

TABLE 2    Tm, Am and  Projected  Intake  by Man  after an  Acute
            Contaminating Event Involving  Pasture

TABLE 3    Intake  Avoided Versus Time  of Initiating  Protective
            Action

TABLE 4    Relation  Between Strontium-89 Intake  Through  Milk
            and the Average Dose to Bone Marrow

TABLE 5    Relation  Between Strontium-90 Intake  Through  Milk
            and the Average Dose to Bone Marrow

TABLE 6    Relation  Between  Cesium-137 Intake Through Milk
            and the Dose to Whole Body
                               IV

-------
                            SUMMARY
This  report  provides  information  and guidance for actions
appropriate  to  situations  involving contamination of  the  en-
vironment by  the radionuclides strontium-89, strontium-90,
and  cesium-137.Two conditions of environmental  contami-
nation have been examined: an acute  localized  contaminating
event in which prompt  action may  be  necessary to avoid the
exposure  that  would  otherwise  result; and a widespread,  gen-
erally increasing,  low-level of  contamination (from  stratos-
pheric fallout)   that  causes  a  continuous  intake  of radio-
active materials by  large  numbers  of people  for  a period of
years.   Special consideration has  been  given to  the  situation
in the arctic region  where,  because of  unusual  ecological
conditions and  food chains,  some  population  groups are
exposed  to  levels higher  than  those in  other parts  of the
United  States.

In developing  this report,  the  Staff  of the  Federal  Radia-
tion  Council has had the  assistance of  an advisory committee
from the  National Academy  of  Sciences  - National Research
Council  in  regard to  the biological  effects  from irradiation
by strontium-89, strontium-90, and cesium-137;  the  assist-
ance  of  an  ad  hoc panel  of scientists  to provide  data  on
biological,   chemical,  and physical  factors  involving radio-
active contamination  of the  environment;  and  a second panel
to provide  information on the  dosimetry models  related to
these  radionuclides.

The Acute Contaminating Event

The  problem of evaluating when protective actions may be in-
dicated following  an  acute  contaminating  event has been
separated  into   three  categories. Category  I   is   limited  to
the  transmission of  radionuclides  through  pasture-cow-milk-
man   pathway. If pasture  is  contaminated  the concentration
of radionuclides  in milk would build up  rapidly,  reach a
maximum in about a week and then diminish by about half
every two weeks as the result  of weathering  losses, new
plant  growth, and  similar  mechanisms.  Protective  actions
initiated at  approximately two  weeks following the  contami-
nating event will avert 50  percent of  the projected intake;
actions  initiated  at  approximately  1 week following  the
event will  avert 75  percent;  and  actions  initiated within
two  days will  avert  90 percent.

Category  II is concerned with the transmission  of radio-
nuclides  to  man  through dietary  pathways  other  than that
specified  as Category  I  during the first  year following  an
                             -1-

-------
acute  contaminating  event. This  involves  the  use  of feed
crops  for animals,  including dairy  cattle,  and plant prod-
ucts used directly  for  human  consumption. Immediate action
to  reduce the  potential  intake  will  not  usually  be  required
because  of the normal  delay in  the  use of such  crops. How-
ever,  an early decision will be  required as to the  need  for
examination  of harvested crops  to determine the  degree of
contamination  before they  enter  normal  marketing channels.
Protective actions in Category  II  are  not normally expected
to  be  indicated unless  action was first  needed  in  Category I.

Category III  is primarily concerned with  the  long-term
transmission of strontium-90 through  soil  into  plants  in the
years  following  a contaminating  event. Residual  contami-
nation of cesium-137 may be a consideration  for 1  to 2 years.

The benefits  of a protective action  taken in one category
are  largely independent of  whether  action  is taken in
another.  The types of  actions  considered  in  the development
of  guidance in  the  report  include:

       1.   Altering  production,   processing or  distribution
practices affecting the  movement  of radioactive  contami-
nation through the food  chain  and into  the human  body.  This
action may include storage  of  food  supplies and  animal feeds
to  allow for radioactive  decay.

       2.   Diverting affected products  to uses  other than
human consumption.

       3.   Condemning  affected products.

The term "Protective Action  Guide"  has  been  defined as
the  projected  absorbed dose to  individuals in  the  general
population  that  warrants  protective  action  following  a  con-
taminating event;  and  a  "protective action" as  an  action
that will avert most  of the  exposure that would otherwise
occur.

It  is  generally  impossible  to  predict  total  doses  solely
from the degree  of contamination of a  particular crop.
Therefore,  the  definition of protective  action   is  extended
in  this  report  so  that  if the  total  projected dose  from  the
use  of all  crops  in Category II  exceeds the Protective
Action Guide,   in  order to make  a substantial  reduction in
the  total  dose,  action should  be initiated against  those
crops  that would make major contributions  to  that dose.

It is the purpose  of  the  recommendations to  discourage de-
liberate  introduction  of  contaminated  food  into  supplies  of
                             -2-

-------
uncontaminated food as an  acceptable solution to environ-
mental  contamination. Rather,   it  is  recommended that if the
contamination  of a  particular  crop  or dietary  component  is
so  high that it would not  be  acceptable  for  local  use, the
crop  or  dietary component not  be considered acceptable for
use  in  other areas  to which it  may be transported.

The recommended Protective Action Guides  are:

For  Category I:   A  mean dose  of 10 rads  in the first year  to
the bone marrow or whole body of individuals in the  general
population;  and provided  further  that  the  total dose resulting
from Category  I  not  exceed  15 rads. For  purposes  of applying
the  guide,  the  total  dose from  strontium-89 and  cesium-137
is assumed  to be  the same as  the  dose in the first year,
whereas the total  dose from strontium-90 is assumed to be
5  times the dose  in  the  first  year.

For  Category II:   A mean dose of 5 rads  in the first year  to
the bone marrow or whole body of individuals in the  general
population. As  an  operational  technique it  is  assumed  that
the  guide  will  be  met effectively  if the average dose to a
suitable  sample  of the population  is  one-third the PAG or
approximately  3 rads  for  Category I and 2  rads  for  Category
II.

For  Category III:   A Protective Action  Guide  is  not recom-
mended. Rather,  if  it appears  that annual  doses to the  bone
marrow  of individuals may exceed 0.5 rad  or 0.2 rad to a
suitable  sample  of  the population,  such  situations  shall  be
appropriately  evaluated.

Worldwide Contamination From Stratospheric Fallout

Studies  of  stratospheric  fallout in  the  United  States  from
past  testing were reported in  FRC Report  Nos. 4 and 6.  On
the  basis  of this  information,  the Council  concluded that
the  health risk  from  radioactivity in food over  the  next
several  years  would be  too small  to justify  protective
actions  to limit  the  intake  of radionuclides  either  by  diet
modifications  or  by  altering  the  normal  distribution  and use
of  foods,   particularly milk and  dairy  products.

In  Alaska,  although  the  amount  of fallout deposited  per  unit
area  is  about  one-fifth as much  as  that deposited  in  the 30°
- 40° latitude  band,  a combination of ecological conditions
and specific dietary  habits of  some  Eskimos and Indians
causes  higher  cesium  body burdens  than are  found in the con-
terminous  United  States.  Average  body  burdens of cesium-137


                             -3  -

-------
in these  inhabitants were  about three  times  as high  in  1964
 as  they were  in  1962. The  estimated  whole body doses  to
these individuals in  1964 ranged  from about one-fourth to
one-half of  the numerical  value of  the Radiation Protection
Guide (RPG)  for  individuals  in the  general  population.

The  practicality and  value  of  protective  actions  against
widespread environmental  contamination from  stratospheric
fallout  is limited  because:

      1.   The  condition to be  alleviated is chronic  exposure
from long-term continuous  intake  (10 years or more).

      2.   A  reduction in potential  intake under  these  condi-
tions requires  basic  changes  in  long-term agricultural  prac-
tices,   food   processing practices,   dietary  habits,   or  all
three.

      3.   The  actions would have to be  applied on  a broad
enough  scale to reduce the  average  quantity of radionuclides
in the  total  diet from foods  produced  throughout  large  areas
or  the  entire   country.

A  Protective Action Guide  is  not  recommended for this  situa-
tion.   Rather,  annual  doses from  fallout equal  to or greater
than the  numerical  values  of the RPG's can be used as  an in-
dication of when there  is  a need  for  a careful  evaluation of
fallout   exposures.

In view of these considerations it is  recommended  that sur-
veillance  of the radionuclide  content  of food products  con-
taminated with worldwide  fallout  be  continued at levels
appropriate  to  the  situation. It  is  also  recommended  that
surveillance  and research  programs  examining the  special
ecological  situations  in the  arctic  region  continue  until
future  trends  can   be predicted with  greater  confidence.
                            -4 -

-------
                           SECTION   I
                          INTRODUCTION

       1.1   This  background staff report  provides  information
and  guidance  for actions  appropriate  to situations  involving
contamination  of the  environment by the radionuclides  stron-
tium-89, strontium-90,  and  cesium-137. In  certain  circum-
stances,  such  as  the  unforeseen  or uncontrollable  dispersal
of  large quantities  of  radioactive  materials  in  the environ-
ment,  the  resulting  exposure can  be reduced  only by protec-
tive  actions taken against  the  radionuclides  in  the environ-
ment. In these  circumstances, changes   in the  normal  produc-
tion,  processing, distribution,  and use  of foods  may  be
required.

       1.2   FRC Report Nos.  1  and 2 provide radiation protec-
tion guidance  for the control  and regulation  of the normal
peacetime  uses of nuclear  technology in  which control is
exercised primarily  on the  design and  use  of the  radiation
source.  The Radiation Protection Guides (RPG's)  in those
reports were  developed  as  guidelines for the protection of
radiation workers  and the  general public against  exposures
which  might  result  from  routine  uses   of ionizing  radiation.
In formulating  those guides there was a judgment,  or  balance,
between the  possible  risks  associated  with a  particular
radiation exposure and the  reasons  for  allowing the exposure.

       1.3   An  important factor in providing guides  for  any
purpose  is  the change in risk  assigned  to higher or lower
doses  and  the  corresponding effort  to  reduce  them. Other
factors influencing informed  opinion  of  where  and why a
particular balance should be made include  views regarding
prevailing  practices  and the  relative importance  of health
risks   in  relation  to economic,  political,  or  other  consid-
erations  of national  welfare. With   respect  to  environmental
levels  of  radioactivity,   the RPG's  reflect  the   residual  risk
considered  acceptable  after engineering  and procedural  con-
trols  have  been  applied at the  source   (i.e.,  place  of
origin)  of  the  radioactivity to  limit releases  to the  en-
vironment.   The  numerical values for these guides were
placed as close  to the annual dose  from  natural background
radiation as technical,  economic,  and  operational   consider-
ations  allowed.

