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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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.
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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
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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
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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
i'i i
MAN
atmosphere
pasturage
animals
fresh fluid milk
processed
miik products
feed crops
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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
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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
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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.
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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.
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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).
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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
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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
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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
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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,
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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.
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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
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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
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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.
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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
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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.
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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:
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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.
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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.
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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
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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
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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
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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
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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
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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U.S. GOVERNMENT PRINTING OFFICE 1965 O—773-982
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