United States
Environmental Protection
Agency
Air and Radiation
(ANR-459)
EPA 520/1-90-015
June 1990
Transuranium Elements
Protection
-------
TRANSURANIUM ELEMENTS
VOLUME I
ELEMENTS OF RADIATION PROTECTION
BY
GORDON BURLEY
OFFICE OF RADIATION PROGRAMS
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
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PREFACE
This document was developed over a number of years as the
technical basis for guidance or criteria for addressing the problem
of environmental contamination by plutonium and other transuranium
elements. It is now published independent of such guidance or
criteria, and is intended to serve as a useful compendium of
information relevant to the making of informed decisions on how to
deal with such contamination. It reflects the author's personal
views and is not intended to provide a comprehensive summary of the
subject.
Volume I presents an overview of selected information on the
chemical and physical properties of the transuranium elements, the
biological effects and risks of exposure, the major environmental
transport mechanisms, and the contamination in the environs of a
number of sites in the United States. Several of these chapters
were prepared during the 1970's and have not been extensively
revised, because relatively little new and different information
has been published since that time.
Volume II presents the general background relevant to
developing criteria for site-specific remedial action options.
The information is intended to provide an overall perspective on
the considerations necessary for the decision-making process and
should not be viewed as giving specific instructions on how to
address a specific situation of environmental contamination.
The information should be used in an advisory context only and
not for purposes of implementation of regulations.
iii
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CONTENTS
CHAPTER
1 INTRODUCTION
2 ENVIRONMENTAL CHEMISTRY OF PLUTONIUM
3 DOSE AND RISK TO HEALTH DUE TO INHALATION
AND INGESTION OF TRANSURANIUM NUCLIDES
4 TRANSURANIUM ELEMENTS IN THE ENVIRONMENT
5 ENVIRONMENTAL TRANSPORT AND EXPOSURE PATHWAYS
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1. INTRODUCTION
The chemical elements with atomic number greater than
uranium (atomic number 92) are known as transuranium elements.
They are entirely man-made or present in nature in only
infinitesimally small amounts. The most important of these
elements is plutonium. Other transuranium elements of importance
include neptunium, americium, curium, and californium.
The transuranium elements, starting with neptunium (atomic
number 93) are members of the actinide series, which also
includes the naturally occurring radioactive elements actinium,
thorium, protactinium and uranium, and consists of elements with
properties that stem from partial vacancies in the 5f electron
shell (Fig 1-1). The chemical behavior of the series is somewhat
similar to the lanthanide series which is characterized by a
similar electron structure. However, the shielding of the
5f electrons by outer electrons is less effective than that of
4f electrons; thus the chemical properties of the actinides are
more complicated than those of the lanthanides. Although the
latter exist primarily in the III oxidation state and exhibit
ionic bonding, the actinides (through plutonium) can exist in
multiple oxidation states. Because of their extreme reactivity,
the II and VII oxidation states are not likely to be encountered
in the environment. The oxidation-reduction behavior of the
triad U-Np-Pu is complicated, and multiple oxidation states can
coexist in solution. From the point of view of geochemical
behavior, the actinides can be considered the higher analogue of
the lanthanides.
Plutonium is formed by a nuclear reaction, in which
neutrons captured by uranium-238 atoms cause the formation
of uranium-239, which then decays radioactively to form
plutonium-239.
1-1
-------
FIGURE 1-1
I
to
1
H
3
Li
11
Na
19
K
37
Rb
55
Cs
87
Fr
PERIODIC CHART OP THE ELEMENTS
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
21
Sc
39
Y
57-71
La*
Series
89-103
Act
Series
22
Ti
40
Zr
72
Hf
(104)
23
V
41
Nb
73
Ta
(105)
24
Cr
42
Mo
74
W
(106)
25
Mn
43
Tc
75
Re
(107)
26
Fe
44
Ru
76
Os
(108)
27
Co
45
Rh
77
Ir
28
Ni
46
Pd
78
Pt
29
Cu
47
Ag
79
Au
30
Zn
48
Cd
80
Hg
5
B
13
Al
31
Ga
49
In
81
Tl
6
C
14
Si
32
Ge
50
Sn
82
Pb
7
N
15
P
33
As
51
Sb
83
&
8
0
16
S
34
Se
52
Te
84
Po
9
F
17
Cl
35
Br
53
1
85
At
2
He
10
Ne
18
Ar
36
Kr
54
Xe
86
Rn
'Lanthanide
Series
tActinide
Series
-------
These nuclear reactions are represented by the following
equations:
..238 . ^ ..239 ^ „ 239 ^ _ 239
92U + n —-* 92U 23755* 93Np 57355* 94?U
The sequence is initiated by fissioning of a uranium-235 nucleus.
Elements with atomic numbers greater than plutonium are formed by
successive neutron capture reactions. The amounts of the higher
isotopes produced depend on the type of reactor and how it is
operated, but generally do not exceed a small fraction of the
plutonium.
The complex interactions between the various oxidation
states of neptunium and plutonium are partly governed by their
total concentration in solution. When concentrations are
sufficient, disproportionation reactions between oxidation states
are common. However, such concentrations are unlikely
to be found in the environment, and the stable oxidation states
will be a function of the chemical environment, e.g., the
presence of oxidizing or reducing agents and complexing ligands.
Standard oxidation-reduction potentials can be used
to predict the stability field for various plutonium species.
The element plutonium is a silvery-white metal, atomic
number 94 in the actinide series. There are at least
sixteen different isotopes of plutonium, of which the four
most important are: plutonium-238 (half-life, 86.4 years),
plutonium-239 (half-life, 24,390 years), plutonium-240
(half-life, 6580 years), and plutonium-241 (half-life,
13.2 years). Plutonium has a melting point of 640°C and a
boiling point of 3327°C. It oxidizes rapidly on exposure to air
to form plutonium dioxide (PuO2) . Plutonium metal exhibits six
different crystalline forms, each in a well-defined temperature
range, with densities between 16.00 and 19.86 grams per cubic
centimeter.
1-3
-------
At room temperature, the most stable oxide is plutonium
dioxide. Plutonium dioxide is a highly refractory material which
melts at 2200-2400°C and is difficult to dissolve by normal
methods. The behavior of Pu02 particles in environmental and
biological systems is greatly influenced by their size and
temperature of formation.
The chemistry of plutonium is very complex and many
different chemical species often co-exist. Plutonium has four
oxidation or valence states, ranging from III to VI, and forms
stable compounds with all the nonmetallic elements except the
rare gases. In aqueous solutions, Pu(III) is oxidized into
Pu(IV), which is the most stable state. The compounds PuF4/
Pu(IO3)4, Pu(OH)4 and plutonium oxalate are insoluble in water.
The chlorides, nitrates, perchlorates, and sulfates are soluble
in water. The most important compounds in processing of
plutonium are PuF4, Pu(N03)4, and Pu02.
Plutonium (IV) ions complex readily with organic and
inorganic compounds. The stability of complexes decreases in
the order Pu(IV) > Pu(III) > Pu(VI) > Pu(V). It is, therefore,
probable that most if not all plutonium in environmental and
biological systems is in the Pu(IV) state. Plutonium ions in
solution rapidly hydrolyse and form polymers. The tendency to
hydrolyse decreases in the order Pu(IV) > Pu(VI) > Pu(III) >
Pu(V). Hydrolysis of Pu(IV) can result in the formation of
relatively insoluble polymers, a process which is only slowly
reversible.
In biological systems, ionic plutonium can be expected to
undergo three kinds of reaction:
o Hydrolysis to yield colloidal or polymeric species
o Complexing by proteins and other macromolecules
o Complexing (chelating) with cell components of small
molecular weight (such as citrate or amino acids)
1-4
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The fissionable property of plutonium makes it an important
source of nuclear energy. When a neutron is absorbed by the
plutonium nucleus, it splits (fissions) to form two atoms of
about half the atomic number of plutonium and releases an
enormous amount of energy in the form of heat. This energy is
equivalent to the difference in mass of the reactants and the
products of the reaction, and is given by Einstein's mass-energy
equation
E = me2
The nuclear energy released from one pound of plutonium is
equivalent to the thermal energy from burning of 3,000,000 pounds
of coal.
The formation-decay scheme for the most important
transuranium isotopes is shown in Fig 1-2. With the exception of
Pu-241, the nuclides are all alpha-emitters and most of them
undergo spontaneous fission. Particle emissions are usually
accompanied by X-ray and gamma-ray emissions of varying energies,
which can be utilized for the detection of transuranium nuclides
in a wide range of circumstances.
The transuranium elements are formed in nuclear power
reactors. The amount of radioactivity and the mass of these
radionuclides present in spent fuel from a light-water reactor
are shown in Table 1-1. The total quantities of the more
significant transuranium elements generated by the end of 1978
were estimated as: neptunium - 4.5 tons; plutonium - 77 tons;
americium - 1 ton; and curium - 260 kg. A projection of total
plutonium inventories is shown in Figure 1-3. Reliable
projections are difficult because of the present uncertain status
of the nuclear power industry, but it has been estimated that
more than 2400 tons of plutonium would be produced by the
commercial industry by the year 2000. Additional amounts are
produced by specially operated reactors for nuclear weapons
production.
1-5
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CTl
> Am-244
Pu-236
A ~
Np-236 > Np-237 > Np-238 > Np-239
— > Pu-240 ...... > Pu-241
Pu-238 > Pu-239 —
...... > Pu-242 ...... > Pu-243
A
E
U-234 > L-235 > U-236 > U-237 > U-238 > U-239
FIGURE 1-2
FORMATION-DECAY SCHEME FOR MAJOR TRANSURANIUM ELEMENTS
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TABLE 1-1
RADIOACTIVITY AND MASS OF IMPORTANT TRANSURANIUM ELEMENTS
IN LWR FUELS AT DISCHARGE FROM A REACTOR
Curies Grams/Tonne
Np-237 3.04 E 01 4.32 E 02
Np-239 2.21 E 07 9.51 E 01
Pu-238 2.19 E 03 1.28 E 02
Pu-239 3.07 E 02 4.94 E 03
Pu-240 5.26 E 02 2.31 E 03
Pu-241 1.26 E 05 1.22 E 03
Pu-242 1.78 E 00 4.60 E 02
Am-241 1.02E02 2.98 E 01
Am-243 1.71 E 01 8.55 E 01
Cm-242 3.87 E 04 1.17 E 01
Cm-244 1.53 £03 1.89 E 01
1-7
-------
I
00
00
03
•o
c
<0
W
o
H
e
••-I
c
o
u
3
200 -
o,
^ 100
o
V)
u
ex
o
u
O
M
1975
1980
1985
1990
PROJECTED CUMULATIVE U.S. NUCLEAR POWER INDUSTRY PRODUCTION
FIGURE 1-3
-------
Plutonium-239 is the most common plutonium isotope. A light
water reactor contains about 600 kilograms; the liquid metal fast
breeder reactor proposed for commercial operation, would contain
about 3000 kilograms. Several tens of tons of plutonium-239 have
been produced for weapons purposes. Reactor-grade plutonium is
roughly 7% plutonium-239 and 20% plutonium-240, whereas weapons-
grade plutonium is roughly 93% and 7%, respectively.
Plutonium-238 is very useful as an energy source for remote
or isolated power supplies, such as in satellites or for cardiac
pacemakers. About 40 kilograms of plutonium-238 have already
been specially produced for such purposes. It is not a
significant component of normal nuclear fuel.
Present levels of the transuranium elements in the
environment have resulted from several sources - regional and
worldwide fallout from the testing of nuclear weapons in the
atmosphere, accidents involving military and related operations,
and local releases from nuclear facilities. The major portion of
the transuranium elements in the environment is the result of
surface and atmospheric nuclear weapons tests during the period
1945-1963. Atmospheric tests injected radioactivity into the
stratosphere which has since then been slowly deposited more or
less uniformly over the lands and oceans of the earth. An
estimated 4.2 tons of Pu-239-240 (about 320 kilocuries, 60% of
which is Pu-239) have been globally dispersed as the result of
atmospheric testing of nuclear weapons mainly before 1963, and
another 110,000 curies of Pu-239-240 have been deposited locally
around the sites of nuclear weapons testing. About 120,000
curies of Am-241, which were produced in nuclear weapons fallout
debris, account for an additional alpha activity equivalent to
about 1/4 of that from the alpha-emitting plutonium isotopes.
A beta-emitting plutonium isotope, Pu-241, will roughly double
the amount of Am-241 originally produced during testing. As a
result of these earlier weapons tests, the existing level of
1-9
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transuranium element contamination in soils of the United States
is about 0.002 uCi/m2 (Fig 1-4). More recent weapon tests have
not added significant amounts to this level.
The accumulated deposition of globally dispersed plutonium
produced from early testing is almost complete. The annual
plutonium deposition rate measured in the New York area shows
that of the 0.3 MCi of Pu-239 globally dispersed by nuclear
weapons testing through 1962, about 90% of it had returned to the
earth by 1965. Of the 320 kCi of Pu-239-240 globally deposited
up to the end of 1973, 250 kCi were in the northern hemisphere
and 70 kCi in the southern hemisphere, in agreement with the
distribution of nuclear explosions.
It is useful to compare the environmental levels of
plutonium from fallout with the quantities of natural alpha
emitters present in the environment. For example, it has been
estimated that the continental U.S.A. contains about 4.4 MCi of
natural alpha emitters in the upper 2 cm layer of soil. Of this
amount, 1.6 MCi are alpha-emitting radionuclides of uranium and
thorium. Thus, the amount of alpha activity from plutonium
radionuclides in the upper 2cm of soil (0.016 MCi) is about 1% of
that from naturally occurring actinide radioactivity and 0.36% of
the total natural alpha radioactivity.
In contrast to global fallout, local contamination is
generally associated with areas close to sites of nuclear weapons
explosions and with areas exposed to low-level releases from the
nuclear fuel cycle or activities related to the production of
nuclear weapons. The local fallout is deposited onto the soil
surface soon after release and enters into the soil weathering
processes immediately.
Areas where there is substantial localized contamination
above the general background level are well documented and
extensive environmental analyses have been carried out at all
1-10
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TABLE 1-2
INVENTORY OF PLUTONIUM FOR SELECTED SITES IN THE UNITED STATES
LOCATION
APPROX INVENTORY
REMARKS
U.S. (Fallout)
Nevada Test Site
(near Las Vegas, NV)
Rocky Flats Plant
(near Denver, CO)
Mound Laboratory
(Miamisburg, OH)
Savannah River Plant
(SW part of SC)
Los Alamos Lab
(NW of Santa Fe, NM)
Hanford Site
(central WA)
Oak Ridge Laboratory
(east TN near Knoxville)
Trinity Site
(near Alamogordo, NM)
20,000 Ci
>155 Ci
8-10 Ci
5-6 Ci
3-5 Ci
1-2 Ci
45 Ci
Worldwide Pu-238= 17,000 Ci
Pu-239=440,000 Ci
US. average=1.5 mCl/km>
Nuclear Test Site
Surface and Subsurface Tests
Weapons Fabrication Plant
(limited cleanup in progress)
Pu-238 in sediments in canaJs
Pu and higher isotopes production
Weapons Development
(high levels in remote canyons)
Pu Production—Research Facility
(high levels in trenches on site)
Research & Development Facility
Site of first atomic bomb test
-------
FIGURE 1-4
CUMULATIVE DEPOSIT OF Pu239 IN mCi PER km2
i
M
N)
200 400 600 800 1000
of
0.9
-------
these sites. Areas of highest contamination are, for the most
part, on Federally owned property and therefore are under the
direct control of the Federal government and access to these may
be restricted. Table 1-2 shows estimates of the amount of
Plutonium in the environment at several known United States
locations.
Plutonium and other transuranium elements can move through
the environment by a variety of transport mechanisms and
pathways. These are determined by the chemical and physical form
of the deposited material, the characteristics of the surface,
local land use patterns, and other factors such as wind or
rainfall. Principal environmental pathways to humans are shown
in Fig. 1-5.
Transuranium elements released to the environment may exist
as discrete particles or they may become attached to other
materials. The principal modes of transport of these elements
from a source to man are by direct airborne movement from the
source or by resuspension of previously deposited small particles
by the action of wind or other disturbance. Resuspension is a
complex phenomenon affected by a number of factors, including the
characteristics of the surface, type of vegetative cover,
meteorological conditions, and age of the deposit. In general,
resuspension will be relatively high immediately after initial
deposition, gradually decrease with time, and approach a long-
term constant within about one year after deposition.
Plutonium suspended by wind can be redeposited on soil or
intercepted by biological surfaces. Redeposition of plutonium on
soils can lead to major changes in the distribution of the
element within an ecosystem. Wind redistributes plutonium in
soil, as inferred from sampling of contaminated sites. Field
studies, primarily in arid regions, imply that wind transport of
soil is highly seasonal and is relatively more important in dry,
sparsely vegetated areas than in heavily vegetated areas. Soil
1-13
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PRINCIPAL PATHWAYS OF THE TRANSURANIUM ELEMENTS
THROUGH THE ENVIRONMENT TO MAN
FIGURE 1-5
1-14
-------
particle sizes and plutonium concentrations in soil affect the
importance of wind as a plutonium transport vector. Plutonium
concentrations of various soil size fractions can differ by
several orders of magnitude and, depending on source
characteristics, are generally highest in the smaller size
fractions.
Plutonium in air is deposited on vegetation or on soil,
contaminating plants by direct deposition or by root uptake.
There is no significant evidence of bioaccumulation through
succeeding trophic levels since metabolic discrimination usually
acts against the transfer of plutonium. Soil chemical reactions
influence the behavior of the various forms of plutonium.
Plutonium in soil may exist in ionic form (positive or negative)
or as a neutral compound depending on the pH and redox potential
(Eh), of the respective soil type. The major factor governing
plutonium availability will be the solubility of the compound.
A number of organic and inorganic substances form complexes with
plutonium, thereby increasing its solubility.
Downward transport of plutonium through the soil will occur
via leaching of soluble plutonium, by transport of soluble oxide
particles and by transport of soil particles onto which plutonium
is adsorbed. The latter two processes are active mainly in the
top soil and leaching will usually terminate at lower depths.
Transuranium elements in terrestrial environments can enter
plants by foliar absorption and root uptake. The route of entry
into plants will depend on the nature of the source; climatic
conditions affecting deposition, retention, and chemistry of
particles on leaf surfaces; the foliar surface area exposed; and
soil conditions affecting resuspension and solubility.
Plants remove very little plutonium from soil.
Concentrations in plants generally range from 0.001 to 0.00001
of the amount in soil. Part of the large reported variation in
1-15
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plant uptake is related to the wide variety of experimental and
field conditions encountered. Plutonium concentrations in food
are generally low, and a very low transfer across the
gastrointestinal tract may make the ingestion pathway in man
relatively unimportant.
There is little evidence to suggest that differing sources
of transuranic elements affect their chemical properties when the
elements are moderately well dispersed in aquatic systems.
Transuranic elements are soluble, to a limited extent, in both
freshwater and marine systems and are therefore available for
transfer across biological membranes.
Transport of plutonium and other transuranium elements
through the food chain and subsequent ingestion is generally of
lesser importance than the air pathway. Transuranium elements
may be deposited on plant surfaces or assimilated through the
plant root system. The uptake by plants is relatively small and
most animals, including humans, have a high discrimination factor
against transfer of these elements into body tissues. The
solubility of plutonium in water is very low and nearly all
plutonium released into lakes and streams is ultimately deposited
and sorbed onto sediments. Other possible routes of entry into
humans include direct ingestion of contaminated soils and
subcutaneous contamination of wounds.
Inhalation is generally the principal pathway to man and
arises from radioactive materials directly injected into the air
and from resuspension of previously deposited materials.
Ingestion is a less significant hazard, because of the cumulative
dilution in transfer from soils or water to food; ingested
plutonium is very poorly absorbed from the gastrointestinal
tract. Contamination of wounds is not a likely occurrence.
Inhaled particles are initially deposited in various regions
of the respiratory tract, where they remain until either cleared
1-16
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or translocated to other body organs. Much of the material
deposited in the lung is cleared within a few days, but some of
the smaller particles which diffuse into the pulmonary regions of
the lung are removed much more slowly and have a biological half-
life of a year or more (rig 1-6). This may lead to an increase
in the risk of lung cancer in exposed individuals, but this has
not been conclusively demonstrated. Inhaled transuranium
elements may also transfer and be retained in other body organs,
and cause cancers of the bone and liver. For the less soluble
transuranium compounds, such as plutonium oxide, this will
contribute only marginally to the total risk for the inhalation
pathway.
Potential health effects caused by the transuranium elements
are a function of several biological and physical parameters
including the biological retention time in tissue, the type of
radioactive emission, and the half-life of the nuclide. For the
more important transuranium nuclides, such as Pu-238 or Pu-239,
biological retention times are very long and radioactive decay
occurs at such a slow rate that uptake of these materials in the
human body will result in prolonged exposure of body organs.
Many of the transuranium nuclides decay by emission of an alpha
particle (ionized helium atom), in a manner similar to radium and
other naturally occurring alpha emitting nuclides. Alpha
particles are highly ionizing and damaging, but their penetration
in tissue is very small (about 40 urn). Thus, biological damage
is limited to tissue in the immediate vicinity of the radioactive
material, and a potential health hazard from transuranium
elements in the environment can only result when these materials
are inhaled or ingested into the body.
Ingestion of transuranium elements generally represents a
smaller environmental risk to humans than inhalation. A
relatively small fraction of any ingested transuranium element
may be transferred to the bloodstream from the digestive tract
and deposited in bone, liver, gonadal tissue, and other organs.
1-17
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ARE THE AMOUNTS DEPOSfTEO IN THE NASOPHARYNGEAL, TRACHEOBRONCHIAL, AND PULMONARY
LUNU HtSPECTIVELY. THE LETTERS (a) THROUGH (j) INDICATE THE PROCESSES WHICH TRANSLOCATE
MATERIAL FROM ONE COMPARTMENT TO ANOTHER
FIGURE 1-6
1-18
-------
In most cases, less than one part in ten thousand of the ingested
material is absorbed by the body, with the remainder excreted.
The cancer risk to individuals as a result of ingestion of
transuranium elements is mainly due to potential bone and liver
cancers.
A potential risk of genetic damage to the progeny of exposed
individuals exists because of possible accumulation of
transuranium elements in gonadal tissues. At the dose rates for
other organs provided by the interim guidance, this risk is very
small compared to the natural incidence of genetic damage.
1-19
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2. ENVIRONMENTAL CHEMISTRY OF PLUTONIUM
2.1 GENERAL PROPERTIES
Plutonium is a silvery white metal which readily oxidizes
in air. The oxidation rate of plutonium depends upon the
temperature and the relative humidity of the air and increases
as the relative humidity increases. In going from 0% to 50%
relative humidity, the oxidation rate will increase by several
orders of magnitude.
Plutonium is capable of forming many compounds with oxygen,
including the simple binary oxides, the peroxide, the hydroxide
(or hydrated oxides), and a series of ternary and quaternary
oxides. Plutonium dioxide (Pu02) is the most stable of the
oxides and is formed under most conditions, especially when
plutonium metal is ignited in air. Calcined Pu02 is unreactive
under normal environmental conditions, is extremely insoluble
in water, and if ingested would be highly insoluble in body
fluids. Because of its desirable properties such as high
melting point (2240°C) , irradiation stability, chemical stability
(Fzsa = -253 kcal) , compatibility with metals, and low vapor
pressure, plutonium dioxide has found widespread use as a fuel
either alone or in combination with other compounds. For
example, plutonium-238 is used as a heat source for
thermoelectric generators employed in devices such as heart
pacemakers and communication satellites. When used as a heat
source, the 238PuO2 is fashioned into pellet form and then
encapsulated in a refractory metal. Other solid forms of
plutonium are possible but are of little concern from the
standpoint of being likely environmental contaminants.
2-1
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2.2 CHEMICAL BEHAVIOR IN AQUEOUS ENVIRONMENTS
Plutonium dioxide is a highly refractory material when
prepared at high temperatures and reacts slowly with aqueous
solutions. The rate at which dissolution proceeds depends on
such factors as the pH and temperature of the solution and the
presence of oxidizing, reducing, and complexing agents. As the
dioxide dissolves, plutonium ions are formed which can undergo
complexation and/or hydrolysis with other species present in
the aqueous phase. Hydrolysis can be viewed as a form of
complexation in which the hydroxyl ion is the ligand.
The most stable hydrolysis product of plutonium in the pH range
generally encountered in natural waters is Pu(OH)4 (Andelman,
1970). This hydroxide has been reported (Taube, 1964) to have
a solubility product constant of 7X10"56 which is indicative of
a high degree of insolubility.
Potentially four oxidation states of plutonium (III, IV,
V, VI) can exist in solution in equilibrium with Pu(OH)4.
The predominant soluble form of plutonium in a soil/water
environment will be determined by the oxidizing or reducing
capability of the solution. The availability of plutonium for
uptake by plants and other biological systems will vary
depending upon the valence state (Adams, 1975 and Price, 1973).
Generally, the availability to plants follows the valence order
V > VI = III > IV.
Most efforts to ascertain the valence of soluble plutonium
have been theoretical because of the difficulty encountered in
determining valence states at typically low environmental
concentrations. One means of predicting the predominant
plutonium species under specified conditions is the use of
stability diagrams (Polzer, 1971). These diagrams examine the
phase relationships between possible plutonium species as a
function of the redox potential of the solution. Their use is
limited, however, to systems which are in equilibrium and for
2-2
-------
which the concentration of additional ions is insignificant.
This approach only considers the thermodynamics of the system and
not the kinetics, thereby indicating which reactions are possible
but not how fast they will occur. Within these limitations,
stability diagrams can be useful in evaluating the observed
environmental behavior of plutonium.
From stability diagrams, Polzer (1971) and Andelman (1970)
both concluded that, when the concentration of complexing anions
is insignificant, the predominant form of soluble plutonium will
be Pu+3. However, natural environments contain complex materials
from the decomposition of plant and animal matter which may
affect the chemical equilibrium of the soil/water environment.