       1.4   Although radiation  doses  numerically  equal  to the
RPG's  may  impose a risk  so small that  they can  be accepted
each  year  for  a  lifetime  if there   is  significant benefit
from the programs causing the  exposure,  they do  not and
   773-982
                            -5-

-------
cannot  establish a  line  that  is  safe on  one  side  and unsafe
on  the  other. Rather,  some risk of  injury  may  exist  at any
level of dose  and  the risk continuously  increases  with dose.
Caution should  be  exercised  in decisions to  take  protective
actions  in  situations where projected  doses  are  near the
numerical  values of  the RPG's, since the  biological  risks
are  so  low that the  actions  could have  a net adverse  rather
than  beneficial  effect  on  the  public  well-being.

1.5  In contrast to the guidance given in FRC Report
Nos.  1  and 2,  FRC Report No. 5 provided general guidance for
the  protection  of the  population  against  exposure  resulting
from the  accidental release,   or  from  the unforeseen appear-
ance,  of  radioactive  materials   in the  environment. Spe-
cific  guidance,  including a numerical value  for the Protec-
tive Action Guide (PAG),  was  provided  for iodine-131. The
PAG represents  a consensus as  to when,  under the  conditions
considered  most likely  to  occur, intervention  is  indicated
to  avoid  radiation  exposure that would  otherwise result from
transient  environmental  contamination. This  consensus   in-
volves  health,   economic,  sociologic   and political  factors
for which the  relative values are  different  than for the RPG.
For the PAG  these  factors may include  agricultural policies,
the  known feasibility  of protective   actions, related  health
impacts  and similar  considerations involved  in  the  national
interest.

Scope

1.6 This report  provides background  material used  in
the development of guidance  for Federal  agencies in planning
activities   to  protect  the population  from  strontium-89,
strontium-90,  and cesium-137 for  certain situations  in which
these radionuclides  may  appear  in the environment. A  basic
assumption in  the development  of  the  guidance  is that a con-
dition requiring protective  action  is  unusual  and  should not
be  expected to occur  frequently. Two conditions  of  environ-
mental  contamination have  been examined:   An acute localized
contaminating  event  in which  prompt action may be  necessary
to  avoid  the  exposure  that would  otherwise  result; and a
widespread,  generally  increasing,  low-level  of  contamination
(from  stratospheric  fallout) that would  cause a  continuous
intake of radioactive nuclides by large numbers  of people
for a period  of years.

1.7  Exposure  of the  general population to  radioactive
materials  in the environment  may result  from external  ir-
radiation,   inhalation,  and  ingestion  of  such  materials. For
most environmental  situations,  ingestion will produce  the
greatest  absorbed  dose. Ingestion  of  radioactive   materials
                               - 6 -

-------
may  be limited by  protectiye  actions  affecting the  normal
production, processing, distribution,  and use or food. As
in FRC Report No.  5, only ingestion is considered  in the
present report. Only  the transmission  pathway from pasture
through fluid milk  to  man  was considered important for
iodine-131. In  this  report  it   is  necessary  to consider  the
additional  routes  through animal  feed crops, human food
crops,  and root uptake  due primarily  to  the longer radio-
active  half  lives  of  the  nuclides   under  consideration.  The
report  also  considers  the  situation  in  the arctic  region
where,  because of  unusual ecological conditions and food
chains, some  population groups are  exposed to levels higher
than  those in  other parts  of  the United States.

       1.8   The numerical values  of absorbed doses  specified
as  guides  for an acute  contaminating event are  not intended
to  authorize  deliberate  releases   expected  to  result  in ab-
sorbed  doses  of these  magnitudes, nor  do they have any  rele-
vance  to  civil  defense   applications.

Preparation of Staff Report

       1.9   The staff  reviewed  the   applicable  literature  on
the  biological  aspects of  exposure   to  the radionuclides  of
interest in   this  report. The  literature   included   reports
from such groups as the National Council on Radiation Pro-
tection and Measurements,  International Commission on
Radiological  Protection,   United Nations  Scientific  Committee
on  the  Effects of Atomic Radiation (UNSCEAR),  International
Atomic Energy Agency, and the Committee on Protection
Against Ionizing Radiations of the United Kingdom's Medical
Research  Council. In  addition, a  review has been  made of
the  practices  and procedures  in  the  agricultural  and  food
processing  fields that might  be  useful  in reducing potential
radionuclide  intake.

       1.10  Upon invitation from the  Federal  Radiation
Council, the National  Academy of Sciences - National  Re-
search Council  (NAS-NRC) selected a committee  of experts to
prepare a  summary  of the  biological effects to be  expected
in  man from  irradiation by  strontium-89,  strontium-90,and
cesium-137. The  committee's findings  have been helpful  to
the  Council  in  developing guidance presented  in  this  report.

       1.11   The staff  also  convened two  ad hoc panels of
scientists   actively  engaged in  research  projects  involving
strontium  and cesium; one panel  to  provide data  on the bio-
logical, chemical  and  physical   factors  involving  radioactive
contamination of pasture,  milk, and other  foods;  and the
                              -7 -

-------
second  panel to provide  information on the dosimetric re-
lations   for  these   radionuclides. Applicable information
provided  by these  panels  has been incorporated  into  this
report.
                              -  8 -

-------
                           SECTION II
                    GENERAL CONSIDERATIONS

Origin  and Distribution  of Radioactive  Materials  in  the
Environment

      2.1   The origin and distribution  of  radioactive ma-
terials  injected into  the  atmosphere and their transport mech-
anisms  through the environment to man have  been studied in-
tensively  both nationally  and  internationally  for  the  past
decade in  connection  with  the atmospheric  testing of nuclear
weapons. The  past and  anticipated  concentrations  of radio-
active materials in the  environment from weapons testing
through  1962  have been  studied and evaluated by the  Council
in its Report Nos. 3, 4, and 6.

      2.2   When  radioactive  materials  are  released  to  the
atmosphere at  ground level,  as would generally be the  case
from an industrial accident,  dispersion  in  the troposphere
is limited in  extent. In this  case,  a  single  incident  may
cause deposition  of  high  concentrations  of radioactive ma-
terials   within    limited   areas.  Similar localized high-level
deposition  might  also  occur  with tropospheric  fallout  de-
posited  under  unusual meteorological  conditions.

      2.3   Material  injected  into the  stratosphere  by
nuclear  weapons  tests  eventually  descends  to  the  troposphere
from which  it  is  deposited  on  the earth's  surface. During
storage  in the stratosphere,   short-lived radionuclides  decay
essentially  to  zero. Long-lived   radionuclides  that   find
their way  to  the  troposphere  deposit relatively  uniformly  on
a  regional basis,   although  the  quantities  vary  with  latitude
and   with  rainfall. A somewhat  similar  distribution  pattern
of  short-lived radioactive  material   such  as  iodine-131  has
been observed  in  the United States for  the  tropospheric dis-
tribution of  debris from  tests conducted outside  the  United
States.

      2.4   Thus,  from past  experience one  can distinguish
two   limiting  situations  of  environmental   deposition. The
first  situation  (see  Section  III)  can  be characterized as  a
high level of contamination that  is limited in time  and  geo-
graphical   area. This   situation  is   generally   identified  with
an  accidental  release of material from  an  industrial  source
or  as the  result  of  a  localized  high-level contamination  re-
sulting   from   deposition  of  tropospheric  fallout  during  un-
usual meteorological conditions.  The  second  situation  (see
Section  IV)  can be  characterized  as a geographically
                              - 9  -

-------
widespread,  low level  contamination,  resulting  from rela-
tively uniform  deposition  of radioactive  materials   origi-
nally  injected   into  the  troposphere   or   stratosphere.  This
situation  is  generally   identified with nuclear  explosions  in
the  atmosphere. There may  be conditions  which  fall between
these  two  situations. However,  for  these  intermediate
cases,  it  is difficult  to predict  the  relative magnitude  of
such factors  as areas  involved,  crops affected,  and  the
population  at  risk.

Radioactive  Nuclides  of  Interest

      2.5   Although  nuclear fission  produces  many nuclides,
most of which are radioactive,  their  chemical and physical
properties  are  such that few  of them  are  of  biological  con-
cern  as  potential   radioactive  contaminants  of food. Some  of
these  radionuclides have  such short  radioactive  half  lives
that  their  radioactive  decay  to stable  nuclides   is  essen-
tially complete  before   the  food is  consumed. Those  of prin-
cipal  interest  are  isotopes  of  elements  readily  utilized  by
vegetation  or   animals   and  of sufficiently  long   radioactive
half  lives  that much of  their radioactivity will  not have
disappeared before  the  food is consumed.

      2.6   The relative  importance  of different  radionu-
clides may depend on  additional factors  such  as:  the  time
that  elapses  between fission  and  the  release  of  fission
products  to  the environment;  chemical  or physical separation
or  fractionation;  conditions  of  release;  and  season of the
year. For  example,  in unseparated fission  products only a few
days  of  age,  the properties  of iodine  make it  the most  im-
portant  radionuclide;  in fission  products aged  a  few weeks
the  longer-lived  strontium-89, strontium-90, and cesium-137
are  the  nuclides  of  importance. Studies  of possible  types
of  release  have  lead to  the  conclusion  that  events requiring
protective  actions   are  most likely  to  involve  iodine-131.

The Transmission Pathways

      2.7   The transmission pathways  of radioactive  material
from the  atmosphere  through the  food chain to man are shown
in  Figure  1. The  radioactive  material  is  scavenged  from  the
atmosphere  by  meteorological  processes,   particularly  rain.
The most serious contamination problems  would arise from
direct deposition of  the  radionuclides  on  animal  feed  crops
or  on food  crops  directly consumed by man. Following  the
initial  deposition   on  vegetation the   radioactive  materials
tend  to be  removed by  various processes,  such as  being
washed off by  rain or  being blown off by the wind. The ex-
tent to which such  removal  occurs depends on  a number  of
                              -  10 -

-------
                         FIGURE I
        IMPORTANT STEPS IN THE TRANSMISSION OF RADIOACTIVE
             MATERIAL THROUGH THE FOOD CHAIN TO MAN
   food crops
        meat and
      meat products
i'i   i
     MAN
                          atmosphere
pasturage
 animals
                         fresh fluid milk
                           processed
                         miik products
feed crops
                            -  11  -

-------
considerations,   including  particle  size and chemical prop-
erties  of the material  deposited and environmental or
biological factors.

      2.8   The  time of deposition relative  to the various
stages  in  the plant growth cycle  is  a major  factor  affecting
the projected intake by man resulting  from a  given depo-
sition. Much  less  radioactive  material will  enter the  food
chain  if  the  deposition occurs  during  a period when  there  is
less vegetation  or when animals are not  on pasture  than  if
the deposition  immediately  precedes the  harvest  of a crop.
With  increasing time between deposition  and harvest the
transmission  of radioactive  materials  through  the  food chain
would diminish  as  a result  of dilution by new plant  growth,
removal by weathering  and decay, and  in  some instances by
fixation  in  the  soil.

