REPORT NO. 5
    background material



  for the  development of



radiation protection



           standards
                   July 1964
             Staff Report of the



   FEDERAL RADIATION COUNCIL

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       REPORT NO. 5
       background material
       for the development of

       radiation protection

       standards
       July 1964
       Staff Report of the

       FEDERAL RADIATION COUNCIL
For sale by the Superintendent of Documents, U.S. Government Printing Office
         Washington, D.C., 20402  - Price 20 cents

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                                    CONTENTS
Section I
Introduction  .
Page  No.


     1
Section II      Origin    and    Distribution    of    Radioactive
                   Contamination	
Section III      Protective   Actions    and    Their   Applications.
Section IV      Guidance     Applicable    to     Iodine-131.
                                                               4


                                                               7


                                                             11
                                         in

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                               SECTION  I

                              INTRODUCTION


  This  report  contains  background material used in the development of
guidance  for  Federal  agencies  in respect  to:   (1)  planning  protective
actions to  reduce potential  doses to  the  population  from radioactive
fission  products which  may gain access to food, and  (2)  doses at
which implementation  of protective actions may be appropriate.

  The material  is directed  to  guidance  concerned  with protective ac-
tions affecting  the  normal  production,  processing,  distribution,   and
use of food for  human  consumption when  the  action is taken  because
of  the  radioactive  content  of  the food.

  The first  two reports of the Federal Radiation  Council  contained
background material  used in  the  development  of guidance  given in the
Memorandums approved by the President on May 13,  1960, and September
13,  1961.   These reports provided a general philosophy of  radiation
protection and general  principles of control based  on the annual in-
take  of radioactive  materials.   The  recommendations  contained there-
in  were  intended  to provide the basis  for the  control  and  regulation
of  normal peacetime operations  in which  exposure  to radiation is a
factor.   Numerical values  for  the Radiation Protection  Guides  de-
signed to  limit  the  exposure of  the whole body and certain  organs as
the result of  normal peacetime  operations were provided.

  During  the period of atmospheric testing of nuclear weapons  in
1961  and 1962  the  question  arose as to the possible  need for protec-
tive  actions and the use  of existing Radiation  Protection  Guides for
determining  the conditions  under which the production,  processing,
distribution,  and  use   of  food,  particularly fresh  fluid  milk,  should
be  altered  to  reduce human  intake of radioactive  materials  from
fallout.

  In  September  1962  the  Federal  Radiation  Council  stated,  in  effect,
that  the  Radiation Protection Guides provided  for  the conduct  of
normal  peacetime  operations  are not intended  to set a  limit  at which
protective action  affecting  the  normal  production,  processing,   dis-
tribution,  and use of food should be taken, nor to  indicate what
kind  of  action should  be taken.    In the   1963  hearings,  "Fallout,
Radiation  Standards,  and Countermeasures," conducted by  the Joint
Committee  on Atomic Energy,  the Council reiterated that  position and
noted that  it would  recommend to the  President guidance  for the  ap-
propriate  Federal  agencies  applicable to  a determination  of the  need
for  protective  actions.
  Limiting the exposure  of members of the population to man-made
radioactive  material can be  accomplished by  controlling  the  release
of such  material  from  its place  of origin or  use,  or  by protecting
the population  after  the material  is  released  to the  environment.

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This  report  is  directed to  guidance  for protecting  the population
from radioactive  material  after  it has  been released  to  the  environ-
ment  in concentrations  which  justify  action.

   Situations  justifying  protective  action  could  occur  from  such
events  as:    (1)  an  industrial  accident,  possibly involving  a  nuclear
reactor  or  a nuclear  fuel  processing  plant,  and (2)  release  of
radioactive  materials  from  the  detonation of nuclear  weapons  or
other  nuclear  devices.