Bondietti (1975) stated that the presence of a complexing agent
such as EDTA can increase the susceptibility of Pu+3 to oxidation
to Pu+4 due to the activity-lowering effect that complexation
produces. His studies have attempted to ascertain the probable
valence state of plutonium in the presence of various organic
substance commonly encountered in the environment. He concluded
that the Pu(IV) valence state would be the most important and
that higher oxidation states would be reduced to the IV state
through the action of phenolic materials like humic substances
and reducing sugars. Further valence reduction to Pu(III),
although possible, was not felt to be likely under the redox
conditions normally encountered. Bondietti observed that only a
small fraction (<20% of the plutonium in a soil contaminated 30
years previously) was desorbable and, therefore, available for
uptake by biological systems. The majority of the plutonium was
strongly associated with the solid phase and, as a result,
leaching losses were concluded to be insignificant compared to
the physical movement of contaminated soil particles.
2.3 FRESHWATER ENVIRONMENT
The above observation is consistent with studies of
plutonium released into aquatic systems. For example, Wahlgren
2-3
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(1973) has shown that 95% of the plutonium added to Lake Michigan
as a result of atmospheric fallout from weapons testing is
rapidly removed from the water column to the sediments. Further
studies of Lake Michigan by Alberts (1974) have demonstrated that
plutonium is strongly associated with the sediments and is not
easily solubilized under aerobic conditions. Stagnant, polluted
systems however could have a greater solubilizing effect due to
high concentrations of complexing organic material.
Studies of the fate of plutonium in flowing water systems
have been conducted in the Great Miami River (Ohio) where
discharges of plutonium form Mound Laboratory have occurred.
These studies (Bartelt, 1975 and Muller, 1977) have attempted
to elucidate the mobility of plutonium in aquatic ecosystems.
Consistent with the Lake Michigan studies, plutonium was found
associated with the sediments and at least 90% of the radio-
activity which moves down the river does so as a result of the
resuspension/entrainment of bottom sediments.
The predominant chemical form of soluble plutonium is,
however, still open to question. For example, the Lake Michigan
study indicates that most of the soluble fraction is in an
anionic form with a particle diameter of less than 30 A. This
may indicate sorption of plutonium to colloidal silica and other
negatively charged colloidal minerals. There has also been
speculation that the VI valence state can be an important
environmental species. The VI valence state can be generated by
the disproportionation of PuO2 during dissolution (Cleveland,
1970):
3 Pu+4 + 2 H20 > 2 Pu+3 -l- PuO*2 + 4 H+
Although simple stability diagrams do not predict the VI
valence to be important, the presence in natural waters of
complexing agents (e.g., carbonates) can stabilize this valence
state (Andelman, 1970). One such reaction which might associate
2-4
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plutonium in anionic form is:
PuO*2 + C0~2 > Pu02(C03)~2
Even though the chemical behavior of plutonium in fresh
water is not completely understood, the many studies to date have
consistently demonstrated that plutonium will quickly associate
with the solid phase and, under the redox conditions normally
encountered in the environment, solubilization will be minimal.
In general, the plutonium activity committed to fresh water will
be bound there in a form which is relatively insoluble in
biological systems.
2.4 MARINE ENVIRONMENT
Because of its long radiological half-life, it must be
assumed that some of the plutonium in any freshwater body will
eventually be carried to an ocean or sea. Knowledge of the
behavior of this radionuclide in a marine environment is
therefore important when evaluating the long term impact of any
release to the environment.
In a study conducted off the coast of Massachusetts by Bowen
et al., the bioturbation and sedimentation rate effects on
plutonium sediment profiles were examined (Bowen, 1975).
Analyses of cores taken prior to 1964 and from 1968 to early
1975 showed a progressive migration of Pu from deeper sediment
layers to areas nearer the surface. It appears that primary
amines emanate from the deeper anoxic or nearly anoxic sediment
layers. These amines seem to be involved in a mechanism for
releasing Pu from the sediments, but when they reach the
oxygenated upper sediment layers what appears to be
microbiological consumption immobilizes the Pu again.
In this study the remobilization of Pu is attributed to a
reducing mechanism, as it was in other studies (Edgington, 1975
and Alberts, 1975). This would indicate a redistribution of Pu
2-5
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in the sediments without a release to the water column. The
distribution of Pu in sediment samples with respect to particle
size was noted as being uniform. No preference for the finer
fractions was observed and concentrations of these nuclides per
gram of sediment varied only by a factor of two from the finest
to the coarsest fractions measured.
The activities of bottom feeders can also have an effect on
sediment Pu profiles. These fish tend to enhance the mixing of
the sediments and the water column. This will either increase
the deposition rate of the Pu from the water column to the
sediments or, in times of relatively low fallout rates, it can
enhance possible resolubilization of the sediment-bound Pu.
However, extremely low and variable Pu levels in the water itself
seem to indicate that the Pu inventory is mostly removed to the
sediment bed.
In another study, the fate of plutonium released to the
Irish Sea over approximately 20 years has been examined. This
study (Hetherington, 1975) has noted that >96% of the plutonium
released was removed to the sediments in a relatively short time
period. The mechanism responsible for carrying the Pu to the
sediment bed does not appear to be biological nor does it seem to
be a simple diffusion mechanism. Sorption to particles in the
water column and subsequent deposition in the sediment bed
appears to be the primary mechanism for removing Pu from the
water. Once these sediments are consolidated, there appears to
be no detectable remobilization of the plutonium.
Similarly, a study of Bombay Harbor Bay (Pillai, 1975)
observed that 99% of the released Pu was localized in the
sediments around the discharge point, but areas of higher
activity were found in locations with particularly high siltation
rates. The Pu-containing sediments were examined to determine
the conditions necessary to release the Pu from the sediment.
Violent agitation for 8 hours did not produce any detectable
2-6
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release of Pu to seawater. Also, extraction tests using
hydrochloric acid at 80°C resulted in no release of
Pu to the solution.
As with freshwater systems, the marine studies have shown
that over 90% of the Pu entering either as fallout or in the form
of liquid effluents was found trapped in the sediments. This
behavior is mostly attributed to the bonding of Pu to the organic
material associated with sediment particles. A very small
fraction of the Pu entering a body of water remains unfilterable.
Most of this is assumed to be Pu in some colloidal form.
Even though Pu is strongly bound to the sediment bed in most
water bodies it can still move with water currents and other
physical actions. The effects of biota on Pu behavior are seen
mostly in the sediments. Both microorganisms and more complex
species can alter the depth profiles. Primary amines released
deep in the sediment by microbes can solubilize the plutonium in
anaerobic regions and carry it towards the surface. Microbes in
the interface regions, along with chemical reactions, bind the Pu
to the sediment again. Larger biota can physically alter
profiles by digging into the bed and allowing the overlying water
to penetrate. The most significant role of biota is the
concentration of Pu in their systems. Seaweeds, with
concentration factors of up to 1000, are by far the most notable.
Shellfish, even though they have a lower concentration factor,
are important because they may be a direct food source.
2.5 CHEMICAL BEHAVIOR IN SOILS
Similar to its aqueous behavior, the interaction of
plutonium with soils is not completely understood and has been
explained to date only qualitatively. This is in part due to the
difficulty in characterizing plutonium at very low environmental
concentrations. Oftentimes the predominant valence state of
2-7
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Plutonium cannot be established - much less its chemical form.
However, several studies conducted at sites where plutonium has
been in the environment for as long as 30 years have yielded some
knowledge of its behavior. One such series has been conducted by
Tamura at four sites having different ecosystems. The selected
sites were: the Nevada Test Site (Nevada), Oak Ridge National
Laboratory (Tennessee), Mound Laboratory (Ohio),and Rocky Flats
(Colorado). The source terms were different at the four sites:
at NTS the source was a "safety shot" series which dispersed
plutonium as the oxide, at ORNL an earthen dike gave way
releasing material from a holdup pond, at Mound Laboratory an
acid solution of plutonium leaked from a waste transfer line, and
at Rocky Flats cutting oil contaminated with plutonium leaked
from storage drums. The association of plutonium with the soils
of these various sites will be affected by factors associated
with the source term and the prevailing local environmental
conditions.
The ease with which plutonium is extracted from the solid
phase can indicate its availability for biological uptake.
Studies by Tamura (1976) have shown low extraction (10-15%) from
soils of the Nevada Test Site and Rocky Flats, while ORNL and
Mound Laboratory soils showed much higher extraction (60-85%).
These results are evidence of the existence of different chemical
species at the various sites. Experiments by other investigators
have provided further evidence of such differences.
Specifically, autoradiographic analyses of soil samples from
Rocky Flats (Hayden 1974; Nathans 1974; Sehmel 1975) have shown
the presence of discrete particles of plutonium (probably the
oxide) attached to larger soil particles, while the same
technique indicated a general dispersion of plutonium in the soil
of Mound Laboratory (Rodgers 1975) .
In order for plutonium to be incorporated into the soil
matrix, it must be available in ionic form and capable of
displacing some other cation from the matrix. This could explain
2-8
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the difference in the extraction and autoradiography studies at
the various sites. At NTS and Rocky Flats the plutonium was
originally released as metal or oxide particles which require
aqueous dissolution to generate plutonium ions. In contrast,
the Mound release was as an acid solution already containing
plutonium in ionic form which probably reacted quickly with the
solid phase and was incorporated into the soil matrix. The Rocky
Flats and NTS soils, on the other hand, could contain hydrated or
polymerized plutonium oxide attached to soil particles via
adhesion. Once polymerized, plutonium is slowly depolymerized by
strong acids (Cleveland 1970) and this could account for the low
extractability of the Rocky Flats and NTS samples.
Rodgers (1975) in his studies around Mound Laboratory
proposed a mechanism for the bonding of plutonium to soils and
the following has been excerpted from his review:
Proposed bonding mechanisms: Basically, soils are made up of silicate materials
and other minerals. Quartz sand has a continuous silicate structure where each
silicon atom is bound to two silicons. This continuous structure is interrupted at
the surface and in natural systems (where water is abundant), the surface is
composed of unsaturated oxygen bonds. That is, each surface oxygen is bound to
only one silicon atom. The remaining bond is usually occupied by other cationic
species. Clays are more complicated, but are also based on the continuous silicate
structure except that some silicon atoms have been replaced by Mg2*, Al3*, Fe3*,
and Fe2* (mostly Al3+). These substituted atoms in the silicate structure result
in variations in long range crystal structure. Rather than forming three-
dimensional silicate networks as in quartz, many clays form two-dimensional sheets
which cleave easily to form plates. The surface of these layered sheets that make
up the clay particles also exhibit unsaturated oxygen bonds. This, in part,
accounts for the higher sorption capacity in clays (relative to the same size
silicate particle) since sorption can take place between the silicate layers within
the clay particles.
The unsaturated oxygen bonds in natural soils and clays are occupied by
cations such as H*, K*, Ca , Mg , or other available cations. The bonding
strength order of these cations is:
Pu4*>H+>Al3*>Ba2+>Caa+>Mg2*>NH/>K*>Na*
In order to bond to the silicate, an ion must displace or exchange with the
cation already bonded:
A-Clay + B+ > B-Clay + A*.
The extent of the exchange depends on the relative strength of the bonds and
the relative solution concentrations of the two cations.
Some cations form silicate bonds that are fairly weak (such as Ma* and K*)
and may be only electrostatic while other metal cations may even develop covalent
character.
2 -
-------
Tetravalent plutonium ions are well noted for the formation of strong
bonding (complexing) with oxygenated ligands. The strength of plutoniurn-oxygen
bonds is also'indicated by the acidic character of plutoniura hydroxide forming
hydrous plutonium oxide.
Plutonium ions can compete with hydrogen ions for the bonding sites on the
silicates even when the Pu**/H* concentration ratio is 10"11 or less. The very
large bonding potential of plutonium suggests that sorbed plutonium cannot
be significantly displaced from soil by the concentrations of cations existing in
nature.
Chemicals that complex the plutonium compete with the silicate particles for
the plutonium and tend to reduce the extent of sorption of the plutonium on soil.
For example, the formation of plutonium hydrolytic species PuCOH}3*, Pu(OH)2 +,
Pu(OH)3*. and Pu(OH)4 (as well as "polymeric" forms) tends to reduce
ion exchange sorption. Some of the hydrolytic plutonium "polymeric" forms may
adsorb to the surface of the soil particles and the precipitation of PuOj (H^) may
be nucleated by the colloidal soil particles when plutonium concentrations are
relatively high (greater than ID"6*). Some moderately strong organic complex ing
agents, such as citric acid, can reduce the sorption of plutonium on soil.
2.6 INTERACTION WITH PLANTS
Consideration of the oxidation-reduction potentials of
the valence state couples in the presence of organic material
generally found in soils indicates that Pu(IV) is the
predominant valence state in the environment (Bondietti 1975).
Since the availability to plants generally follows the order
VI > VI = III > IV, a low uptake of plutonium by plants would
be expected. This expectation has been confirmed by the studies
conducted in the laboratory and in the environmental where many
varieties of plants have been grown in contaminated soils.
Several reviews (Bernhardt 1976; Bulman 1976; Mullen 1976; and
Thomas 1976) describe such details as the types of crops grown,
the amount and chemical form of the plutonium used, and the
method by which plutonium was added to the growing medium.
The results of these studies are usually expressed in
terms of a "concentration factor" defined as the ratio of the
plutonium concentration per gram of plant material to the
plutonium concentration per gram of soil. This index indicates
the degree to which plutonium is concentrated or discriminated
against in the soil to plant pathway. Even though a variety of
2 - 10
-------
methods and conditions have been used in these studies, the
concentration factors are generally of the order of 10"* to 10"5.
On occasion some higher values, ranging as high as 10"', have been
reported, but these are usually attributed to external
contamination of the plant surface rather than incorporation into
the plant tissue.
Such small concentration factors tend to support the
conclusion that the terrestrial food chain does not constitute
a significant exposure pathway. However, the observation has
been made that these experiments were all of a short-term nature
and, as such, did not consider the possibility of increases in
concentration factors over time due to a variety of possible
influencing factors. As a result of preliminary investigations,
several mechanisms of increased uptake have been reported
(Cleveland 1976; Bondietti 1975; Romney 1970; Lipton 1976; Price
1973; and Beckert 1975). Included among these are: 1) chelation
by organic constituents in the soil or through the addition of
fertilizers, 2) increased root absorption zone contact as
Plutonium migrates down through the soil, 3) increased
radiocolloid size due to aging, and 4) the long-term action of
microorganisms present in the soil.
Much of the research into these mechanisms is in the early
stages; however, the preliminary data have not demonstrated that
substantial changes will occur under conditions generally
encountered in the environment. It is most likely that, if such
changes take place, that they will occur slowly over the order of
years to decades.
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2.7 REFERENCES
Adams, W.H., Studies of Plutonium. Americium. and Uranium in
Environmental Matrices. Los Alamos Scientific Laboratory, LA-5661
(1975)
Alberts, J.J., Wahlgren, M.A., Reeve, C.A., and Hehn, P.J.,
"Sedimentary "9'240pu Phase Distribution in Lake Michigan
Sediments," in Radiological and Environmental Research Division
Annual Report. Argonne National Laboratory, ANL-75-3 Part III,
p!03 (1974)
Andelman, J.B. and Rozzell, T.C., "Plutonium in the Water
Environment, I. Characteristics of Aqueous Plutonium," in
Radionuclides in the Environment. Advances in Chemistry
Series No. 93, American Chemical Society, Wash., D.C. (1970)
Bartelt, G.E., Wayman, C.W., and Edgington, D.N., "Plutonium
Concentrations in Water and Suspended Sediment from the Miami
River Watershed," in Radiological and Environmental Research
Division Annual Report. Argonne National Laboratory, ANL-75-3
Part III, p72 (1975)
Beckert, W.F. and Au, F.H.F., Plutonium Uptake by a Soil Fungus
and Transport to its Spores. IAEA-SM-199/72, International Atomic
Agency, Vienna (1975)
Bernhardt, D.E. and Eadie, G.G., Parameters for Estimating the
Uptake of Transuranic Elements by Terrestrial Plants. USEPA
Report, ORP-LV-76-2 (1976)
Bondietti, E.A., Reynolds, S.A., and Shanks, M.H., Interaction of
Plutonium with Complexing Substances in Soils and Natural Waters.
IAEA-SM-199/51, International Atomic Energy Agency, Vienna (1975)
Bowen, V.T., Livingston, H.D., and Burke, J.C., Distribution of
Transuranium Nuclides in Sediment and Biota of the North Atlantic
Ocean. IAEA-SM-199/96, International Atomic Energy Agency, Vienna
(1975)
Bulman, R.A., Concentration of Actinides in the Food Chain.
National Radiological Protection Board, URPB-R 44 (1976)
Cleveland, J.M., The Chemistry of Plutonium. Gordon and Breach
Science Publishers, Inc., New York (1970)
Cleveland, J.M. and Rees,, T.F., "Investigation of Solubilization
of Plutonium and Americium in Soil by Natural Humic Compounds, "
Env. Sci. Tech.. 10, p802 (1976)
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J.A. Hayden, "Characterization of Environmental Plutonium by
Nuclear Track Techniques," in Atmospheric-Surface Exchange of
Particulate and Gaseous Pollutants. Report CONF-740921, USERDA,
Wash., D.C. (1974)
Hetherington, J.A., Jefferies, D.F., Mitchell, N.T., Pentreath,
R.J. and Woodhead, D.S., Environmental and Public Health
Consequences of the Controlled Disposal of Transuranic Elements
to the Marine Environment. IAEA-SM-199/11, International Atomic
Energy Agency, Vienna (1975)
Larsen, R.P. and Oldham, R.D., "Oxidation of Pu(IV) to Pu (VI) by
Chlorine - Consequences for the Maximum Permissible Concentration
of Plutonium in Drinking Water," in Radiological and
Environmental Research Division Annual Report. ANL-77-65 Part II,
p97, Argonne National Laboratory (1976)
Lipton, W.V. and Goldin, A.S., "Some Factors Influencing the
Uptake of Plutonium-239 by Pea Plants," Health Phvs.. 31, p425
(1976)
Mullen, A.G. and Mosley, R.E., Availability. Uptake, and
Translocation of Plutonium Within Biological Systems. USEPA
Report EPA-600/3-76-043 (1976)
Mullen, R.N., Sprugel, D.G., Wayman, C.W., Bartelt, G.E., and
Bobula, C.M.,"Behavior and Transport of Industrially Derived
Plutonium in the Great Miami River Ohio," Health Phvs.. 33. p411
(1977)
M.W. Nathans, The Size Distribution and Plutonium Concentration
of Particles from the Rocky Flats Area. Report TLW-6111, LFE
Corporation (1972)
Pillai, K.C. and Mathew, E., Plutonium in Aquatic Environment -
its Behavior. Distribution and Significance. IAEA-SM-199/27,
International Atomic Energy Agency, Vienna (1975)
Polzer, W.L., "Solubility of Plutonium in Soil-Water
Environment," in Proceedings of the Rocky Flats Symposium on
Safety in Plutonium Handling Facilities. CONF-710401, USAEC,
Wash., D.C. (1971)
Price, K.R., "A Review of Transuranic Elements in Soils, Plants,
and Animals" J. Environ. Quality. 2 p62 (1973)
Rogers, D.R., Mound Laboratory Environmental Plutonium Study
1974. MLM-2249 (1975)
Romney. E.M., Mork, H.M., and Larson, K.H., "Persistence of
Plutonium in Soil, Plants, and Small Mammals, Health Phys..
19, p487 (1970)
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G.A. Sehmel, "A Possible Explanation of Apparent Anomalous
Airborne Concentration Profiles of Plutonium at Rocky Flats,"
Pacific Northwest Laboratory Annual Report for 1974. BNWL-1950,
Part III
T. Tamura, Physical and Chemical Characteristics or Plutonium in
Existing Contaminated Soils and Sediments. LAEA-SM-199/152,
International Atomic Energy, Vienna (1975)
T. Tamura, "Transuranics in Natural Environments. M.G. White and
P.B. Dunaway, editors, pp. 97-114 Nevada Applied Ecology Group,
U.S. Energy Research and Development Administration (1977).
Taube, M., Plutonium. Pergamon Press, Oxford, (1964)
Wahlgren, M.A. and Nelson, D.M. , "Residence Times for 239Pu and
137Cs in Lake Michigan Waters," in Radiological and Environmental
Research Division Annual Report. Argonne National Laboratory,
ANL- 8060 Part III, p85 (1973)
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3. DOSE AND RISK TO HEALTH DUE TO
INHALATION AND INGESTION OF TRANSURANIUM NUCLIDES
3.1 INTRODUCTION
Most of the transuranium nuclides decay by emission of an
alpha particle (ionized helium atom}. Alpha particles transfer
much of their energy for each collision (high-LET) and are very
damaging to tissue, but their range is very small (less than
100 microns). Thus, biological damage is limited to tissue in
the immediate vicinity of the radioactive material, and a
potential health hazard from transuranium elements in the
environment can only result from inhalation or ingestion into the
body. For the more important transuranium nuclides, such as
Pu-238 or Pu-239, biological retention times are very long and
radioactive decay occurs at such a slow rate that uptake into the
body will result in prolonged exposure of body organs.
Risk estimates for internal organs are in accord with the
recommendations published by the International Commission on
Radiological Protection and by the NAS-BEIR Committee
(popularly known as the BEIR-3 and BEIR-4 Reports). Lung
inhalation dosimetry is in accord with the recommendations
of ICRP Reports 19 and 30.
3.2 CURRENT STATUS
3.2.1 SOMATIC RISK
At the low levels of radiation exposure attributed to
radionuclides in the environment, the principal health detriment
is the induction of cancers (solid tumors and leukemia), and the
expression, in succeeding generations, of genetic effects.
3-1
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Most of the observations of radiation-induced carcinogenesis
in humans are on groups exposed to low-LET radiations. These
groups include the Japanese A-bomb survivors and medical patients
treated with x-rays for ankylosing spondylitis in England from
1935 to 1954. The United Nations Scientific Committee on the
Effects of Atomic Radiation (UNSCEAR) and the National Academy of
Sciences Committee on the Biological Effects of Ionizing
Radiations (NAS-BEIR) have provided knowledgeable reviews of
these and other data on the carcinogenic effects of human
exposures (Table 3-1).
Observed excess cancers have occurred, for the most part,
following relatively high doses of ionizing radiation compared to
those likely to occur due to environmental contamination from
controllable sources of radiation. Therefore, a number of
assumptions must be made about how observations at high doses
should be applied at low doses and low dose rates for radiation
of a given type. These assumptions include the shape of the dose
response function, the risk projection model, and possible dose
rate effects.
The 1980 BEIR-3 report examined three dose response
functions in detail: (1) linear in which effects are directly
proportional to dose at all doses; (2) linear quadratic in which
effects are very nearly proportional to dose at very low doses
and proportional to the sguare of the dose at high doses; and
(3) a quadratic dose response function where the risk varies as
the square of the dose at all dose levels. These define a range
of predicted somatic effects and represent an envelope of risk
estimates. The first two of these functions appear to be
compatible with most of the data on human cancer.
3-2
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TABLE 3-1
A COMPARISON OF ESTIMATES OF THE RISK OF FATAL CANCER
FROM A LIFETIME EXPOSURE AT 1 RAD/YEAR
(Low-LET Radiation)
Cases per 10 person rad
Projection Model
UJ
I
u>
BEIR-3 (a)(b)
BEIR-3 (a)(c)
BEIR-3 (a)(d)
UNSCEAR (e)
UNSCEAR (e)
ICRP (f)
BEIR-5 (g)
ICRP (h)
158
403
270
240-440*
160-200*
200
770/810
500
Absolute Risk
Relative Risk
Absolute/Relative Risk
"Multiplicative"
"Additive"
None
Absolute/Relative Risk
None
(a) Based on Tables V-3 and 4 in BEIR-3 Report (1980)
(b) Absolute Risk (All Organs) - Linear Dose Response Model
(c) Relative Risk (All Organs) - Linear Dose Response Model
(d) L-L Absolute Risk Model for Bone Cancer and Leukemia;
L-L Relative Risk Model for All Other Cancer
(e) Based on Table 10 in UNSCEAR Report (1988)
(f) ICRP Como Statement (1987)
(g) Appendix 4 in BEIR-5 Report - Male/Female (1989)
(h) ICRP (1990)
* Dose Rate Effectiveness Factor (DREF): UNSCEAR (1988) =2.5
ICRP (1990) = 2.0
-------
The BEIR-3 committee limited its risk estimates to a
minimum dose rate of 1 rem per year and stated that it "does not
know if dose rates of gamma rays and x-rays of about 100 mrad/y
are detrimental to man." At dose rates comparable to the annual
dose that everyone receives for naturally occurring radioactive
materials, a considerable body of scientific opinion holds that
the effects of radiation are reduced. The National Council on
Radiation Protection and Measurement (NCRP) Committee 40 has
suggested that carcinogenic effects of low-LET radiations may be
proportionally less for small doses and dose rates by a factor
of from 2 to 10 times than have been observed at high doses.
The International Commission on Radiological Protection and the
United Nations Scientific Committee on Atomic Radiation have used
a dose rate effective factor of about 2.5 to estimate the risks
from occupational and environmental exposures. Their choice is
fully consistent with and equivalent to the reduction of risk at
low doses obtained by substituting the BEIR-3 linear-quadratic
response model for the linear model.
To estimate the risk of radiation exposure that is beyond
the years of observation, either a relative risk or an absolute
risk projection model (or suitable variations) must be used.
These models are described in detail in Chapter 4 of the 1980
BEIR-3 report. The relative risk projection model projects the
currently observed percentage increase in cancer risk per unit
dose into future years. An absolute risk model projects the
average observed number of excess cancers per unit dose into
future years at risk. Because the underlying risk of cancer
increases rapidly with age, the relative risk model predicts a
larger probability of excess cancer towards the end of a persons
lifetime. In contrast, the absolute risk model predicts a
constant incidence of excess cancer across time. Therefore,
given the incomplete data we have now, with less than lifetime
followup, a relative risk model projects somewhat greater risk
than that estimated using an absolute risk model.