      2.9   As  seen  in  Figure 1,  man's ingestion  of  radio-
active material  may result from contaminated  food crops,
from  contaminated meat or meat products,  and  from contami-
nated milk or  milk products. The  relative  importance  of  the
various pathways of intake  depends  on the  radioactive  half
lives  of  the  radionuclides, the  rate  and  routes  by which
they pass  through the  transmission chain,  and the  dietary
habits  of the  population.

      2.10  The  immediate  and usually the most  significant
transmission  of all  these radionuclides  will  occur  through
the pasture-cow-milk-manpathway. Because of the various
types of plant  losses   the  immediate phase  will  ordinarily
not be  of  importance   after  the first  100 days following
deposition.

      2.11   A  later  transmission of  radionuclides through
milk may occur from use  of stored feed if  this feed  was con-
taminated  in  the  field at the  time  of  the deposition.  The
relative  importance  of  this  pathway may  vary  greatly due  to
differences  in  time  between  deposition  and  harvest, the  por-
tion of the feed supply contaminated,  and  the  use of the
feed  supply.

      2.12  Foods other than  milk  may be contaminated to
some extent  as  a result of deposition of radionuclides  on
food  crops  or on pasture  and feed crops  used  for meat  ani-
mals.  The  variables  involved  are  similar to  those  of the
transmission  to  milk through stored feed. Cesium-137 would
usually  be  the  only significant  contaminant present  in meat.

      2.13  After the  first  year there may  be a  residual


                             -  12 -

-------
problem resulting  from  deposition  on  soil  and subsequent
root  uptake. This  problem  would generally  concern only
strontium-90. Strontium-89  would be  essentially  removed by
radioactive decay  and  cesium-137 in  the  soil  is  generally
unavailable  to  plants.

       2.14  Once the  radioactive material  is  ingested by
man,  the  uptake  depends upon the chemical properties  of the
elements  and  the  physiology  of the  organ  involved. Thus,
iodine-131  tends  to  concentrate  in  the  thyroid  and
strontium-89 and-90 in the bone,  while  cesium-137 is
more-or-less uniformly  distributed  throughout  the  body.

Concentrations  of Radionuclides  in  Milk and  Projected Intake
by Man Following a  Contaminating Event

       2.15  The  ad hoc  panel that  provided data on the fac-
tors  involving radioactive  contamination of pasture,   milk
and  other  foods  following  a postulated acute  deposition,
used  the  following   assumptions: (1)  physical  and   chemical
properties  of the radionuclides were the same  as  found  in
worldwide  fallout,  (2)  deposition time was short,  (3)  depo-
sition was  on  pasture for dairy  cows,  and  (4)  the  background
and  previous  cumulative soil contamination levels  were  neg-
ligible. Animal tracer  and  surveillance  network data were
used  to derive  the   relationships  between  concentrations  of
strontium-89,  strontium-90, and cesium-137 in  milk and  the
projected  intakes  by man.

       2.16  Three  factors  are involved  in  estimating  concen-
trations  of  radionuclides  in  milk after a   contaminating
event: (1)   the secretion  rate of  the  radionuclides  into
milk  following ingestion of  a constant  daily  intake of  con-
taminated  vegetation by  the  cow,  (2)  reduction of the pas-
ture  contamination by  weathering and dilution by  plant
growth,  and  (3)   radioactive  decay. When   all  of these fac-
tors  are   considered,  the  concentrations  of strontium-89,
strontium-90,  and cesium-137 in milk,  as  a function  of the
cow's intake,  are described  by the  equation:

           A = (ceV)   (l-e-1^) (e~^3t)   (e-^*)          (1)

A is  the  radionuclide  concentration in  milk;   c, ki,  k2,  k3,
and  k4 are constants  for  a given radionuclide,  and t  is  the
time  in days  after   deposition. The  first two  terms of  the
equation  describe  the  radionuclide  concentration  in milk re-
sulting from  a constant  intake  by  the  cow. The third  term
describes  the  rate  of  loss  from vegetation, and the  fourth
term  describes the   radioactive  decay. This equation  is
                              -  13 -

-------
illustrated in  Figure  2  as  the radionuclide  concentration  in
milk at any  time,  expressed as a fraction  of the  maximum
concentration  (Am).

      2.17   In order  to derive  the  constants (Table  1)  for
the  equation it was necessary  to  relate  the radionuclide
concentration  in  milk to  the  cow's  radionuclide  intake  dur-
ing  the  first  day after  contamination  of the  pasture,  but
knowledge of  the  cow's  intake is  not needed to  apply the
equation.  The  secretion  rate  of radionuclides  into  milk
following deposition was estimated from animal  experiments
in which  there was  a constant daily intake  of the  radionu-
clides  by each cow. The rate  of loss  from  vegetation was
estimated from surveillance data and  from experimental  field
work. There  is  a  range  of  measured values for the  effective
half-time of the  radionuclides  on grass, most of which are
close to  14 days. This  value  has been selected for  use  in
this  report. The effect  of radioactive  decay in  the  case  of
strontium-90 and  cesium-137 can be neglected because of the
short grazing season compared to the  long half lives of
these  radionuclides.
                           TABLE 1
       (nCi/day)

   ki  (days"1)

   k2  (days"1)

   k3  (days"1)

   k4  (days"1)
                  Constants for Equation (1)

                  Strontium-89    Strontium-90
             0.001


             0.008

             0.26

             0.05

             0.014
0.001


0.008

0.26

0.05

 NA
Cesium-137

  0.013


  0.01

  0.41

  0.05

   NA
   NA
Not applicable
   nCi  =  nanocurie = 1 x 10
                            -9
                       curie
      2.18  The values for Tm,  Am normalized  to 1  nanocurie
per  liter  of milk, and the projected intake by  man  in  nano-
curies assuming a daily consumption  of 1 liter  of milk,  are
listed in Table  2.
                             - 14 -

-------
	 A
        m
0
V  20
                   FIGURE 2

THE RELATIVE CONCENTRATION OF RADIONUCLIDES IN MILK
      FOLLOWING A SINGLE DEPOSITION 'ON PASTURE
  40         60        80       100

   TIME AFTER  DEPOSITION  (days)
120
140
!Tm = time maximum concentration occurs.

-------
       2.19   The  reduction of  radionuclide  concentration in
milk  after changing  cows  from pasture to an uncontaminated
feed  source  has been estimated from  the exponential decline
of  radionuclide  concentration in milk following  a single in-
take  of a tracer by cows. After  the  shift  to  uncontaminated
feed,   and  assuming  a constant  daily consumption of milk by
man,   it has  been calculated that the remaining intake  will
equal  2.9, 3.4,  and  5.1  times the  daily  intake  of strontium-
89,  strontium-90, and  cesium-137,  respectively, at  the  time
of  the  shift. These   relations make  it  possible to  estimate
when  the shift  has  to be  made  in  order  to  avoid various per-
centages  of  the  total  projected  intake  by  man. The  results
are summarized in Table 3.
                           TABLE 2

        Tm,  Am and Projected  Intake by Man after an
        Acute Contaminating Event  Involving Pasture

                       Strontium-89  Strontium-90   Cesium-137
   Tm  (days)                 776

   Am  (nCi/liter)           111

   Projected Intake       27             33            32
     (nCi)


                           TABLE 3

                Intake Avoided Versus Time of
                 Initiating  Protective   Action

Projected Intake   Strontium-89   Strontium-90    Cesium-137
  Avoided (%)         (days)*         (days)*        (days)*

        50                13              17             14

        75                675

        90                222
*Days after the  initial  contamination  of pasture at which
 cows would have to be  shifted to uncontaminated  feed.
                             -  16  -

-------
Biological Risk Considerations

      2.20   The  possible biological effects that  might  fol-
low irradiation of  human  tissue  under differing conditions
have been previously  reviewed by the FRC in Report Nos.  1
and 2, and more recently  by  the UNSCEAR (1962 and  1964). In
1964  the Federal  Radiation Council  asked the National Acad-
emy of  Sciences  -  National  Research Council to prepare a re-
port on  the  effects to  be expected  in  man from irradiation
by  internally  deposited  strontium-89,  strontium-90,  and
cesium-137 for doses of  25 rads or less from  a single  con-
taminating  event.

      2.21  The Academy in turn established a committee of
experts   to  evaluate  the  possible effects  of  these radio-
nuclides  in  man. The  committee  considered the  particular
metabolic  properties  of these radionuclides, the known
effects  of  irradiation  from  these  and  other  internally  de-
posited   radionuclides,  and  from  external  sources. The  com-
mittee  gave  particular  consideration  to  the  effects  that
might result from the  short-term uptake of any one  of these
radionuclides  by  a small fraction of the  population.

      2.22   The possible  risk to  segments  of  a population
with  a   typical distribution   of  adults,  including  pregnant
women,  as  well as  of children and infants  has  been examined.
The population at risk  from  local contamination of the en-
vironment will be  small. In  a  population  with  a typical
distribution of  ages about  50 percent are age  30  or  younger,
about 10 percent  will be  of age 4 or younger,  and about 2
percent  are pregnant women.

      2.23   In regard  to hereditary effects,  it  is assumed
that any increase  in radiation  exposure  to the genetic  cells
causes  some  increase  in the mutation rate. The  hereditary
load  induced in  a  population is proportional to the  average
dose  to the  entire population. However,  the  dose  to the
individual must also be  considered. The NAS-NRC Committee
on  Genetic Effects  of Atomic Radiation expressed  the opinion
in  1956 that  the  chance  of genetic  damage  of such a nature
as  to be expressed in  an individual's immediate family  would
be  acceptably small  if the  dose to the individual was  less
than  50 rads  in  30  years. This   opinion was  reaffirmed in
1964,  and  it was concluded that genetic  considerations are
not  limiting  under circumstances for which protective  action
may be  needed provided  that the exposed population  is small
and the  dose to an individual is small  compared to 50 rads
(NAS Report to FRC, 1964,  par.  4.10).
                              -  17 -

-------
       2.24   Available  estimates  of the  risk  of somatic
injury  following irradiation  have  beep  obtained largely  from
high  dose rates (a few rads or  greater  per minute),  high  ra-
diation doses   (exceeding  100  rads),  or both. These  esti-
mates can be  considered valid only  for the  conditions  of ir-
radiation  for which they were obtained,  since  there  is  evi-
dence  indicating that  the  effect  of  an irradiation  depends
on  both the total  dose  and the dose  rate.

       2.25   It  has  not been established whether  internal
emitters  selectively  deposited  in   bone  (bone-seekers) are
leukemogenic  in man. In  addition the specific sites  of
leukemogenesis, particularly  as a  function  of  age,  are  es-
sentially  unknown. However, for  the  purposes  of  this  report,
bone  marrow is considered to  be  the most  significant tissue
from   the  standpoint  of  susceptibility to harmful  effects  of
irradiation.

