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165
6. POTENTIAL FOR HUMAN
EXPOSURE
Mexico, may release treated radioactive wastes under controlled conditions. Production facilities, such as
the Hanford and Savannah River Plants, and experimental reactor stations, for example,
the Idaho
National Engineering Laboratory, Idaho Falls, Idaho, also released treated plutonium-bearing radioactive
wastes under controlled conditions to soils (Hanson 1975).
Atmospheric weapons testing fallout has been a global source of transuranics, including plutonium, in
soils (Agency for Toxic Substances and Disease Registry 1999; Harley 1980; NEA/OECD 1981). The
Centers for Disease Control and Prevention (CDC) has estimated that the total deposition of plutonium
from weapons tests at the Nevada Test Site was 1.8x10
4
Ci (6.7x10
14
Bq) (CDC 2005).
During 2004, only facilities in the 200 Areas of the Hanford Site discharged radioactive liquid effluents to
the ground at a State-Approved Land Disposal Site. Releases of
238
Pu and
239,240
Pu were 6.9x10
-6
and
7.5x10
-6
Ci (2.5x10
5
and 2.8x10
5
Bq), respectively (DOE 2005c).
Several of the major nuclear facilities in the United States use plutonium and some of these have released
plutonium to the environment. These releases have taken place at remote
sites and generally have not
been measurable outside the plant property. Approximately 2 Ci (7x10
10
Bq) of plutonium have been
disposed in the Los Alamos National Laboratory canyon waste disposal sites (Harley 1980). The
Savannah River Plant, Aiken, South Carolina, has released a total of 5 Ci (2x10
11
Bq) of plutonium to
local soil (Harley 1980). Leakage of stored waste released between 10–100 Ci (3.7x10
11
–3.7x10
12
Bq) of
plutonium to the soil over a period of several years at the Rocky Flats facility, Golden, Colorado (DOE
1980g). A break in a waste transfer line caused the release of about 300 Ci (1x10
13
Bq) of
238
Pu at the
Mound Plant, Miamisburg, Ohio, in 1969 (DOE 1980g).
A fire on May 11, 1969, occurred at the plutonium processing facility at Rocky Flats,
which caused
concerns about possible contamination of the surrounding areas (Agency for Toxic Substances and
Disease Registry 2005). Studies showed that while trace amounts of plutonium were present in soil, the
distribution was not consistent with the wind direction at the time of the fire. It was determined that the
major source of plutonium contamination was leakage from drums of machine oil containing plutonium
that were being stored in an outdoor area (Eisenbud and Gesell 1997).
Another source of soil contamination at Rocky Flats was the leakage of plutonium-contaminated oil.
Plutonium was present as the dioxide when it was released. The dioxide was then adsorbed to the soil.
Fugitive dust emissions caused plutonium-contaminated soil to be distributed away from the spill. Most
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166
6. POTENTIAL FOR HUMAN EXPOSURE
of the plutonium remained on the surface, although some was released and
migrated downward through
the soil column (Little and Whicker 1978).
A U.S. military aircraft carrying four nuclear bombs collided with a tanker aircraft during refueling in
Palomares, Spain, in January, 1966. The bombs broke free of the airplane and the high explosive in two
of the weapons detonated when the bombs hit the ground. Initial surveys showed plutonium
concentrations of 3x10
-5
Ci/m
2
(1x10
6
Bq/m
2
), in the form of a finely powdered dioxide, were spread over
2 hectares (20,000 m
2
) (Harley 1980). A large amount of the contaminated soil was brought back to the
Savannah River facility in the United States for decontamination
and the soil with low-level
contamination was plowed to a depth of 30 cm (Harley 1980).
Plutonium has been identified in 6 soil and 9 sediment samples collected from 1,689 NPL hazardous
waste sites, where it was detected in some environmental media (HazDat 2007).
6.3 ENVIRONMENTAL FATE
6.3.1
Transport and Partitioning
Plutonium enters the environment primarily through releases to the atmosphere or direct discharge to
ponds, streams, or oceans. Emissions to the atmosphere will result in plutonium fallout. In the case of
weapons testing, approximately one-fifth of the plutonium released falls on the test site (Harley 1980).
The rest is carried in the
atmosphere, adsorbed to particulate matter and is transported back to earth via
dry or wet deposition. Once plutonium is deposited either on the land or surface water, sorption to soils
or sediments is the primary environmental fate of plutonium. A small fraction of plutonium reaching the
soil will become solubilized either through chemical or biological processes, depending upon its chemical
form.
In soluble form, plutonium can either migrate in groundwater or surface water or be available for
uptake into plants; colloidal forms of plutonium are not as available for uptake as soluble forms.
Atmospheric releases of plutonium occurred as a result of former atmospheric nuclear weapons testing or
routine or nonroutine nuclear reactor operations and fuel reprocessing. The rate at which plutonium is
removed from the atmosphere depends on the chemical and physical properties of the particles, as well as
the meteorological conditions. The larger the particles, the faster fallout will occur.
The particle size
expected to be released from either of the above mentioned sources ranges from 0.3 to 1.1 μm. At the
highest altitudes, aerosols in the atmosphere descend by gravity; at lower levels, they are transported with
the general air movement (UNSCEAR 2000a). In the lower stratosphere,
the mean residence time of