3-4
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The National Academy of Sciences BEIR Committee and other
scientific groups, e.g. UNSCEAR, have not concluded which
projection model is the appropriate choice for most radiogenic
cancers. However, evidence is accumulating which favors the
relative risk projection model for most solid cancers. As
pointed out by the 1980 NAS BEIR Committee:
"If the relative-risk model applies, then the age of the exposed
groups, both at the time of exposure and as they move through
life, becomes very important. There is now considerable evidence
in nearly all the adult human populations studied that persons
irradiated at higher ages have, in general, a greater excess risk
of cancer than those irradiated at lower ages, or at least they
develop cancer sooner. Furthermore, if they are irradiated at a
particular age, the excess risk tends to rise pari passu (at
equal pace) with the risk of the population at large. In other
words, the relative-risk model with respect to cancer
susceptibility at least as a function of age evidently applies to
some kinds of cancer that have been observed to result from
radiation exposure."
Leukemia and bone cancer are exceptions to the general
validity of a lifetime expression period for radiogenic cancers.
Most, if not all, of the leukemia risk has apparently already
been expressed in both the A-bomb survivors and the spondylitics.
Similarly, bone sarcoma from acute exposure appears to have a
limited expression period. For these diseases, the BEIR-3
Committee believed an absolute risk projection model with a
limited expression period to be appropriate for estimating
lifetime risk.
A life table analysis can be used to estimate the number of
fatal radiogenic cancers in an exposed population of 100,000
persons. This analysis considers not only death due to
radiogenic cancer but also the probabilities of other competing
causes of death which are, of course, much larger and vary
considerably with age. The use of life tables in studies of risk
due to low-level radiation exposure is important because of the
time delay inherent in radiation risk. After a radiation dose is
received, there is a minimum induction period of several years
3-5
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(latency period) before a cancer is clinically observed.
Following the latency period, the probability of occurrence of a
cancer during a given year is assumed to be constant for a
specified period, called a plateau period. The length of both
the latency and plateau periods depends upon the type of cancer.
Estimates of the cancer risk from low-LET, whole-body,
lifetime exposure can be based on different assumptions. If one
assumes linearity and no dose rate effects, and a relative risk
projection (the BEIR-3 L-L model) for solid cancers and an
absolute risk projection for leukemia and bone cancer, this
yields an estimated 400 fatalities per million person rad whole-
body exposure. The International Commission on Radiological
Protection provided estimates of 100 fatalities per million
person rad exposure in 1977, and revised this to 200 fatalities
per million person rad in 1987.
For environmental contamination by transuranium elements,
inhalation and ingestion are the most common modes of exposure.
In many cases, depending on the chemical and physical
characteristics of the radioactive material, this may result in a
nonuniform distribution of radioactivity within the body so that
some organ systems receive much higher doses than others. For
example, plutonium isotopes concentrate in the bone and liver,
and the doses to these organs can be orders of magnitude larger
than the average dose to the body.
Information on the proportion of fatal cancers due to cancer
in a particular organ is not precise. One reason is that the
data in BEIR-3 are based on whole-body exposures and it is
possible that the incidence of radiogenic cancer varies,
depending on the number of organs that are exposed. Except for
breast and thyroid cancer, very little information is available
on radiogenic cancer due to exposure of only one region in the
body. Another reason is that most epidemiology studies use
mortality data from death certificates, which often provide
3-6
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questionable information on the site of the primary cancer.
Moreover, when the existing data are subdivided into specific
cancer sites, the number of cases becomes small, and sampling
variability is increased. The net result of these factors is
that numerical estimates of the total cancer risk are more
reliable than those for most single sites.
The probability that fatal cancer occurs at a particular
site has been derived from life table analyses for each cancer
type using the information on cancer incidence and mortality in
the BEIR-3 report, and normalized to the fraction of fatal cancer
due to radiogenic cancer at a particular site. Results are
listed in Table 3-2 and compared with similar estimates published
by UNSCEAR and ICRP.
3.2.2 EXPOSURE TO HIGH-LET RADIATION
In some cases, ingestion and inhalation of alpha particle
emitting radionuclides can result in a relatively uniform
exposure of the body organs by high-LET radiations. Unlike
exposures to x-rays and gamma rays, where the resultant charged
particle flux results in linear energy transfers (LET) of the
order of 0.2 to 2 KeV per micron in tissue, 5 MeV alpha particles
result in energy deposition at a track average rate of more than
100 KeV per micron. High-LET radiations have a larger biological
effect per unit dose (rad) than low-LET radiations. For cell
killing and other readily observed endpoints, the relative
biological effectiveness (RBE) of high-LET alpha radiations is
often ten or more times greater than low-LET radiations.
Charged particles have been assigned quality factors, Q,
to account for their efficiency in producing biological damage.
Unlike an RBE value, which is for a specific and well defined
endpoint, a quality factor is based on an average overall
assessment by radiation protection experts of potential harm.
In 1979, the ICRP assigned a quality factor of 20 to alpha
3-7
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U)
I
00
TABLE 3-2
COMPARISON OF PROPORTION OF THE TOTAL RISK OF
RADIOGENIC CANCER FATALITIES BY BODY ORGAN
Site
Lung
Breast
Red Marrow
Thyroid
Bone
Liver
Stomach
Intestine
Pancreas
Urinary
Colon
Gonads
Other
BEIR-3(a)
.21
.13
.16
.10
.010
.085
.084
.039
.058
.025
—
—
.11 (e)
UNSCEAR
.24
.16
.13
.065
.023
.081
.081
.12
.023
.023
—
—
.046
ICRP-26fb)
.16
.20
.16 (C)
.04
.04
(.08) (d)
(.08)
(.08)
(.08)
(.08)
—
—
ICRPf
. 13
.05
.12
.02
.01
.03
.16
—
—
.04
.18
.13
.13
1990)
(f)
(a) Lifetime exposure and cancer expression.
(b) Normalized for risk of fatal cancer.
(c) Leukemia
(d) Five additional organs which have the highest dose
are assigned 0.08 for a total of 0.4.
(e) Total risk for all other organs including the esophagus,
lymphatic system, pharynx, larynx, salivary gland, and brain.
(f) Population average (male-female)
-------
particle irradiation from radionuclides. The reasonableness of
this numerical factor for fatal radiogenic cancers at a
particular site is not well known, but it is probably
conservative for all sites and highly conservative for some.
The dose equivalent, in units of rem, is the dose, in units
of rad, times the appropriate quality factor for a specified kind
of radiation. For the case of internally deposited alpha
particle emitters the dose equivalent from a one rad dose is
equal to 20 rem. It should be noted that prior to ICRP Report 26
the quality factor for alpha particle irradiation was ten, that
is, the biological effect from a given dose of alpha particles
was estimated to be ten times that from an acute dose of low-LET
x-rays or gamma rays of the same magnitude in rad. The ICRP
decision to increase this quality factor to 20 followed from its
decision to estimate the risk of low-LET radiations, in
occupational situations, on the assumption that biological
effects were reduced at low dose rates for low-LET radiation.
There is general agreement that dose rate effects do not occur
for high-LET (alpha) radiations. The new ICRP quality factor for
alpha particles of 20 largely compensates for the fact that the
low-LET risks are now based on an assumed dose rate effectiveness
factor (DREF) of 2.5.
The NAS BEIR-3 Committee has stated that, "For high-LET
radiation, such as from internally deposited alpha-emitting
radionuclides, the linear hypothesis is less likely to lead to
overestimates of the risk and may, in fact, lead to
underestimates". However, at low doses, departures from
linearity are small compared to the uncertainty in the human
epidemiological data and assumption of a linear response probably
provides an adequate model for evaluating risks in the general
environment.
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In 1980 the ICRP published a task group report "Biological
Effects of Inhaled Radionuclides" which compared the results of
animal experiments on radiocarcinogenesis following the
inhalation of alpha particle and beta particle emitters. The
task group concluded that "the experimental animal data tend to
support the decision by the ICRP to change the recommended
quality factor from 10 to 20 for alpha radiation."
The estimates of the risk of fatal cancer due to a uniform
organ dose from internally deposited alpha particles have been
calculated for both the data from the BEIR-3 report and Report 26
of the International Commission on Radiological Protection and
compared with the estimates of the BEIR-4 report. A comparison
of results is shown in Table 3-3.
The organ risk estimates based on the ICRP model assume
an overall risk of 200/million person-rad as given in the Como
Statement, a quality factor of 20, and the organ weighting
factors of ICRP Report 26. The organ risk estimates based on
BEIR-3 were prepared by multiplying the relative risk estimate
of 400/million person-rad for a uniformly distributed whole body
dose of low-LET radiation by a quality factor of 20, dividing by
a dose rate effectiveness factor of 2.5 (except for endosteal
bone which is based on data for high-LET (alpha) radiation),
and then apportioning this risk by organ. The risk coefficient
for leukemia was derived directly from the data in BEIR-3 as
43.5 fatalities per 106 person rad of low-LET radiation, or
360 fatalities per 106 person rad of high-LET radiation.
Comparison of risk estimates indicates that the several
models all agree within better than a factor of two, and the
choice of a calculational model may be dictated by an effort to
establish uniformity. The BEIR-4 Committee noted that the risk
of leukemia from intake of transuranium elements is not well
established and all the estimates are subject to considerable
uncertainty. It further stated that "dose calculations that
3-10
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U)
I
TABLE 3-3
ESTIMATED NUMBER OF FATALITIES FROM EXPOSURE
TO INTERNALLY DEPOSITED ALPHA (HIGH-LET) EMITTERS
Target Organ/Cancer Fatalities per 106 Person-Rad
BEIR-3* ICRP-26** BEIR-4
Lung
Liver
670
274
480
240
700
260-300
Red Bone Marrow/Leukemia 350 480 400
Skeletal Bone/Bone Cancer 240 120 300
* Relative Risk Model and 'Tables V-14/15 (BEIR-3 Report)
Endosteal Bone = 12 x Skeletal Bone (ICRP-26/30 models)
** Risk = 2xlO~4/rem (ICRP 1987 Como Statement)
Organ Weighting Factors (ICRP Report 26)
-------
may be appropriate for radiation protection purposes may be
entirely misleading for projecting risks of cancer mortality".
3.2.3 UNCERTAINTIES IN RISK ESTIMATES FOR RADIOGENIC CANCER
Numerical estimates of risks due to radiation are neither
accurate nor precise. A numerical evaluation of radiogenic
cancer risks depends both on epidemiological observations and a
number of ad hoc assumptions which are largely external to the
observed data set. These assumptions include such factors as the
expected duration of risk expression and variations in
radiosensitivity as a function of age and demographic
characteristics. A major assumption is the shape and slope of
the dose effects response curve, particularly at low doses where
there is little or no epidemiological data. In 1971, the BEIR
Committee based its estimates of cancer risk on the assumption
that effects at low doses are directly proportional to those
observed at high doses, the so called linear-nonthreshold
hypothesis. The BEIR-3 Committee considered three dose response
models and indicated a preference for the linear quadratic model.
The risk coefficients derived for their linear quadratic model,
and to a lesser extent their linear model, are subject to
considerable uncertainty primarily because of two factors:
1) systematic errors in the estimated doses of the individual
A-bomb survivors and 2) statistical uncertainty due to the small
number of cancers observed at various dose levels. In addition
to a dose response model, a "transportation model" is needed to
apply the risks from an observed irradiated group to another
population having different demographic characteristics.
3.2.4 GENETIC RISK
Genetic harm, or the genetic effects of radiation exposure,
are those effects induced when radiation damages the nucleus of
the cells of exposed individuals which become the eggs or sperm.
The damage, in the form of a mutation or chromosome aberration,
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is transmitted to and may be expressed in a child conceived after
the radiation exposure and in subsequent generations.
One of the first estimates of genetic risk was made in 1956
by the National Academy of Science Committee on the Biological
Effects of Atomic Radiation (BEAR Committee) . Based on fruit fly
(Drosophila) data and other considerations, the BEAR Genetics
Committee estimated that 10 Roentgens per generation continued
indefinitely would lead to about 5,000 new instances of "tangible
inherited defects" per 10G births, and about one-tenth of them
would occur in the first generation after the irradiation began.
UNSCEAR estimated that one rad of low-LET radiation would cause a
1% to 10% increase in the spontaneous incidence of genetic
effects.
In 1980, an ICRP Task Group summarized recommendations that
formed the basis for the genetic risk estimates published in ICRP
Report 26. These risk estimates are based on data similar to
that used by the BEIR and UNSCEAR Committees, but with slightly
different assumptions and effect categories. The 1980 NAS BEIR
Committee revised genetic risk estimates. Estimates for the
first generation are about a factor of two smaller than reported
in the BEIR-1 report. A summary of genetic risk estimates is
shown in Table 3-4.
Although genetic risk estimates are made for low-LET
radiation, some radioactive elements, deposited in the ovary or
testis can irradiate the germ cells with alpha particles.
The ratio of the dose (rad) of low-LET radiation to the dose of
high-LET radiation producing the same endpoint is called RBE and
is a measure of the effectiveness of high-LET compared to
low-LET radiation in causing the same specific-
Studies of the RBE for alpha-emitting eipineul'* In germina]
tissue have only used plutonium-239. The estimated UBE for
plutonium-239 alpha radiation versus chronic gr.i»uiFi T-adiation Cn
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Ul
I
TABLE 3-4
SUMMARY OF GENETIC RISK ESTIMATES PER 106 LIVE-BORN
(Average Population Exposure of 1 Rad of Low Dose Rate
Low-LET Radiation in a 30-Year Generation)
Serious Heriditary Effects
Source First Generation Equilibrium
(All Generations)
BEAR, 1956
BEIR-I, 1972
UNSCEAR, 1972
UNSCEAR, 1977
ICRP-TG, 1980
BEIR-3, 1980
UNSCEAR, 1982
_ __
49* (12-200)
9* (6-15)
63
89
19* (5-75)
22
500
300*
300
185
320
257*
149
(60-1500)
(60-1100)
Numbers in parentheses ( ) are the range of estimates
* Geometric Mean
-------
NASOPHARYNGEAL
(N-P)
(bl
TRACHEOBRONCHIAL
(T-B)
PULMONARY
(P)
Id)
S
T
C
M
A
C
H
S I
M N
A T
L E
L S
T
I
N
E
T
0' IS THE TOTAL AEROSOL INHALED; 0' IS THE AEROSOL IN THE EXHALED AIR; DJ, D«, AND O1
ARE THE AMOUNTS DEPOSITED IN THE NASOPHARYNGEAL, TRACHEOBRONCHIAL, AND PULMONARY
LUNG KbSPECTIVELY. THE LETTERS (a) THROUGH (j) INDICATE THE PROCESSES WHICH TRANSLOCATE
MATERIAL FROM ONE COMPARTMENT TO ANOTHER
FIGURE 3-1
3-15
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.001.
.001
20 30 40
DURATION OF EXPOSURE
50
(YEARS)
60
70
DOSE RATE TO ORGANS AS A FUNCTION OF TIME DUE TO CHRONIC INHALATION
OF ONE MICRON (AMAD) PLUTONIUM PARTICLES AT A CONCENTRATION OF
2.6 fCi/m1. EQUILIBRIUM DOSE RATE TO PULMONARY LUNG 1 MRAD PER YEAR
ADULT REFERENCE MAN - BREATHING RATE 2.3 x 10' LITERS PER DAY.
FIGURE 3-2
3-16
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reciprocal translocations as determined by cytogenetic analyses
is between 23 and 50. However, the observed RBE for single
locus mutations in developing offspring of male mice given
plutonium-239 compared to those given x-ray irradiation is 4.
The average RBE for reciprocal translocations and for specific
locus mutations is 20. Since reported neutron RBE's are similar
to those listed above for plutonium-239 alpha radiation, we used
an RBE of 20 to estimate genetic risks for all high-LET
radiations. This is consistent with the RBE for high-LET
particles recommended for estimating genetic risks associated
with space flight.
Human genetic risk estimates are limited by the lack of
confirming evidence of genetic effects in humans, and depend on a
presumed resemblance of radiation effects in animals to those in
humans. The study with the largest data base, the Japanese
A-bomb survivors, appears, at best, to provide only an estimate
of the minimum doubling dose for calculating the maximum genetic
risk in man. However, doubling dose estimates are also uncertain
since the number of human disorders having a recognized genetic
component is constantly increasing, and the type of genetic
damage implicated in a specific disorder may change.
The combined uncertainties in doubling dose estimates and the
magnitude of genetic contributions to various disorders probably
introduces an overall uncertainty of about an order of magnitude
in the risk estimates.
3.2.5 CALCULATIONAL MODELS
Estimates of the annual dose rate to organs and tissues of
interest are calculated using models recommended by the
International Commission on Radiological Protection, supplemented
by comparable models proposed by the British National Radiation
Protection Board. These dose rates are used in conjunction with
a life table analysis of the increased risk of cancer due to
3-17
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radiation. This analysis takes account of both competing risks
and the age of the population at risk.
Internal exposures occur when radioactive material is
inhaled or ingested. The RADRISK code developed by the U.S.
Environmental Protection Agency implements current dosimetric
models to estimate the dose rates at various times to specified
reference organs in the body from inhaled or ingested
radionuclides. The dosimetric methods in RADRISK are adapted
from those of the INREM II code, based primarily on models
recommended by the International Commission on Radiological
Protection and the British National Radiation Protection Board.
The principal qualitative difference is that RADRISK computes
dose rates to specified organs separately for high and low linear
energy transfer (LET) radiations, whereas INREM II calculates the
committed dose equivalent to specified organs. The direct intake
of each nuclide is treated as a separate case. For chains, the
ingrowth and dynamics of daughters in the body after intake of a
parent radionuclide are considered explicitly in the calculation
of dose rate. Consideration is also taken of different metabolic
properties for the various radionuclides in a decay chain.
The ICRP Task Group Lung Model (Figure 3-1) is used to
calculate particulate deposition and retention in the respiratory
tract. This model has four major regions: the naso-pharyngeal,
tracheobronchial, pulmonary, and lymphatic tissues. A fraction
of the inhaled activity is initially deposited in each of the
naso-pharyngeal, tracheobronchial, and pulmonary regions.
The material clears from the lung to the blood and the gastro-
intestinal tract. Deposition and clearance of inhaled
particulates in the lung are controlled by the particle size and
solubility classification. The size distribution of the
particles is specified by the activity median aerodynamic
diameter (AMAD); in this study, all particulates are assumed to
have an AMAD equal to 1.0 micron. The model employs three
solubility classes, based on the chemical properties of the
3-18
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nuclide; classes D, W, and Y correspond to rapid (days),
intermediate (weeks), and slow (years) clearance, respectively,
of material deposited in the respiratory passages.
Activity absorbed by the blood from the GI or respiratory
tract is assumed to be distributed immediately to systemic
organs. The distribution of activity to these organs is
specified by fractional uptake coefficients. The list of organs
in which activity is explicitly distributed (herein termed source
organs) is element-dependent, and may include such organs as bone
or liver.
Parameters for the uptake factors across the intestinal
(gut) wall as recommended in ICRP Report 48 have been used.
These are larger than those given in ICRP Report 30, and are
generally similar to f, values for transuranium elements in the
general environment published by the British National Radiation
Protection Board. Use of these larger f, values results in
greater estimated doses and risks from ingestion of transuranic
materials than those calculated by use of the earlier ICRP
recommendations, but has little effect on doses following
inhalation.
3.3 RADIATION RISK - A PERSPECTIVE
To provide a perspective on the risk of fatal radiogenic
cancers and the hereditary damage due to radiation, we have
calculated the risk from background radiation to the U.S.
population using the risk coefficients presented in this chapter.
The risk due to background radiation is very largely unavoidable;
therefore, it is a good basis of comparison with the estimated
risks of doses from radionuclides in the environment. Moreover,
if there is bias in the estimated risk of radionuclides, the same
bias is present in the risk estimates for background radiation.
3-19
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Low-LET background radiation has three major components:
cosmic radiation, which averages to about 28 mrad per year in the
United States, terrestrial sources, such as radium in soil, which
contribute an average of 26 mrad per year, and the low-LET dose
due to internal emitters. The latter differs between organs, to
some extent, but for soft tissues is about 24 mrad per year.
Fallout from nuclear weapons tests, naturally occurring
radioactive materials in buildings, etc. contribute about another
10 mrem for a total low-LET whole body dose of about 90 mrad per
year. The lung and bone receive somewhat larger doses due to
high-LET radiations. Although extremes do occur, the
distribution of this background annual dose to the U.S.
population is relatively narrow, and analysis indicates that 80%
of the U.S. population would receive annual doses that are
between 75 millirad per year and 115 millirad per year.
The BEIR-3 linear models yield an average lifetime risk of
fatal radiogenic cancer of 400 per 106 person rad for low-LET
radiation. The average is for a group having the age and sex
specific mortality rates of the 1970 U.S. population. This is
reduced by a dose rate effectiveness factor of 2.5 to give a risk
of 160 per 10s person rad. More recent evaluations, such as the
BEIR-5 Report and the 1989 UNSCEAR evaluation have provided
similar estimates of risk. The average lifetime risk to an
individual due to low-LET background radiation is calculated as
follows:
The average duration of exposure in this group is 70.7 years and
at 9 x 10"2 rad per year, the average lifetime dose is 6.36 rad.
The risk of fatal cancer per person in this group is:
160 fatalities
106 person rad
x 6.36 rad = l.OxlO'3
3-20
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The probability of death from cancer in the U.S. is about 0.16,
i.e. 16%. Thus the calculated percentage of deaths due to
low-LET background radiation indicates that about 0.1% of all
deaths, or about 0.6% of all cancer deaths, nay be due to
low-LET background radiation.
The spontaneous incidence of serious congenital and genetic
abnormalities has been estimated to be about 105,000 per 106 live
births, about 10.5% of live births. The low-LET background
radiation dose of about 90 mrad/year in soft tissue results in a
genetically significant dose of 2.7 rad during the 30 year
reproductive generation. Since this dose would have occurred in
a large number of generations, the genetic effects of the
radiation exposure are thought to be an equilibrium level of
expression. Since genetic risk estimates vary by a factor of 20
or more, the Agency uses a log mean value of this range to obtain
an average value for estimating genetic risk. Based on this
average value, the background radiation may cause 700 to 1000
genetic effects per 106 live births, depending on whether or not
the oocyte is as sensitive to radiation as the spermatogonia.
This result indicates that about 0.67% to 0.95% of the current
spontaneous incidence of serious congenital and genetic
abnormalities may be due to the low-LET background radiation.
3-21
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3.4 TRANSURANIUM ELEMENTS - EXPOSURE PATHWAYS AND BIOEFFECTS
3.4.1 INHALATION
In general, the most important pathway for human exposure
from plutonium oxide and other transuranium radionuclides in the
environment is expected to be inhalation. This route provides a
direct pathway for alpha particles to enter a sensitive organ,
the pulmonary lung. Subsequently, a fraction of the inhaled
material is redistributed via the blood to such important organs
as the bone, liver and gonadal tissues. This is in contrast to
the ingestion pathway, where the gut walls act as a barrier to
plutonium absorption by blood. The dose to the gut wall itself
is not a major cause of concern because plutonium alpha particles
have a short finite range in tissue, 41 microns (Mm), i.e., less
than two-thousandths of an inch. Radiosensitive dividing cells
in the gut wall are over 100 /im distant from the gut contents and
are effectively isolated from the alpha radiation.
The dose to various tissues from inhaled plutonium is highly
time dependent. Insoluble material deposited in the pulmonary
lung is removed fairly rapidly; half is assumed to be cleared
within 500 days. Clearance from other organs is much slower; the
estimated biological half-life in the liver is assumed to be
40 years, and 100 years for bone. The dose delivered to an organ
is directly related to the residence time of the radioactive
material. Following a single acute exposure to airborne
plutonium, the lung (pulmonary) dose rate decreases due to the
clearance of particles from the lung so that almost all of the
dose is received in a few years. In contrast, the dose rates to
the liver and bone are relatively constant over this time span.
In the case of chronic environmental contamination leading
to a constant annual intake, the temporal pattern of the dose
rate to various organs due to inhalation is different. For
pulmonary tissues, a constant (equilibrium) dose rate is realized
3-22
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within relatively few years of the start of exposure. The dose
rate to liver increases more slowly and does not equal that to
lung tissue until after about 70 years of exposure. The dose
rate to bone never approaches that to the lung and liver.
Therefore, the total risk from chronic inhalation will vary with
the duration of exposure.
3.4.2 DOSE TO LUNG TISSUES
In most cases, the lung is the organ of primary concern when
assessing the risks from plutonium and other transuranium
elements in soil. Animal studies, particularly those with dogs
which have a relatively long life span, indicate that lung cancer
can result from inhaled plutonium aerosols. Even so, the
assessment of the risk to humans cannot be directly inferred from
animal evidence. Almost all lung cancers in dogs exposed to
plutonium occur in a different location than radiogenic cancers
in humans following exposure to radon daughters. The animal
cancers are in the peripheral parts of the lung and often to
different cell types than human lung cancers. They are
histologically classified as bronchilar carcinomas (a type of
adenocarcinoma). In humans, the inhalation of alpha particle
emitters (but not transuranium elements) has usually resulted in
bronchial cancers (hilar bronchogenic carcinomas). These are
primarily epidermoid and anaplastic carcinomas, but include some
adenocarcinomas. Cancers histologically similar to those in
animals (peripheral adenocarcinomas) are found much less
frequently. This difference may be due to differing exposure
conditions but must, in part, be due to differences in tissue
sensitivity between species.
A National Academy of Sciences committee concluded that "the
risk from alpha irradiation of the deep lung tissues would not be
underestimated by applying risk factors from human experience
with cancer induced by irradiation of the bronchial tree".