       2.26   Evidence  based  largely on the  survivors  of
Hiroshima and  Nagasaki  indicates  that,  if  a population of a
million people  were to  receive a  radiation  dose of 100  to
500 rads,  the  average  increase in  the incidence of leukemia
over  a period of about 15 years would be from  one to  two
cases  per year  per rad. (NAS  Report  to FRC,  1964,  par. 5.15;
UNSCEAR,  1964, Appendix B,  par. 30). An approximately  equal
number of  other neoplasms  attributed to the  irradiation  was
found in the same population (UNSCEAR,  1964, Appendix B,
par.  179) giving a total increase  of  2 to 4  cases per year
per million persons per rad averaged over the same number of
years.

       2.27   An association between antenatal exposure and an
increased incidence  of cancer  in  childhood  has also  been  re-
ported.   This  has been related to single exposures  (essen-
tially whole  body)  to  the fetus that may have been as low as
2 to  5 R (NAS Report to FRC, 1964,  par.  5.10). The  in-
creased incidence  of  leukemia and total  neoplasms calculated
on  the assumption of  linearity  was 4  to  10  and 8 to 20  cases
per year,  respectively,  per  million  fetuses  exposed  per rad
up  to the  age of 10 years (NAS Report to FRC,  1964,  par.
5.11). The risk  following  antenatal  exposure  at high dose
rate was  accordingly  estimated to  be  about  2  to 5 times the
risk  per  rad   following  postnatal   irradiation.

       2.28   These  estimates  of radiation risk  cannot  be cor-
rected  to account for  the  effects  of  differences  in  dose
rate  and  dose   distribution. For  comparable  total  doses  the
dose  rate from strontium and cesium  under  the  conditions  of
present  interest  is   about 105 to  106   of the  dose rates
                             -  18 -

-------
associated  with  the  estimates  of  radiation  risk  in  antenatal
exposure. Since   the  strontium  nuclides  irradiate  only   that
portion  of the  tissue  adjacent to  the  sites  of deposition  in
the  skeleton,  the  dose  distributions  are very  different  from
those  for which there  are  risk estimates.

       2.29  However,  there is evidence from radiobiological
experiments indicating that somatic cells,  even in the  em-
bryo,  and  genetic  cells generally  sustain  less  injury from a
given  dose  if irradiated  at low  dose rates  than  if  irradi-
ated  at  high  dose  rates. For  example,  genetic  studies  on
mice  led to the estimate that  when  both parents  are irradi-
ated  at  low   dose  rates,  the  effectiveness  of  irradiation  in
producing mutations  may be  as little as  one-sixth that  of
the same dose given at  high dose rates (FRC Report No.  3,
p.  7). Similar observations  on the influence  of  dose  rate
have  been  made  for  radiation-induced leukemogenesis  in  ani-
mals  (NAS Report  to FRC,  1964,  par.  5.17). Hence, the  mag-
nitude of the  dose  rate  effect  may be considered  to  be  in
the  same  range  as the  reported  difference  in  radiation  sen-
sitivity  between  antenatal   and postnatal  populations  exposed
at  high  dose  rates. From   these  considerations  it is  esti-
mated that the  upper  limit  of risk per  rad related  to  ante-
natal exposure under  the conditions  of interest (low dose
rate)  will  be  no greater than the  risk  heretofore related  to
postnatal exposure  to the same dose  at high dose rates.

Dosimetry  Considerations

       2.30   The small  organ size  of  infants results  in  a
relatively  larger dose  per  unit intake  of  radioactive ma-
terial  than for  older  age   groups.  Also,  from  the  preceding
discussion, the  fetus  is more  susceptible   to  injury  than  in-
fants  or adults  per  unit  dose. For  these   reasons special
consideration  has been  given  to  antenatal  and  infant expo-
sure.

       Strontium

       2.31   The metabolism of strontium  is linked to the
metabolism of calcium in a  complex  way. The body preferen-
tially  absorbs calcium  and  preferentially   excretes   strontium.
However,  strontium and calcium are incorporated into new bone
in  the  same   ratio  as  they  exist  in blood.  It is not  known
whether  the  biological  risk  from  radioactive  strontium
depends  upon  the dose to bone marrow  adjacent to the sites
where  strontium  is  incorporated in the  skeleton,  or  upon the
mean dose  to  all the bone  marrow in the  skeleton. Under the
linear  hypothesis the mean  dose to all bone marrow  is the
                             - 19  -

-------
dose  of  interest  for  the  evaluation  of  biological  risk,  and
is the  one used in this report.

      2.32   The  radiation dose  to  mineral bone  that would
result  from  the  ingestion  of radioactive  strontium from the
diet  depends on the fraction of  ingested strontium reaching
bone  and  the  length  of time  it  remains  there. Inadequate
knowledge  of the way  strontium may  be initially distributed
in the  skeleton makes  a  calculation  of radiation  dose, par-
ticularly  to  bone  marrow,  very  difficult. If uniformly  dis-
tributed throughout  the  mineral bone  of the  adult, 1  nano-
curie  of strontium-89 per gram of calcium  would  result in a
dose of 0.3 rad to mineral bone  (derived  from UNSCEAR, 1962,
Annex  F,  par.  52,  p. 356). One nanocurie  of strontium-90
per gram calcium uniformly distributed  in adult  bone would
result in a dose of 2.7 rads in a year (UNSCEAR, 1962, Annex
F, par.  29,  p.  353). The  dose to  mineral bone  of the  fetus
and infant may  be  about one-half the  adult values  because
the young skeleton has  less mineral per gram of bone,  and
because the young skeleton absorbs  less  of the available
beta energy  (Some Aspects  of  Internal  Irradiation,  Pergamon
Press,  Oxford 1962, p.  447).

      2.33   The  estimation of the  dose  to bone marrow re-
sulting  from  the  incorporation  of radioactive  strontium in
the surrounding mineral bone is  a complex problem. The
energies of  the beta particles  from  the  radioactive decay of
strontium are  distributed over  a broad  spectrum,  and  for
each energy  a  specific  range of the  particle in  bone,   soft
tissue,  or  in a combination of the two must  be considered.
The dose to bone marrow from  strontium-89 and strontium-90
uniformly  distributed  in the adult skeleton  has  been  esti-
mated  to be  about one-fifth the  calculated  dose  to mineral
bone for  strontium-89 and  about one-fourth the dose  to min-
eral bone from strontium-90 (UNSCEAR, 1962).  The Federal
Radiation Council used  a value of one-third for  both
nuclides in FRC Report No. 2.

      2.34   Although  the lower  density of mineralization in
the infant  and fetal skeleton results  in a  lower  dose  to
mineral bone than the dose  from the same concentration of
strontium  in  the adult  skeleton,  the  resulting  dose to  bone
marrow of  the  infant or  fetus  will be relatively  higher for
the same  reason. Therefore,  one-third  of  the dose that
would  be calculated for mineral  bone  per unit  of strontium
in the  adult  skeleton is also  a  reasonable estimate  of the
dose from the same concentration to bone marrow  of the fetus
and  infant. The  calculations  in this  report  accordingly  as-
sume  that  for estimating radiation  dose to the bone marrow
                             - 20  -

-------
of  a  fetus or  infant  from  radioactive  strontium in  the
skeleton  (1)   the  radioactive  strontium  is  uniformly  distrib-
uted in  the mineral bone,  (2) a  concentration of 1  nanocurie
strontium-89  per gram calcium  in the skeleton will  give  a
total dose of 0.1 rad  to bone marrow, and (3) a concen-
tration  of 1 nanocurie strontium-90 per gram calcium  in  the
skeleton will  give  a  dose of 0.9  rad in one  year to bone
marrow. With  present  information, these  dose conversion
factors   give  the best available   estimates  of the  biologi-
cally  important  dose,  i.e.,  the average dose  to  bone marrow
following  short-term  intake  of  radioactive   strontium.

      2.35  The relationship  of  strontium and calcium  in
children's  bones  compared  to  the strontium  to  calcium ratio
in  the  diet is based  on results obtained  from measurements
made on  strontium-90 from  fallout. The  proportion  of radio-
active   strontium incorporated  into  the skeleton  from  the
diet mainly  involves  two   factors: first,  discrimination   by
the body against strontium  in favor of calcium;  and second,
the amount of calcium  with  its  associated strontium which is
incorporated  into the  skeleton each  day by  the  formation of
newbone.

      2.36  The first factor, discrimination  between  stron-
tium and calcium in  the passage  of  these  elements from the
diet to  a  given tissue in the body,  is  usually  expressed as
the Observed  Ratio (OR). The OR relates  the ratio  of stron-
tium to calcium that  exists  at equilibrium in a  given  com-
ponent  of the body to the  ratio  of strontium to calcium  in
the diet. If the  body  component  is  the bone,  then:

                 OR,     ,,.  ,  .. Sr/Ca  in bone
                   bone/dxet - Sr/Ca  in diet

The OR, fetal  bone to mother's  diet is estimated to be about
0.1. The OR,  bone to diet  changes  from  about  1 at birth,  to
about 0.5  at  6 months to  1  year,  and to about  0.25 shortly
thereafter  (NAS Report  to FRC,   1964,  par.  3.14). An OR  of
0.35 has been  selected  as  the most  representative value  for
the age group  of  interest  (i.e.,   6 months to 2  years).

      2.37 The second factor is  related  to  the  sum of the
calcium involved  in  skeletal  growth (net accretion) plus the
quantity of calcium  in  the  existing  skeleton that  is  re-
placed  (turnover). Mitchell,   et  al.   (J. Biol.  Chem.  158,
625,  1945) have estimated  the net annual calcium accretion
from  birth to 20  years,  after which skeletal  growth ceases.
The quantity  of calcium  in  the  skeleton  at birth and  at  ages
1 and 2 has been estimated  to be  28,  100, and 150 grams,


                             - 21   -

-------
respectively.   The  estimated net  accretion  of calcium  is  28
grams in the  fetal period,  72 grams during  the  first year of
life,  and 50 grams in the  second year  of life. The  bone
mineral  turnover rate during  the first  two  years of  life  is
estimated to be  about 50 percent per year (NAS Report to
FRC,  1964, par.  3.12). The turnover rate decreases  to  an
adult value  of about  1  percent per year  in the  shafts  of
long bones  and  10  percent in cancellous bone.

       2.38   The radiation  dose  delivered  to  the skeleton
during  the   first  year following  a contaminating event varies
with  the length  of time  the  diet  is  contaminated. Estimates
have  been made  for a contaminating event that would result
in  a  total  intake of one  microcurie of strontium-89 or
strontium-90 in  100  days,   the period  of interest for the
transmission of  these radionuclides  through  the  pasture-cow-
milk-man pathway.  Assuming that the  typical  calcium intake
is about 1  gram per day,  the radioactive  strontium intake
would then  be  associated  with 100  grams  of calcium. Thus,
an  intake  of one microcurie of  radioactive strontium in  100
days  would  result  in an average dietary level of 10  nano-
curies of radioactive  strontium per  gram of  calcium.

