7
PLUTONIUM
1. PUBLIC HEALTH STATEMENT
The USNRC has recommended the following radiation exposure limits for the general public and for
workers:
General public
0.1 rem/year for the general public and 0.5 rem/year for people who work
with medical patients. These regulations are for all forms of radiation
combined, so they are not only for plutonium.
Workers
5 rem/year for workers in industries where exposure
to radiation may occur
and 0.5 rem for the pregnancy period following the declaration of pregnancy
by a woman in an industry where exposure to radiation may occur.
These recommended radiation exposure limits are for all forms of radiation combined and are not specific
to plutonium. The limits are expressed in units called rem (roentgen equivalent man). A rem is a
radiation unit that expresses the radiation equivalent dose to a particular organ or tissue. The limits on
equivalent dose are used to calculate the limits on the amount of radioactive substances that can be
inhaled or ingested.
Additional information on governmental regulations regarding plutonium can be found in Chapter 8.
1.10 WHERE CAN I GET MORE INFORMATION?
If you have any more questions or concerns, please contact your community or state health or
environmental quality department, or contact ATSDR at the address and phone number below.
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics
specialize in recognizing, evaluating, and treating illnesses that result from exposure to
hazardous
substances.
Toxicological profiles are also available on-line at www.atsdr.cdc.gov and on CD-ROM. You may
request a copy of the ATSDR ToxProfiles
TM
CD-ROM by calling the toll-free information and technical
9
PLUTONIUM
2. RELEVANCE TO PUBLIC HEALTH
2.1
BACKGROUND AND ENVIRONMENTAL EXPOSURES TO PLUTONIUM IN THE
UNITED STATES
Plutonium is primarily a human-made radioactive element of the actinide series and was the first human-
made element to be synthesized in weighable amounts. Plutonium was first synthesized by the
bombardment of uranium with deuterons (
2
H) by Seaborg and co-workers in 1940. Although 20 isotopes
of plutonium (
228-247
Pu) have been identified, the alpha-emitting
238
Pu and
239
Pu isotopes are the ones most
commonly encountered and widely studied for potential adverse health effects.
The isotope
239
Pu was
first used in fission weapons beginning in 1945 and is produced during the bombardment of uranium
(
235
U) by neutrons in nuclear reactors. Approximately one-third of the total energy produced in a typical
commercial nuclear power plant comes from the fission of
239
Pu produced from
235
U. The isotope
238
Pu
has been used as a heat source in nuclear batteries to produce electricity in devices such as unmanned
spacecraft and interplanetary probes. Plutonium is a carefully regulated material under government and
International Atomic Energy Agency (IAEA) control and has no commercial usage, with the exception of
small quantities used in research laboratories. Approximately 1,855
metric tons of plutonium was
estimated to exist worldwide at the end of 2003; most of which was found in spent fuel from nuclear
power plants. A plutonium production rate of 70–75 metric tons/year was estimated for reactors
worldwide in 2003.
The main sources of plutonium in the environment are releases from research facilities, nuclear weapons
testing, waste disposal, nuclear weapons production facilities, and accidents. Atmospheric testing of
nuclear weapons, which ended in 1980, is the source of most of the plutonium in
the environment
worldwide, which released approximately 10,000 kilograms of plutonium. Trace amounts of plutonium
(including
238
Pu,
239
Pu,
240
Pu, and
241
Pu) are found worldwide, mostly due to fallout from atmospheric
nuclear testing. Trace amounts of
239
Pu are found in naturally occurring uranium ores, although in such
small amounts that extraction is not practical. Small amounts of
244
Pu also exist in nature from remnants
of primordial stellar nucleosynthesis and from “natural” reactors such as the
Oklo natural reactor in the
African nation of Gabon, which existed about 2 billion years ago. Plutonium released to the atmosphere
reaches the earth's surface through wet and dry deposition to the soil and surface water. Once in these
media, soluble plutonium can sorb to soil and sediment particles or bioaccumulate in terrestrial and
aquatic food chains.
10
PLUTONIUM
2. RELEVANCE TO PUBLIC HEALTH
Humans may be exposed to plutonium by breathing air, drinking water, or eating food containing
plutonium; however, the levels of plutonium in air, water, soil, and
food are generally very low, and of
little health consequence. Average plutonium levels in surface soil from fallout range from 0.01 to
0.1 picocuries (pCi) per gram of soil (1 picocurie equals one-trillionth [10
-12
] of a curie). In general,
plutonium concentrations in air are low. Baseline
239
Pu concentrations in air ranging from 1.6x10
-6
to
3.8x10
-6
pCi per cubic meter of air (pCi/m
3
) have been reported.
2.2 SUMMARY OF HEALTH EFFECTS
Risks for adverse outcomes of plutonium exposures are strongly dependent on radiation doses received by
specific tissues and organ systems. Most of the body burden of plutonium resides in the skeleton and
liver, and
following inhalation exposures, in the lung and lung-associated lymph nodes. As a result, these
tissues receive relatively high radiation doses following exposures to plutonium. Radiation-induced
toxicity to these tissues has been documented in human epidemiological studies and in animal models.
The relatively high radiation doses received by bone, liver, and lung lend greater credibility to the
epidemiological findings for these tissues than for outcomes in other tissues that receive much smaller
radiation doses. All epidemiological studies that have reported adverse outcomes in these tissues have
studied populations (i.e., workers in plutonium production and processing facilities) that experienced
exposures and radiation doses that greatly exceed those experienced by the general public. Accordingly,
risks for these outcomes in the general population are substantially lower than
reported for these more
highly exposed worker populations.
Death.
Possible associations between exposure to plutonium and mortality have been examined in
studies of workers at the U.S. plutonium production and/or processing facilities (Hanford, Los Alamos,
Rocky Flats), as well as facilities in Russia (e.g., Mayak) and the United Kingdom (e.g., Sellafield). The
Mayak studies provide relatively strong evidence for an association between cancer mortality (bone, liver,
lung) and exposure to plutonium. Plutonium dose-response relationships for lung cancer mortality have
been derived from studies of Mayak workers, who received much higher uptakes of plutonium compared
to other epidemiological cohorts (i.e., mean body burdens 0.09–9.2 kBq, with much higher individual
exposures [up to 470 kBq] in relatively large numbers of these workers). Excess relative risk (ERR)
estimated in three studies (adjusted for smoking) were 3.9 per Gy (95% confidence interval [CI]: 2.6–
5.8) in males, and 19 per Gy (95% CI: 9.5–39) in females (attained age 60 years), 4.50 per Gy (95% CI:
3.15–6.10) in males, and 0.11 per Sv (95% CI: 0.08–0.17) or 0.21 per Sv (95% CI: 0.15–0.35),
depending on the smoking-radiation interaction model that was assumed (these estimates per Sv