AMERICIUM, RADIOACTIVE: Nuclear Power Plant Emissions
Atmospheric
Concentrations :
SOURCE DOMINATED: The total estimated amount of americium-241 released to the
atmosphere from weapons testing was 130 kCi (4,800 TBq) during the period of
1951-1978. The accident at the Chernobyl nuclear power plant in the Ukraine
(April 1986) also resulted in the release of about 140 kCi (5,200 TBq) of
plutonium-241, which is the radioactive precursor to americium-241, into the
atmosphere(1).
Artificial Pollution Sources :
In the environment, americium is present as a result of basically three sources:
fallout from nuclear explosions, releases from nuclear reactors and reprocessing
plants, and production and disposal of smoke detectors by producers and
consumers(1).
Disposal Methods :
/SRP/ Wastes in the Waste Isolation Pilot Plant (WIPP) are from the nuclear
weapons industry (plutonium) - research and development. For a waste to be
accepted at WIPP it must be a transuranic "TRU" waste and: (1) </=
100 nanoCi/gram, (2) an alpha emitting transuranium isotope with atomic number
greater than uranium, and (3) have a half life greater than 20 years. The wastes
must be handled remotely if they produce >/= 200 millirems/hr; if less, they
can be contact handled.
Human Toxicity Excerpts :
/CASE REPORTS/ /BONE/ Pathological changes ... were found in the bones of a
worker at the Hanford nuclear weapons plant who had been extensively
contaminated with americium-241 /USTUR Case 246/. When he died 11 years after
his accident from a pre-existing heart condition, his skeleton contained an
estimated 500 kBq of radionuclide - an amount that had already been much reduced
by decorporation therapy from an initial estimated intake of 185 MBq. The bones
examined were the patella, clavicle, sternum, rib, vertebral body and ossified
thyroid cartilage; all showed evidence of radiation damage. The cellularity of
most bones was reduced, and little evidence of recent active bone remodeling was
seen in any bone other than the vertebra, as concluded from the redistribution
of the americium in the vertebral body. In several bones, the architecture was
disrupted, with woven bone, abnormal appositional bone deposits, bizarre
trabecular structures and marked peritrabecular fibrosis. Growth arrest lines
were common. When compared with trabecular bone modeling, that of cortical bone
in the rib appeared less disrupted. Overall, the results obtained are consistent
with those observed in dogs at a similar level of actinide intake.
/Americium-241/
Environmental Fate/Exposure Summary :
Most of the radioactive americium released to the environment occurred as a
result of atmospheric testing of nuclear weapons in the 1950s and 1960s. Nuclear
weapon testing injects radioactive material into the stratosphere, which results
in wide dispersal of radioactive americium and other radionuclides. Routine
releases of radioactive americium also occur from releases from nuclear reactors
and reprocessing plants, and production and disposal of smoke detectors
(americium-241, half-life=432.2 yrs) by producers and consumers. When released
to the atmosphere, radioactive americium exists in the particulate-phase and is
removed by wet and dry deposition. Americium has slight mobility in soils and
sediments, and adsorbs strongly to metal oxides and clays, but may be
transported on colloids. Americium occurs most commonly in the +3 oxidation
state in the environment and the trivalent state is the only state of importance
in biological systems. Americium bioconcentrates in aquatic organisms and
accumulates in bones and muscles. Workers involved in producing ionization smoke
detectors or other devices containing americium (americium dioxide), workers at
nuclear reactors or Department of Energy (DOE) facilities, and workers who use
americium-containing devices (neutron backscatter sources for checking roof
leaks and road undermining, and well logging equipment) may be exposed to higher
levels of americium. Since atmospheric testing of nuclear weapons has been
discontinued for many years and Chernobyl-related fallout was low in the US,
current exposure of the general population of the US to radioactive americium is
expected to be low. The primary route of exposure to radioactive americium for
the general population is through inhalation of dust and ingestion of foods. (SRC)
Fish/Seafood Concentrations :
In a study performed in a nuclear waste pond where the levels of americium-241
were about three orders of magnitude above background levels, concentrations in
fish filet were rarely greater than ten times that of controls. In marine
organisms consumed by humans, uptake is generally highest in mussels where the
target organs are mainly the digestive gland, gill, and exoskeleton(1). The mean
activity concentrations of americium-241 detected in the edible portion of 34
crabs and 35 lobsters caught commercially in the Sellafield coastal area
offshore from the Sellafield nuclear fuel reprocessing plant in the northeast
Irish Sea between May 25 and June 5, 1997 were 1.7 and 8.3 Bq/kg (wet),
respectively(2).