       2.39   For  estimating  dose  following  the ingestion  of
radioactive  strontium,  the  ad  hoc dosimetry  group recom-
mended  a model  embodying: formation of a  specified amount
of new  bone per day; further resorption and remodeling of a
specified amount of existing bone per day; and use of the OR
to  relate the  strontium  to  calcium ratio  in  the  diet to  that
in bone. A dynamic model which simulates incremental changes
in skeletal  strontium on a  day to day  basis  was  developed
utilizing  computer   techniques. Evaluation  of  the   results
from  the computer model  indicated that a less refined  ap-
proach  using strontium diet  levels  averaged  for  the  period
of  intake  and other  simplifying  assumptions  regarding  net
calcium  accretion and bone  turnover would provide comparable
estimates of dose.

       2.40   An estimate  of the dose to bone marrow from
radioactive  strontium in the diet  can be reduced to two  con-
siderations:

             1.   An estimate of the average  strontium to
       calcium  ratio in the  skeleton  from  average dietary
       levels for a  short-term intake.

             2.   The  use  of a dose  conversion factor  to
       convert  the  skeletal  concentrations  of  strontium into
       dose  to  the bone marrow.
                            - 22  -

-------
The average strontium to calcium ratio (Ra) in the skeleton
may  be estimated  from:

                       Ra = Rd x OR x F               (3)

where:

    Rd  =  strontium to calcium  ratio  in  the diet averaged
           over the period  of intake.

    OR = Observed Ratio.

      F  =  Fraction  of skeletal  calcium  incorporated  by  ac-
           cretion  and turnover  during  the  period of  intake.

An estimate of dose  (D) can be calculated  by:

               D =  Ra  x  Dose Conversion  Factor       (4)

Application  of the  appropriate  dose  conversion factors  from
par.  2.34  will  give the total dose  from strontium-89 or the
dose  in one year from strontium-90, which would  result from
the  calculated  average  skeletal strontium  to  calcium  ratios.

      2.41   For the antenatal period the maximum strontium
burden  of the developing  skeleton  would result when the 100
day  intake  coincides  with  the  third trimester,  i.e., when
essentially  all  of  the  mineralization  of  the  fetal  skeleton
occurs.   Thus F would be  1.0.   Using an Rd of 10 nanocuries
of  radioactive strontium (denoted  as Sr*  in  the  equations)
per gram of calcium in  the mother's diet and an OR of  0.1
for mother's  diet  to  fetal  bone,  the average strontium  to
calcium ratio  in  the  fetal  skeleton  would  be:


              Ra =  10  x  0.1 x 1.0 = 1.0  nCl Sr*
                                         g  Ca

       2.42   For the  infant  one to two years  old,  the frac-
tion F must be  estimated from  the  annual net accretion and
turnover.   The  net  accretion  during the  second year  of life
is estimated to be about 50 grams of  calcium.   The turnover
is estimated to  be  an additional 50  grams  of calcium  during
this year.   The fraction of calcium  in the  skeleton  that  is
incorporated during  the  100 day  intake is:

                   F =  50 +  50 x 100 =  o  18
                          150     365

Using  an Rd of  10  nanocuries of  strontium per gram of cal-
cium in the diet and an OR of 0.35,  the average  strontium to
                             - 23  -

-------
calcium ratio  in the  infant skeleton  would  be:


             R  -- 10 x 0.35 x  0.18 =  °'65
       Strontium- 89

       2.43   The total dose  resulting  from the  100 day  intake
of  strontium- 89 can  be  calculated using the  dose conversion
factor previously  given. A  concentration  of 1  nanocurie
strontium- 89 per  gram of calcium  in  the  skeleton  would  give
a total dose  of 0.1   rad  to  bone marrow. For the  two cases
presented the doses  would be:

               Fetus:    D = 1.0 x  0.1 = 0.1  rad

               Infant:   D =  0.65 x 0.1 =  0.065  rad

Thus the resulting total dose  to the bone  marrow of the
infant is estimated  to be  about two-thirds  of  the total dose
to the bone marrow of the  fetus for the same intake by  the
infant and  the  pregnant  mother. This  difference  is  less
than  the  uncertainties  inherent in  the  estimate,   and is not
considered  significant.

       Strontium-90

       2.44   Using  the relationship that  one  nanocurie of
strontium-90 per  gram of calcium  in the  skeleton will give
dose  of  0.9 rad  in  one year to  the bone marrow,  the doses
from strontium-90 for the two cases presented would be:

       Fetus:   D =  1.0  x 0.9 = 0.9  rad  in  one year

       Infant:  D  =  0.65  x  0.9 =  0.6 rad  in  one  year

       2.45   Since one trimester is about  one-fourth of a
year,  the dose  to the  fetus before birth would be  about one-
fourth the  dose  in  one  year estimated  from  the strontium-90
to  calcium  ratio  in  the  fetal  skeleton,  or  approximately 0.2
rad. The  strontium-90 burden  at birth would  be one  nano-
curie of strontium-90 per gram  of  calcium times 28  grams of
calcium  or  28 nanocuries. With a  bone turnover  rate  of 50
percent per year there would be 28 x 0.5 =  14  nanocuries
strontium-90 per 100 grams  calcium  in  the skeleton at age 1,
and 7 nanocuries  strontium-90 per  150 grams of calcium  at
age  2. These concentrations  of strontium-90 give  dose  rates
of  0.1  and 0.04 rad per year,  respectively. Computer  analy-
sis  led to  the estimate  that the total (70 year)  dose from a
                            - 24  -

-------
short-term intake of strontium-90 would be  about 5  times the
dose  in the year  when  the infant is age 1. Assuming that
the dose  in  a  year can be  reasonably approximated by the
average  of  the dose rates  at the beginning  and end  of the
year,  the projected total dose  to  bone marrow  of an  individ-
ual whose mother  had an intake  of  1 microcurie of strontium-90
during the last 3 months of pregnancy would be:
  D = 0.2
             0.9 + 0.1
E
.l + 0.04
          = 1.1 rads,  total dose
The  total bone  marrow dose for the infant would be:

               D = 0.6 x 5 =  3  rads,  total dose

It is concluded that  for an  identical intake over  100  days
by the  infant and  by the pregnant woman the total  dose to
the  infant would be  approximately three  times  the  total  dose
to the  individual  exposed  as  a fetus.

      2.46   In view  of the considerations discussed  in the
previous  paragraphs,  the  estimates  of projected doses  to  in-
dividuals in the general  population  are based on a dose  of
0.1  rad  to bone marrow following the  ingestion of  1  micro-
curie of  strontium-89 associated with  100  grams of calcium,
and  a dose  of 0.6 rad in  the  first  year with a total dose of
3 rads to bone marrow following the  ingestion  of 1  micro-
curie of  strontium-90 associated with  100  grams of calcium.

      Cesium-137

      2.47   Cesium-137 is an alkali metal which is chemi-
cally  and  metabolically  similar   to   potassium. Its  distribu-
tion   after  ingestion  is relatively  uniform  throughout  the
body resulting  in  irradiation  of  the  whole body,  including
bone marrow. It is eliminated from the body at a  rate which
may   be  expressed  in  terms  of  the  biological  half  life. This
is the  time required for the  body to  eliminate  one-half of
an initial body burden of cesium.

      2.48   The dose resulting from a given  intake  of
cesium-137  is  directly  proportional  to the  biological  half
life  and  inversely  proportional  to the  lean body  mass. A
review  of  the  literature  indicates  that  the  biological half
life  ranges  from about  60 to 180 days  in adults. The  value
for  normal  adults  in  the  general population  is  estimated to
be about 100 days (NAS Report to FRC,  1964,  par. 2.12). The
data  for persons younger  than 25 years  suggest that the bio-
logical  half life before maturity may be  a function  of age.
                            - 25  -

-------
Biological half  lives of  about 20  days or  less have been  re-
ported  for infants. For  this  report a  value of  30  days  is
used  as the  biological  half  life  of cesium-137  in  infants.

       2.49  The radiation dose per microcurie of cesium-137
ingested may be approximately  related to the body size and
the biological  half  life  by the  formula:


                    D = |r x 0.03 x 1.44 TB            (5)

where:

           D =  the total  dose  in rads

           I  =  the total  intake  in microcuries of cesium-137

           W  =  the body weight in kilograms

        0.03  = kilogram  rads per microcurie day (based  on
                the absorption of  0.59  MeV  per  disinte-
                gration).

         TB  =  the biological  half life  in days

       2.50 An  infant weighing  10 kg (about 22 pounds) and
ingesting  1 microcurie of cesium-137 would  receive  a dose of
0.13  rad. An  adult weighing 70 kg and  ingesting  1  micro-
curie  of cesium-137 would receive  a dose  of 0.06 rad. The
dose  rate  to  the fetus  is considered to be  the  same  as the
dose  rate  to the mother. Therefore,  for  equal  intakes of
cesium-137 the   dose  to  the infant  would be  about twice the
maximum  dose  to the fetus. Most of the dose  from a short-
term  intake  of  cesium-137 would be received in  one year. A
value  of  0.13 rad following the ingestion of 1 microcurie of
cesium-137 is used  to  estimate projected doses to the  gen-
eral   population.

Protective  Actions and  Guides

       2.51  As   stated in FRC  Report No.  5, a protective
action is  an action or measure  taken to avoid most  of the
exposure  to  radiation  that  would  occur  from future  ingestion
of  foods  contaminated   with  radioactive  materials. In  the
present report the  concept of  protective  action must be ex-
tended  in  its  application because  the  longer  half lives of
strontium-90 and cesium-137 may  lead to a more  persistent
contamination of a number  of  food and  animal feed crops.
Therefore,   in  order  to  achieve  a substantial reduction in


                            - 26 -

-------
the  total  dose,   it  is  necessary  to  consider protective
actions against those  animal feed crops or  food crops  that
would make major  contributions to that dose.

       2.52   Some basic considerations in the development of
protective  actions  and guides  are:

             1.   The occurrence of an acute  contaminating
       event which  will require protective action  is  con-
       sidered  to  be  so infrequent  that  it  is unlikely  that
       the  same individual will  be exposed to more  than one
       event.

             2.   Exposure  to the  public  from radionuclides  in
       the  environment is  directly related to  the concentra-
       tion  of  the radionuclides in  food supplies and the
       length of time (weeks, months, or years)  over  which
       unusual  exposures would  be expected  to  occur. The
       need for protective  actions is generally  independent
       of the  source of contamination.

             3.   The substitution  of  food or  feeds  of lower
       radionuclide  content for   contaminated  products is both
       effective  and   practicable.

             4.   The potential  intake of  radionuclides  by in-
       dividuals in  the general  public from  radionuclides in
       the  environment  can be reduced whenever  modifications
       in  the normal  production,  processing,  distribution,   or
       dietary  practices are  considered  to be less objection-
       able  than the  radiation risk that would otherwise have
       to be accepted.

             5.   Protective  actions,  by  their  very nature,
       are  short-term  modifications   in  such  practices.

             6.   If  the contamination of a particular crop  or
       dietary component  is so  high  that it  would not be ac-
       ceptable  for  local use, the crop  or dietary component
       is not  considered acceptable  for use  in  other   areas  to
       which it  may be transported.