Therefore, the risk estimates are based on the highest dose rate
3-23
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received by any lung tissues (pulmonary lung) and risk estimates
appropriate for the most sensitive tissues within the lung, the
site of bronchial cancers. It should be noted that the dose to
bronchial tissues following plutonium inhalation is small
compared to that received in the pulmonary lung; we therefore
believe this is a very conservative approach.
In assessing the dose and risk due to the inhalation of
transuranium elements, only retention in the pulmonary region is
of primary importance. Residence time of inhaled materials in
the nasopharyngeal and tracheo-bronchial regions is short
compared to that in pulmonary tissues.
Dosimetric models for projecting the average distribution of
ionizing radiation within body organs due to the inhalation of
radioactive aerosols are still somewhat crude. A general model
was published in ICRP Report 19, "The Metabolism of Compounds of
Plutonium and Other Actinides", as an amended version of a model
developed earlier for the ICRP.
Inhaled aerosols are considered on the basis of particle
size and other aerodynamic parameters. The fraction of inhaled
materials initially retained or exhaled, and the deposition in
various portions of the respiratory tract, is a given function of
the activity median aerodynamic diameter (AMAD) of the aerosol
particles. The rate at which deposited material is removed from
the lungs is considered to be a function only of the chemical
state of the inhaled material, and not of size or radioactive
content. Environmental sources of plutonium and other
transuranium elements are likely to be in the oxide or hydroxide
form. Actinides in either form are currently classified as Class
Y (insoluble) materials by the ICRP.
The dose estimates made below apply only to Class Y compounds.
Radioactivity is assumed to leave the pulmonary tissues by
three routes; elevation up the tracheobronchial tree via the
3-24
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mucus elevator into the gut by way of the esophagus and stomach,
transport of particulate materials into the lymphatic system and
lymph nodes and, most importantly, dissolution into the blood
stream. Most of the activity in blood is redeposited into the
liver and bone.
The dose to different organs from inhaled aerosols of
various sizes has been considered by a number of workers who have
written computer codes to quantify the ICRP model. Since the
ICRP model is not described in the form of unambiguous equations,
there are minor differences between the results obtained with
various codes. The EPA code PAID has been used to calculate the
annual dose rates due to isotopes of plutonium, americium, and
curium for a number of particle sizes. Typical results for five
micron, one micron, and five-tenths micron AMAD plutonium-239
aerosols (1 fCi/m3) are shown in Table 3-5 for the various
compartments in the lung for the case of lifetime exposure
(70 years). It is seen that most of the radiation dose is
received by pulmonary tissue. Given equal concentrations in air,
the dose to the pulmonary lung is not very sensitive to particle
size; for example, in the size range from 0.05 to 5.0 micron
(AMAD) the pulmonary dose decreases by a factor of about five.
The aerosol concentration, as a function of AMAD, required to
produce a 1 millirad equilibrium dose to Reference Man is shown
in Table 3-6.
The ICRP Lung Model classifies inhaled aerosols into three
groups depending on the length of time they are retained in the
lung: Class Y compounds are retained for years, Class W for
weeks, and Class D for days. The retention times are largely
controlled by the solubility of the inhaled material in body
fluids. There is some evidence from animal experiments that high
specific activity plutonium oxides such as 238PuO2 are more
soluble than the long half-life transuranium nuclides and should
be considered Class W compounds. Americium-241 and curium-244
may in some cases be in a chemical form that leads to Class W
3-25
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behavior. Because of their shorter residence time in lung
tissues, inhaled Class W transuranics results in a relatively
small lung dose compared to that received by other organs, due to
the translocation and deposition of dissolved material.
Therefore, the dose rate to other organs, rather than the dose
rate to pulmonary lung may become limiting.
For most transuranium elements (except plutonium-241) the
limiting concentration in air of a Class W material is greater
than that for a C]ass Y material containing the same
radionuclide. For 1 micron (AMAD) particles the limiting
concentration of Class W compounds is about 3 times greater than
for Class Y compounds. The aerosol concentration of several
transuranium nuclides which would produce a 3 mrad skeletal bone
dose in the 70th year of continuous exposure to transuranium
radionuclides in the Class W form are shown in Table 3-7, and the
annual dose rates for particles with concentration of 1 fCi/m3
and 1 micron (AMAD) following 70 years of inhalation exposure are
shown in Table 3-8. More than 99 percent of the equilibrium dose
rate to pulmonary lung tissue is achieved after five years of
exposure. For other organs the dose rate increases with the
duration of exposure. Lifetime exposure to a constant
concentration of curium-244 aerosols is unlikely because of its
relatively short half-life (17 years).
The inhalation of Class W compounds results in both somatic
and genetic risks. Although the limiting dose rate for inhaled
Class W compounds is in terms of the dose to bone, the dose to
lung tissue is not negligible. The genetic risk for inhaled
Class W transuranium materials is larger than for inhaled Class Y
aerosols, and nearly the same as the genetic risk for ingestion.
3-26
-------
TABLE 3-5
ANNUAL DOSE RATE TO VARIOUS LUNG COMPARTMENTS
FROM CHRONIC EXPOSURE TO PLUTONIUM-239 AEROSOLS
Concentration: 1.0 fCi/m3 Particle AMAD: 0.05, 1.0 and 5.0 Microns
Duration of Pulmonary Tracheobronchial Nasopharyngeal
Exposure mrad/yr. x 10 mrad/yr. x 10~ mrad/yr. x 10
(Years)
0.0 5u 1. Ou 5.0u 0.05U l.Ou 5. Ou 0.05U l.Ou 5.0u
1 3.9 1.5 .7 2.7 1.1 6.1 .04 11. 30.
5 9.1 3.5 1.7 3.7 1.5 7.9 .04 11. 30.
10 9.8 3.8 1.8 3.8 1.6 8.1 .04 11. 30.
70 9.9 3.8 1.8 3.8 1.6 8.1 .04 11. 30.
-------
TABLE 3-6
AEROSOL CONCENTRATIONS IN fCi/m3 PRODUCING A 1 MRAD/YEAR
EQUILIBRIUM DOSE RATE TO THE PULMONARY REGION OF REFERENCE MAN
(Class Y Clearance)
u>
NJ
00
Aerosol
AMAD (u)
0.05
0.10
0.30
0.50
1.0
2.0
3.0
5.0
Pu-238
1.0
1.1
1.6
1.8
2.5
3.4
4.1
5.2
Pu-239
1.0
1.2
1.7
1.9
2.6
3.5
4.3
5.4
Pu-240
1.0
1.2
1.7
1.9
2.6
3.5
4.3
5.4
Pu-241*
330
390
540
630
850
1,100
1,400
1,800
Am-241
1.0
1.1
1.6
1.8
2.4
3.3
4.0
5.1
Cm-244
1.0
1.1
1.6
1.8
2.5
3.4
4. 1
5.2
only alpha dose rate due to Am-241 daughter is considered
-------
U)
I
10
VO
TABLE 3-7
AEROSOL CONCENTRATIONS IN fCi/m3 PRODUCING
A 1 MRAD/YR SKELETAL BONE DOSE IN THE 70th YEAR
(Lifetime Inhalation by Reference Man - Class W Solubility)
Size
(AMAD)
0.05
0.10
0.30
0.50
1.0
2.0
3.0
5.0
238PU
94
1.9
2.1
2.9
2.9
2.6
2.4
2.2
2.1
239PU
94
1.6
1.8
2.1
2.2
2.2
2.0
1.9
1.8
241PU*
94
65
75
85
90
90
85
80
75
241Am
95
1.6
1.8
2.1
2.1
2.1
2.0
1.8
1.8
244Cm
96
3.7
4.0
4.7
5.0
5.0
4.7
4.3
4.0
Beta Emitter - includes only alpha dose rate due to the Am-241 daughter
-------
U)
o
TABLE 3-8
ANNUAL DOSE RATES TO VARIOUS ORGANS OF REFERENCE MAN
FOR LIFETIME EXPOSURE TO TRANSURANIUM RADIONUCLIDES
Class W Concentration = 1 fCi/m3 Size = 1 micron (AMAD)
Equilibrium Dose Rate
(microrad/v)
Nuclide
Pu-238
Pu-239
Pu-241
Am-241
Cm-244
Pulmonary
Lung
41
39
0.04
41
44
Tracheobronchial
Lung
16
15
0.01
41
17
Dose rate in the
70th year (microrad/v)
Liver
930
930
20
960
460
Bone Marrow
400
400
9
410
180
-------
3.4.3 DOSE TO BONE, LIVER, AND THE TOTAL BODY
A portion of the aerosols initially deposited in lung tissue
is soluble, eventually enters the bloodstream and is redeposited
into other body organs. The current ICRP model assumes that 45%
of plutonium is redeposited in bone, 45% in liver, and a small
fraction in gonads. Release from these organs is slow; 40 years
is the assumed half-life in liver and 100 years the assumed
half-life in bone and perhaps longer (no observed release) in
gonadal tissue. For this assessment it is assumed that a
100 year half-life is appropriate for both bone and gonadal
tissue. Percent deposition of other transuranium elements is
similar to that for plutonium and ICRP Report 19 has recommended
that the percentages shown above be used for all transuranium
elements. However, ICRP Report 48, based on more recent data,
suggests that the distribution may differ substantially for the
other transuranium elements. There is also considerable evidence
that the retention times in body organs are shorter than earlier
estimates.
The dose rates to various body organs from continuously
inhaled plutonium-239 (oxide), americium-241, curium-244 and
plutonium-241 as a function of years of exposure are shown
in Table 3-9, based on the assumption that all are Class Y
particulates. Dose rates have been calculated by averaging the
energy absorbed over the total organ: 1800 grams for liver;
5000 grams for bone; 15 grams for the respiratory lymph nodes.
Almost all of the dose to liver and bone is from material in the
lungs and lymph nodes that has been dissolved and transferred via
the blood. Transfer to blood of swallowed materials is much less
important.
3.4.4 INGESTION
The magnitude of calculated doses due to the ingestion of
transuranium elements is directly proportional to the fraction of
3-31
-------
INGESTION
EXCRETION
FIGURE 3-3
-------
TABLE 3-9
ANNUAL DOSE RATES TO VARIOUS ORGANS
FROM CHRONIC INHALATION OF TRANSURANIUM RADIONUCLIDES
(In Millirad/Year)
Aerosol AMAD: 1 urn
Concentration: 1 fCi/mJ
f1=io
-3
Nuclide: Pu-239
Nuclide PU-241/AB-241*
Duration of
00
1
U)
U>
1
s
10
15
20
30
40
50
70
Exoosure
year
years
years
years
years
years
years
years
years
Liver
1.0
1.8
5.2
8.9
1.3
1.9
2.4
2.9
3.6
E-3
E-J
E-2
E-2
E-l
E-l
E-l
E-l
E-l
Skeletal
5.0
6.5
1.9
3.4
4.9
7.8
1.1
1.3
1.7
E-4
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
Bone
Red
4.
6.
1.
3.
4.
7.
1.
1.
1.
Marrow Endosteal
8
2
8
2
7
4
1
2
6
E-4 6.6
E-3 a. 6
E-2
E-2
E-2
E-2
E-l
E-l
.5
.5
. 5
.0
.5
.7
E-l 2.3
E-3
E-2
E-l
E-l
E-l
E-0
E-0
E-0
E-0
Nuclide: An-241
Duration of
EXDOSure
1
5
10
IS
20
30
40
50
70
year
years
years
years
years
years
years
years
years
1
1
5
9
1
2
2
3
3
.5
.9
.5
.5
.3
.0
.6
.0
.7
E-3
E-2
E-2
E-2
E-l
E-l
E-l
E-l
E-l
5.0
7.0
2.1
3.6
5.2
8.2
1.1
1.4
1.8
E-4
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
4
6
1
3
4
7
1
1
1
.6
.3
.9
.3
.8
.5
.0
.3
.7
E-4
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
5
8
2
4
6
9
1
I
2
.8 E-3
.1 E-2
. < E-l
.2 E-l
.0 E-l
5 E-l
.3 E-0
.6 E-0
.1 E-0
Bone
Liver Skeletal
1
a
4
1
1
3
5
6
8
.4
.7
.6
.1
.8
.4
.0
.4
.0
E-6 5
E-5 3
E-4 1
E-3 4
E-
E-
E-
E-
E-
7
1
2
3
4
.0
.2
.7
.1
.1
.4
.2
.0
.4
E-7
E-5
E-4
E-4
E-4
E-3
E-3
E-3
E-3
Red
4.
3.
1.
1.
6.
1.
2.
2.
4.
Harrow
6
O
6
6
6
3
0
8
1
E-7
E-5
E-4
E-4
E-4
E-3
E-3
E-3
E-3
Endosteal
5.
3.
2.
2
4.
1.
2.
3.
5.
8
7
O
0
8
6
6
5
1
E-6
E-4
E-3
E-3
E-3
E-2
E-2
E-2
E-2
Nuclide: Cn-244/Pu-240
1.6 E-3
1.8 E-2
4.7 E-2
7.3 E-2
9.4 E-2
I 2 E-l
1.4 E-l
1.5 E-l
1.6 E-l
6.0 E-4
1.6 E-3
1.7 E-2
2.8 E-2
3.7 E-2
4.9 E-J
5.7 E-2
6.3 E-2
6.8 E-2
5.6 E-4
1 5 E-3
1.6 E-2
2.6 E-2
3.4 E-2
4.5 E-3
5.3 E-2
5.8 E-2
6.3 E-2
6.4 E-3
1.7 E-2
1.8 E-l
3.0 E-l
3.9 E-l
5.2 E-l
6.1 E-l
6.7 E-l
7.3 E-l
•Alpha dosa only - 70th year beta dose rates: liver » 0.11 urad:
bone • 0.049 urad.
-------
the ingested material that is assumed to cross the gut wall and
enter the blood stream. This fraction is not well known and it
is reasonable to assume that it varies considerably depending on
the solubility of the ingested material. Animal experiments to
measure gut transfer, which used highly insoluble laboratory
prepared materials in the oxide form, yield transfers in the
parts per million range. However, plutonium oxide found in the
environment has been shown to be much more soluble than the
refractory oxides utilized in animal experiments. This is in
agreement with recent experiments showing plutonium oxides formed
at low temperatures are more soluble than those formed at high
temperatures. Therefore, it is reasonable to assume that
plutonium oxidized in the environment will not be as insoluble as
the materials which have been used to determine plutonium gut
transfer in animals. A tabulation of recently published values
for the transfer coefficient of transuranium elements across the
gut wall is shown in Table 3-10.
In contrast to inhalation, the ingestion dose to liver and
the resultant risk is a direct function of the amount of
radioactivity transferred to blood via the gastrointestinal
tract. For transuranium elements having a physical half-life
comparable to the residence time in liver, the risk will be
somewhat greater since the dose approaches the equilibrium value
earlier in life. Averaging the estimates of early death yields
an estimated risk of two deaths per 100,000 exposed persons,
somewhat less than for cancer of the bone. For Am-241, Pu-241,
and Cm-244 this average lifetime risk is 2.1, 1.2 and 3.2 per
100,000 exposed, respectively.
The transfer factors from gut to blood have been utilized to
calculate annual dose rates as functions of the duration of
ingestion. Dose rates to bone, liver, and the total body of
reference man due to the chronic ingestion of 1000 pCi/year of
plutonium-239 oxide, americium-241, and curium-244 are shown in
Table 3-11. Pu-241, half life 14.8 years, and Cm-244, half life
3-34
-------
TABLE 3-10
FACTORS FOR ABSORPTION FROM THE GASTRO-INTESTINAL TRACT
FOR TRANSURANIUM ELEMENTS
Element/Chem FormICRP-30*ICRP-48**
Oxide 10~d 10~a
Pu-238 Nitrate 10~* lo'^
Other 10 10
w Oxide 10l4 10-4
Pu-239 Nitrate i0^-A 10-3
1 Other 10 10
OJ
(Jl
Am
Cm
Np
5x10
5xlO~4
10-*
10
1C"3
io-3
* ICRP-30 = occupational exposures
** ICRP-48 general population exposure (via food pathway)
for plutonium = 10~3
for all other transuranium elements = 10~3
children under one year = 10 x value for adults.
-------
17.9 years, are the most rapidly decaying transuranium elements
capable of causing chronic exposures in a contaminated environ-
ment. Because of their short half lives, the occurrence of
lifetime ingestion of these radionuclides is remote. This is
even more true of curium-242, half life 0.045 years, where only
acute intake is a plausible mode of exposure.
The organ dose rates were calculated on the basis of organ
masses appropriate for reference man, not children. However,
there is enough proportionality between food intake and organ
mass as a function of age so that the results are applicable to a
lifetime exposure situation. Because there is some evidence from
animal studies that the newborn have a particularly high transfer
of transuranium elements across the gut wall to blood, the
average transfer fractions may not be applicable to infants,
(less than one year old). The duration of this increased
transfer is unknown for humans, perhaps a few weeks or
considerably longer. A comparison of average skeletal dose
rates with and without increased infant uptake is shown in
Table 3-12.
3.4.5 RISK OF BONE CANCER
Unlike radium-226, which is distributed throughout the bone
volume following long-term ingestion, plutonium is preferentially
deposited and retained on endostial bone surfaces, principally in
the organic matrix. In some cases as much as 30-50% of the
endostial plutonium has been shown to be retained on osteogenic
cells. Americium and curium are also retained on bone surfaces.
Alpha particle emitters which are retained on bone surfaces have
been shown to be more tumorgenic than radium-226 and other bone
volume seekers. Surface seekers deliver a higher dose to
osteogenic cells adjacent to bone surfaces, and such doses are
thought to be the cause of radiogenic bone sarcomas.
3-36
-------
TABLE 3-11
ANNUAL DOSE RATE DUE TO CHRONIC INGESTION OF
PLUTONIUM-239 OXIDE, AMERICIUM-241, PLUTONIUM-241, & CURIUM-244
(In Microrad/Year)
Annual Intake = 1000 pCi/Year
fl=
,-3
i
U)
Duration of
Ingestion
(Years)
1
5
10
15
20
30
40
SO
70
PlutoniuB-239 Oxide
Red Marrow
7.6
36.5
71.2
102
136
204
254
314
407
Endoateal
E+2
E+2
9.8 E+2
1.4 E+3
1.9 E+3
2.8 E+3
3.5 E+3
4.3 E+3
5.6 E+3
1.1
5.0
Liver
24
116
220
320
410
560
690
810
980
Duration of
Ingestion
(Years!
1
5
10
15
20
30
40
50
70
Aaericium-241
Bone
Red Marrow
7.7
38
74
HO
14O
200
260
320
410
E
9
4
9
1
1
2
3
5
5
nfli
.8
.8
.4
.4
.8
.6
.3
.2
.2
>stee
E+l
E»2
E+2
E+3
E+3
E+3
E+3
E»3
E+3
Liver
25
120
230
340
43O
590
720
830
990
Duration of
Ingestion
tYearsl
1
5
10
15
20
30
40
50
70
PlutoniuB-241/Americiun-241
Bone
Red Marrow Endosteal
0.006
0.14
0.51
1.0
1.7
3.2
4.9
6.5
9.4
0.08
1.8
6.5
13
22
41
62
82
119
Liver
0.02
0.45
1.6
3.1
4.9
8.7
12
16
21
Duration of
Ingestion
fYearsl
1
5
10
15
20
30
40
SO
70
Curiun-244/Plutoniun-240
Red Marrow
7.9
37
65
92
108
133
150
160
175
Bane
Endosteal
9.0 E+l
4.2 E+2
7.5 E+2
1.1 E+3
1.2 E+3
1.5 E+3
1.7 E+3
1.8 E+3
2.0 E+3
Liver
2.6 E+l
1.2 E+2
2.1 E+2
2.8 E+2
3.3 E+2
3.9 E+2
4.3 E+2
4.6 E+2
4.8 E+2
-------
TABLE 3-12
AVERAGE SKELETAL DOSE RATES DUE TO CHRONIC INGESTION OF
OF PLUTONIUM-239 OXIDE
WITH AND WITHOUT INCREASED INFANT UPTAKE
Annual Intake = 1000 pCi/Year
Average Skeletal Dose Rate in Microrad/Year
U)
I
CJ
00
Age
1
5
10
15
20
30
40
50
70
Without Enhanced
Infant Absorption*
9
43
84
124
162
235
303
366
480
With Enhanced
Infant Absorption**
86
76
108
133
170
242
310
372
485
*GI tract to blood transfer 10~ all ages.
**GI tract to blood transfer 10 first year of life.
-------
There is no clinical evidence of bone cancer being caused
by plutonium. The most relevant human data is for medical
patients treated with radium-224, which, because of its short
half-life (3.64 days), is retained mainly on bone surfaces.
A large number of patients (approximately 900) who were treated
with radium-224 for tuberculosis and ankylosing spondylitis have
been followed for bone cancer incidence. The dose to these
patients has been calculated in terms of the average skeletal
dose, defined as total alpha energy emitted divided by bone mass,
even though the dose distribution is very nonuniform. On this
basis, it has been estimated that for chronic irradiation due to
Pu-239, 200 bone cancers will be produced per 106 rad to a 7 kg
skeletal mass. In terms of the dose to mineral bone, these
results yield 140 bone cancers per rad to osseous tissue.
Because of uncertainties in the redistribution of Ra-224
following its initial deposition on bone surfaces, the above
estimate of the average skeletal dose delivered in the Ra-224
cases may be too high, leading to an underestimate of the risk
per rad for radium-224. While the above analysis assumes that
half of the skeletal radium-224 decays on bone surfaces and half
in the bone volume, others have stated that only 1.5% of the
skeletal radium-224 decays within the bone volume away from bone
surfaces. This would increase the risk per rad by 174%.
Furthermore, this model predicts that for radium-224 on bone
surfaces, the dose rate to osteogenic cells near the bone surface
is 8.9 times the average skeletal dose rate; for plutonium-239,
12.8 times. In terms of average to osseous tissues as calculated
for these risk estimates, plutonium-239 would therefore deliver
1.44 times as much alpha particle dose to osteogenic cells as
radium-224. This estimate is likely to be too high, since it
assumes all the plutonium is retained on bone surfaces and none
is buried in the remodeling or bone growth process.
The residence time of plutonium on bone surfaces depends on
age. In rapidly growing animals, it is relatively short, while
3-39
-------
there is a prolonged Pu-239 bone surface residence time in adult
bone and they accumulate more Pu-239 with time. Since almost all
of the body burden is assumed during adult life, the exposure
regime due to chronic plutonium inhalation and ingestion may
favor a surface dose distribution. After giving due
consideration to the smaller number of bone precursor cells in
adults, Jee, et al. have characterized the plutonium-239 injury
to bone as low in rapidly growing beagles, moderate for young
adults, and high for adults. A similar characterization for
degrees of insult would appear to hold for humans, particularly
when subject to chronic exposure.
3.4.5 CANCER OF THE LIVER
The magnitude of the potential risk of inducing liver cancer
by means of plutonium and other transuranium elements has been
recognized only recently. Earlier regulations were based on the
1959 NCRP-ICRP assumption that the critical organ for plutonium
deposited from blood is bone. More recently, it has been
recognized that deposition in liver is as likely as in bone, and
ICRP Report 19 assumes that 45% of the plutonium and other
transuranium elements dissolved in blood is deposited in the
liver and an equal amount in bone. Based on the results of
animal studies, deposition in liver may be somewhat lower for
plutonium and somewhat higher for americium and curium.
The risk to humans from alpha emitters deposited in the
liver can be assessed on the basis of rather limited information
obtained from epidemiological studies of medical patients.
Earlier in this century, a low specific activity alpha particle
emitting contrast medium called Thorotrast was utilized in some
diagnostic x-ray procedures. In subsequent years patients who
were treated with it, mainly European, have been followed
clinically and shown to have a higher than expected incidence of
liver cancer. These data are pertinent although they do have
limitations. Because the amount of material injected into the
3-40
-------
blood in these studies was quite large, its deposition in the
liver was uneven. Liver cancer incidence in this group would
not necessarily be higher than might be expected for a more
uniform deposition. On the contrary, there is a general
consensus that highly localized concentrations of alpha particle
emitters are likely to be less carcinogenic than a more uniform
distribution. Another possible limitation of these data is that
the relatively large quantity of Thorotrast deposited in the
liver could lead to a foreign body response, which might in turn
result in cancer. While the quantitative applicability of the
human experience with Thorotrast to the prediction of plutonium
risks to liver is tentative, there is an abundance of
experimental animal data showing that liver cancers can be
induced by plutonium. Liver cancers are seen less frequently
than bone cancers in most experiments with animals, but since
liver cancers have a longer latent period than bone cancers, they
may be more important in a longer-lived species such as man. The
primary source of data on Thorotrast patients is Faber's review,
also cited by the British Medical Research Council (MRC) as a
basis for its assessment of plutonium toxicity. Estimates of
risk for liver cancer are: absolute risk, 4.2 x 10"6 liver cancer
for each organ rad per year at risk; relative risk, an
11% increase per rad.
3.4.6 LEUKEMIA DUE TO BONE MARROW IRRADIATION
Several authors have pointed out that there is a potential
risk of leukemia from plutonium incorporated into bone tissues.
Alpha particles originating in trabeculae may irradiate a
significant fraction of the bone marrow, and the plutonium in
marrow itself will act as a source. Based on auto-radiographic
studies of bone and bone marrow, it has been estimated that the
dose to trabecular marrow is 88 percent of the average skeletal
dose due to plutonium-239.
3-41
-------
The International Commission on Radiological Protection
states in ICRP Report 26 that "The red bone marrow is taken to be
the tissue mainly involved in the causation of radiation-induced
leukemia; other blood-forming tissues are thought to play a minor
role in leukemogenesis." Observations on humans irradiated for
therapeutic purposes or on Japanese survivors of nuclear
explosions indicate that the incidence of radiation-induced
leukemia reaches its peak within a few years of irradiation,
and returns to pre-irradiation levels after about 25 years.