Absorption, Distribution & Excretion :
Ingestion: The only data on the absorption of americium in humans are from two
studies of the absorption of plutonium and americium by volunteers who ate
winkles collected on the Cumbrian coast near to the nuclear-fuel reprocessing
plant at Sellafield. The average fractional absorption value obtained for
americium was 1x10-4 ... . /Americium and plutonium, NOS/
Plant Concentrations :
Vegetation samples collected in 1994 and 1995 from the industrial area of a
plant for the utilization and repair of nuclear-powered submarines in the
coastal area of Cut Bay in Olenjya Bay in the Kolsky Gulf, Russia contained an
americium-241 concentration of 0.2-0.4 Bq/kg of air dry sample(1). Seaweeds
collected from the water area of Cut Bay had an americium-241 concentration of
0.2 Bq/kg of moist sample(1). Americium-241 was detected at a mean concentration
of 0.299 Bq/kg in mosses collected from Antarctica in 1989-1996(2). Terrestrial
moss and tree trunk moss samples collected from the central Italy had a mean
americium-241 concentration of 0.0518 Bq/kg and 0.653 Bq/kg, respectively(2).
One lichen sample collected from Antarctica had an americium-241 concentration
of 1.94 Bq/kg, while the mean concentration in tree trunk lichens collected from
central Italy was 0.436 Bq/kg(2).
Environmental Bioconcentration :
BCF values for americium-241 measured for various plants at the Department of
Energy's Savannah River Site were reported in 1996 as follows: Macrophyte
(rooted vascular), 1,400-21,000; Macrophyte (floating vascular), 75,000; Bahia
grass, 0.03-0.12; and Pine tree leaves, 0.0052-0.021(1). Various studies
indicate that americium-241 uptake by plants is on the order of 10-2 to 10-6.
Uptake is somewhat greater under acidic conditions and greater to the leaves
than to the grain or fruit(1). Plant uptake experiments with potatoes, peas, and
corn were performed using fallout background soil (low levels found in
environmental media worldwide from atmospheric nuclear weapons tests are
referred to as fallout background) in North Eastham, Massachusetts. The
americium-241 in the plant was compared with the average activity in the upper
30 cm of dried soil, 0.0033 Bq/g. The concentration ratios (CRs) (activity per
unit wet weight of plant/activity per unit dry weight of soil), also referred to
as the transfer coefficient, were 1.7X10-3 for husked corn plus cob, 1.0X10-3
for peeled potatoes, and <1.6X10-3 for shelled peas(1).
Effluent Concentrations :
In nuclear reactors, americium-241 has been detected in primary coolant water,
stack aerosols, and waste water(1). Water sampling data were used to estimate
effluent releases from the Department of Energy's Savannah River Site from the
plant's startup in 1954 through 1989. From this monitoring, it was estimated
that 290 mCi (11 GBq) of americium-241 was released into seepage basins between
1977 and 1989; however, no americium-241 was released directly into streams. In
1999, 1.34X10-5 Ci (0.496 MBq) of americium-241 was released from the Savannah
River Site into surface waters(1). The annual liquid effluent discharges from a
typical U.K. Magnox Station contained 34.3?121 Bq/L (0.926?3.27 nCi/L) of
americium-241 for the years 1991?1995(1).
Preventive Measures :
In a nuclear weapon accident involving fire or conventional explosion, most of
the radiation dose received by people in the immediate vicinity would result
from inhalation of plutonium-239. This is accompanied by the nuclide
americium-241, which is much easier to determine by external counting because of
the 60 keV gamma ray emission. In the event of an accident, a priority would be
to identify any people who have had intakes of plutonium-239 which were so large
that decorporation therapy should be considered. Direct measurement of lung
content provides the most rapid and convenient method for assessing intakes by
inhalation. A transportable system has been considered as this could be deployed
close to the site of the accident and would allow rapid measurements to be made.