   The guidance concerns protective  actions  which might be applied  to
the  production,  processing,  distribution,  or use of  food  to  reduce
the  potential human  intake  of  such radioactive  material.   This guid-
ance  is  confined  in  application to  those conditions  under which  the
hazard  of  concern  is that  associated with  the  ingestion  of radio-
active materials.    Conditions  requiring  protection  from  external
gamma radiation or protection when  inhalation  may  also be  a  signif-
icant mode  of entry  for radioactive material  into the human body  in-
volve   different   considerations.

   This  report includes  guidance  as to  the   general  principles  con-
cerned  with  protective  actions  and specific  guidance  applicable   to
iodine- 131.


Preparation  of  the  Staff Report

   In  the development  of this  report,  the Staff  has  reviewed  the
literature on the   origin,  distribution,   mechanisms  of transmission
through  the  environment,  and potential  biological  effects  of  radio-
active materials.    In  particular,   the   Staff has studied  the  trans-
scripts of the hearings  conducted  by  the  Joint Committee  on Atomic
Energy;  the  reports by the National Committee  on  Radiation Protec-
tion and Measurements,  the World Health Organization  and Food and
Agricultural  Organization of the United Nations,  the  United Kingdom
Medical  Research  Council's Committee   on Protection  against Ionizing
Radiations,   the  National Advisory Committee  on  Radiation  —  an ad-
visory committee  to the Surgeon  General,  United States Public Health
Service;  and the "Proceedings of the Hanford Symposium on the Biol-
ogy of Radioiodine ."

   The Staff  also  has  had  considerable   assistance from many individ-
ual  scientists  and  technical  experts.


Definitions

   The absorbed  dose  is  the  energy imparted to  a volume  of irradiated
material  per  unit  mass  of that volume.

   The rad is  a unit  of absorbed dose  equal  to  100  ergs per gram.

   The projected dose  is the dose  that  would be  received  in  the
future by  individuals  in the  population  group  from  the contaminating
event  if no  protective  action  were  taken.

                                  - 2  -

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  The Protective  Action Guide (PAG)  is the projected absorbed dose
to  individuals  in  the  general  population  which  warrants  protective
action  following  a contaminating  event.

  The  curie  is  a  unit  of radioactivity  defined  as  3.7  x  1010  trans-
formations  per  second.  Commonly used multiples of the curie  are  the
following:

                     1   millicurie    = 1  x  10 3  curie
                     1   microcurie   = 1  x  10s curie
                     1   nanocurie   = 1  x  10 9  curie
          1  picocurie  = 1  micromicrocurie =  1  x 10 12  curie
                                  - 3 -

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                                SECTION II

         ORIGIN AND DISTRIBUTION OF RADIOACTIVE CONTAMINATION


  The  origin  and distribution  of  radioactive  material  injected  into
the  atmosphere  and its transport  mechanisms  through the environment
to man  have  been  studied intensively both nationally  and  inter-
nationally for the past decade in  connection with  the atmospheric
testing  of nuclear weapons.   The  past and anticipated concentrations
of radioactive materials  in the  environment  from  weapons  testing
through  1962  have been studied and  evaluated by the  Council in its
Reports No.  3 and No.  4.

  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 radionu-
clides which  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  ob-
served  in the  U.S.  for the  tropospheric  distribution of  debris   from
tests conducted  outside  the  U.S.

  When  radioactive  material is released to the  atmosphere  at ground
level,  as  would generally  be  the  case in an industrial  accident,
diffusion  in  the troposphere  is  limited and  the passage  of  the
radioactive  cloud  over an  area takes  a relatively  short  time.  How-
ever, the  concentrations  in the  cloud  can be high.   The  deposition
of radioactive  materials  in  this  case  can  lead to  possible  radiation
doses  that  warrant  protective  action.


Radioactive  Nuclides  of  Interest

  Although  nuclear  fission  results  in many  nuclides,  most  of which
are  radioactive,   their  chemical  and  physical  properties  are  such
that   few of them are  of   interest  as  potential  radioactive  contami-
nants of  food.   Some  of  these radionuclides  have  such short radio-
active  half-lives  that  their radioactive  decay   to  stable  nuclides  is
complete  before the  food  is  consumed.   Those  of  principal  interest
are  isotopes of chemical  elements  readily  utilized by vegetation  or
animals,  and  of  sufficiently   long  radioactive  half-lives that much of
their radioactivity  will  not  have  disappeared  before   they  have
reached the  human diet.