For radiation protection purposes the risk factor (for gamma
radiation) is taken to be 2xlO"3 per Sievert. [This is equivalent
to 4xlO"4/rad, or 400 per 106 person year rad, for alpha radiation
with an RBE of 20] Using this factor, the incremental risk due to
leukemia for the inhalation mode of exposure is comparable to the
risk to pulmonary tissue. However, the BEIR-3 Report states that
"It should be recognized that risk (of leukemia) estimated at a
selected point in the high- dose region may overestimate the
magnitude of hazards of low-dose exposures by a factor of 2-10,
depending on the type of radiation, its rate of delivery, and the
high-dose point at which the observations were made."
The estimated risk of leukemia due to the ingestion of
transuranium elements is somewhat greater than for the inhalation
mode. For a 3 mrad limiting dose in the 70th year to skeletal
bone, the leukemia risk ranges from 0.4 to 1.6 cases per 100,000
exposed for the absolute and relative risk models respectively
and is comparable to the estimated risk of liver cancer.
3.5 COMPARISON OF INHALATION AND INGESTION RISKS
The total somatic risks to persons from exposure at dose
rates in accord with the objectives of the Recommendations on
Dose Rates from Transuranium Elements have been calculated in
accord with the above discussion. A summary of estimated
lifetime risks from inhalation and ingestion of plutonium-239
is shown in Table 3-13.
3-42
-------
TABLE 3-13
ESTIMATED RISKS IN THE 70th YEAR
FROM INHALATION AND INGESTION OF PLUTONIUM-239
Inhalation
Class Y *
Ingestion **
Class W
OJ
I
OJ
Lung Cancer
Liver Cancer
Leukemia
Bone Cancer
Total
0.67xlO~6
0.25xlO~6
0.15xlO~6
0.12xlO~6
1.19x10
-6
0.62xlO~6
0.34X10~6
0.26X10"6
1.22xlO~6
* Inhalation: Class Y is normalized to an equilibrium dose rate to pulmonary
lung of 1 mrad/yr (AMAD = 1 urn and air cone =2.6 fCi/m )
** ingestion; Class W is normalized to a dose rate of 1 rarad/yr to skeletal
bone in the 70th year of continuing exposure
-------
3.6 GENETIC DAMAGE
The degree to which transuranium elements are translocated
from human blood to gonadal tissues is not well known due to the
analytical difficulty of making reasonably precise measurements
at the low activity levels usually involved, and the large
variability between individuals in the general population.
In addition to limited information from studies of laboratory
animals, there are three sources of post-mortem human data: the
general population exposed to fallout plutonium, industrially
exposed radiation workers, and a few clinical studies with
hospital patients. Richmond and Thomas reported that for the
five animal species considered in their 1974 review, an average
of 0.03% of the plutonium in blood was transferred to gonadal
tissue. The data on which this average is based varied by a
factor of about ten. A review of clinical data, based on only
four persons, also leads to an estimate of about 0.03% for
transfer from blood to gonadal tissue.
The British Medical Research Council (MRC) also reviewed
this problem in its 1975 analysis of plutonium toxicity and
concluded that 0.05% of the plutonium in blood would be
transferred to gonadal tissue. Since the mass of the ovary is
11 grams, the MRC estimate on transfer from blood is equivalent
to 0.005% per gram of ovary. The mass of testes is greater than
that of the ovary by a factor of about 3. The MRC assumed equal
quantities of plutonium in each, so that the concentration
(percent per gram) in the testes would be about one-third of that
in ovarian tissue, or 0.002% per gram. Other authors have
estimated that the amount of plutonium in the smaller female
gonad was a factor of five to ten less than males, a somewhat
less conservative assumption. Recent data reported for plutonium
in beagle gonads indicates that the concentration per gram is
about 0.0055% in ovaries and 0.0012% in testes.
3-44
-------
Risks due to transuranium element are not only to persons
directly exposed to the radiation but also to their progeny.
Alpha particles can damage the male progenitor cells producing
sperm and the egg cell (oocyte) in the female. The expression of
this damage is either genetic impairment of the live-born
offspring or fetal death.
Risk estimates for genetic damage are based on the gonadal
dose received in a reproductive generation, i.e., the first
30 years of life. The 30-year gonadal doses due to chronic
ingestion of transuranium elements that would also cause a
3 millirad per year dose rate to red bone marrow after
70 years,are shown in Table 3-14. Chronic ingestion of Cm-244
would cause genetic risks about two times larger. For the given
recommendations, genetic effects due to inhalation are
substantially less important than those due to ingestion.
It is estimated that a 30-year dose of one millirad due to
alpha-emitting transuranium elements in gonadal tissue may cause
between 0.1 and 2 genetic effects per 100,000 live births in the
first generation. If this gonadal dose were to continue
indefinitely so that a new equilibrium of genetic damage was
established in the population, the risk might increase to 0.6 to
15 per 100,000 live births. Currently, the rate of observed
genetic effects in the U.S. is about 6000 per 100,000 live
births.
3-45
-------
TABLE 3-14
OCCUPATIONAL EXPOSURE
ANNUAL LIMIT OF INTAKE (ALI) AND DERIVED AIR CONCENTRATION (DAC)
FOR THE MORE IMPORTANT TRANSURANIUM NUCLIDES
(Fiom F*d«nl Culdanco Report No 11 CPA 520'1-U-020)
Inhalation Ingesdon
ALI DAC ALI
Nuclide/tIR Class/r, pC, (iC/m1 f, >iC.
Ni:i"l L'NIUM
Np-236
5 10' )
Np-2J7
214 10°;
Np-2JX
2ll7d
Np-239
2355 d
PLUTONIUM
l»u-23R
8774;
l'u-23V
24065;
Pu-240
6537 ;
l'u-241
144,
I-U-U2
376 10';
AMI KICIUM
Am-241
4322;
Am-242
152;
Am-242iD
1602 h
Am-243
73*0;
Ara-244
10.1 h
An-244111
26 m
CURIUM
Cm-242
1628 d
Cm-244
18 II y
W 10'
W 10'
W IB1
W 10'
W 10'
Y 10'
W III1
V 10'
W 10"
Y in'
W 10'
V 10'
W III1
Y 10'
W 10'
W 10'
W ID'
W 10'
W 10'
W 10'
VV 10'
W 10'
on:
0004
(0
2000
0007
002
00116
002
OOOA
II 112
UJ
OH
OIKI7
on:
0006
0006
HO
0006
200
•1000
03
001
» 10'
2 10"
3 I0>
9 10'
3 10"
H ID1'
J IB'1
7 10"
3 I01'
7 II)1'
1 10"
1 III™
J 10"
7 10"
3 10 ''
3 10"
4 10'
3 10"
« 10"
2 10*
1 III"1
5 10"
1)001
0001
0001
0001
0001
1 10*
I) 001
1 10'
0001
1 III*
0001
I iu-
0001
1 10'
1 10-
1 10-
1 10-
1 10-
1 10-
1 10-
1 10'
1 10'
3
05
1000
2000
09
9
OS
11
OR
S
40
41)1)
OH
8
OK
08
4000
OH
3000
6 10'
30
1
3-46
-------
TABLE 3-15
THIRTY-YEAR GONADAL DOSE DUE TO AN INGESTION PATTERN
RESULTING IN A 3 MILLIRAD/YEAR ALPHA PARTICLE DOSE RATE
TO BONE IN THE 70th YEAR
(Chronic Lifetime Ingestion At A Constant Rate)
U)
I
Transuranium Element
Pu-238
Pu-239
Pu-240
Pu-241
Am-241
Cm-244
Gonadal Dose
fmillirad)
4.3
3.7
3.7
2.0
4.0
7.0
-------
3.7 SELECTED REFERENCES
Proposed Guidance on Dose Limits for Persons Exposed to
Transuranium Elements in the General Environment: Summary Report.
Report EPA 520/4-77-016, U.S. Environmental Protection Agency,
Washington, D.C. (1977)
Response to Comments; Guidance on Dose Limits for Persons Exposed
to Transuranium Elements in the General Environment. Report EPA
520/4-78-010, U.S. Environmental Protection Agency, Washington,
D.C. (1978)
Selected Topics; Transuranium Elements in the General
Environment. Technical Note ORP/CSD 78-1, U.S. Environmental
Protection Agency, Washington, D.C. (1978)
Report of the United Nations Scientific Committee on the Effects
of Atomic Radiation. Supplement No. 13 (A/7613), United Nations,
New York (1969)
United Nations Scientific Committee on the Effects of Atomic
Radiation, Ionizing Radiation: Sources and Biological Effects.
1982 Report to the General Assembly. No. E.82.IX.8, United
Nations, New York (1982)
National Academy of Sciences, The Biological Effects of Atomic
Radiation. Report of the Committee on Genetic Effects of Atomic
Radiation, Washington, D.C. (1956)
The Effects on Populations of Exposure to Low Levels of Ionizing
Radiation: 1972 (BEIR-1 Report) Report by the Committee on the
Biological Effects of Ionizing Radiation, National Academy of
Sciences, Washington, D.C.
The Effects on Populations of Exposure to Low Levels of Ionizing
Radiation; 1980 (BEIR-3 Report), Report by the Committee on the
Biological Effects of Ionizing Radiation, National Academy of
Sciences, Washington, D.C.
Health Effects of Alpha-Emitting Particles in the Respiratory
Tract. Report of Ad Hoc Committee on "Hot Particles" of the
Advisory Committee on the Biological Effects of Ionizing
Radiations, National Academy of Sciences, EPA 520/4-76-013,
Office of Radiation Programs, Environmental Protection Agency,
Washington, D.C. 1976.
3-48
-------
Health Risks of Radon and Other Internally Deposited Alpha
Emitters: 1988 (BEIR-4 Report), Report by the Committee on the
Biological Effects of Ionizing Radiation, National Academy of
Sciences, Washington, D.C.
Health Effects of Exposure to Low Levels of Ionizing
Radiation: 1990 (BEIR-5 Report), Report by the Committee on
the Biological Effects of Ionizing Radiation, National Academy
of Sciences, Washington, D.C.
Deposition and Retention Models for Internal Dosimetry of the
Human Respiratory Tract, ICRP Task Group on Lung Dynamics, Health
Physics 12:173-208 (1966)
General Concepts for the Dosiroetrv of Internally Deposited
Radionuclides. NCRP Report No. 84: National Council on Radiation
Protection and Measurements, Bethesda, MD (1985)
International Commission on Radiological Protection,
ICRP Publication 2, Report of Committee II on Permissible Dose
for Internal Radiation. Pergamon Press, New York.(1959)
International Commission on Radiological Protection, ICRP
Publication 14, Radiosensitivity and Spatial Distribution of
Dose. Pergamon Press, New York.(1969)
International Commission on Radiological Protection, ICRP
Publication 19, The Metabolism of Compounds of Plutonium and
Other Actinides. Pergamon Press, New York.(1972)
International Commission on Radiological Protection, ICRP
Publication 23, Report of the Task Group on Reference Man.
Pergamon Press, New York.(1975)
International Commission on Radiological Protection, ICRP
Publication 26, Radiation Protection. Pergamon Press, N.Y.(1977)
International Commission on Radiological Protection, ICRP
Publication 30, Limits for Intakes of Radionuclides by Workers.
Pergamon Press, New York. (1979)
International Commission on Radiological Protection, ICRP
Publication 48, The Metabolism of Plutonium and Related Elements.
Pergamon Press, New York. (1986)
National Radiological Protection Board, Gut Uptake Factors for
Plutonium. Americium. and Curium. NRPB-R129, Her Majesty's
Stationary Office, 1982
National Radiological Protection Board, Radiological Problems in
the Protection of Persons Exposed to Plutonium. G.W. Dolphin et
al. Report NRPB-R29, Harwell, Great Britain, 1974
3-49
-------
The Toxicity -of Plutonium. 1975. British Medical Research
Council, Her Majesty's Stationary Office, London.
World Health Organization, Nuclear Power - Health Implications
of Transuranium Elements. WHO Regional Publications: European
Series No. 11, Copenhagen (1982)
Commission of the European Communities, The Toxicity of
Plutonium. Americium. and Curium (1979)
International Atomic Energy Agency, Basic Safety Standards
for Radiation Protection; Safety Series 9. Vienna (1982)
World Health Organization, Environmental Health Criteria 25:
Selected Radionuclides. WHO, Geneva (1983)
Tamplin, A. R. and Cochran, T. B., Radiation Standards for Hot
Particles: A Report on the Inadequacy of Existing Radiation
Protection Standards Related to Internal Exposure of Man to
Insoluble Particles of Plutonium and Other Alpha-Emitting Hot
Particles. Natural Resources Defense Council, Washington, D.C.
(1974)
Killough, G. et al, INREM II; A Computer Implementation of Recent
Models of Estimating the Dose Equivalent to Organs of Man from an
Inhaled or Ingested Radionuclide. Oak Ridge National Laboratory
Report ORNL/NUREG/TM-84 (1978)
Dunning, D. E. et al, A Combined Methodology for Estimating Dose
Rates and Health Effects from Exposure to Radioactive Pollutants
(RADRISK). ORNL/TM-7105 (1980)
Houston, J. R., Strenge, D. L. and Watson, E. C., 1974. DACRIN -
A Computer Program for Calculating Organ Dose from Acute or
Chronic Radionuclide Inhalation. BNWL-B-389, Battelle Pacific
Northwest Laboratories, Richland, Washington.
Sullivan, R., Plutonium Air Inhalation Dose (PAID).
ORP/CSD Technical Note, 77-4, U.S. Environmental Protection
Agency, Washington, D.C. (1974)
Bair, W.J., 1975. The Biological Effects of Transuranium
Elements in Experimental Animals, pp 464-536 in Proceedings of
Public Hearings; Plutonium and Other Transuranium Elements.
ORP/CSD-75-1, Volume 1, U.S. Environmental Protection Agency,
Washington, D.C.
Cook, J., Bunger, B., and Barrick, K., 1978. A Computer Code for
Cohort Analysis of Increased Risks of Death (CAIRO). Report EPA
520/4-78-012, U.S. Environmental Protection Agency, Washington,
D.C.
3-50
-------
Bair, W. J. , Toxicology of Plutonium. Adv. Rad. Biol. 4., 255-313
(1974)
Durbin, P.W.: Plutonium in Man; A New Look at Old Data in
Radiobioloqy of Plutonium. Editors B.J. Stoer and W.S. Jee, J.W.
Press, University of Utah, Salt Lake City, 1972.
Durbin, P.W., 1974. Behavior of Plutonium in Animals and Man, pp
30-56 in Plutonium Information Meeting. CONF-740115; US Atomic
Energy Commission, Oak Ridge.
Bair, W. J. and Thomas, J. M., 1976. Prediction of the Health
Effects of Inhaled Transuranium Elements from Experimental Animal
Data, pp 569-585 in Transuranium Nuclides in the Environment.
International Atomic Energy Agency, Vienna.
Oftedal, P. and Searle, A., An Overall Genetic Risk Assessment
for Radiological Protection. J. Med. Genetics, 17:15-20 (1980)
Richmond, C. R. and Thomas, R. L., 1975. Plutonium and
Other Actinide Elements in Gonadal Tissue of Man and Animals.
Health Physics, 29:241-250.
Fish, B. R., Keilholz, G. W., Snyder, W.S. and Swisher, S.D.,
Calculation of Doses Due to Accidentally Released Plutonium from
an LMFBR. ORNL-NSIC-74, Oak Ridge National Laboratory, Oak Ridge.
(1972)
Land, C.E. and Pierce, D.A. Some Statistical Considerations
Related to the Estimation of Cancer Risk Following Exposure to
Ionizing Radiation, pp. 67-89 in Epidemiology Applied to Health
Physics. CONF 830101. National Technical Information Service
#DE83014383, NTIS, Springfield, VA. 1983.
Dolphin, G. W. and Eve, I. S., 1966. Dosimetrv of the
Gastrointestinal Tract. Health Physics, 12:163-172.
Vaughan, J. M., 1973. The Effects of Irradiation on the
Skeleton, Clarendon Press, Oxford.
Spiess, H. and Mays, C. W., 1973. Protraction Effect on Bone
Sarcoma Induction of Ra in Children and Adults, pp 437-450 in
Radionuclide Carcinogenesis. CONF-720505, C. L. Saunders, R. H.
Busch, J. E. Ballou and D. D. Mahlum, editors, AEC Symposium
Series 29, U.S. Atomic Energy Commission, Oak Ridge.
Mays, C. W., et al., 1976. Estimated Risk to Human Bone
from Pu, pp 343-362 in "The Health Effects of Plutonium and
Radium". W. S. S. Jee, editor, The J. W. Press, Salt Lake City.
3-51
-------
Rowland, R. E. and Durbin, P. W., 1976. Survival, Causes of
Death and Estimated Tissue Doses in a Group of Human Beings
Injected with Plutonium, pp 329-341 in The Health Effects of
Plutonium and Radium, W. S. S. Jee, editor, The J. W. Press, Salt
Lake City.
Jee, W. S. S., et al., 1976. The Current Status of Utah Long-
Term Pu Studies, in "Biological and Environmental Effects of Low-
•Level Radiation". Vol II, International Atomic Energy Agency,
Vienna.
Durbin, P. W., 1975. Plutonium in Mammals: Influence of
Plutonium Chemistry. Route of Administration, and
Phvsioloqical_Status of the Animal on Initial Distribution and
Long- Term_Metaholism. Health Physics 29:495-510.
Newcombe, H. B., 1975. Mutation and the Amount of Human
111 Health, pp 937-946 in Radiation Research: Biomedical.
Chemical, and Physical Perspectives. O. F. Nygaard, H. I. Adler
and W. K. Sinclair, editors, Academic Press, Inc., New York.
Vaughan, J., 1976. Plutonium - a Possible Leukemia Risk,
pp 691-705 in The Health Effects of Plutonium and Radium.
W. S. Jee, editor, The J. W. Press, Salt Lake City, Utah
Spiers, F. W. and Vaughan, J., 1976. Hazards of Plutonium with
Special Reference to the Skeleton. Nature 259:531-534.
National Council on Radiation Protection and Measurements.
Natural Background Radiation in the United States.
NCRP Report No. 45, NCRP, Washington, D.C., 1975.
Environmental Protection Agency. Population Exposure to External
Natural Radiation Background in the United States. Technical
Note: ORP/SEPD-80-12. Office of Radiation Programs, USEPA,
Washington, D.C., 1981.
3-52
-------
4. TRANSURANIUM ELEMENTS IN THE ENVIRONMENT
[Reprinted with Minor Changes from "Proposed Guidance on Dose
Limits for Persons Exposed to Transuranium Elements",
EPA/520/4-77/016]
4.1 INTRODUCTION
Plutonium and other transuranium elements have been
released into the general environment primarily from four
sources. In order of decreasing importance, these include:
a. Aboveground testing of nuclear weapons
b. Accidents involving nuclear weapons and
satellite power sources
c. Accidents at nuclear facilities
d. Planned discharges of effluents from nuclear
facilities
The aboveground testing of nuclear weapons during 1945-1963
caused a worldwide dispersal of plutonium and americium. For the
most part, this radioactivity was injected into the stratosphere
and has been redeposited more or less uniformly over the earth's
lands and waters. This redeposited plutonium and americium is
available to people through inhalation and ingestion pathways and
exists as an ubiquitous source in the general environment upon
which is superimposed the releases of transuranium elements from
other sources. Fallout plutonium is primarily a mixture of
Pu-239 and Pu-240 with lesser amounts of Pu-238, Pu-241 and
Pu-242. About 58% is Pu-239 and 39% Pu-240; because these two
radionuclides are essentially identical with respect to chemical
behavior and alpha energies, the sum of their activities in the
environment will be referred to as "Pu-239" (l). The daughter of
Pu-241 (t|/2= 12y) is Am-241, so that as the Pu-241 continues to
decay, the concentration of Am-241 in the environment increases
relative to the amount of Pu-239. The Am-241/Pu-239 activity
4-1
-------
ratio in soil is now about 0.25 and will eventually increase
to 0.40 (2).
Aboveground nuclear weapons testing produced approximately
430 kilocuries of Pu-239 over the period 1945 to 1974. About
105 kilocuries deposited quickly near the various detonation
sites. Of the 325 kilocuries injected into the stratosphere,
250 kilocuries have deposited in the mid-latitudes of the
northern hemisphere, 70 kilocuries have deposited in other
latitudes and about 5 kilocuries still remained in the
stratosphere as of 1974. This has led to cumulative
depositions of Pu-239 on ground surfaces in the United States
that range from 0.001 to 0.003 /iCi/m2. Since 1967, sporadic
aboveground nuclear tests have held the air concentration level
of plutonium to relatively constant values, currently ranging
from 0.01 to 0.1 fCi/m3 in ground level air. These levels are
not believed to be the result of resuspension from soil surfaces.
The cumulative deposition of fallout Pu-239 at selected
locations in the United States (3) is shown in Table 4-1. The
distribution in soil with respect to depth at both an undisturbed
site and a cultivated site is shown in Table 4-2 (4.5).
Table 4-3 is a summary of fallout Pu-239 levels in New York City
for both air and ground deposition as a function of time from
1954 to 1975 (6). The total amount of Pu-238 injected into the
stratosphere from aboveground nuclear tests is about 9 kilocuries
(3). In addition, 17 kilocuries of Pu-238 were released in the
high stratosphere of the southern hemisphere when a satellite
containing a nuclear power source (SNAP-9A) failed to orbit and
disintegrated (9). As a result, there are measurable amounts of
Pu-238 in most environmental media. An estimated 90 curies of
curium (Cm-245 and Cm-246) have been produced as the result of
weapons tests (1).
A potential source for future release of the transuranium
elements to the general environment are operations associated
4-2
-------
TABLE 4-1
Cumulative Deposit of Fallout Pu-239 at Selected
Locations in the United States
Approximate Location
Pu-239 Concentration (a)
Rich I and, Washington
San Francisco, California
Los Angeles, California
National Test Site, Montana
Rapid City, South Dakota
Topeka, Kansas
Tulsa, Oklahoma
Corpus Christi, Texas
Chicago, Illinois
Augusta, Maine
Cape Cod, Massachusetts
Long Island. New York
Raleigh, North Carolina
Miami, Florida
Average (± 2ff)
O.OOU
0.0009
0.0007
0.0019
0.0025
0.0024
0.0022
0.0010
0.0021
0.0017
0.0023
0.0024
0.0024
0.0010
0.0018 ± 0.0006
(a) Top 30 cms of soil
4-3
-------
TABLE 4-2
Concentration of Fallout Pu-239 in Soil as a
Function of Depth at North Eastharo, Massachusetts
Depth
(cm)
0-2 (Includes Vegetation) (a)
2-4
4-6
6-8
8-10
10-12
12-U
H-16
16-21
21-26
Depth
(Cm)
0-5
5-10
10-15
15-20
20-25
25-30
30-35
35-40
40-45
45-50
50-55
Undisturbed Site
Concentration of Pu-239
(uCi/m )
0.91x10
0.37
0.15
0.12
0.052
0.035
0.028
0.027
0.047
<0.004
Cut 1 1 vated Si te(5)
Concentration of Pu-239
(uCi/m
0.42x10
0.45
0.34
0.37
0.32
0.20
0.02
0.02
0.02
0.02
0.02
X of Total
52 (a)
21
8
7
3
2
2
1
3
<0.1
X of Total
19
20
16
17
15
10
0.01
0.01
0.01
0.01
0.01
(a) 1ZX of the total plutonium was associated with vegetation
4-4
-------
TABLE 4-3
Fallout Pu-239 in New York City
rear
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
Deposl t ion
(uCi/m )
0.07xlu'3
0.09
0.12
0.12
0.16
0.23
0.04
0.06
0.32
0.62
0.41
0.14
0.05
0.04
0.04
0.06
0.03
0.03
0.02
0.01
0.02
0.01
Cumulative deposit
CuCi/m )
0.00007
0.00016
0.00028
0.00040
0.00056
0.00078
0.00082
0.00089
0.0012
0.0018
0.0022
0 0024
0.00245
0.0025
0.0025
0.0026
0.0026
0.0026
0.0027
0.0027
0.0027
0.0027
Surface air concentration
(fCi/n )
0.14
0.18
0.23
0.23
0.32
0.45
0.081
0.13
0.63
1.68
0.91
0.33
0.12
0.051
0.08
0.06
0.068
0.06
0.027
0.013
0.039
0.02
4-5
-------
with the Light-Water Reactor Fuel Cycle. About 250 kg of
Plutonium, which is inside the spent fuel rods, is removed per
year from a 1000 Mw(e) light-water reactor. The isotopic
composition of this plutonium is typically 59% Pu-239,
29% Pu-240, 11% Pu-241, 4% Pu-242 and 2% Pu-238 (9).
Table 4-4 is a listing of the nuclear properties of the more
significant transuranium nuclides (7).
Sections that follow briefly discuss specific controlled
sites and other areas in the general environment which have
become contaminated with transuranium elements significantly
above levels attributed to atmospheric fallout. These include:
local fallout from aboveground nuclear tests, accidents at
nuclear facilities, and effluent releases from nuclear
facilities. Data were selected to be representative of
conditions at these sites during the mid-1970's. Additional
information is available in the documents that have been
referenced. Table 4-5 provides a summary of these sites, their
locations, inventories, and approximate onsite and offsite
maximum soil concentration levels.
This chapter was prepared in the mid-70's and has not
been revised. The environmental data represent conditions at
that time and do not necessarily represent current levels of
environmental contamination. In general, concentrations in near-
surface soils are depleted with time and the hazards to exposed
persons are diminished.
4.2 MAJOR SITES OF ENVIRONMENTAL CONTAMINATION
4.2.1 The Nevada Test Site (NTS)
The Nevada Test Site (10) is an area of about 3500 km2
located in Nye County, Nevada, 90 kilometers northwest of Las
Vegas. It is surrounded by an exclusion area 25 to 100 kms wide
between the test site itself and public lands. The climate is
4-6
-------
TABLE 4-4
Nuclear Properties of Environmentally Significant Transuranium Radionuclldes
Radiological
Energy of
Radlonuclide
Pu-238
Pu-239
Pu-240
Pu-241
Pu-242
Am-241
Am-243
Cm-242
Cm-244
half-life
(y)
87.4
2.4xlOA
6.6xl03
14.3
3.9xl05
443.