The feasibility of a transportable americium-241-in-nose-blow and nasal swab
measurement system has also been considered. This would be used to help select
people for americium-241-in-lung measurements. /Americium-241 and plutonium-239)
Other Chemical/Physical Properties :
DECAY PATHWAY: Americium-242, half-life 16.02 hrs, 82.7% decays via beta(-)
emission (46%, 662.5 keV maximum energy; 46%, 620 keV maximum energy) to
curium-242, half-life 162.8 days, decays via alpha emission, 6216 keV (74% 6113
keV; 25% 6069 keV), to plutonium-238, half-life 87.7 yrs, decays via alpha
emission, 5593 keV (70.9% 5499; 28.9% 5456 keV), to uranium-234, half-life
245,500 years
Other Chemical/Physical Properties :
DECAY PATHWAY: Americium-243, half-life 7,370 yrs, decays via alpha emission,
5438 keV (87.4% 5275 keV; 11.0% 5233 keV), and gamma emission (abs intensity:
68.2% 74.66 keV) to neptunium-239, half-life 2.36 days, decays via beta(-)
emission (45%, 438 keV maximum, 126 keV average energy; 40%, 341 keV maximum, 93
keV average energy), to plutonium-239, half-life 24,100 years
Radiation Limits & Potential :
DECAY PATHWAY: Americium-242, half-life 16.02 hrs, 82.7% decays via beta(-)
emission (46%, 662.5 keV maximum energy; 46%, 620 keV maximum energy) to
curium-242, half-life 162.8 days, decays via alpha emission, 6216 keV (74% 6113
keV; 25% 6069 keV), to plutonium-238, half-life 87.7 yrs, decays via alpha
emission, 5593 keV (70.9% 5499; 28.9% 5456 keV), to uranium-234, half-life
245,500 years
Radiation Limits & Potential :
DECAY PATHWAY: Americium-243, half-life 7,370 yrs, decays via alpha emission,
5438 keV (87.4% 5275 keV; 11.0% 5233 keV), and gamma emission (abs intensity:
68.2% 74.66 keV) to neptunium-239, half-life 2.36 days, decays via beta(-)
emission (45%, 438 keV maximum, 126 keV average energy; 40%, 341 keV maximum, 93
keV average energy), to plutonium-239, half-life 24,100 years
Environmental Bioconcentration :
In shellfish, americium is attached to the shell and not to the parts normally
consumed(1). BCF values for americium-241 measured for various plants and
animals at the Department of Energy's Savannah River Site were reported in 1996
as follows: Macroinvertebrates (larvae), 78,000-240,000; Turtle (muscle), 5,600;
American coot (muscle), 650(1). In marine organisms, the target organs and
tissues of americium bioaccumulation are mainly the digestive gland, gill, and
exoskeleton. Uptake in mussels appears to be primarily from seawater rather than
ingested sediment(1). The depuration profiles in mussel populations chronically
exposed to radioactive waste discharges from the BNFL reprocessing plant at
Sellafield, Cumbria, into the northeast Irish Sea were studied. Apart from
clearance from the digestive tract (half-life of 0.9 hours), the half-time of
americium-241 is 303 days. Essentially all of the americium-241 taken up by a
euphausiid, a shrimp-like zooplankton, was by passive adsorption onto
exoskeletons, so that negligible americium was retained by the animal after
molting. Wet weight concentration factors were of the order of 100 after a week
of exposure, with the BCFs varying linearly with the surface area-to-weight
ratio of the organism. Americium was also taken up by feeding on suspensions of
diatoms, but there was negligible assimilation and most americium passed through
the gut and was defecated(1). Uptake and retention of americium by benthic
organisms is quite variable. In general, filter feeders such as tunicates can
clear particles containing americium-241 from seawater by filtration through the
branchial basket and accumulate small amounts in internal tissue. Echinoderms
and some large crustaceans assimilated americium with their ingested prey,
although large differences in half times and assimilation efficiencies in
different groups suggest different feeding-digestion physiologies. Uptake in
benthic marine isopods, is to a great extent, by surface adsorption to the
exoskeleton and to a lesser extent through the gut, digestive gland, muscle, and
haemolymph. The half-time in the long-lived compartment was 261 days.