  The relative  importance  of different  radionuclides may depend on
many 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
of year.   For example,  in unseparated  fission products only a few
days of  age,  the  properties  of  iodine make  it the  critical radio-
nuclide,  while  a  few weeks later the  disappearance of iodine-131
will   leave   the  longer-lived strontium-89, strontium-90,  and

                                  - 4 -

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cesium-137 as  the nuclides  of interest.   Many studies  of possible
types  of release  important to  this  report have  led  to  the  conclusion
that  events  requiring protective  actions  are  most  likely  to  involve
iodine-131  as  the  critical nuclide.
The Transmission Chain

  The path of  radioactive material  from  the  atmosphere through  the
food  chain  to man  is  shown in Figure I.   The material is scavenged
from  the  atmosphere  by  meteorological  processes,   particularly  rain.
If the  air  mass  containing the  radioactive  material  is  at  ground
level  the radionuclides may be directly removed from  the air by
vegetation.   Following  the  initial   deposition,  the  radioactive   con-
tamination  tends  to be removed  by various processes,  such as being
washed off by  subsequent rainfall  or being blown off  by the wind.
The  extent  to which such  removal  occurs  varies widely  depending on
the particle size  and  chemical  properties  of  the material  deposited.
Although radionuclides may be  incorporated  subsequently  into  plants
through  absorption  by  the root  system,   their  concentration  on the
surfaces of vegetation  will  be  the  dominant  factor  leading  to a
possible need  for  protective   action.
                                  -  5 -

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                         FIGURE  I

     IMPORTANT  STEPS IN  THE TRANSMISSION OF  RADIOACTIVE
          MATERIAL  THROUGH THE FOOD CHAIN  TO MAN
food crops
     meat and
  meat  products
4
 MAN
                          atmosphere
                             I
         pasturage
animals
                        fresh fluid milk
                          processed
                        milk products
                                     i
                         feed crops
                            - 6  -

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                              SECTION III

              PROTECTIVE ACTIONS AND THEIR APPLICATIONS


  A protective action,  within  the scope  of  this  report,   is  an  action
or measure taken to avoid most of  the  exposure  to  radiation  that
would occur  from  future  ingestion  of foods  contaminated with radio-
active  materials.

  Since  a protective action is  taken to abate  such  an  exposure  risk
after  the radioactive material  has been released,   in the development
of  guidance  for  taking such  action  it  is necessary  to  consider:

    1.  the possible  risk  to health  associated with  the  projected
  dose  to the  population from fission  products.

    2. the amount  by which  the projected  doses can  be reduced by
  taking  certain  protective  actions.

    3.  the total impact,   including  risks  to  health  associated
  with  these   protective  actions,  and

    4.  the feasibility  of  taking the  actions.

  Protective   actions  are  appropriate  when the  health  benefit  asso-
ciated with the reduction in dose that  can  be achieved  is  considered
sufficient  to   offset  the  undesirable factors  associated  with  the
action.

  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  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  re-
quired  in such areas  rather  than  over  large regions.

  It  is  possible  to  estimate  the  projected  dose  that will  result
from  measured concentrations of radionuclides  in the environment.
This  estimate  is usually  related  to  a  daily or total intake  of
radioactive  materials and can be based  either  on the assumption  that
more  materials will not be  added  to the  food  chain  during the  period
of  concern,   or  that  potential  additions   can  be  quantitatively esti-
mated.   A  quantitative  estimate of  the  projected dose  is  necessary
for determining whether  or not protective  action  should be taken.