7.4xl03
0.45
18.1
Mode of
Decay
alpha
alpha
alpha
beta
alpha
alpha
alpha
alpha
alpha
Major Radiations
(MeV)
5.50; 5.46
5.16; 5.11
5.17; 5.12
0.021 (max)
4.90; 4.86
5.49; 5.44
5.28; 5.23
6.12; 6.07
5.81; 5.77
Daughter.
Radionuclide
U-234
U-235
U-236
Am-241
U-238
Np-237
Np-239
Pu-238
-------
TABLE 4-5
INVENTORY OF PLUTONIUM FOR SELECTED SITES IN THE UNITED STATES
LOCATION
APPROX INVENTORY
REMARKS
i
CO
U.S. (Fallout) 20,000 Ci
Nevada Test Site >155 CI
(near Las Vegas, NV)
Rocky Flats Plant 8-10 Ci
(near Denver, CO)
Mound Laboratory 5-6 CI
(Miamisburg, OH)
Savannah River Plant 3-5 CI
(SW area of SC)
Hanford Site *
(central WA)
Los Alamos Laboratory *
(NW of Santa Fe, MM)
Oak Ridge Laboratory *
(east TN near Knoxville)
Idaho National Engineering Lab *
(central ID)
Trinity Site >45 Ci
(near Alamogordo, NM)
Worldwide Pu-238 = 17,000 CI
Pu-239 = 440,000 Ci
U.S. Average = 1.5 mCi/km2
Nuclear Test Site
Surface and Subsurface Tests
Weapons Fabrication Facility
Pu-238 Processing Facility
Pu Production Facility
(Pu and higher isotopes)
Pu Production-Research Facility
(high levels of Pu on site)
Weapons Development
(Pu-239 In remote canyons)
Research and Development Facility
Separation, Test, and Research Facility
(Pu-239 in soil/groundwater)
Site of first atomic bomb test
-------
POPULATION DISTRIBUTION BY AZIMUTH AND DISTANCE
AROUND NTS (10)
FIGURE 4-1
4-9
-------
Si
§1
• 1.3*0.4
! J
• 2.2*1.0
Tl
i
i
i
i
0.7i0.4 •>
I
1.110.2 |
1.1*0. lo° I
0?.
f
** I MP| i
ONA I ~ ~
SO 100
k il o mt I ir i
I
700
O
O
x
HI
2
UJ
Z
CUMULATIVE NTS DEPOSIT OF Pu-239,240 (12)
(mCi per km2)
FIGURE 4-2
4-10
-------
a
«/
o/
•1.8«0.3
• 2.8*1.0
•1.7*0.3
•l 1.7*0.8
I
• 2.0*0.7
•1.U0.5
il.UO.l
"I
;O-,
I NTS
•1.5*0.5 /
I
•1.5t0.7
I
I
i
I
1_.
1.8*0.2
'§
o2.1t0.2 | 5
o
I
o3.3i0.3
o20±0.2i___«lL9*0_2__
ol.7»0.5
ol.5i0.4 °
o
•2.1*0.4
• 1.4*0.3
l.BsO.l
1.0-0.2*
°1.2iQ7
•2.6i0.3
• 1.2*0.4
2.2i0.1
2.0*0.1
'ir-1
UTAH
,8
ARIZONA
^ /
\
\
°^x
t. ^
- -
lo
15
'i
IS
50 1
I
00
?do
CUMULATIVE GLOBAL FALLOUT DEPOSIT OF Pu-239,240(12)
(mCi oer km 2
FIGURE 4-3
4-11
-------
TABLE 4-6
Estimated Inventory of Plutonium in Surface Soil at Specific
Areas within the National Test Site and Tonopah Test Range
Area
13
5 (GMX)
*• Double Track
1 Clean Slate 1
1X0 Clean Slate 2
Clean Slate 3
Plutonium Valley
Size of Estimated
Area Inventory
(m2) (curies Pu-239)*
3.6xl06
2.4xl05
3.0xl05
2.2xl05
7.9xl05
1.3xl05
4.8xl06
Total
44
3
5
5
29
30
39
155
± 9
i 0.3
± 1
± 2
± 6
± 5
i 4
Range of Soil .
Concentrations
(uCl/m2) Pu/Am Activity Ratios'
2
3
7
15
4
12
1
to 840 9
to 530 10
to 2,800 1
to 120 \ 22 to 26
to 260
to 370 J
to 6,200 5 to 8
(a) Inventory as measured to 5 cm soil depth.
(b) Soil concentration range values refer to concentrations within sub regions of each site
as selected by stratified random sampling.
-------
TABLE 4-7
Pu-239 In Air Siaplti Mttr tht UTS
loc • t 1 on
Furnice C r t tk , CA
Otnh V« 1 1 ty Jet •
C< 1 1 1 orn I •
Stilly, NV
Ollblo. NV
N 1 ko. NV
Indian Spring. NV
Ll throp U.I 1 •, NV
Plhruop, NV
Scatty' i Jet . , NV
Uir* Springs, NV
04 C I
2/20/71
10/30/72
2/20/71
3/31/71
10/24/72
10/28/72
12/11/72
2/03/71
2/2S/71
3/01/71
3/17/71
10/2S/71
4/25/72
4/20/71
5/04/71
J/26/71
3/26/71
4/25/71
6/26/71
9/25/71
J/l J/71
W1J/7Z
3/1S/70
9/25/70
3/18/71
10/24/72
5/17/71
10/30/72
2/19/70
3/31/71
10/24/72
10/29/72
12/13/72
3/12/71
3/26/71
4/2S/71
Dounu 1 nd
Concent r •
< »CI/«
.0.05
0.04
0.20
0.12
0,10
0.07
0.03
0.09
o.ot
0.06
0.19
0.08
0.088
0 20
0.20
0.40
0.20
0.20
0.20
0. 70
0 10
o oar
0. 06
0.17
0.20
0.04
0.30
0. 12
0.15
0.20
0.068
0.15
0.059
0.14
0.08
0. 13
Pu-239
I Ion
) 0«t.
4/20/71
12/7/72
5/2/71
5/3/71
10/2/72
12/6/72
12/7/72
6/28/70
4/20/71
5/2/71
5/20/71
10/16/71
4/16/72
2/20/71
3/1/71
3/31/71
9/25/70
2/20/71
3/18/71
10/28/71
4/ZO/ 71
4/16/75
4/20/71
6/26/71
9/25/71
10/2/72
4/20/71
10/2/72
4/20/71
5/3/71
5/27/71
12/4/72
12/6/72
•12/7/72
2/19/70
3/18/70
3/31/70
2/3/71
2/20/71
3/17/71
3/31/71
Upwind Pu-239 Concentration
Concentration Oounulnd
( f C 1 /• vf Upwind
020 No 0 1 f f irtnet
0.051
0.20 No 0 i (( if me i
0.20
0.065
.0.048
0 055
0.40 Sf jni f icint
0.17 D 1 f f trtncf
0.20
0.12
0.20
0.075
0. 06 Mo 0 1 f f trtne*
0.07
0.30
0.07 Significant
0.07 Difference
0 09
0.06
01! Probibli
017 0 1 1 1 erenc e
0.20 No 0 I f t erincf
0.30
0. 20
0.042
0.10 No 0 i f f er i nee
0.044
0.17 No 0 I 1 f trtnce
0.20
0. 20
0.035
O.OS6
0.042
0.09 No 0 i f f erencc
0.23
0.10
0.60
0.60
0.20
0 12
4-13
-------
for the most part arid, with insufficient rainfall (from
10 to 25 centimeters/year precipitation) to support trees or
crops without irrigation. Winds blow primarily from the north,
except for May through August when they are predominantly from
the south-southwest. Fig. 4-1 shows the population distribution
around this site by azimuth and by distance.
Major programs conducted at NTS have included nuclear
weapons tests, tests for peaceful uses of nuclear explosives,
nuclear reactor engine development, basic high energy nuclear
physics research, and seismic studies. As the result of these
activities, the test site exclusion area and, to a much smaller
extent, areas outside the exclusion areas have become
contaminated with plutonium.
Although the total inventory of plutonium in soils within
the NTS is not known, detailed surveys have been made of certain
specific locations in the site and the Tonopah Test Range (TTR)
which are believed to be the areas most highly contaminated with
plutonium and americium (11), As shown in Table 4-6, the
inventory of plutonium in these areas is about 155 curies.
Estimates of offsite plutonium concentration in soil as the
result of activities at NTS have been made (12) in units of
mCi/km2 (1 mCi/km2 = 0.001 /LtCi/m2) . Fig. 4-2 shows isopleths
for this material; Fig. 4-3 shows, for comparison, the additional
amounts of plutonium at the same locations due to fallout.
Offsite levels of plutonium in soil are less than 0.1 /iCi/m2,
most areas being far lower. A limited special study was made of
plutonium concentrations in air at locations close to the NTS
(13). Results are shown in Table 4-7 and indicate that, while
resuspended plutonium from NTS has probably been detected at
three locations, the air concentration level has not exceeded
0.5 fci/m3. Long-term air surveillance from 1966 to 1972 at
eight major centers of population in western states was performed
for ambient plutonium levels in ground level air (13). Within
annual cycles, these levels, which are ascribed entirely to
4-14
-------
fallout plutonium from the stratosphere, indicated concentrations
varying from 0.01 to 0.5 fCi/ra3 with mean annual values of
approximately 0.1 fCi/m3. The milk surveillance network around
the NTS does not analyze samples for plutonium. Water samples
from wells both onsite and offsite in surrounding communities
were analyzed for Pu-239 and Pu-238. Plutonium was not detected,
indicating levels less than about 0.1 pCi/1 Pu-239 or Pu-238.
4.2.2 Rocky Flats Plant (RFP)
The Rocky Flats Plant (10) is located in Jefferson County,
Colorado, 26 kilometers northwest of Denver. Currently, the
site consists of 6,500 areas of Federally owned land of which
385 acres is enclosed within a security fence. The area is arid
(40 cm/y precipitation) with predominant winds from the
northwest. Figure 4-4 is a wind rose for the site; Figures 4-5
and 4-6 provide population densities around the site by azimuth
and distance. Less than 10 /iCi of plutonium was released from
plant stacks and vents to the atmosphere in 1975 (10). Data on
the total amount of plutonium released to surface waters from
1973 to 1975 have not been published. The plant produces
components for nuclear weapons, which involves the processing of
plutonium. As the result of leakage from barrels of plutonium-
contaminated cutting oil, parts of the site and, to a lesser
degree, the general environment around the site have been
contaminated with plutonium and americium. The total amount of
plutonium released to the environment is estimated to be about
11 curies of which 3.4 + 0.9 curies is estimated to be at offsite
locations (14). Of the approximately 8 curies onsite, more than
half is stabilized by cover with an asphalt pad and remedial
measures have been taken to control the remainder to the extent
practicable. Figures 4-7 and 4-8 show values for Pu-239
concentrations in soils (5 cm depth) around the site
(15, 16). Concentrations of Am-241 within the site boundaries
are about 10% -of Pu-239 values (17). Table 4-8 provides selected
4-15
-------
TABLE 4-8
Plutonium Concentration in Ambient Air at Selected Locations-
Rocky Flats Site, 1975
Location
Onsite
Three to six
Kilometers Distance
from Plant
Boulder
Marshall
Superior
Walnut Creek
Wagner
Leyden
Station
S-U
S-16
S-4
S-6
S-11
S-31
S-34a
S-37a
S-41
Average Plutonium
Concentration
(fCi/m )
<0.02
<0.06
0.1
1.
0.01
<0.03
<0.04
0 06
<0.03
<0.03
<0.03
<0.04
<0.03
<0.04
0.04
Station Location with
Respect to the Plant
West
Northwest
North
East
South
West
North
East
South
Northwest
North
North
East
East
South
(a) Site Boundary
4-16
-------
yearly average plutonium concentrations in ambient air within the
plant boundary, at distances of 3 to 6 kilometers from the plant
and in nearby communities (10) . Liquid effluents released from
the Plant may eventually reach the Great Western Reservoir, while
storm water runoff from the site tends to collect both there and
in Standley Lake. Both reservoirs are sources of drinking water.
Table 4-9 gives estimates of plutonium and americium
concentrations in these water supplies as well as in finished
drinking water for nearby communities (10). Modifications of the
Rocky Flats Plant operations have been made that will eventually
halt all of its liquid effluent discharges. In summary, in
offsite areas around the Rocky Flats plant, the plutonium
concentration in ambient air is 0.06 fCi/m3, plutonium in
finished drinking water is 0.03 pCi/1, and plutonium in soil
is 0.1 jiCi/m2 for 5 cm deep samples (17).
4.2.3 Mound Laboratory (ML)
Mound Laboratory (10) is located in Miamisburg, Ohio,
16 kilometers southwest of Dayton. The 180 acre site is within
an industrialized river valley in a region that is predominantly
agricultural. Corn and soy beans are major crops and livestock is
pastured. Winds are predominantly from the south or west;
average precipitation is 91 cm/yr. The population distribution
around the site is given in Figures 4-9 and 4-10. The mission
of the laboratory includes research, development and production
of components for the nuclear weapons program, and fabrication of
radioisotopic heat sources for medical applications and space
operations. This latter operation involves processing large
quantities of Pu-238 which has become the plutonium radionuclide
of primary concern associated with this site. Pu-238 in airborne
effluent discharges from the plant has, over time, contaminated
the site and, to a lesser degree, offsite areas. Figure 4-11
shows estimates of the levels of Pu-238 in soil around the site.
Approximately 0.5 curies of Pu-238 have been released to the
offsite environment. The concentration of Pu-238 in various
4-17
-------
TABLE 4-9
Concentrations of Plutonium and Americium in Water Supplies
and in Finished Drinking Water - Rocky Flats Site, 1975
Location
Great Western
Standley Lake
Boulder
Broomf ield
Denver
Golden
Lafayette
Westminister
(Walnut Creek at
Indiana Street)
Water Supply
Reservoir
Reservoir
Drinking Water
it
ii
ii
H
ii
(Discharge to
Great Western
Reservoir)
Concentration
Plutonium Anericium
(pCl/1) (pCi/4)
< 0.1
< 0.04
< 0.007
< 0.04
< 0.008
< 0.009
< 0.007
< 0.04
(0.6)
< 0.03
< 0.03
< 0.006
< 0.03
< 0.04
< 0.009
< 0.007
< 0.03
(0.2)
4-18
-------
A = frequency for a direction (%)
B = average velocity (meters per
second) for a direction from
which the wind blows
C = calms (%)
0 = variable direction (%)
0 10 20 30 40
lit i i
Scale for length of wind frequency lines (%)
WIND ROSE FOR THE ROCKY RATS SITE (10)
FIGURE 4-4
4-19
-------
POPULATION DISTRIBUTION AROUND ROCKY FLATS
<• T0 16 KM)
FIGURE 4-5
4-20
-------
*••«
MI'9Z
POPULATION DISTRIBUTION AROUND ROCKY FLATS
(10 TO 80 km)
FIGURE 4-6
4-21
-------
ROCKY FLATS 1974
PLUTONIUM CONCENTRATIONS IN SOIL.
(VALUES IN PICOCURIES PER GRAM. (15)
FIGURE 4-7
4 - 22
-------
ROCKY FLATS
PLUTONIUM-239 CONTOURS mCi/km2 (16).
FIGURE 4-8
4-23
-------
environmental media around the Mound Laboratory is given in
Table 4-10 for 1975 (10). The annual average concentration of
Pu-238 in offsite ambient air did not exceed 0.03 fCi/m3; in
surface waters it was as high as 1.4 pCi/1 (in an off-site pond)
but in water supplies it did not exceed 0.05 pCi/1. In 1969, an
underground pipe carrying acid radioactive waste solutions
ruptured. During repair work on this pipe, heavy rains eroded the
radioactive soil, and carried about 5 curies of Pu-238 off-site
into waterways adjacent to the Laboratory. This plutonium now is
in sediments that are mostly buried under approximately 1-3 feet
of additional non-contaminated sediments added by normal
processes later in time (18). A special study of this incident
was also conducted by the U.S. Environmental Protection Agency;
results are given in Fig. 4-12 and in Table 4-11.
4.2.4 Savannah River Plant (SRP)
The Savannah River Plant (10) is located on a 790 km2
Federally owned site along the Savannah River in Aiken and
Barnwell Counties. South Carolina, about 100 kilometers southwest
of Columbia. The surrounding area is predominantly forested with
some diversified farming, the main crops being cotton, soy beans,
corn, and small grains, and the production of beef cattle. The
climate is mild,with an annual rainfall of 115 cm/y. Population
density around the site ranges from 10 to 400 people per square
mile. SRP produces plutonium, tritium and other special nuclear
materials. Facilities include nuclear reactors, nuclear fuel and
target fabrication plants, nuclear fuel reprocessing plants, a
heavy water production plant and various supporting laboratories.
Two airborne releases, in 1955 and 1969, from fuel reprocessing
plant operations are believed to have caused the detectable
plutonium contamination of soil that is found within a 2 km
radius around those facilities within the site perimeter.
Approximately 1 curie of plutonium is estimated to be within the
isopleths shown in Fig. 4-13 (20). During the 1960's,
radioactive liquid effluents were released from SRP such that
4-24
-------
TABLE 4-10
Concentration of Pu-238 in Environmental Media
Mound Laboratory
Ambient Air
Sample Location
(Location Number)
onslte (211)
(212)
(213)
(214)
North of Plant (101)
East of Plane (103)
South of Plant (104)
West of Plant (105)
Miamisburg (122)
Dayton (108)
(National Average from Fallout)
Average Concentration of Pu-238
(fCl/m3)
0.2
0.05
1.0
0.06
0.02
0.01
0.01
0.009
0.02
0.008
(0.003)
Waters
Sample Location
(Location number)
Great Miami River
Above the Plant (1)
Below the Plant (4)
Canal/pond area
North Pond
South Pond
Miamlsburg Drinking Water
Private Well J
Private Well B
Average Concentration of Pu-238
(pci/o
0.019 i 0.0022
0.052 1 0.004
0.22
1.4
0.043 1 0.003
0.020 l 0.002
0.006 * 0.00003
Foodstuff Collected Close to thg Plant-
Sample
Milk
Fruit8 & Vegetables
Crass
Field Crops
Aquatic life
Average Concentration of Pu-238
(PCI/Hi
2x10"*
< 6x10"*
IxlO"2
IxlO"3
< 3xlO~4
4-25
-------
TABLE 4-1 1
MOUND LABORATORY
U.S. ENVIRONMENTAL PROTECTION AGENCY
1974 SURVEY
Plutonlua in Saaples fron the Vicinity of Mound Laboratory
I.D. 1
EA-1
EB-1
EC-1
EP-1
tt-l
EF-1
EC-1
EH-1
EI-1
EJ-1
IA-1
FE-1
CA-1
HA-1
IA-1
JA-l
KA-1
LA-1
CE-1
QE-1
EPA-l
EPA-20
EPA-17
EPA-18
Locaclon
Cor* sedlnenc simple* collected by Mound Ltboratory, pCl/it dried
North Canal ac touch end of South Pond
»
••
••
11
II
11
"
11
••
North end of North Canal
ii
North end of North Pond
Middle of Nortli Pond
South and of North Pond
North end of Suuth Fund
Middle of South Pond
South end of South Pond
South Canal at weit drainage ditch
South Canal where It crosses US 25
Sediment samples, top 1 Inch. pCl/g dried weight
South Canal ac west drainage ditch
East drainage ditch, '200 ft south of Hound Rd culvert
South drainage ditch. 15 ft fron Junction with South Canal
South Canal. 10 ft from Junction with louth drainage ditch
J3'Pu
weight
0.13
0.09
0.13
0 11
4.8
1.1
440
1170
1090
10.8
26
0.98
0.89
1.30
8 9
7.5
9.1
16.9
19 2
0.48
5.1
2.5
0 70
27
10 9
24
920
230
1.9
47
60
Concentration
J"Pu
< 0 02
< 0.02
< 0.02
< 0 02
0 07
< 0 02
2.3
15.4
7 9
0.18
0.16
0.06
0.05
0.06
0.51
0.44
0.18
0.05
< 0.02
0.07
0 06
0.02
0 2>
0 30
0 46
10.9
3.54
0.06
0.84
0 77
Surface soil and Bud caaples. cop 1 Inch. pCl/u dried uelchc
EPA- 2
EPA- 3
EPA-6
EPA- 7
EPA-13
EFA-K
EPA-15
EPA- 12
Railroad cut touch of control box
Railroad cut north of control box
Run-off hollow
Ac shelter houce SE of South Pond
NE of Lab, at fence between tennis court and Harmon Field
SE of Lab. at SU corner of Hound Park
SU of Lab. at Junction of US 25 with South Canal
Ml of Lib, at illcy loulh of Hound Rd
0.12
0.39
3.8
0.44
0.10
0 44
0 96
0 19
0.17
0 02
0.13
0.11
0.07
0.02
0.04
0 04
0 05
0.05
4-26
-------
A
POPULATION DISTRIBUTION AROUND MOUND LABORATORY
(0 to 10 km)(LAT 396305 LONG 842897)
FIGURE 4-9
4-27
-------
"fist
TOTAL POPULATION IN SECTOR
POPULATION DISTRIBUTION AROUND MOUND LABORATORY
110 to 80 Km) LAT 39.6305 LONG 84.2897)
TOTAL P - 2.903.384
FIGURE 4-10
4-28
-------
MOUND LABORATORY
PRELIMINARY ESTIMATE OF PLUTONIUM • 238 AIRBORNE DEPOSITION
(m G/km2)(io)
FIGURE 4-11
4-29
-------
LINDEN AVE.
ULLU. JJllLi
MORMON
FIELD
U.S. ENVIRONMENTAL PROTECTION AGENCY SAMPLING SITES
MOUND LABORATORY (19)
FIGURE 4-12
4-30
-------
GEORGIA
QUANTITIES:
ON ISOPLETHS (3) - mCl/km2
IN ZONES (1.0) - CURIES
DEPOSITED IN ENTIRE ZONE
o > i i i
SAVANNAH RIVER PLANT PLUTONIUM DEPOSITION (10)
FIGURE 4-13
4-31
-------
TABLE 4-12
PLUTONIUM CONCENTRATION IN ENVIRONMENTAL MEDIA
AROUND THE SAVANNAH RIVER PLANT - 1975
AMBIENT AH
Sample location
Average Plutonium Concentration
Pu-239 Pu-238
(fCi/m )
(fCi/m
Plant Perimeter
(Locations not specified)
25 mile radius
(Locations not specified)
0.02
0.02
0.001
0.001
RAIH WATER
Sample Location
Average Plutonium Concentration
Pu-239 Pu-238
(pCi/m
(pCi/m
Plant Perimeter
25 mile radius
2.2
1.9
0.11
0.15
SOIL (0-5 cm depth)
Location
Average Plutonium Concentration
Pu-239 Pu-23fj
(uCi/m )
Plant Perimeter
NU quadrant
NE
SE
SU
Springfield, SC
Aiken Airport, SC
Clinton, SC
Savannah, GA
0.0009
0.0014
0.0010
0.0012
0.0003
0.0010
0.0008
0.0005
5x10
8
6
8
7
3
2
4-32
-------
radioactive materials, including Cs-137, Co-60, and plutonium
deposited in offsite swamp areas. The plutonium concentrations
in these remote areas range from about 3 to llxlO'3 /jCi/m2 Pu-239
and 0.3 to 6X10"3 pCi/m2 Pu-238. The amount attributed to fallout
sources is approximately IxlO"3 /iCi/ra2 Pu-239 and O.lxlO"3 jiCi/m2
Pu-238 (10). Levels of plutonium in various environmental media
in the general environment around SRP are given in Table 4-12 for
1975 (10). Resuspended plutonium from the contaminated areas
within the site was not detected in offsite ambient air. Values
for plutonium concentration levels in ambient air at onsite
locations have not been published. In 1975, the plant released
2 mCi Pu-238 and 0.5 mCi Pu-239 to the atmosphere; the plant
released 8 mCi Np-239 and 19 mCi Pu-239 in liquid effluents.
4.2.5 Los Alamos Scientific Laboratory (LASL)
The Los Alamos Scientific Laboratory (10) is located on a
110 km2 site in Los Alamos County in North Central New Mexico
about 40 kilometers northwest of Santa Fe. The site is on a
series of mesas separated by canyons that run eastward from the
Jemez Mountains to the Rio Grande Valley. The climate is semi-
arid with rainfall of 46 cm/y. While the land around the site is
undeveloped, about 16,000 people reside in the immediate area.
The primary mission of LASL is associated with nuclear weapons
research and development. Industrial effluents from these
operations have for some time been discharged onsite into
canyons, where the transuranium nuclides in these effluents soon
become attached to soil particles. It is estimated that less
than 1 Ci of transuranic waste has been disposed of to Pueblo,
DP-Los Alamos, and Montandad canyons. Liquid effluents are
usually absorbed in the soil so they do not flow beyond the site
boundaries, but, during periods of heavy runoff, storm waters
have carried detectable amounts of transuranium elements down the
canyons and offsite. Plutonium concentrations in sediments in
the canyons receiving liquid waste are given in Table 4-13 (21).