Elimination from the internal tissue was more rapid than from the exoskeleton.
The fraction assimilated into tissue from food was <5%(1).
Major Uses :
Soft gamma emission from americium-241 is used to measure the thickness of metal
sheets and metal coatings, the degree of soil compaction, sediment concentration
in streams, and to induce X-ray fluorescence in chemical analysis. As an alpha
emitter, it is mixed with beryllium to produce a neutron source for oil-well
logging and to measure water content in soils and industrial process streams.
The alpha source is also used to eliminate static electricity and as an
ionization source in smoke detectors. /Americium-241/
Other Chemical/Physical Properties :
DECAY PATHWAY: Americium-241, half-life 432.2 yrs, decays via alpha emission,
5637 MeV (84% 5485.6 keV; 13% 5442.78 keV), to neptunium-237, half-life
2,144,000 years
Other Chemical/Physical Properties :
DECAY PATHWAY: Americium-242m, half-life 141 yrs, 99.54% decays via isomeric
transition (gamma emission, 48.63 keV) to americium-242
Radiation Limits & Potential :
DECAY PATHWAY: Americium-241, half-life 432.2 yrs, decays via alpha emission,
5637 MeV (84% 5485.6 keV; 13% 5442.78 keV), to neptunium-237, half-life
2,144,000 years
Radiation Limits & Potential :
DECAY PATHWAY: Americium-242m, half-life 141 yrs, 99.54% decays via isomeric
transition (gamma emission, 48.63 keV) to americium-242
Methods of Manufacturing :
Americium-241 and americium-243 can be made from uranium-239 or plutonium-239 by
neutron activation involving an operating nuclear reactor or nuclear bomb
detonation. In this process, neutron activation of uranium-238 can produce
uranium isotopes up to at least uranium-241, and each of these beta decays to a
neptunium isotope of the same mass. Neutron activation of neptunium can produce
isotopes starting with neptunium-239 up through at least neptunium-244, and each
of these isotopes beta decays to a plutonium isotope of the same mass. Neutron
activation of plutonium isotopes starting with plutonium-239 can produce
isotopes through at least plutonium-246, and of these, plutonium-241,
plutonium-243, plutonium-245, and plutonium-246 beta decay to americium isotopes
of the same mass. /Americium-241, Americium-243, Americium-245, Americium-246/
Environmental Abiotic Degradation :
Americium isotopes are transformed by radioactive decay. However, the half-lives
of americium-241 and americium-243 are very long, 432.2 and 7,370 years,
respectively, and there is only a small amount of transformation over a human
lifetime(1). There is limited information available regarding the abiotic
transformation of americium in the atmosphere. Oxidation is the most common
reaction that occurs in the atmosphere(1). Americium will occur in soil in the
trivalent state. The transformations that may occur would involve complexation
with inorganic and organic ligands and precipitation reactions with anions and
other substances present in the soil solution(1). Americium released to the
atmosphere will be associated with particulate matter and will be deposited on
land or surface water by dry or wet deposition. Dry deposition results from
gravitational settling and impaction on surfaces. Wet deposition returns
americium to earth by rainout caused by droplet formation on aerosols within
clouds and wash-out by falling precipitation. Residence half-times of
americium-241 particles in the lower stratosphere range from 3 to 12 months in
polar regions and from 8 to 24 months in equatorial regions, with removal being
highest in the spring and lowest in the fall. Half-times for particles in the
troposphere are about 1 month(1). In atmospheric nuclear weapons tests,
radionuclides are often injected into the stratosphere. The amount of
americium-241 present in the atmosphere from nuclear weapons testing depends on
the amount of unfissioned americium-241 and plutonium-241, as well as lower
isotopes of plutonium neutron activated to plutonium-241 during detonation and
injected into the atmosphere, and the transport and residence time of both
americium-241 and its precursor in the various atmospheric compartments (e.g.,
stratosphere and troposphere)(1).