Impact of Protective Actions

  A decision  to  implement  a protective  action  involves a comparison
of  the  risk   due  to radiation exposure  with  the  undesirable  features
of  the  contemplated action.
                                  - 7 -

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  The impact of  the  protective  action will involve  such  factors as
the  degree of  departure  from  the usual practice,  the  length of time
over  which  the action is  applied,  the relative  ease  with  which the
action can be  executed,   and  possible  health  risks  associated with
the  action.

  One of the well-established actions to  reduce the  intake  of con-
taminants  on   foods is based  on the  fact  that  they  are  on  the  sur-
face  of fresh  fruits and  vegetables.   A large  proportion  of these
contaminants,  including radioactive material,  can  be removed by ap-
plying the usual  practices of  food  preparation.   The  only  departures
from these usual  practices are that:   (1)  more attention  is given to
insuring that the  surfaces are washed,  (2) the  outer  leaves of  leafy
vegetables are removed, and  (3) more than normal preference is given
to  peeling.

  The impact of these actions  is  small  because  they are  already ac-
cepted practice  and no innovations  are  involved.  If it  were  required
that all  fruits  be peeled  before eating,  the  impact  would be greater:
and hence the  risk  would have had  to be  correspondingly  greater to
warrant  this  degree of  intervention  in accustomed  activities.

  Some  actions,  such  as  discarding a food  item,  involve a marked de-
parture from usual practice.   They  may, nevertheless,  be  of low im-
pact  if  limited  to a small quantity  of produce  or to  a  small area,
or  if applied  infrequently and only  for  short  periods.

  The feasibility  of executing  a  protective action depends  on the
ease  with which it  can be applied by diversion of  available resource
factors  such as  the  facilities,  equipment,  personnel,  and  alterna-
tive supplies of animal feeds  or  agricultural  produce  needed to  im-
plement  the  action.   Diversion  of a  small fraction  of  readily  avail-
able  resources  is usually  easy,  but  diversion  of  a  large proportion
increases  the  impact   and decreases  the  feasibility  very  rapidly.
There  will be  very  few  factors,  possibly  only  one,  that  are limiting
in  any complex of  resources.  These will  not necessarily be  the same
at each  place  or time  the protective  action may be needed.


Types of  Protective Actions

  The types of actions to which guidance  in this  report  may be
related  are:

     1.  Altering  production,   processing,  or   distribution  practices
  affecting the movement  of radioactive contamination through the
  food chain and  into  the human  body.  This  action  includes a
  storage  of food and animal  feed supplies to  allow for  the radio-
  active  decay  of  short-lived nuclides.

    2. Diverting affected  products to  uses  other than human con-
  sumption.

    3. Condemning foods.


                                 - 8  -

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  Other  possible types  of action  currently  are  judged  to be  less de-
sirable   for  reasons  of  effectiveness,  safety,   or  practicality.    The
use  of  additives  in cattle  rations,  soil   treatment,  and  the  chemical
removal  of radionuclides from milk  are not included among  the types
of  actions  listed.

  Protective actions  to  reduce  the  intake  of  radioactive  materials
by  special  alterations  of the normal diet  are  accomplished best  on
an  individual  basis  under  the  supervision  of  medical  authorities.


Application  of  Protective  Actions

  In  providing  guidance  for  protective  actions  applicable  to radio-
active contamination of  the  environment,  the Council  is concerned
with  a balance between  the  risk  of radiation  exposure  and the  impact
on  public well-being associated with  the  alteration  of  the  normal
production,  processing,  distribution,  or  use  of  food.

  It is recommended that the term "Protective Action Guide"  (PAG)
be  used to  indicate  the  projected  dose at  which the  above  balance
is judged to  occur  for  the  general  types of protective  actions  con-
sidered  in  this  section.   Thus,  the  Protective  Action  Guide  serves
as  a basis  for  deciding when such  protective  actions  are  indicated.

  In  the application of  the  Protective  Action  Guides  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  protec-
  tive action  will   increase  as  the  projected dose  increases.

    3. The  objective of  any  action  is  to  achieve a  substantial re-
  duction  of dose  that would otherwise  occur — not  to limit it
  to  some  prespecified value.