       2.53   Also,  in the  development of guidance  for  taking
protective   action  it  is necessary to  consider:

             1.   The  possible  risk  to health associated
       with the projected  dose  to  the population  from
       radioactive    materials.
                             -  27 -

-------
             2.   The amount by which the projected dose can
      be  reduced  by  taking  certain  actions.

             3.   The total  impact,  including risks to  health,
      associated  with  these  actions.

             4.   The  feasibility  of taking  the  actions.

      2.54   Decisions  to  implement protective  actions  in-
volve a  comparison of the risk due  to radiation exposure
with  the  undesirable  features of the  contemplated  actions.
The  critical  decisions to be  made are  whether  to permit un-
restricted use  of  feed crops or  food  products,   to place  re-
strictions on the normal  use of  feed crops  or  food  products,
or to  destroy  feed  crops  or food products. The  value  of  a
protective  action depends on how much the projected dose  per
individual can be  reduced by the  action and the  number of
people   affected.  Protective  actions   affecting   a  particular
population  group  will  yield a  greater return in relation  to
their  disadvantages  if projected  doses are  high rather than
low. Since  high  levels  of contamination probably  will be
limited to  small  areas,  protective  actions  are  more likely
to be  required  in  such areas rather than over  large regions.

      2.55   The Council has adopted the term  "Protective
Action Guide" (PAG),  defined  as the projected absorbed dose
to individuals  in the  general  population that  warrants pro-
tective  action   following  a  contaminating  event. The  pro-
jected dose  is  the dose  that would be received  by   individ-
uals  in the  population group from  the contaminating event  if
no  protective  action  were  taken. If the projected  dose ex-
ceeds  the PAG,  protective  action is  indicated.

      2.56   Protective actions  are  appropriate  when the
health benefits  associated  with the  reduction in exposure to
be  achieved are  sufficient  to offset  the undesirable  fea-
tures  of the  protective  actions.  The  PAG's  represent  the
judgment as to  where this  balance should be for the condi-
tions  considered  most  likely  to  occur. If,  in  a particular
situation,  there  is  available  an  effective  action with low
total  impact,  initiation  of such  action  at  a projected dose
lower than  the  PAG  may  be justifiable.  If only  high  impact
action would  be  effective,  initiation  of  such action may  be
justifiable only  at a projected dose  higher  than the PAG.
The  types of  actions  considered  in the development  of guid-
ance  in  this  report  include:
                             - 28  -

-------
             1.   Altering  production,  processing,   or  distri-
      bution  practices  affecting  the movement of  radioactive
      contamination through  the  food chain  and into the
      human  body. This action may  include  storage  of food
      supplies  and animal feeds  to allow for  radioactive
      decay.

            2.   Diverting  affected  products  to  uses other
      than human consumption.

            3.   Condemning affected products.

      2.57  An alteration of  the  normal  diet  of an  individ-
ual  is  generally  less  desirable than the  measures   listed and
should  not  be undertaken  except on the personal  advice of a
physician.

      2.58   In the  situations where there are  slowly  in-
creasing levels of  widespread  contamination over  a period of
months  or  years throughout  the  nation's food  producing areas,
protective   actions  presently   contemplated  for  acute,  local
contamination  situations  would not be  effective.  The  con-
sideration  of  long duration  protective  actions  to  reduce the
average  intake of  radioactive  materials  for  large  popu-
lations  involves many  complex  interacting  factors   of  avail-
able, or  potentially  available,  resources.  In  addition,  a
decision to require  changes  in agricultural  and  food  proc-
essing practices or dietary habits could be  implemented only
through  policy decisions  involving  land  utilization, work
force  distribution,  and  the   allocation of  technical  talent
to  the  long-term control  effort.
                             -  29 -

-------
                          SECTION III
           THE ACUTE LOCALIZED CONTAMINATING EVENT

        3.1    Situations  justifying  protective  actions  could
occur from such  events as  an  industrial  accident,  possibly
involving  a nuclear reactor  or  a nuclear  fuel  processing
plant,  and release  of radioactive materials  from nuclear ex-
plosions. The  considerations  involved  in  determining  appro-
priate  criteria  for  protective  action following  an  acute  con-
taminating  event have led to the  development of three cate-
gories  of  dietary  pathways. Categories  I  and  II  relate  to
intake  in   the  first  year  following  acute   deposition,  while
Category  III considers  intake  after  the  first year.

        3.2   Category I is concerned with  the immediate  trans-
mission of the  radionuclides  through the  pasture-cow-milk-man
pathway. The  three  nuclides  of  interest  may be  transmitted
through this pathway simultaneously when  they  are  deposited
simultaneously   on  pasture. Experimental  data  indicate  that
nearly  all  the  radioactive materials  appearing  in  milk
through this pathway will have  occured within  100 days,  and
protective  actions may  have  to  be applied  for  this  length  of
time. Protective  action  must be  initiated  within about  a
week to be effective in averting most  of  the  potential expo-
sure. This  category  of transmission  may be the only one  of
importance for  strontium-89  because of  its relatively  short
radioactive half  life  (50.5  days).

        3.3   Category II is  concerned with  the  transmission of
radionuclides to  man through dietary pathways  other  than that
specified as Category  I during  the first  year  following  an
acute  contaminating  event. This   involves  the use  of  feed
crops  for   animals,   including dairy  cattle,  and plant  products
used directly  for human  consumption. The  radioactive mate-
rials  initially  deposited  on  such  crops  in  the  field  do  not
gain access to  the  human food  chain until after the  crops  are
harvested.  Immediate  action  to  reduce  the  potential  intake
will not usually be required  because  of the normal  delay  in
the  use of such crops. However,  an early decision will be
required as to  the need for  examination of  the  radionuclide
content  of harvested  crops before they  enter  normal  marketing
channels. Strontium-90  and cesium-137  may be  transmitted
through the cow's  feed to milk;  cesium-137,  in particular,
may be  transmitted  through  feed to meat;  both may  be trans-
mitted to man through the direct consumption of plant
products.
                             -  30  -

-------
        3.4   Category III is primarily  concerned  with the
long-term  transmission  of  strontium-90 through  soil  into
plants  in the  years  following a  contaminating  event.
Residual contamination  of cesium-137  on pasture when there
is a heavy  root mat  may  be a consideration for one to two
years  following  a sufficiently  severe  contaminating  event.
Because of  the long lead time available to  assess  the  pos-
sible  radionuclide  intakes,  immediate  action is  not  neces-
sary. Any action  that may be taken  must be  based on the
long-term  reduction   of  the  radionuclide concentrations in
products grown in the area.

        3.5   In  considering  the  desirability  of  initiating
protective  actions  following  a  contaminating event,  it  is
necessary  to   consider  the  three  categories  separately.  The
benefits of  a   protective  action taken  in  one  category  are
largely independent  of  whether action is  taken  in  another.
Individuals  may  be  exposed  to  radioactivity  from all three
categories;  however,  the guides  for  individual  categories
recommended  in  this report  are  sufficiently  conservative
(i.e.,   low)  that   it  is  unnecessary  to provide  an  additional
limitation  on   combined doses. Actions that  are  likely  to  be
taken  in  Categories  I and  II would  be effective  against  any
of  the  three   nuclides. Since  all  nuclides   contribute  to
bone  marrow dose, the  sum of the projected  doses to  the  bone
marrow should be compared to the  numerical value of the  re-
spective guide in the appropriate  category when  the  need  for
protective  action   is  considered.

Guidance Applicable  to  Category  I

        3.6   Conditions  in Category  I  develop  rapidly from the
onset  of radionuclide  deposition,  and protective  actions  must
be  initiated  within about a week to  avert  most  of the intake.
The  protective  actions   considered  effective   are:

                1.   The  change of cattle from pasture to  stored
        feed.

               2.    The  substitution  of unaffected  fresh  milk
        for  affected  fresh milk by  alteration of  processing or
        distributing practices,  with   subsequent  diversion
        (depending  on the radionuclides)  or disposal  of  contam-
        inated   milk.

Since  these  actions   are  effective  for all  radionuclides  of
concern,  actions  taken  for  one  contaminant will  simultaneously
reduce  the  intake   of  others. Protective  actions  to  avert
exposure  may   be  appropriate  for  a shorter or longer  time  than


                             - 31  -

-------
 100 days,  depending on the  circumstances.

        3.7  The  concept  of  the  Protective  Action Guide,  as
 presented  in Report No.  5,  was  developed  for use as  guidance
 in  situations  involving  the  rapid  transmission  of  radionu-
 clides from pasture to  milk  to man with  the inherent  limita-
 tions on the  types  of  effective  actions for  which  the  neces-
 sary  resources would  be  generally available.  Such  a  situation
 has  many  of the  characteristics  of an  emergency  requiring  an
 immediate  decision  as  to  the need for protective  actions.
 The possible need for  early  actions to avoid most  of the pro-
jected intake  that may  result  from  an acute  localized  con-
 taminating  event  involving  strontium-89,  strontium-90, and
 cesium-137 is also present  in Category I.

       3.8   In the application of the  PAG's the following
 guidance is provided:

               1.   If the projected dose exceeds the PAG,
       protective  action  is   indicated.

               2.   The  amount of effort that  properly  may be
       given to  protective  action will increase  as  the  pro-
       jected  dose  increases.

               3.   The  objective of any action is to  achieve
       a substantial reduction of  the  dose  that  would other-
       wise occur—not to  limit  it to  some  prespecified
       value.

               4.   The  value  of the proposed protective actions
       must be  weighed  against  their total  impact. Each
       situation   should  be  evaluated  individually.  As   the
       projected  doses   become  less the value  of protective
       actions becomes  correspondingly less.

       3.9   The  guidance  applicable  to strontium-89, stron-
tium-90, and cesium-137 is given  in terms of  the projected
dose  to  the whole body  or bone marrow. Because of the risk
associated  with irradiation of bone  marrow  or the whole body
as  compared to  irradiation  of the thyroid, and the comparability
of  the  protective  actions available  to avert  the  exposure,
it  is considered  appropriate   that  the  PAG's applicable  to
these radionuclides be  lower than the PAG recommended for
iodine-131. In  view  of  these considerations  it is recommended
that:

               1.   The  PAG  for the  transmission  of  strontium-89,
       strontium-90, and cesium-137 through milk under  the
                             - 32  -

-------
        conditions of Category I be a mean dose  of 10 rads in
        the  first  year   the  bone marrow or  whole bodyof
        individuals in  the  general population;  and  provided
        further,  that  the total  dose  resulting  from  Category  I
        not  exceed  15  rads. For  purposes  of  applying this
        guide  the  total  dose  from strontium-89  and cesium-137
        is assumed to be the  same as  the dose in  the  first
        year, whereas the total  dose from strontium-90 is
        assumed to be  five times  the dose from strontium-90 in
        the  first year.   As  an  operational technique  it  is
        assumed that the guide  will  be  met effectively if  the
        average  projected dose to a  suitable sample of the
        population  (children approximately 1 year of age)  does
        not  exceed one-third of  the  numerical  value prescribed
        for  the  individual.