Probable Routes of Human Exposure :
The general population may be exposed to elevated levels of americium-241 from
nuclear accidents or from residing in areas in the proximity of hazardous waste
sites where this radionuclide is present. Exposure is generally through the
inhalation and ingestion of dust from these sites. Workers involved in producing
ionization smoke detectors or other devices containing americium-241, workers at
nuclear reactors or Department of Energy (DOE) facilities, and workers who use
americium-containing devices (neutron backscatter sources for checking roof
leaks and road undermining, and well logging equipment) may also be exposed to
higher levels of americium-241(1).
Human Toxicity Excerpts :
/CASE REPORTS/ /WOUND CONTAMINATION/ Glovebox Accident Involving
Plutonium-Americium Contamination and Hand Amputation. An employee ... in
plutonium fuel fabrication reached for an item in his glovebox and his glove was
caught by a milling machine that tore off his right hand. /An hour later/ ...
patient /arrived at the treatment center. ... The patient was surveyed for
external contamination while in the ambulance. No widespread removable
contamination was found, so the patient was brought in and placed on a
decontamination table /at which time the attending physician/ learned that the
patient had lost his right hand at the wrist. /A half-hr later/ the plant health
physics supervisor arrived with the contaminated hand wrapped in plastic in an
ice bucket. The hand was immediately counted ... and the patient's stump was
counted ... with a ... NaI crystal. An initial estimate ... indicated ... an
amount, if entering bone, /that/ could result in bone dose commitments in the
tens of millions of rem ... Additional measurements /after ... debridements/
indicated that ... remaining contamination on the hand and stump was still more
than 100 times the Maximum Permissible Body Burden (MPBB). .... The difficult
decision was made by the patient and his family, as well as the involved
physicians and health physicists, to reattach the hand despite its excessive
residual radioactivity. Considerations included the youth of the worker, his
right-handedness, location of the radioactivity, the availability of DTPA
chelation therapy, and the likelihood of the patient's availability of multiyear
observation. ... Unfortunately, circulation in the fingers of the reattached
hand did not improve quickly enough for tissue survival, so the hand was
reamputated, ... infused with formaldehyde and recounted ... showing about 4 uCi
(about 100 MPBB) still on the surface. ... Since reamputation of the hand was
done approximately an inch higher than the original accidental amputation, the
reamputated hand turned out to contain practically all of the remaining
contamination. ... The medical management of an injured and contaminated patient
in this case required at least about two person-days of professional dedication
of a medical-health physics team already experienced with accidents involving
external and internal contamination with americium-plutonium mixtures; this
input was in addition to collaboration with a number of other physicians and
medical and health physics technicians. The average medical institution likely
to receive contaminated victims of a terrorist attack will not have such
personnel or equipment resources. Any expectation of a medical capacity for
triage and management of such patients requires prior training and equipping of
personnel in each medical institution for the simplest counting and
spectrometric measurements, and ready-made methods of data interpretation.
/Plutonium-239 and americium-241 nitrates/
Food Survey Values :
Flours that were milled from crops of wheat, rye, barley, and oats grown on
German soil where radionuclides resulted exclusively from global fallout
contained less than or equal to 5.2, 11, 31, and 70 uBq/kg of americium-241,
respectively. The concentration of americium-241 in the bran was a factor of
10?38 higher than in the flour for wheat, rye, and oats(1). Geometric mean
concentration ratios of americium-241 (Bq/kg dry plant/Bq/kg dry soil) in the
various crops were: corn kernel, 0.0011; corn husk, 0.0016; bush beans, 0.0072;
turnip green, 0.0528; and turnip tuber, 0.0053(1).
Animal Concentrations :
Small mammals inhabiting areas containing radioactive contamination or
radioactive waste sites may become contaminated with americium by consuming
contaminated soil or plants and disturb americium-241 contaminated soil through
their burrowing and excavating activities. In addition, small mammals may be
consumed by animals higher in the food chain such as hawks and coyotes, which
would add to the dispersal of americium from disposal areas(1).