    4. 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.

    5. The  Protective  Action Guide  is  based on  the assumption that
  the  occurrence,   in a  particular  area,  of environmental contami-
  nation  that  would require  protective  action  is  an  unlikely event.
  Circumstances  that  involve  either repetitive  occurrence  or  in
  which   there  appears  a  substantial probability  of recurrence  with-
  in  a period of  one  or  two  years  would require  special considera-
  tion.    In  such a  case the  total  projected dose  from  the  several
  events  and  the  total impact of  the  protective  actions  that might
  be  taken to  avoid  the  dose from one  or more  of these events must
  be  considered.   In  contemplating the  possibility of a  future
  event  it  is  necessary  to  consider not  only the  possible  magni-
  tude  but  also  the probability that the event  will  occur.


                                  -  9  -

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  6.  Federal  agencies  should plan  protective  action  programs
designed  to  reduce  the projected dose  to individuals in  the
general public  by modifying the normal  production,  processing,
distribution,  or  use  of  food products or  animal  feeds.   The
need  for  implementing  such plans should  be  determined on the
basis  of  the  estimated  projected dose and the  appropriate  PAG.
                               - 10  -

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                               SECTION IV

                  GUIDANCE APPLICABLE TO IODINE- 131


The Environmental Pathway

  The physical  and biochemical  characteristics  of iodine-131 make it
the  radionuclide most likely to  warrant  rapid application  of protec-
tive  actions.    This   is  especially  true   if  radioactive  contamination
occurs  before  appreciable  radioactive  decay  has  taken place.

  The important pathway  for  iodine-131 from  the  source to the body,
and the  one  considered  applicable  to  protective  action   criteria,  is
through pasture  to the cow, milk,  and into the human body.

  The shortest  time-span from  source  to  individual occurs when  fresh
milk  has  not gone  through processes of pasteurization  and  distribu-
tion.   Iodine-131  may appear in  milk a  few hours  after deposition on
pasturage.   From a  single  deposition it can reach  a maximum  concen-
tration  in  milk  as  early  as two  to four  days  after  deposition;  it
then  decreases  by half about  every five  days  due  to  a  combination of
radioactive decay  and weathering  losses  from  grass.

  Deposition  of iodine-131  can  vary  greatly  within  a relatively
small  geographical  area.   As  a  result,  there  can be  large   differen-
ces between  the iodine-131 concentrations in milk produced  on farms
only  a few  miles  apart.    Because of  variations in  deposition and  in
animal  feeding  habits,  and  inadequate  data  for evaluating  the  ef-
fects   of   these  variations,  it   is  not  yet possible to  predict relia-
bly the maximum  concentration  of iodine-131  in milk  from deposition
data.


Development  of the Protective Action  Guide Against  Iodine-131

  Factors  affecting  the  relationships between  exposures of humans  to
iodine-131 and  subsequent  biological  effects have been discussed  in
FRC Reports  No. 1  and No. 2,  in a report* prepared for the FRC by
the National  Academy of Sciences Committees on  the  Biological  Effects
of Atomic Radiation,  and in the "Proceedings of the Hanford  Sympos-
ium on the Biology of Radioiodine."

  According  to  these  reports,  the uptake  of iodine-131 in the thy-
roids  of children  and  adults is approximately  the  same.  Thus a
given  intake  would  result  in a  ten  times larger  dose to  the  thyroid
of  a  one  year  old  child  (thyroid  weight  2 grams)  than to an  adult
(thyroid weight  20 grams).   Children,  one year  of age  are assumed to
be  the critical  segment  of the population.
*Pathological Effects  of Thyroid Irradiation  -  A report of  a panel
of experts  from the Committees  on the Biological Effects of  Atomic
Radiation;  National  Academy  of Sciences;  National  Research  Council,
published by the Federal  Radiation Council,  July 1962.