Concentration levels of plutonium and americium in various
4-33
-------
TABLE 4-13
PLUTONIUM IN SEDIMENTS IN THE LIQUID WASTE RECEIVING
CANYONS ON THE LASL SITE - 1975
Distance from
outfall
(kms)
0
0.6
1.3
3.6
5.1
10.2
Estimated Canyon
Average
Acid Pueblo
Canyon
(pCi/g)
3
10
2
0.4
1
0.2
Inventory
Plutonium Concentration in
DP-Los Alamos
Canyon
(pCi/g)
40
1
0.2
0.4
0.1 to 0
..(a)
dry sol I
Mortandad
Canyon
(pCi/g)
220
20
9
11
0.1
0.03
.3 curies
(u) top 5 cm of HO! I
4-34
-------
TABLE 4-14
PLUTONIUM AND AMERICIUM CONCENTRATIONS IN ENVIRONMENTAL
MEDIA AT THE LASL SITE - 1975
Ambient Air
Average Radionucl ide Concentration
Station Location
(Station Number)
On Site 22
23
24
25
26
Perimeter 12
14
18
20
Off Site 1
^
8
(Santa Fe) 11
Pu-239
3
(fCi/m )
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
Pu-238,
3
(fCi/m )
.
.3
1x10
-4
•4
5x10
•4
5x10
•4
6x10
•4
9x10
-4
1x10
•4
5x10
6x10 "*
7x1o"
•4
9x10
4x10"
Am-241,
3
(fCi/m )
.
.3
3x10
.
-3
7x10
•
0.02
-3
1x10
.3
4x10 ,
.3
4x10
4x10"
Surface Water and Water Supplies
Sample Location
Regional Surface Waters
Perimeter Surface and
Ground Waters
Los Alamos Water Supply
Average Radionucl ide Concentration
Pu-239 Pu-238
(pCi/l) (pCi/l)
9x10
8x10
3x10
6x10
2x10
3x10
Soils
Sample Location
On site
Average Radionucl ide Concentration
Pu-239
(pCi/g)
40x10
Site Perimeter and Regional areas 12x10
(a) Top 5 cms of soil .
Pu-238
(pCi/g)
1x10 3
0.5x10
4-35
-------
environmental media around the LASL site are given in Table 4-14
for 1975 (10). During the same year, the Laboratory discharged
less than 0.3 mCi of plutonium to the air; the amount of
transuranium elements discharged in liquid effluents was not
published.
4.2.6 The Trinity Site
The first nuclear device was tested at the Trinity Site,
100 kilometers northwest of Alamogordo, New Mexico, on
July 16, 1945. During 1973 and 1974, the site was surveyed by the
U.S. Environmental Protection Agency to determine the extent of
resulting plutonium contamination (22). Figure 4-12 shows
plutonium contours based on this study. Highest soil activity
levels were 0.05, 0.09 and 0.02 jzCi/m2 found along arcs IA,
2 and 3, respectively. The total amount of plutoniura estimated
to be within the 3 nCi/m2 contour is approximately 45 curies
(1 nCi = 10"9 curies) .
4.2.6 Other Sites of Underground Nuclear Detonations
A listing of major underground tests conducted at
locations other than the Nevada Test Site is shown in
Table 4-15. All transuranium elements are believed to be
contained at the site of detonation.
4-36
-------
TRINITY SITE
1973-1974 PLUTONIUM
SOIL SAMPLING RESULTS
(nCi/m2)-(14)
FIGURE 4-14
4-37
-------
TABLE 4-15
Underground Turing Cooducctd Off Chi Nevada Tcit Slc«
Mama o( Tail.
Uporttlon or
Prolacc
Yl.ld
0«ptn
•
111)
e(
*
rrojact Cnoma/ 12/10/01 t» kit (30 ill SC of J.I
Coach Lirl.
360 Nulll-pvtpoaa
(lilt) aiptrlunt.
166 Nllo> L>«1 10/19/45 tachlc
Shoe Al«.k.
U lilind.
?lt 000 nui.l (21 .1) Su of
(Sltrllnf [vine) HjllKiburi, Ml>i.
ftoj.cl C<.t>g|(y* I2/1U/6) SS k. (55 .1) t
r«nln|ion, N.H.
F (Olodt Tubol* K4tll..bur|, Ml.s. n.» l.jr (2IIIO) Sjloxin/Slorl Uf
titpUiclun cavity. Solialc
•luJloo.
Projaci lullnon* OV/IO/ty 19 kn (12 nl) SV or
Klfl«. Liilomdu
Oparatlon Huron* 10/02/69 Amchlclu laland.
Projoct Hlr:
Flay (|ju.ld
W«c»r)
tl.- IM/I9/7II It k. (II nl) SV ..r
to
%1000
Ms,.!-
nu. U,
2568 Cat «t Inilotloo
(»425) .ip.rU«nl.
121« Calibration tool.
(«000)
nil Ihl ..... In) In
Oparatlon
Cannikin1*
Frojoct Mo
ll.nco
11/Ub/M AaKhltka lalanil.
Alaaka
OS/17/7} «J kn (30 mil SU or 3l30
Hcokor. Colorado
1624 TolC of vic-
(6000) ho ad (or
Spuctn
olnlo.
1780 C«l ictniU-
ce clon uporl-
2040 Mnc.
(5»tO
to
6690)
flowoharo Lvunto
bv.la Uniform Ivonto
'viapono Toaci
Information Iroo "lovlaod Nvcloar Toac Stallatlca," dlolrlbutid on $
-------
4.3 PRODUCTION/UTILIZATION FACILITIES
A number of other sites in the United States have
utilized plutonium in various aspects of weapons production.
Tables 4-16 to 4-22 show levels of the transuranium elements in
the general environment several of these facilities known to use
the transuranium elements in their operations. At this time,
the total amount of the transuranium radionuclides in the
environs of these sites is believed to be less than 1 curie.
4-39
-------
TABLE 4-16
Environmental Monitoring for the Transuranium Elements
at the Pantex Plant Site
Site: Pantex Plant
Location: 25 kilometers northeast of Amarillo, Texas
Mission: Atomic Weapons Assembly involving significant quantities
of uranium, plutonium, tritium
Transuranium Elements Released to the Environment
Media
Air<»
No releases during
Location of
Sample Collection
10 kilometers from
plant in various
directions
25 kilometers from plant
Soil(b)
Offslte in various
directions from
the plant
Jackrabbita Onsite
the period
Sample
Station
1
2
3
4
5
6
8
9
10
11
12
31
Different
Stations
11
samples
1973-1975
Average Plutonium
Concentrations - CY 1975
0.03 fCi/m3
0.07
0.03
0.02
0.00 ± 0.01
0.01
0.4
0.00 ± 0.01
0.09
0.5 (1 sample only)
0.00 (1 sample only)
0.00 ± 0.02
to
0.05 ± 0.02 pCi/g
3.00 ± 0.02 pCi/g
(wet) in kidney,
liver, lung, flesh,
and bone
(a)
Average air concentrations of plutonium in 1973 ranged from
0.4 to 2 fCl/m3 (10), which is higher than any other site. These high
levels are believed to have been caused by analytical errors.
(b)
Soil samples collected to a depth of 5 cm.
4-40
-------
TABLE 4-17
Environmental Monitoring for Che Transuranium Elements
at Argonne National Laboratory
Site: Argonne National Laboratory
Location: DuPage County, Illinois, 43 kilometers southwest of Cnicago
Mission: Research and Development including chemical and
metallurgical plutonium laboratories
Transuranium Elements Released to the Environment (CY 1975)
To air - not published
To surface waters (Sawmill Creek) - 0.1 nCl Pu-239;
O.S mCl Np-237;
O.OS md Am-241;
<0.05 mCl Curium and
Californium
Surface Water
(Sawmill Creek)
Sawmill Creek
Phytoplankton
Dea Plains
River
Illinois
River
Soil
(a)
Location of
Sample Collection
Site Perimeter
Offslte
Downstream
from
Outfall
Upstream from Oucfall
Downstream from Outfall
Upstream froa Sawmill Creek
Downstream from Sawmill Creek
McXlnley Woods State Park
Below Dresden Power Station
Site Perimeter
Offslte
Number of
Stations
Av.
of 2 Stations
1 station
Av. of 10
Locations
Av. of 10
Locations
Average Plutonium
Concentrations - CY 1975
0.02 fCl/m3
0.02
< 5 x 10"* pCi/1 Pu-239
< 3 x 10, Pu-238
4 x 10 ,
4 x 10",
< 1 x 10,
5 x 10
2.4 x 10"* pCl/g
1.5 x 10"3
Am-241
Np-237
Cu-242
Cu-244
Pu-239
Pu-239
5 x 10"* pCl/1
8 x 10
2 x 10"* pCl/1
3 x 10
Pu-239
Pu-239
Pu-239
Pu-239
2 x lO'
1 x 10,
2 x 10 ^
2 x 10
Pu-239
Pu-238
Pu-239
Pu-238
(a)
Soil samples collected to depth of 30 cm.
4-41
-------
TABLE 4-18
Environmental Monitoring for che Transuranium Elements ac
Bactelle-Columbus Laboratories (West Jefferson Sice)
Sice; Baccelle Laboratories (Wesc Jefferson Sice)
Location; Columbus, Ohio
Mission; Reactor Fuel Research (Plutonium Laboratory)
Transuranium Elements Released to the Environment (CY 1975)
To air - 1.5 uCi Pu-239
To surface waters - not published
Media Sample Collection Location
Air (Sice Boundary concentration as
calculated using atmospheric
dispersion equations)
Silt Above and Below Outfall
Crass Onsite and Various Locations
Onsite, 3-8 kilometers
Food Crops Corn, Soybeans, Rye, Vegetables
0.4 Co 8 kilometers in Various
Directions around Site
Average Plutonium
Concentrations - CY 1975
(4xlO~3 fCi/m3)
<2xlO~2 pCl/g (dry)
<2xlO~2 pCi/g (dry)
<2xlO~2 pCi/g (dry)
4-42
-------
TABLE 4-19
Site
Location
Mission
Environmental Monitoring Cor the Transuranium Elements at
the Idaho National Engineering Laboratory
Idaho National Engineering Laboratory
Southeastern Idaho; 35 kilometers west of Idaho Falls
Includes - Fuel reprocessing, calcining liquid radio-
active waste,and storage and surveillance of solid
transuranlc waste
Transuranium Elements Released to the Environment (CY 1975)
To air - 2 mCi Pu-238, Pu-239, and Np-237
To disposal well - "very small amounts"
Media
Air
Surface Soils
Sample Collection Location
Boundary Stations
Boundary Stations
18 Samples
Distant Location
12 Samples
Average Plutonium
Concentratlons-CY 1975
0.02 fCl/m3 Pu-239
0.01 fCl/m3 Am-241
2 ± 2xlO~2
3 t «xlO~2
(a)
Soil Samples Collected to Depth of 5 cm.
4-43
-------
TABLE 4-20
Sice
Location
Mission
Environmental Monitoring for the Transuranium Elements
at the Oak Ridge Facilities
Oak Ridge Facilities
Oak Ridge, Tennessee
Multipurpose Research Laboratory. Caseous Diffusion Plant.
and Nuclear Weapons Operations (Y-12 Plant)
Transuranium Elements Released to the Environment (CY 1975)
To air - 4 pCi sum of all transuranium elements
To Clinch River - 20 mCl sum of all transuranium elements
(CY 1973 - 80 mCl: CY 1974 - 20 mCi)
Media
Air
Soil
Water
Sample Collection Location
Perimeter Stations
Remote Stations
Perimeter Stations(")
White Oak Creek
Clinch River
Average Plutonium
Concentratlons-CY 1975
0.014 fCl/m3 Pu-239
< 0.001 fCi/m3 Pu-238
0.013 fCl/m3 Pu-239
< 0.001 fCl/m3 Pu-238
4xlO~2 pCl/g Pu-239
Not published
Not published
(a)
Soil Samples Collected to Depth of 1 cm.
4-44
-------
TABLE 4-21
Site
Location
Mission
Environmental Monitoring for Che Transuranium Elements
ac Hanford
Hanford
Southeastern Washington, 320 kilometers east of Portland, Oregon
Includes Fuel fabrication, liquid waste solidification and
radioactive waste burial. Originally, plutonium for nuclear
weapons was produced here.
Transuranium Elements Released to the Environment (CY 1975)
To air 1 rnCl sun of all plutonium elements
To surface waters - 0.9 mCi sum of all plutonium elements
Media Sample Collection Location
Air Perimeter Stations
Distant Stations
Soil Perimeter Stations
Water Columbia Rlver-Upstream
-Downstream
Vegetation Perimeter Stations
Average Plutonium
Concentrations-CY 1975
<0.03 fCi/m3 Total Pu
<0.04 Total Pu
<7xlO~3 pCi/g (dry) Pu-239
<«xlO~
-------
TABLE 4-22
ENVIRONMENTAL MONITORING - LAWRENCE LIVERMORE LABORATORY
Hedia
Sample Collection Location
Average Plutonium
Concentrations • 1975
Air
Site 300
Perimeter
Pu-238 9.0x!0'4 fCi/m3
Pu-239 0.28 fCi/m
Pu-238 2-10x10** fCi/m3
Pu-239 0.02-0.035 fCi/m
Soil
(top 1 cm)
Site 300
Llvermore Valley
Pu-239 0.001-0.03 pCi/g (dry)
Pu-239 0.001-0.1 pCi/8 (dry)
Water
Reclamation Plant (effluent)
Pu-239 0.6 pCi/l
4-46
-------
4.4 REFERENCES
1. Wrenn, McD. E., "Environmental Levels of Plutonium and
the Transuranium Elements", in Proceedings of Public
Hearings: Plutonium and the Other Transuranium Elements.
Vol 1 (ORP/CSD-75-2), U.S. Environmental Protection Agency,
Office of Radiation Programs, Washington, D.C. (1974).
2. Krey, P.W. et.al. "Mass Isotopic Composition of Global
Fail-Out Plutonium In Soil", IAEA-SM/199-39, International
Atomic Energy Agency, Vienna, (1976).
3. Hardy Jr., E. R., "Worldwide Distribution of Plutonium", in
Proceedings of Public Hearings: Plutonium and the Other
Transuranium Elements. Vol 1 (ORP/CSD-75-2). U.S.
Environmental Protection Agency, Office of Radiation
Programs, Washington, D.C. (December 1974).
4. Hardy, E., "Depth Distribution of Global Fallout Sr-90,
Cs-137 and Pu-239-240 in Sandy Loam Soil" in Fallout Program
Quarterly Summary Report (HASL-286), U.S. Atomic Energy
Commission, New York, N.Y. (October 1974).
5. Bennett, B. G. HASL, U.S. Energy Research and Development
Administration, New York, N.Y., Personal Communication,
(December 1976).
6. Bennett, Burton G., "Transfer of Plutonium From the
Environment to Man" in Transuranium Nuclides in the
Environment (IAEA-SM-199/40), International Atomic Energy
Agency, Vienna (1976).
7. Chart of the Nuclides. Knolls Atomic Power Laboratory
U.S. AEC (operated by the General Electric Company) llth Ed,
Revised April 1972.
8. Krey, P. "Atmospheric Burnup of a Plutonium-238 Generator,
Science. Vol. 158, No. 3802, pp. 769771 (Nov. 10, 1967).
9. Erdman, C. A. and A. B. Reynolds, Nuclear Safety 16, 43
(1975).
10. "Environmental Monitoring at Major U.S. Energy Research and
Development Administration Contractor Sites - Calendar Year
1975" (ERDA-76-104) Energy Research and Development
Administration, Division of Safety, Standards and
Compliance, Washington, D. C. (August 1976) 2 Vols.
4-47
-------
11. Gilbert, R. 0. et. al., "Statistical Analysis of Pu-239-240
and Am-241 Contamination of Soil and Vegetation on NAEG
Study Sites" in The Radioecology of Plutonium and Other
Transuranics in Desert Environments (NVO-153) U.S. Energy
Research and Development Administration, Nevada Operation
Office, Las Vegas, Nevada (June 1975).
12. Hardy, E., "Plutonius in Soil Northeast of the Nevada Test
Site", in Health and Safety Laboratory - Environmental
Quarterly, (HASL-306) Energy Research and Development
Administration, New York, N.Y. (July 1976).
13. "Environmental Monitoring Report for the Nevada Test Site
and Other Test Areas Used for Underground Nuclear
Detonations - Jan. through Dec. 1973" in Environmental
Monitoring at Major U.S. Atomic Energy Commission
Contractor Sites - Calendar Year 1973, (WASH-1259 (73) U.S.
Atomic Energy Commission, Division of Operational Safety,
Washington, D.C. (June 1973).
14. Krey, P. W. "Remote Plutonium Contamination and Total
Inventories from Rocky Flats", Health Physics. 30, 209
(1976).
15. " Environmental Monitoring at Major U.S. Energy Research and
Development Administration Contractor Sites - Calendar Year
1974" (ERDA-54) U.S. ERDA, Division of Operational Safety,
Washington, D.C. (August 1975).
16. Krey, P. W. and Hardy, E. P., "Plutonium in Soil around the
Rocky Flats Plant" in Fallout Program Quanterly Summary
Report (HASL 235) U.S. Atomic Energy Commission, New York,
N.Y. (1974).
17. Werkema, G. J. and M. A. Thompson, "Annual Environmental
Monitoring Report - Rocky Flats Plant" in "Proceedings of
Public Hearings; Plutonium and the Other Transuranium
Elements. Vol. 2", ORP/CSD-75-1, U.S. Environmental
Protection Agency, Office of Radiation Programs, Washington,
D. C. (Jan. 10, 1975).
18. Rogers, D. R., Mound Laboratory Environmental Plutonium
Study-1974, (MLM-2249) Mound Laboratory, Miamisburg, Ohio
(September 1975).
19. U.S. Environmental Protection Agency, National Environmental
Research Center, Cincinnati, Ohio. Letter to Mr. Gary
Bramble, State of Ohio, Environmental Protection Agency,
from Bernd Kahn (Oct. 1, 1974).
20. McLandon, H. R., "Soil Monitoring for Plutonium at the
Savannah River Plant," Health Physics 28. 347 (1975).
4-48
-------
21. "Annual Report of the Biomedical and Environmental Research
Program of the LASL Health Division - Jan. through Dec.
1974" (LA-5883-PR) Los Alamos Scientific Laboratory, Los
Alamos, New Mexico (Feb. 1975).
22. Douglas, R. L. U.S. Environmental Protection Agency,
Office of Radiation Programs, Las Vagas, Nevada.
23 "Cleanup, Rehabilitation, Resettlement of Enewetak Atoll -
Marshall Islands (Final EIS), Defense Nuclear Agency,
Washington, D. C., 4 Vols. (April 1975).
24. "Environmental Monitoring at Major U.S. Atomic Energy
Commission Contractor Sites - Calendar Year 1973"
(WASH-1259) U.S. Atomic Energy Commission, Division of
Operational Safaty, Washington, D.C. (June 1973).
4-49
-------
5. ENVIRONMENTAL TRANSPORT & EXPOSURE PATHWAYS
5.1 Introduction
This chapter provides a brief overview of the transport of
the transuranium elements through the environment and the
potential exposure pathways through the biosphere. Availability,
uptake, and translocation of the transuranium elements within the
ecosystem depend upon many factors, including: the mode of
release (e.g., accidental fire or spillage), the physical form
upon release (e.g., particulate or liquid), the chemical form
(e.g., elemental, oxide, or nitrate), and the nature of the
environment where the contamination occurs (e.g., desert soil or
aqueous media). Also important is use of the environment, which
can significantly effect the mobility of the transuranium
elements and, subsequently, their effect upon exposed
populations. Because there are so many variables, potential
pathways of exposure should be evaluated on a site-by-site basis.
However, some general conclusions can be made based upon present
knowledge of the environmental behavior of these elements. For a
terrestrial ecosystem, the major environmental transport pathways
are illustrated in Figure 5-1. These pathways include:
1) exchange between air and soil, water, and vegetation as a
result of deposition and resuspension, 2) exchange between soil
and water by erosion, leaching, absorption, and precipitation,
and 3) uptake from air, soil, and water by plants, animals, and
man. A comprehensive summary of the environmental transport
models has recently been published by the National Council on
Radiation Protection and Measurement as NCRP Report No. 76,
Radiological Assessment: Predicting the Transport, Bio-
accumulation, and Uptake by Man of Radionuclides Released to
the Environment. The pathways expected to produce the principal
exposures to people are discussed in greater detail in the
following sections.
5-1
-------
PRINCIPAL PATHWAYS OF THE TRANSURANIUM ELEMENTS
THROUGH THE ENVIRONMENT TO MAN
FIGURE 5-1
5-2
-------
5.2. Environmental Transport
5.2.1 Aerosol Transport
Airborne releases of the transuranium elements result from
both normal and accidental occurrences. Normal operational
releases are small and are expected to decrease in the future due
to improvements in containment. Accidental releases - such as
those resulting from transportation accidents and fires, can lead
to localized contamination, and would probably necessitate some
form of protective and remedial action. Generally accidental
releases of the transuranium elements will be as the element, the
oxide, or in soluble form. When the release is in the form of
the element, it will convert rapidly to the oxide form, which is
relatively insoluble and stable thermodynamically. Airborne
releases of the transuranium elements will generally be in the
oxide form and contain a substantial percentage of particles
within the respirable size range. Because of the small
gravitational settling velocities associated with such particles,
they can be transported long distances by air currents before
depositing on the ground. These particles then will become
incorporated into soil and aquatic systems. When deposited on
soil, the aerosol particles can attach themselves to the larger,
less mobile soil particles. For example, Mork (1) found that
Plutonium at most sites was usually bound to soil particles with
a diameter greater than 44 /un. Likewise, Tamura (2) has analyzed
the plutonium bound to soil particles at the Nevada Test Site and
showed that the plutonium bound to coarse particles (5-20 urn) was
present as Pu02, while the plutonium bound to fine particles
(2-5 urn) was present as hydrated PuO2. Subsequent transport will
be as a result of wind and mechanical forces which transfer their
energy to the surface particles causing them to roll, slide or
even become airborne. The smaller the particle diameter the
greater will be the tendency for the particle to stay airborne
5-3
-------
and the greater will be the distance that it will travel before
returning to the surface. Some of the many factors which can
influence the redistribution of surface particles by wind are
listed in Table 5-1. The multiplicity of factors and their
complex interrelationship makes the prediction of soil
resuspension and transport a very complex problem. Accordingly,
the resuspension of soil particles has been the focus of much
research over the past several years.
One of the more commonly used indexes of resuspension has
been the concept of a resuspension factor which is defined as the
ratio of the air concentration to soil concentration. A wide
range of values has been reported for resuspension factors for a
variety of surfaces and modes of disturbance. Table 5-2 is a
summary of some values reported (3) for newly deposited Pu02
released during weapons testing. Such a wide range of values
makes the prediction of the resuspension factor for a particular
set of conditions a difficult task. In general, values for newly
deposited material seem to fall in the range lO'^m"1) to lO'^m"1)
under conditions of low mechanical disturbance. In areas where
the surface is rocky or paved, the resuspension factor may range
up to 10"3(m1) due to these smoother, harder surfaces and because
little mixing with noncontaminated surfaces occurs (4).
Mechanical disturbances, such as vehicular traffic, will also
increase the resuspension factor by as much as a factor of 10 to
100 (5). For planning purposes, Stewart (3) and others (6) have
recommended a resuspension factor of lO^fm'1) for freshly
deposited material under quiescent conditions but recommended
increasing this value to I0"5(m"1) if there is moderate vehicular
or other disturbing activity. As the freshly deposited material
becomes aged, fixed to the soil, or mixed with the soil, the
characteristics of the contaminant approach the resuspension
characteristics of the soil itself. On the basis of empirical
information, a model has been proposed (7) in which the
resuspension factor decreases from I0"5(m"1) to I0"9(m"1) within
two years. Bennett has reportedly (8) estimated that in a humid
5-4
-------
TABLE 5-1
FACTORS AFFECTING RESUSPEN5ION
METEOROLOGICAL FACTORS
Wind Frequency Distribution:
Mean Wind Speed
Wind Direction
Intensity of Gusts
Vertical Turbulent Exchange
Air Density (Temperature-Pressure)
Frequency and Amount of Rain/Snowfall
GROUND-SURFACE PROPERTIES
Soil Characteristics
Soil Type
Moisture Content
Density
Texture
Particle Characteristics
Shape
Density
Size Distribution
Cohesiveness
Land Use
Surface Roughness
Type and Amount of Vegetative Cover
Topography/Terrain Irregularities
Soil Disturbance Activities
5-5
-------
TABLE 5-2
SUMMARY OF SELECTED EXPERIMENTAL RESULTS
FOR RESUSPENSION (after Stewart)
Measurement Conditions
Resuspension Factor, Rf(m )
Range
Mean
Plutonium sampled at 1 ft above
ground (1)
Vehicle traffic
Pedestrian traffic
Particle size: Mainly 20-60 pro,
with IX in hazardous range
(^ 3 urn for PuO_)
Uranium sampled downwind from a
crater (1)
At 1 ft. above ground (dust stirred up)
At 1 ft. above ground
At 2 ft. above ground
to
1.5x10 to 3x10
1x10
3x10
1x10
-3
-4
-5
Brick/plaster dust sample contaminated
with 1-131 (2)
Enclosed space
Open space
to 4xlO
~5
2x10
-6
Sample in cab of Landrover, after
a test (1)
Round 1 (H + 18 hr)
Round 2 (H + 5 hr)
2.5x10
6.4x10
-5
-5
Airborne material without artificial
disturbance of ground, consisting of
limestone rock and sand with coarse
grass and small bushes (3)
Random samples following a tower shot,
without artificial disturbance,
near crater (3)
On two roads formed by soil grading
-no artificial disturbance (3)
lxlO~6 to 8xlO~5 1x10 5
(12 results)
IxlO"8 to IxlO"6 2xlO~7
(9 results)
l.Sxlfl"6 to lxlO~8 2.5xlO~7
results)
At back of a moving Landrover (3):
D-Day + 4 (21 results)
D-Day -f 7 (21 results)
D-Day + 7 over tailboard
8xlO~? to
6xlO~7 to 4xlQ~6
1.6 and 3. 1x10°
1.5x10
2.5x10
,
(1) From nuclear weapon and other tests at Maralinga
(2) From Civil Defense trial at Falfield, Gloucester
(3) From Hurricane Trial
5-6
-------
eastern climate the resuspension factor reaches lO"6^"1)
to I0"7(m"1) after the first good rain or wetdown and then rapidly
decreases to I0'9(m"1). If the transuranium material is released
as a solution rather than as the oxide, its resuspension will
probably be in the low range (see Section 2.2). Experiments (3)
with yttrium chloride solution sorbed onto soil have indicated a
resuspension factor of 10'(m'1) , while measurements at Mound
Laboratory (4) of Pu-238 released from a waste transfer line
produced resuspension factors in the range of 10'*(m"1) to lO'^m'1) .