        3.10   For  the   radionuclides  of  interest,   the  total in-
take by man  in Category I following a  contaminating  event is
estimated from  the assumptions that:    (1) Equation (1)  de-
scribes  the radionuclide concentrations  in milk  as a  function
of time;  (2)  the  average calcium content of milk is 1 gram
per liter;  (3) the daily intake  of milk is  1   liter; and  (4)
the total intake will  occur  within  100  days. Tables 4,  5  and
6  are based on these  assumptions and the relationships  be-
tween  total intake and projected dose,  given  in paragraphs
2.46 and 2.50.

                           TABLE 4

    Relation Between  Strontium-89 Intake Through Milk
            and the Average Dose to Bone Marrow*

         Maximum        Total Intake   Average Dose to
    Concentration in                     Bone  Marrow
           Milk
       (nCi 89Sr/l)      (M>Ci 89Sr)         (rads)	

             63               1.7             0.17
            370              10                1.0
            740             20                2.0
           1110             30                3.0
           1870              50                5.0
           3700            100               10
          18700            500               50
     *Based on a dose of 0.1  rad to bone marrow follow-
      ing an  intake  of 1 microcurie associated with  100
      grams of calcium

       i = microcurie = 1  x  1Q-6 curie


                            -  33 -

-------
8
51
100
155
250
510
0.28
1.67
3.34
5.0
8.3
16.7
                           TABLE 5

     Relation Between  Strontiuni-90 Intake Through Milk
            and the Average Dose to Bone Marrow*

   Maximum        Total        Average Dose    Total Dose to
Concentration     Intake      to Bone Marrow    Bone Marrow
  in Milk**                   in First Year
(nCi 90sr/l)    (H^Ci 90SrJ        (rads)          (rads)

                                   0.17             0.85
                                   1.0              5.0
                                   2.0             10.0
                                   3.0             15.0
                                   5.0             25.0
                                  10               50

*Based on  a  dose of 0.6 rad  in the  first year  and a total
 (70-year)  dose of 3 rads  to bone  marrow  following an intake
 of one microcurie associated with 100  grams of calcium.

**Numbers  below 100 have be-en rounded to the  nearest unit;
  numbers  above  100 to the nearest  5 units.

      = microcurie = 1  x 1Q-6  curie
                           TABLE 6

      Relation Between Cesium- 137 Intake Through Milk
                 and the Dose to Whole Body*

         Maximum        Total Intake        Dose to
      Concentration                        Whole Body
         in Milk
      (nCi 137Cs/l)      (M-Ci  137CS)          (rads)

              41               1.3              0.17
            240               7.7              1.0
            480              15.4              2.0
            720              23                3.0
           1190              38                5.0
           2400              77               10
       *Based on a dose of 0.13 rad following an intake
        of one microcurie

       jiCi  = microcurie =  1  x 1Q-6  curie
                            - 34 -

-------
Guidance Applicable to Category II

        3.11   Conditions  in  Category II that may warrant
action develop more slowly,  in  comparison  to  those of Cate-
gory  I,  and generally permit more time for application of
protective  actions  after  the deposition  of  radioactive  ma-
terial  has  occured. The  time  of  deposition  of  radioactivity
relative  to the various  stages in  the  plant growth cycle  will
be  a major factor affecting the  concentration of radionuclides
in  food and feed. Although the  variations  can  be large, de-
pending on the time of year and the particular produce  grown
in  the  contaminated area,   the  concentrations  of  radionuclides
reaching man through  Category  II  pathways  will be  less, in
most cases, than those  in   Category  I. The need  for  initiating
a program to assess the  degree  of contamination and the
use of  crops in  Category II  can  generally be deduced  from
the  situation  found  in  Category  I. Protective  actions
usually will not  be required in Category II if they were not
required in  Category I.

        3.12   The  significance of  radioactive  contamination
should  be evaluated  in terms  of  potential  daily  and  total
intakes by  persons who are  assumed to derive major portions
of  their diets  from the  use of locally grown  crops. A wide
range  of  situations may  exist  within  Category   II. It  is
generally  impossible  to  predict  total  radiation  doses  solely
from the  degree  of contamination of  a  particular crop. The
complexity of such situations and the  fact  that  for most crops
immediate action,  beyond assuring that the questionable crops
are not marketed before appropriate assessment can be  made,
make  it impractical to  provide  numerical  guides  applicable  to
individual  products. However,  if  it  appears  that the  total
projected dose to a suitable sample  of a population group from
the use  of all crops in Category  II  is  larger  than the PAG
recommended  for this  category,  protective  actions should be
initiated against  those  crops  that  would  make major  contribu-
tions to  that  dose. In  order to meet  the  objective of Item  6,
paragraph  2.52,  this suitable sample would  be from a  group
considered  to  live in  a contaminated area and also  be  con-
sidered to make  maximum utilization of locally  produced food
products.

        3.13   Depending  on  the circumstances,  the protective
actions  considered appropriate for  Category  II  are:

               1.    Modification of animal  feed  utilization
        practices  or of  food processing and marketing  practices.

               2.    Diversion of one  or more crops so  that  the


                              - 35  -

-------
       radionuclides  of interest are  removed from  access to
       the human food chain.

               3.   Destruction of one or more  food crops or
       animal feed crops.

The effectiveness  of the  actions  in eliminating  potential  in-
take from the  use  of  the  crops increases in  the  order listed.
The kinds of protective  action  applicable to the use  of
animal feed  crops and food crops  directly contaminated by
deposition and their  relative  feasibility  can  be expected to
vary  quite  widely  from  one  situation   to  another. Destruction
of  food  crops  should  seldom be  required. The  selection of
individual foodstuffs  for  disposal  or  for diversion to  non-
human use will  depend on many factors, including:  (1) the
fractional  contribution of radioactive  material  that  each
dietary  item  makes  to the total diet, assuming  a  normal  diet;
(2)  the  reduction in  projected  dose that could  result  from
the  elimination of  each dietary item;  and  (3)  the possible
access to  the food  chain  through  diversion to  alternate non-
humanuses.

       3.14   In view of  these  considerations  it  is recommended
that:

               2.   The Protective Action  Guide  for the  trans-
       mission of strontium-89, strontium-90, and cesium-137
       through food  crops  or animal feed crops  under  the
       conditions in  Category II be  a  dose of 5 rads  in the
       first year  to  the bone marrow or whole body of indi-
       viduals  in the general  population. As an  operational
       technique  it  is  assumed  that  the guide will be  met
       effectively  if  the  average   projected  dose  to  a  suit-
       able sample of the local population  is no  larger than
       2  rads in  the  first  year  to  the whole  body or bone
       marrow.

       3.15   The intent of the recommendation  is  to discourage
deliberate  introduction of  contaminated foods into  supplies   of
uncontaminated foods  as an acceptable means  of  solving a
problem  involving radioactive  contamination  of  the  environment.
It is recognized  that all  crops  that might  be affected  by a
contaminating event  will  not be harvested at  the same  time,
In addition,  some crops might  not  normally be used until  more
than a  year  after the  event. The PAG  for  this  category  is
intended  to apply to  the  evaluation of  the  projected  dose
from the  use  of crops  that were contaminated at the time of
the  event  and are harvested within a year.
                            - 36  -

-------
        3.16  The  transmission  of  strontium-89, particularly
to children  approximately  1  year of age,  through  dietary
products  other  than  milk  should  generally  be  insignificant
in  comparision  to its transmission  through  milk.  Under  cer-
tain  conditions   it  is conceivable  that  significant  quantities
of  strontium-89 could be transmitted to milk if contaminated
crops  are used  to feed  dairy  cattle before  the strontium-89
has  been  lost by radioactive  decay. Once  the crop  has been
harvested,  strontium-89  is lost only by the  process of radio-
active decay during  storage,  and the  relationship  between  the
concentration of strontium-89 in milk  and the  total intake
differs  from  that  in  Category I. The maximum  projected  in-
take  in  this  case  is  74   (1.44  x radioactive half  life) times
the measured concentration per  liter of milk assuming  a con-
sumption of  1  liter of milk per day.

       3.17  The  strontium-90 and cesium-137 content of
animal  feed depends  on  the concentration  at  the time  the
crop  is   harvested. There is   no significant   loss of these
radionuclides by  radioactive decay in time periods  of  1 to 2
years.  If  the feed  is  used for  dairy cows  the strontium-90
and  cesium-137 concentration  in milk would  reach a steady
state  value  related  to the cow's  daily  intake.  The  concentra-
tion in milk would remain at  that value as  long as the feed
is used.  Therefore,  the  relation  between the   concentration
of strontium-90 and cesium-137 in  milk and  the total  quantity
secreted into the milk would vary,  depending on how long  the
particular  feed  crop   is  used. However, this  quantity   can  be
estimated  in advance  if  the  concentrations in  the  feed are
known and the use of the feed has been determined.

       3.18  In  addition to  the transmission of strontium-90
and  cesium-137 to milk through the  use of contaminated crops
for  feeding  dairy  cattle,  the   possible   contribution  result-
ing  from the use of  other crops such  as  fruits, vegetables,
or cereal grains growing  in the same area must also be con-
sidered.    In these  cases,  it   is  expected  that   the  largest
part of the  contamination will  be  associated  with one  or  two
particular  crops and   the  action should be directed at  elimi-
nating this  part  of  the  potential  exposure.

       3.19  The relationship between  the total intake of
strontium-89 and  strontium-90 and the  projected doses  as
shown in columns 2 and  3 of Tables 4  and 5 is valid if the
particular  intake  is  to be  evaluated over  a  period  of  1 to 3
months. The  relationship   between  the  total   intake  of
cesium-137 and dose shown in  columns 2 and 3 of Table  6 may
be used  in estimating the projected  dose from  cesium-137.
                            - 37 -

-------
Guidance Applicable to Category III

        3.20  In  this category  there  can be  extremely wide
variations  in  the  situations  that  might  exist  in  relation  to
(1)  areas  involved,  (2)  crops  affected,  (3)  possible rate  of
the  decrease in  strontium-90  gaining  access  to  plants,  and
(4)  possible actions. In  addition,  one is now  concerned with
problems of long-term chronic exposure. Actions that may  be
effective in Category  III involve  major  long-term changes  in
farming practices such  as selection  of crops,  chemical  or
mechanical  treatment  of soil,   land  utilization,  or  all   three
of  these. Following  a  sufficiently  severe   event,   long-term
restrictions may  be  placed on  the use of farmland  for  food
or  feed production. The  range  of considerations that  may
enter  into  a decision  to  take  action  in  this category  to-
gether  with the  length of  time available for  detailed  evalu-
ations make it less  meaningful  to  provide a  numerical PAG
than  to  provide  guidance for  evaluation  of  long-term   situa-
tions. The  nature of the  situation  is such  that  detailed
evaluation  would  not be  required  except in situations  in
which levels of  environmental  contamination  are  greater  than
those  that  might occur under guidance provided for normal
peacetime  operations.