                                  - 11 -

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  Young  children  treated  with X-rays in  the neck  region for  enlarged
thymus or for  other benign head  and neck  conditions  have had a sig-
nificantly  higher  incidence  of  tumors,  including thyroid  carcinoma,
than  have children  in  control groups.   Radiation doses  to the  thy-
roid found to be  associated  with thyroid carcinoma under these con-
ditions  range upward from about  150 rads.   Experience with exposure
of  the  thyroid  to large  doses  of  radiation from iodine-131 for  thera-
peutic  reasons  is  extensive  but  is  almost  entirely confined   to
adults.  The report of the panel of experts of the NAS-NRC Commit-
tees  states  that,  although therapeutic doses  from  iodine-131 to the
thyroid have been in the  range  of a few  thousand rads upward,
iodine-131 has not  been  identified  in a  causative way with  the de-
velopment of thyroid cancer  in  humans,  except  in  one doubtful  case.
X—ray doses  to the thyroid appear to be  from 5  to  15 times  as effec-
tive in producing biological  changes  as  iodine-131.

  The  initiation  of protective  action against  contamination  in the
environment  resulting  from a  single event  (i.e.,  an  event  isolated
in time from any  other event that might affect  the same area)  in-
volves  undesirable features that may be expected to  vary  in  impor-
tance  from  one circumstance  to  another.    Of various actions  that
might  be  effective in  averting  the  major part of  the projected dose,
two  appear to provide the most  acceptable combination of maximum  ef-
fectiveness and minimum  undesirable  consequences.   One  of these is
the  diversion  of contaminated milk  to  the production of dairy  prod-
ucts that   may  be stored  conveniently until the  iodine-131 essen-
tially has  decayed,  a  matter  of a few weeks.   The  other is the sub-
stitution  of  stored  feed  for  pasturage  until  most  of the iodine-131
has decayed.   The choice  may depend upon many factors.

  Considering   existing  information   on  the  biological risks   asso-
ciated with  doses  from iodine-131 and  the kinds of  protective  action
available  to  avert the  dose  from iodine-131 that has been deposited
on  pastures  used by dairy  cows,   the  Council has concluded that such
protective  action  as  the  diversion   of  milk  or  the  substitution of
stored  feed  for pasturage  to  avert  individual doses   less than 30
rads would  not usually  be justifiable under  the  conditions  consid-
ered most likely to  occur.  This  dose is recommended as  the Protec-
tive Action  Guide for iodine-131.

  Generally  it will  not  be  practical  to estimate  individual   doses.
In  such cases  decisions  to  take  an  action  will  be  based  on average
values.   As  noted in FRC Report  No.  1,  paragraph 5.4,  it is  assumed
that the majority  of the  individuals do  not vary from the  average  by
a  factor  greater  than  three.   As  an  operational  technique,   it  is
considered that  the  PAG  will not be  exceeded if the  average  projected
doses  to  the thyroids  of a suitable  sample of the population do not
exceed 10 rads.   A  suitable  sample  is  considered  to consist   of
children of  approximately one year of age  using milk from a reason-
ably homogeneous  supply.
                                 -  12  -

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  The PAG is stated in terms  of a projected  dose;  i.e.,  the  dose
that might otherwise  be received if the  protective  action were not
initiated.    However,   since  the  value  of the  contemplated action and,
consequently,  the justification  of the  action,  depends  on the  dose
averted,   it  is  valid  to use  the  projected  dose  as  a  basis  for  imple-
mentation of  a proposed  protective  action  only  if it  is  expected
that most  of  the projected dose  will  be  averted.