Because of the propensity for greater mobility on the part of
freshly deposited material, stabilization of newly contaminated
land should be undertaken as soon as possible after the initial
accident in order to reduce the resuspension and inhalation
exposure.
5.2.2 Soil Transport
Soil contamination by plutonium has been the most prevalent
situation encountered and, therefore, is the most widely studied.
Plutonium dispersed onto soil has demonstrated a tendency to bond
chemically and/or physically with the soil rather than exist as a
separate entity (4,9,10,11,12). Plutonium oxide is relatively
inert and initially attaches itself to the soil matrix as a
result of adhesive forces established between the plutonium
particle and the soil substrate. Over a period of time,
weathering processes such as freezing, thawing, and
precipitation, will begin to "solubilize" the oxide.
Although generally considered to be insoluble, plutonium
oxide can undergo dissolution in a neutral aqueous media. The
plutonium oxide particle dissolves, producing plutonium ions
until the formation of a hydrated coating inhibits further
dissolution. The rate and degree of dissolution depends on many
factors including pH, temperature, the presence of oxidizing,
reducing, and complexing agents, as well as the specific activity
of the radionuclide. The dissolution rate of 238PuO2, for
5-7
-------
example, has under certain circumstances been found (13) to be
100 times greater than that of 239PuO2. Plutonium ions formed
during the dissolution can undergo ion exchange reactions with
the oxygenated ligands commonly found in soil (e.g., silicates)
and become sorbed onto the soil, or react with other agents
present in the aqueous phase and form soluble complexes.
Chemicals that complex the plutonium compete with the silicate
particles for the plutonium and tend to reduce the extent of
plutonium sorption on soil.
When plutonium is released to soil in soluble form
(e.g., as a nitrate) it will already be in ionic form and,
in such situations, has been shown (4) to react rapidly with
soil. Plutonium ions are capable of displacing most cations
(e.g., calcium, magnesium, sodium, etc.) generally found in soils
and of forming strong chemical bonds. Several studies (2,14,15)
have shown that, after sorption of plutonium has occurred, it
will not be readily displaced from the soil by natural processes.
Once in the soil, the transuranium elements can be depleted
through the migration of particles down through the surface or
through the resuspension of a fraction of the material back into
the air stream. Of these two mechanisms, the resuspension of
soil particles, with which these nuclides have associated in one
form or another, will be the principal mode of further
environmental transport. The resuspension of soil particles
occurs as a result of wind action and more intermittently as a
result of mechanical forces, such as plowing and vehicular
disturbances. The size of the particle will determine its
distance and mode of transport. Particles with diameters greater
than 1000 /im generally slide or roll along the surface (creep),
while particles with diameters in the range of 50 /im to 1000 /am
move in short hops along the surface, usually at a small distance
from the surface (saltation). The suspension of particles is
5-8
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generally restricted to those below 50 /um, which will be carried
along with the air stream.
5.2.3 Aqueous Transport
Studies have been conducted on various water bodies,
streams, rivers, lakes, estuaries and oceans to determine the
final disposition of plutonium in these environs. The following
behavior has been noted:
(1) More than 90% of the plutonium becomes bound to suspended
sediments and carried to the sediment bed.
(2) Situations where reducing and complexing agents are both
present can lead to resolubilization of the plutonium in the
sediment bed
(3) Seaweeds generally have the ability to concentrate
plutonium with concentration factors of >1000.
(4) Benthic biota can alter the plutonium concentration
profiles in the sediment beds.
Specifically, plutonium oxide exposed to an aqueous medium
undergoes slow dissolution, producing various complex ions of
plutonium as well as polymers in colloidal form and the hydrous
oxide as a precipitate (13). In 1972 Langham (16) studied the
fate of Pu02 following the Thule incident and found that the
majority of the plutonium agglomerated into inactive debris with
only about 1% suspended as fine particulates in the water.
Further studies (17) after the Thule incident showed 95% of the
plutonium to be associated with the bottom sediments to a depth
of at least 10 cm. In addition, a study (18) of nuclear waste
discharged into the Irish Sea from Windscale has found most of
the Pu-239 and Am-241 to be associated with the sediments close
to the discharge area. Similar findings were observed (4) around
Mound Laboratory where plutonium was accidentally discharged into
a freshwater canal. Again the plutonium was found to be largely
associated with the bottom sediments. Therefore, although the
movement of the transuranium elements through aqueous systems is
5-9
-------
not yet well defined, the information now available would
indicate a limited mobility for environmental transport via such
systems.
5.3. Exposure Pathways
The principal hazard that arises as a consequence of soil
being contaminated with the transuranium elements is exposure
to radiation through the inhalation and ingestion pathways.
For a detailed discussion of the entry of plutonium and other
actinides into animals and man and the resultant biological
behavior, the reader is referred to ICRP Publication 19 (19) and
the chapter entitled "Dose and Risk to Health due to the
Inhalation and Ingestion of Transuranium Radionuclides". The
following section will be limited to a description of the
environmental factors affecting the inhalation and ingestion
pathways.
5.3.1 Inhalation
Inhalation exposures arise from direct injection of
transuranium radionuclides into the atmosphere (e.g., normal
emissions and accidental fires)and also from the resuspension of
previously deposited material. For the latter pathway, only a
very small fraction of the material on the surface actually
becomes airborne and available to man. In general, the
respirable size is considered to be that range of particles with
aerodynamic diameters less than 10 jum. An assessment can be
made, using dosimetry models, of the potential health hazard
resulting from the inhalation of airborne particles. Such a
model requires knowledge of the total airborne activity and of
the activity median aerodynamic diameter associated with it.
(Aerodynamic diameter is the diameter of a sphere of unit density
having the same settling velocity as the particle in question of
whatever shape and density). The assumption made by most
5-10
-------
dosimetry models is that the aerosol distribution is log normal
and can, therefore, be described through the use of two
parameters - the activity median aerodynamic diameter (AMAD) and
the geometric standard deviation of the distribution, og.
Sampling should be conducted so that 1) the total airborne
distribution is being measured, and 2) the AMAD determined
actually describes the corresponding distribution of airborne
activity. Healy (20) and others (21) have emphasized the
necessity of considering the resuspension of soil by mechanisms
other than normal wind activity. The possibility exists that
other mechanisms could, under certain circumstances, produce
exposures exceeding those normally received via the resuspension
pathway. Although this possibility has been recognized,
relatively little experimental data is currently available to
determine quantitatively the importance of the many possible
secondary resuspension mechanisms. Two commonly encountered
disturbances (agricultural operations and vehicular disturbance)
have recently been investigated, however, and some conclusions
can be drawn from these studies.
For the agricultural situation, the vicinity of a field
contaminated over a period of twenty years was monitored.
Increase in airborne activity was measured during such activities
as plowing, disking, and planting (22). During these operations,
the air activity was found to increase by a factor of
approximately 30 at the location of the tractor operator and by a
factor of 6 at a distance 30 meters away from the edge of the
field. Assuming that these activities take place 30 days of the
year for 8 hours each day (i.e., 1/36 of the year), it can be
calculated that the average yearly air activity will increase by
80 percent for the tractor operator and 10 percent for an
individual in the vicinity of the field. This level of increased
air concentration will occur for only the first year. Subsequent
agricultural activities should generate lower air concentrations,
because the activity originally on the surface will be diluted
5-11
-------
through mixing with soil previously below it. The conclusion
that can be drawn from such an analysis is that these
agricultural operations would pose an increased inhalation hazard
to the vehicle operator during the first cultivation cycle, and
some protective action might be in order during that time.
Subsequent cultivation, however, should not lead to significant
increases in the inhalation hazard. For surrounding areas, no
significant inhalation hazard would be predicted during any of
these operations.
Regarding vehicular disturbances, Sehmel (5) has examined
the importance of auto and truck traffic in increasing
resuspension. It was concluded that such disturbances, in the
case of an asphalt surface with newly deposited material, will
lead to increased resuspension, with a fraction resuspended of
the order of 10'5 to 10'2 per vehicle passage. The higher rates
occurred at speeds typical of freeway driving; after the passage
of about 100 cars only a small fraction of the original
contamination remained on the road surface. The material
resuspended from the road surface deposited on the ground at
various distances from the road and was again available for
resuspension, but at a much lower rate.
The potential for increased exposure from such situations
will depend upon many factors in addition to the quantity of
contaminating material, including the time of exposure, the
frequency of vehicular passage and the speeds, and the distance
from the road to the receptor. Based upon Sehmel's experiment,
it can be expected that the integrated inhalation exposure due to
the vehicular disturbance will be smaller than the chronic
exposure received from daily living within the generally
contaminated area. The material deposited on the road surface
will be depleted quickly and, once it is removed from there, its
resuspension will be orders of magnitude lower. Sehmel's results
indicate that the material transferred to the road parking strip
is resuspended at a rate only one tenth of that on the road
5-12
-------
itself. In addition, the total quantity of material resuspending
at the higher rate would be small relative to the surrounding
area; once redistributed over the larger area, it should show
little increase in the average air concentration.
5.3.2 Ingestion
Under normal circumstances, exposures via ingestion will
arise from the consumption of crops and animals grown on land
contaminated by the transuranium elements. Studies to date have
made assessments of the ingestion pathway by two methods: some
studies have looked at the uptake factors for various plant
species grown in contaminated soils, while others have measured
the residual amounts of fallout plutonium in processed foods.
Two publications (23,24) have tabulated the results of
uptake studies performed on plutonium and other transuranium
elements. These studies have shown plant and animal uptakes to
be very small, with the concentration in plants (fresh weight
basis) being generally less than 10'4 of that in dried soil and
the concentration in animal tissue (fresh weight) being about
10"5 of that in the plants they eat. Preliminary studies (23) for
transuranium elements other than plutonium produced uptake
factors somewhat higher than comparable studies with plutonium.
Initial studies (25,26) indicate an increase in uptake with time,
possibly as a result of bacterial action or increased
solubilization. The use of chelating agents as a part of
agricultural practices may also increase the uptake of the
transuranium elements with time (27).
Measurements of plutonium in "market basket" food samples,
in which proportions of processed foods are chosen to represent
the annual total diet, can be used as indicators of the quantity
of plutonium ingested (28). Such findings apply to a given soil
contamination level when all consumed food is grown on
5-13
-------
contaminated lands. The methodology gives an overestimate of
activity ingested, because foods from other areas not as highly
contaminated will make up part of the diet. These studies have
observed uptake factors for plutonium in the range of 10"4 plus or
minus an order of magnitude. Based upon such uptake factors and
food consumption estimates, the annual estimated intake during
1972 of fallout plutonium was 1.6 pCi while the intake for 1965
was estimated to be 2.6 pCi. There is no reason to believe that
the uptake factors for crops grown on land with concentrations
higher than fallout levels should vary significantly from those
obtained through this "market basket" sampling technique. Some
evidence indicates that americium is concentrated in certain
species of plants relative to plutonium. Preliminary analyses
(29) of the "market basket" samples indicate that the Am 241/Pu
239 ratios in diets are not greatly different from current Am
241/Pu 239 ratios in soil. The ingestion of plutonium through
drinking water is another possible pathway to humans. The
concentration of fallout plutonium in finished drinking water has
been found (28) to be low (<3 fCi/1). However, in areas of
elevated levels, plutonium could migrate over time into cisterns
and wells, thus increasing the activity in drinking water. It
has been suggested (20) that a significant ingestion pathway
could be the accidental ingestion of contaminated soil by adults
or the deliberate ingestion of soil by children (pica).
However, assumptions of very large soil consumption rates would
be required for this pathway to become as significant as the
inhalation pathway, because of the small transfer rate of most
transuranium nuclides from the gastrointestinal tract to blood.
5.4. Methods of Relating Soil Concentration to Airborne Activity
The relationship between soil and air concentrations is
affected by many complex factors (see Table 5-1). Attempts to
derive values for them have resulted in many different
approaches; each uses different concepts and methods of
5-14
-------
measurement, selecting some physical factors as important and
tending to neglect others or include them as constants. The
purpose of this section is to describe briefly some of the more
commonly used approaches to relate soil contamination levels to
airborne radioactivity.
5.4.1 Resuspension Factor
One of the earliest and still most widely used methods of
predicting the relationship between soil and air contamination is
the resuspension factor. It is defined as the ratio of the
Plutonium concentration in air, measured at some distance above
the ground, to that of plutonium in the soil:
K = concentration in air (activity/m3)
concentration in soil(activity/m2)
The resuspension factor has limitations in its application.
In the first place, it assumes that the air concentration above a
contaminated surface is directly proportional to the surface
contamination level, rather than on the extent of ground
contamination upwind of the sampling site which is indeed the
case. In the second place, the resuspension factor is an
empirically determined value which can be applied only to
prevailing conditions at a given site and at a given time.
Most resuspension experiments have been conducted for a
relatively short duration of time and do not necessarily
represent the long-term average situation for a particular area.
Finally, applying a resuspension factor derived at one particular
site to predict airborne contamination levels at another site
would be a questionable extrapolation. However, for areas where
the resuspension factor has been measured over a period of time,
sufficiently long to average out the variability of the local
meteorology, then this approach can be useful in assessing the
potential hazard from existing soil contamination.
5-15
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ANNUAL MEAN MASS CONCENTRATIONS (,ug/mj) OF AIRBORNE
PARTICLES FROM NON-URBAN STATIONS OF THE U.S. NATIONAL
AIR SAMPLING NETWORK. 1964 - 1965
FIGURE 5-2
5 - 16
-------
TABLE 5-3
OBSERVED AIR CONCENTRATIONS
COMPARED WITH PREDICTIONS BY MASS LOADING MODEL
[Adapted from Anspaugh et al (1974)]
Air Concentration
Location, etc.
GMX site. USAEC Nevada
Test Site
NE, 1971-1972
CZ, 1972, 2 weeks
Lawrence Livermore
Laboratory
1971
1972
1973
1973
Argonne National
Laboratory
1972
1972
Sue con, England
1967-1968
Radionuclide
239
239
Pu
Pu
238
238,,
40,,
232
Th
nac.
nac.
Predicted
a
7200 aCi/m"
120 fCi/m3
150 pg/in
150 pg/m3
150 pg/m3
1000 aCi/nT
320 pg/m"
215 pg/ra3
110
Measured
6600 aCi/m'
23 fCi/ra3
52 Pg/mJ
3
100 pg/m
86 pg/m3
980 aCi/mJ
240 pg/nf
170 pg/m]
62 pg/ra'
a
Predicted value is equal to the soil concentration (activity/g) x
ID'* g/ra3.
b
Most values are annual averages.
5-17
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5.4.2 Mass Loading
One attempt to increase the capability of predicting soil
resuspension has been the mass loading approach. This technique
assumes the mass loading of the air with particulates to be an
index of resuspension and derives the airborne concentration of a
specific radionuclide by a comparison with its concentration on
the adjacent surface. Specifically:
Air Concentration = Soil Concentration x Mass Loading x C.F.
where C.F. is the units conversion factor based upon the depth of
sampling and the soil density.
Airborne particulate mass loading is one of the criteria for
clean air standards and measurements are widely available for
urban and nonurban locations through the National Air
Surveillance Network (NASN). The data recorded at nonurban
stations are a better indicator of the levels of resuspended
material than are urban measurements. In general, annual mean
mass concentrations of airborne particulate material at the
nonurban stations range from 5-50 micrograms per cubic meter
(see Fig. 5-2); the mean arithmetic average for 1966 of all
30 nonurban NASN stations was 38 ug/m3 (30). Anspaugh (30,31)
employed this model to predict air concentrations at a number of
sites. Predicted values did not exceed measured values by more
than a factor of roughly five (Table 5-3). The fallacy of the
model is in assuming that the resuspendible fraction of the soil
would carry with it an equal fraction of the activity, which
implies essentially that: 1) activity is distributed
homogeneously in the top soil and, 2) activity exists independent
of particle size. For instance, if the specific ground activity
is associated mostly with particles of size greater than 50 /im,a
very small air concentration would result, although the model
would predict the same air concentration for this case as it
would for all the activity being distributed among particles of
5-18
-------
resuspendible size. In either case the model would fail. Data
obtained (2,4,15) at sites of present contamination have shown a
nonuniform distribution of activity with particle size, probably
caused by such factors as: 1) the chemical form of the Plutonium
when released, 2) the ion exchange capacity of the soil, and 3)
the surface area of the soil particles. It would seem
reasonable, however, that the error associated with using the
mass loading approach would be least for soils in which the
contaminant has been present for some time and in making
predictions of average annual air concentrations.
5.4.3 Resuspension Rate and Other Approaches
Other approaches of a more sophisticated nature have been
developed to describe the resuspension of particles from a soil
surface. These approaches have attempted to include in their
formulations as parameters some of the physical forces which
control the resuspension phenomenon. One such technique proposed
by Healy and Fuquay (32) is the resuspension rate approach. This
model combines atmospheric transport and diffusion along with
particle resuspension to calculate airborne concentration. This
is achieved by assuming that the rate of pickup of particles from
a surface is directly proportional to the ratio of wind forces to
gravity forces on individual particles. Taking the wind force on
a particle as proportional to the square of the wind velocity and
to the particle area exposed to wind, the model develops a
formulation for the resuspension rate, i.e., the rate at which
particles will be resuspended by wind from a soil surface. Once
the resuspension rate has been determined it can be used as the
source term in a standard atmospheric diffusion equation to
predict the resultant air concentration at some distance from the
contaminated site. Healy (20) has refined the model formulations
to be capable of handling various geometric configurations of the
contaminated area and the variability of surface concentration
within the contaminated area. The advantages of a model of this
type are that it recognizes some of the physical conditions and
5-19
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processes which affect resuspension as well as providing a method
to calculate air concentration at various distances away from the
contaminated area.
One assumption by Healy in the original formulation of the
resuspension rate model was that the pickup rate for particles is
a function of the square of the wind velocity. Studies have been
conducted to establish the relationship between resuspension rate
and wind velocity. One such study conducted by Sehmel (33) at
Rocky Flats, for only short time periods and for one sampling
station, found the air concentration to be a function of the
square of the wind velocity, implying that the pickup rate was a
function of the cubic power of the wind speed. However, other
experiments by Sehmel (34) have shown resuspension rates to
increase with wind speed to the 6.5 power. Studies are
continuing to better elucidate this functional relationship.
Other approaches (35,36) have also been proposed which
attempt to relate particle resuspension to such factors as the
soil erodibility index, surface roughness factor, and quantity of
vegetative cover. These models generally require the
determination of several empirical constants in their
application. Although these constants may be applicable for the+
conditions under which they have been measured, the general
applicability of these formulations in predicting air
concentration has not been demonstrated at this time.
5-20
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5.4.4 Enrichment Factor
In order to take into consideration the non-uniform
distribution of activity with soil particle size as well as the
non-uniform resuspension of particle sizes, an "enrichment
factor" can be derived which is included in the mass loading
calculation. Potential exposure due to contaminated soil depends
largely on the amount of activity associated with particles in
the respirable size range (generally 10 pm)• It has been
suggested by several investigators that sampling of only those
particles in a soil sample which are within the inhalable size
range would give the best measure of risk to the public health.
However, the weight fraction of particles in the less than
10 /zm range is small in most soils, and sampling, separation, and
analysis techniques are correspondingly more difficult and
inaccurate. There is also considerable evidence that some of the
larger particles really consist of aggregates and are relatively
easily broken down into smaller ones, so that an instantaneous
measurement of a single size range may not give a good picture of
long-term trends. Another important objection to limited
sampling is that larger particle sizes may make a substantial
contribution to other possible pathways (e.g., ingestion), and
hence should be measured. To evaluate the potential hazard of
the inhalable fraction of soils, while retaining the advantages
and conveniences of analyzing the entire soil sample, the mass
loading approach can be modified by use of an "enrichment
factor". The proposed method weights the fraction of the
activity contained within the respirable range in terms of its
deviation from the activity to mass ratio for the entire sample
and, at the same time, addresses the problem of the nonuniform
resuspension of particle sizes mentioned in the previous section.
The inhalable fraction of the soil is weighted by considering the
relative distribution of activity and soil mass as a function of
particle size for representative samples of soil. To accomplish
this, the sample of contaminated soil is segregated into size
increments, and the activity and mass contained within each size
5-21
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increment is determined. The factor gi is then defined as the
ratio of the fraction of the total activity contained within a
size increment i to the fraction of the total mass contained
within that increment. A value greater than 1 for g, implies an
enrichment of activity in relation to mass within that
incremental fraction, while a value less than 1 indicates a
dilution of the activity with respect to mass relative to the
average for the sample.
In order to evaluate the potential for inhalation of
resuspended plutonium, the nonuniform resuspension of particle
sizes in each size increment of the surface soil must also be
considered. Accordingly, the mass loading can be derived as a
function of the measured particle size spectrum. The fraction of
the airborne mass contained within each size increment, i, is
calculated and designated as f|. The factors of fj and g, can then
be incorporated into the mass loading formulation as follows:
Air Activity, = Air Mass Loading x fi x Soil Activity x g,
Summation over all the size increments results in the total air
concentration:
Air Activity = Air Mass Loading x Soil Activity x Sf.g,
The term Ef,g, weights the contribution of the plutonium
from each soil size fraction to the total resuspended material,
thereby taking into account both the nonuniform resuspension of
particle sizes as well as the nonhomogeneous distribution of
activity. The summation of f,g, will be referred to as the
"enrichment factor", where f-, accounts for the distribution of
airborne mass as a function of particle size and g, accounts for
the variability of both soil activity and soil mass as a function
of particle size.
5-22
-------
.100
o
•10
m
m
a
o
•
8
3J
Z
fc
12 5 10 20 30 40 SO 60 70 80 90 95 9S 99 99.8 99.99
PERCENT OF MASS ASSOCIATED WITH PARTICLES OF LESS THAN EQUIVALENT DIAMETER
PARTICLE SIZE DISTRIBUTION OF RESUSPENDED SOIL
FIGURE 5-3
5-23
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TABLE 5-4
EXPERIMENTAL DATA FOR WEIGHT AND ACTIVITY FRACTIONS
FOR SOILS IN THE ENVIRONS OF THE ROCKY FLATS PLANT
[Sampling and Analysis by US Environmental Protection Agency]
Sample
RF 1A
RF IB
RF 1C
RF 2A
Size Increment (urn)
2000-105
105-10
2000^105
105-10
2000-105
105-10
2000-105
105-10
VJgc Fraec
.62
.18
.20
.63
.17
.20
.64
.16
.20
.46
.34
.20
Act Fract
.07
.40
.53
.39
.06
.55
.43
.07
.49
.13
,37
.50
.12
2.21
2.65
.63
.34
2.74
.68
.46
2.47
.28
1.10
2.48
^
.7
.3
_
.7
.3
.7
.3
.7
.3
2.J4
1.06
1.06
av.
-------
5.4.5 Correction for Area Size
Use of the mass loading approach implies that the air
concentration is at equilibrium with the ground surface, i.e.,
a steady state situation exists in which the amount of material
coming up from the surface is balanced by the amount of material
depositing back onto the surface. In the strictest sense this
limit can only be achieved for source are?.s approaching infinite
dimensions. For source areas of finite dimensions a fraction of
the airborne mass loading can be arising from an uncontaminated
area upwind which, although contributing dust to the atmosphere,
contributes no radioactivity. The smaller the size of the
contaminated area the less it will contribute to the mass loading
level and the greater the uncertainties involved in applying the
mass loading model.
Healy (37) has attempted to quantify the relationship
between the size of the contaminated area and the air
concentration that would result from it. His calculations show
that, for a contaminated area which is 50 meters in horizontal
depth, the air concentration would be approximately a factor of
one hundred smaller than from an area 5000 meters in depth (based
upon certain assumptions regarding meteorological conditions).
Therefore, a precise calculation requires a correction for area
size when applying the mass loading approach to small areas of
contamination. However, since one cannot predict a priori the
extent of a contamination incident nor the prevalent meteorology,
a conservative estimate can assume that the area contaminated is
sufficiently large that a correction for area size is not
necessary.
5-25
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5. 5 REFERENCES
General:
National Council on Radiation Protection and Measurement,
NCRP Report No. 76, Radiological Assessment: Predicting the
Transport. Bioaccumulation. and Uptake by Man of
Radionuclides Released to the Environment (1984)
W C Hanson, Editor, Transuranic Elements in the Environment.
Publication DOE/TIC-22800, U.S. Department of Energy (1980)
J E Till and H R Meyer, Editors, Radiological Assessment.
U.S. Nuclear Regulatory Commission, NUREG/CR-3332 (1983)
The Environmental and Biological Behaviour of Plutonium
and Some Other Transuranium Elements. Report by a Group
of Experts, OECD/Nuclear Energy Agency (1981)
Other:
l. H. M. Mork, Redistribution of Plutonium in the Environs of
the Nevada Test Site, UCLA-12-590, University of California
Press, Los Angeles (1970).
2. T. Tamura, "Distribution and Characterization of Plutonium
in Soils from Nevada Test Site," in The Dynamics of
Plutonium' in Desert Environments, NVO-142, USAEC, Las Vegas,
Nevada (1974).
3. K. Stewart, "The Resuspension of Particulate Material from
Surfaces," in Surface Contamination. B. R. Fish (ed.),
Pergamon Press, New York, N. Y. (1964), pp. 63-64.
4. D. R. Rogers, Mound Laboratory Environmental Plutonium Study
1974, MLM-2249, Mound Laboratory (1975).
5. G. A. Sehmel, "Particle Resuspension from an Asphalt Road
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