        3.21  In  view  of  these considerations it is recom-
mended that:

               3.   The  desirability  of protective  action
        against  exposure  to  environmental radioactivity  from
        situations in  Category  III  be  determined on  a case-by-
        case basis. If  it  appears  that  annual  doses  to  the
        bone marrow  after the  first year  may exceed  0.5  rad to
        individuals  or 0.2 rad  to a suitable  sample  of  the
        population,  such  situations  shall  be  appropriately
        evaluated.

        3.22  Strontium-89 will  have  essentially disappeared
through  radioactive decay within  12  to 18 months  after  the
initial  deposition.  This   radionuclide, therefore,  is not  a
consideration in  the utilization  of  land  in  the years
following  a high deposition.

        3.23 Long-term exposure from strontium-90 entering
the food chain through root  mats  on  pastures  or through  the
soil  into plants  may be  an important factor in  land  util-
ization  for  several   years  following  a sufficiently  high
deposition of strontium-90 in the environment. Land  used  for
                            - 38  -

-------
pastures,  animal  feed  crops,  or  other  crops  such as  fruits
and  vegetables may be affected  in varying degrees.

        3.24   Cesium-137,  particularly  on pastures with a
heavy root mat,  may  be an  important  factor  in  land util-
ization  for 1 to 2 years   after  an  acute  contaminating  event.
Direct  transmission to plants  from  cesium-137  in the  soil  is
generally  not  expected to  be  limiting  since  cesium-137  is
tenaciously  bound  by soil particles.
                             - 39  -

-------
                           SECTION IV
                   WORLDWIDE CONTAMINATION
                  FROM  STRATOSPHERIC  FALLOUT

       4.1   Stratospheric  fallout  from  past atmospheric
testing  of nuclear weapons has  led to  a worldwide deposition
of  fission  products  in  the  environment. It has  led to  a
generally  fluctuating but  gradually  increasing  level  of  long
lived radionuclides  in  food  products. These  levels  reached
their peak  in  1964. All food supplies  may be  affected
simultaneously  to a greater or  lesser degree  but  the  average
radionuclide levels in  the  food produced  in a  large  area,
such as  a  state,  are  more significant  than local  fluctuations
within  the  area. The general  situation  has been  studied  by
the FRC  from the standpoint of worldwide fallout  from past
atmospheric testing (FRC Report Nos. 3, 4, and 6).

       4.2   It   appears  that  the   intra-regional variations  of
food contamination  are relatively  small. In 1963   the  highest
annual  average  strontium-90 content  of milk  from  stations
among  "wet"areas was  less than three times the annual
average  of  all  stations in  these   areas. The highest  monthly
average  for this  station was about twice  its  annual  average
and  its  highest weekly  sample  was about three  times its
annual  average.  In  the  United  States the  annual  average  of
the  station with  the highest  average  was  about 20 times that
of  the  station   with  the  lowest  average.  Regional variations
in cesium-137 and strontium-89 concentrations  were
comparable.  (FRC Report No. 6)

       4.3   The  relationship  between the amount of  fallout
deposited  per  unit area and the resultant dietary  intake  by
man is  not  constant, but  is  influenced by a  variety  of fac-
tors. These  include  those  factors  influencing   the subsequent
movement of radionuclides  through the environment to the  diet
and  the dietary  habits  of  specific population  groups  or
individuals.

       4.4   The  studies of  fallout in the  United  States  from
past testing (FRC Report Nos.  4 and 6)  have indicated that:

               1.   From tests  conducted  in 1962,  strontium-89
       gave an estimated average dose  of 0.04  rad to bone  and
       O.Olradto bone marrow.  These doses were divided about
       equally between  1962 and 1963, giving an annual  dose in
       each year equal  to  about 3  to  4 percent of the numerical
       values of the RPG's for bone and bone marrow. In 1964
       the  estimated  dose from strontium-89 was  negligible.


                             - 40 -

-------
               2.   The  average annual  strontium-90 content of
        the  total  diet  in  the  "wet"  areas of  the United
        States  from all  past testing  reached a  peak value  of
        approximately 40  picocuries  of  strontium-90 per gram
        calcium in  1964. During  the period  this concentration
        is maintained,  it  would lead to  annual doses of  about
        0.03  rad in new bone and  about  0.01  rad in bone marrow
        These values are  about 6  percent of the  numerical
        values  of the RPG's for bone  and bone  marrow.

               3.   Internal  exposure  from cesium-137 to  be
        taken in  through  the diet in the  conterminous  United
        States  during  the  next  30 years  has been estimated to
        be  about  0.01  rad. This  is  about  0.2  percent  of the
        RPG for the gonads (5  rems  in 30 years  averaged over
        the   population).

        4.5  The RPG's were developed  for controlling normal
peacetime  operations  assuming a  condition of  continuous intake
and  chronic exposure  affecting large numbers  of people for
time-spans of generations. The numerical values  of the RPG's
do  not and  cannot establish a line  which is safe on one  side
and  unsafe  on  the other. Nevertheless,  annual radiation
doses  from  fallout equal  to or greater than  the numerical
values  of the  RPG's can  be used as  an  indication of when
there  is a   need  to  initiate a careful  evaluation  of  fallout
exposures.  Caution  should be exercised  in  instituting  pro-
tective actions in  situations  where  exposures are near  the
numerical  values  of the  RPG's,  since  the biological risks
are so  low  that the actions could  have  a net adverse rather
than  beneficial effect  on  the public well-being.

        4.6   The  practicality and value  of protective actions
against widespread environmental contamination from  strato-
spheric  fallout is  limited because:

               1.   The condition to  be  alleviated  is  chronic
        exposure from  long-term continuous  intake  (10  years
        or more).

               2.   A reduction in potential intake under  these
        conditions  requires  basic  changes in  long-term agri-
        cultural practices,  food  processing  practices,   dietary
        habits,  or  all  three.

               3.   The  actions would have to  be applied  on a
        broad enough scale to  reduce the average quantity of
        radionuclides  in  the total diet  from  foods produced
        throughout  large  areas or the  entire  country.


                             -  41 -

-------
Cesium— 137 and Strontium-90 in Arctic Alaska

        4.7   Although  the  amount of fallout  deposited per
unit area in  the  Arctic is  about  one-fifth  that  deposited  in
30°  -  40°  latitude  band,  a  combination  of ecological condi-
tions and  specific  dietary habits  of the  Eskimos  and Indians
result   in  higher strontium and cesium body burdens than are
found   in  the conterminous  United  States. The  lichen-caribou
(reindeer) —man pathway  is the  most  important  food chain
contributing to these  body  burdens.

        4.8   Lichens  accumulate  nutrients and certain other
materials  which are deposited  directly  on them  from  the  air.
Their  growth  is  slow and they  tenaciously  retain  the fallout
materials  to  which  they  are  exposed.  The  concentrations  of
cesium-137 and strontium-90 in lichens are  among the highest
in  plant  life  measured  anywhere in the  world.  These radio-
nuclides also  tend to  accumulate  in other  persistent vegeta-
tion,  such as sphagnum moss and the crowns  of sedge.

        4.9   Lichens are important in the diet of  caribou  and
reindeer,   particularly  during  the   winter. Other  plants   such
as  sedges   are  also  consumed  by these animals.  This  diet
leads  to  relatively high concentrations  of cesium-137 and
strontium-90 in the meat  of these  animals. High  levels  in
the food  chain can be  expected to  persist  for several years
in  the arctic  region. The  individuals  and   small  population
groups  with the highest  body burdens of cesium-137 are those
whose  dietary preference  is  caribou meat. Average body  bur-
dens  of cesium-137 in these inhabitants  were  about three
times  as high in 1964 as  they were in 1962. People with  more
diversified  diets  have  lower body  burdens. In  1964  the
annual  dose to the  Eskimos  having the highest body  burdens
was  slightly more  than one-half the RPG of  3,000  nanocuries
for whole  body exposure  of individuals  in  large population
groups. Average doses  for adults of the  same village are
less than  one-third the  RPG. Although the   Federal  Radiation
Council did not set a specific  RPG  for  cesium-137, in either
Report  No.  1  or No.  2,  it did  state in  the Memorandum for  the
President   (Federal  Register,  September  26,   1961):  "The   char-
acteristics   of  cesium-137  lead to  direct  comparisons  with
whole body exposure for which  recommendations by the Council
have  already  been made. "This  implies  that the RPG would be
0.5 rem*  in a year  to  the  whole body of individuals in the
general population when the  doses can be measured directly,
or an  average of 0.17 rem to a  suitable  sample  of the popula-
tion group,  when  direct measurement is  not practicable.
*For the purposes of this report the units "rem'knd "rad"
 are  considered numerically  equal.

                             - 42 -

-------
Therefore,  an annual average  body burden in adults  of 3,000
nanocuries  and  1,000  nanocuries would be  estimated  to  result
in  these  respective  doses. The body  burdens  of cesium-137 in
the  groups  of  interest are  being measured  directly. If a
comparison with the guidance  provided by the FRC is to  be
made, the applicable RPG  is  0.5  rad per year and the corre-
sponding annual average body burden is  3,000 nanocuries of
cesium-137 in  adults. Strontium-90 burdens in  bone  appear to
be  about four times as high  as  those found in  the
conterminous United States.

Conclusions

        4.10  Reduction in transmission  of radionuclides to
man under  worldwide  fallout conditions could only be achieved
by  long-term changes  in  (1) agricultural  practices,   (2)  food
processing  practices,   or   (3)   basic  dietary   habits. Consid-
eration of such  basic  economic  and  social  changes  is not war-
ranted when annual  doses  from environmental  contamination are
comparable to the numerical value of the annual dose recom-
mended  for  the RPG. It  has not  been possible  to visualize
circumstances in which the balancing of the risk of radiation
against the  undesirable consequences of  the  protective  measures
on  social,  economic,   and  political  institutions  can  be  re-
duced in  advance to numerical guides for mandatory  action
under  these  circumstances.

        4.11   On the  basis  of this  information  on  stratospheric
fallout the Council  concluded that  the  health  risk  from  radio-
activity  in  food over  the  next  several years  would be too
small  to justify  protective actions  to  limit  the intake  of
radionuclides  either by diet  modifications or  by  altering
the  normal  distribution and  use  of  food,  particularly milk
and dairy products.

        4.12   In view  of these considerations  it  is recommended
that:

               5.  Surveillance  of the radionuclide  content in
        food products  contaminated with worldwide fallout be
        continued at  levels appropriate  to  the  situation.

               6.  Surveillance and research programs  examining
        the  special   ecological  situations  in  the arctic  region
        continue  until  future  trends  can  be predicted with
        greater  confidence.
                              - 43  -

-------
        7.   Nationwide programs  to reduce  potential
exposure of  the  population  from  gradually  increasing
levels  of environmental  contamination,  such as  that
associated with  worldwide  fallout,  are  not  necessary
now  nor for  future  levels  of  fallout  from  past  testing.
                          - 44  -
                                        U.S. GOVERNMENT PRINTING OFFICE 1965 O—773-982

-------