  Because  of  the differences that may  exist in various circumstances
it  is  necessary  to   evaluate  each  situation  individually.   It  is not
feasible   to  provide  detailed criteria  for  taking  into  account  dif-
ferences  that may occur.   In general,  the  PAG represents the  Coun-
cil's judgment  regarding the  benefit-impact balance   for  the  two pro-
tective actions  considered  acceptable  and  for  the conditions  con-
sidered 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  justifi-
able.   If  only  high  impact protective  action would  be  effective,
initiation  of such action at  a projected dose higher  than the  PAG
may be justifiable.   For example, diversion of milk  from fresh milk
channels  to processed products  may be less  difficult  in a  locality
where surplus  production makes allocation  between the two uses a
normal practice.   The  action would  be  more difficult and expensive,
and the  total  impact  would  be  high if  the  milk had  to be transported
large  distances  to a  processing  center,   or  if there  were adverse  ef-
fects  on  the  quality  or  quantity  of milk available to  the consumer
or  adverse effects on the  dietary  habits  of individuals  in  the
population.

  In  considering  the  net  benefit  of a  protective  action,  assuming
the  protective  action  is  initiated  at  progressively  lower values  of
projected  dose,  as the projected dose  becomes  less,  the net  benefit
to  public  well-being from  reduction  of  exposure becomes less.


Application  of Protective Actions Against  Iodine-131

  The benefit  of  avoiding  a potential  dose  from iodine-131 must be
evaluated  against the  feasibility  and  the  disadvantages  of any pro-
tective action   under   consideration.  A  selected  action  must  be  feas-
ible  for  the  particular situation.    It  must  not be   subject  to  limi-
tations such as lack of communications  or  transportation  which  would
nullify its  effectiveness.    If  warranted  under  certain  unusual  con-
ditions,   the  application of protective  actions  in  consecutive  or
concurrent  operation  may  be  considered.   Local  conditions must also
be  considered.   For  example,  the proportion of fresh milk use to
processed milk use  in the  area,  or the seasonal  feeding pattern for
cattle  may  affect  the  efficacy of  a  specific  protective  action.

  Iodine-131 concentrations may  vary  widely within  a given  milkshed.
Therefore  concentrations  at the  point  of milk production  must  be
known if efficient protective actions  are  to  be  taken.   On  the other
hand,  concentrations  at the point of consumption must be  known in
order  to  evaluate the  projected  doses  received  by the  population
group.

                                 -  13 -

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  Protective  actions  cannot  attain  maximum  effectiveness without
adequate  communications.   Information regarding  deposition patterns
and  concentrations of radioiodine  in  milk must be  obtained promptly
for  those  groups  responsible  for  taking protective action.   The  ac-
ceptance  of  and  participation  in  protective  actions  by  milk produc-
ers,  processors, distributors,  and  consumers must  be  achieved.   Such
acceptance  and participation  will  tend  to   avoid  unnecessary rejec-
tion  of  acceptable fresh  milk supplies  by  the  public.

  The  specific  protective  actions   considered in  selecting  the  Pro-
tective  Action  Guide  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 prac-
  tices.

  Preference  for the  second  action may depend upon  the practica-
bility  of diverting the  affected  milk to  the production  of  dairy
products which may be  stored  for  several  weeks  before use.   This
does not influence  the effectiveness of the  action  in averting  a
dose from  iodine-131.   In a  sufficiently  severe  situation in which  a
more desirable  alternative did not  exist,   it  might be  appropriate  to
substitute  unaffected  milk for  current   use  with  no  utilization  of
the  affected  milk.

  The  projected future  intake  at  any  time  after  the maximum concen-
tration  has  been reached  is  approximately  seven  times the  estimated
daily intake  at that  time,  provided that  additional  iodine-131 is
not  being  deposited  on the  pasture.    If  the concentration  of  iodine-
131  in  milk has passed  its maximum value  and is  decreasing  by half
every  five  days,  the relationship  between  the  daily  rate  of  intake
at any  time  and  the  total  projected subsequent  intake  is  indicated
in columns  1 and  2  of Table I.

  Using  the  projected  total  intake,  a  projected dose  for  children
approximately one year  of age may be  calculated by assuming that 30
percent of  the ingested iodine  is  retained  in a 2  gram thyroid, and
by selecting  an estimated  value  of 1 liter  as the daily  consumption
of milk.   The relationship  between the total  intake  of iodine-131
and  the  projected  dose  is  indicated in  columns  2  and 3 of Table I.

  A  total  intake of iodine-131 of  600  nanocuries  would  result  in  a
dose of about  10  rads to a 2  gram thyroid.   In a single  event,  about
20 to  25 percent  of the  total intake may  result from the use  of that
portion of the  milk produced before the maximum concentration was
reached.  Under  these conditions,   and   if no protective action  were
taken,  an estimated maximum concentration in milk of 60 to  70  nano-
curies  per  liter would result  in a total  intake of  about  600 nano-
curies  and  a dose to the thyroid  of 10 rads.
                                  -  14 -

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                             TABLE I

       INTAKE OF IODINE-13IFOR DIFFERENT RADIATION DOSES
        TO A 2 GRAM THYROID FOLLOWING A SINGLE DEPOSITION
                   OF IODINE-131 ON PASTURAGE "
Estimated intake
of iodine- 131 in
one day at the
time of the max-
imum concentra-
tion or later
(nanocuries)
4.2
8.4
25
42
84
250
1250
2500

Projected intake
of iodine- 131
(based on column 1)
(nanocuries)
29
58
175
290
580
1750
8750
17500

Projected
thyroid dose
(based on column 2)
(rads)
.5
1
3
5
10
30
150
300
This  table  is  illustrative  and  does not  indicate  specific  intake
 values  at which protective  actions  should  be  initiated  or  discon-
 tinued.
                             -  15  -

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   The  effectiveness  of a  protective  action,  if  taken,  will be  highly
dependent upon the  promptness  with which it  is  initiated.   If  milk
from an  unaffected  area  is  to be  substituted  for  the contaminated
milk,  delay of  initiation  of the action by as  much as  10 days  after
the  deposition occurs  will  reduce  the  total  exposure  that can  be
avoided to  substantially less  than  half  of the  total  exposure  that
would  result  if no action were taken.   In the  case  of substitution
of stored  feed for pasturage,  the  same  delay  would reduce  even  fur-
ther  the  benefit  of  the  action because  of the  time required  for  the
iodine-131 in the  cow  and,  consequently,  the concentration  in  the
milk  to  decrease   to negligible  levels.

   The  exposure  avoided will also depend upon the  length  of time the
protective  action  is  maintained.    In  the case  of  substitution  of un-
affected milk  for   contaminated milk,  the reduction  in the  dose  that
would result  from  subsequent  intake would be  about 90  percent  if the
action were  maintained  for  15  to 20  days,  and about  99 percent  if
maintained for 30  to 40  days.  In the  case  of substitution  of stored
feed  for  pasturage,  reductions would  be  less.


Summary

   Following release  of fresh  fission products  iodine-131  is  the
radionuclide  considered most  likely to  reach  concentrations  in  foods
which warrant  protective  action  to reduce  the projected  dose.   The
important  mode  of transmission to  humans is through the consumption
of fresh   fluid milk.

   Iodine-131 can  appear in  milk  within  a few hours after  its depo-
sition on  pasture.   The  concentration  in milk may reach  a  maximum in
two to  four  days,  after which the concentration  diminishes by  half
about every five days.

   Removal of dairy  cattle  from contaminated  pastures or  the  diver-
sion  of contaminated milk to  processed dairy  products  are recom-
mended as protective  actions to reduce  human  exposure from iodine-
131.

   The Federal Radiation  Council has  developed  the concept  of the
Protective  Action Guide.  The  PAG is  defined as  the  projected  ab-
sorbed  dose  to  individuals  in the  general population  which  warrants
protective  action  following  a  contaminating  event.

   A projected dose of 30  rads to  the  thyroid of  individuals  in the
general population  has been  recommended as the Protective Action
Guide  for iodine-131.  As  an  operational technique  it is  assumed
that  this   condition will be  met  effectively  if  the average  projected
dose  to a suitable  sample  of  the population does  not  exceed  10 rads.
                                 -  16  -
                                           1 U.S. GOVERNMENT PRINTING OFFICE: 1964 O - 752-501 PO 11

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