Cleanup Methods :
Decontamination is most successful when the material can be recycled for use in
a nuclear facility since the need to prove releasability (cleanliness) is
eliminated. Nevertheless, cleaning material for unrestricted release is also
possible in some cases. It may also be possible to decontaminate an item enough
to change its classification from TRU/transuranic/ waste to LLW /low-level
waste/, thereby allowing immediate disposal of the item, while a relatively
small quantity of decontamination waste is stored as TRU waste. Electropolishing
to remove the thinnest metal surface has been very effective and produces a
relatively small waste volume, especially when one of the wetted sponge units is
used rather than an emersion tank. Surface scabbling has been used in
decontamination of concrete, and various abrasive blasting methods have also
been effective. Strippable and self-stripping coatings may be used to
decontaminate surfaces, even though the primary application of strippable
coatings has been in preventing contamination of surfaces. /Plutonium
facilities/
Human Toxicity Excerpts :
/BIOMONITORING/ Chromosomal aberrations (symmetrical translocations and
dicentrics and ring chromosomes) in lymphocyte preparations were elevated for an
entire group of 7 nuclear fuel production workers who were exposed for 11-22 yrs
to external gamma radiation, with an additional internal exposure for 6 of these
workers to americium-241 5 yrs prior to the analysis. The total effective dose
equivalent from exposure to external gamma radiation and internal contamination
with americium-241 /ranged from 29 to 393 mSv./ /Americium-241/
Non-Human Toxicity Excerpts :
/ALTERNATIVE IN VITRO TESTS/ Tumor induction by americium is well known but
there are no data on the biological effects of this radionuclide at the
subcellular level. In order to study the possible ultrastructural lesions
induced by this element, ... rats were injected with Americium-241 citrate (9
kBq), once a week for five weeks and sacrificed 7 days after the last injection.
/The authors/ describe the alterations observed in the cortex kidney using
cytochemical (TUNEL reaction) and histochemical (PAS staining) methods for light
microscopy as well as electron microscopy techniques. Various types of lesions
were detected: condensation of nuclear chromatine, fragmentation of the nuclei,
swollen mitochondria, disappearance of mitochondrial crest, and shrinking of the
cytoplasm. This study clearly demonstrated the induction of apoptosis by
americium in rat cortex kidney cells. /Americium-241 citrate/
Environmental Bioconcentration :
Fish may take up americium, but little builds up in the fleshy tissue(1). BCF
values for americium-241 measured for various fish at the Department of Energy's
Savannah River Site, SC were reported in 1996 as follows: largemouth bass
(muscle), 2,500; bullhead catfish (bone), 4,200. In a study performed at a
nuclear waste pond at Hanford, WA, the maximum concentration of actinides,
including americium-241, that would accumulate in the whole fish and fish fillet
were measured. In this waste pond, the sediment concentration of americium-241
was about 5.5 Bq/g, approximately 3 orders of magnitude above background levels.
Both the bluegill and largemouth bass were studied. The concentration of
americium-241 in the water was about 7 uBq/mL. The results from the Hanford
study indicate that both short- and long-term uptakes of americium were low;
that uptake was similar for short-term (5 days) and long-term (430 days)
experiments; and that direct sediment-to-fish transfer was the primary route for
americium uptake. In both species of fish, there were only a few cases where
fillet concentrations were >10 times those in controls. The maximum
concentration of americium-241 obtained in bass and bluegill were 1.1 and 1.0
mBq/mL dry weight in fillet and 2.5 and 74 mBq/mL in whole fish(1).
Soil Adsorption/Mobility :
Americium has been shown to be largely associated with the high molecular weight
organic factions of dissolved organic matter in the soil solution of two
grassland soils, a soddy podzolic soil and a peat soil, in the vicinity of the
nuclear reactor at Chernobyl, Ukraine. The distribution coefficients for
americium-241 in these soils were (soil type (depth), Kd in mL/g): soddy
podzolic-sod layer (0 to 2 cm), 1,220; soddy podzolic-mineral layer (2 to 5 cm),
810; peat (0 to 2 cm), 2,760; and peat (2 to 5 cm), 4,550(1). While it was
similarly shown that the concentration of americium-241 was 2 to 3 times higher
in organic matter than in whole sediment from Lake Michigan, organic matter was
a very minor constituent of the sediment (<0.5%), so organic matter was
associated with a smaller percentage of americium despite its higher
concentration. The bulk of the americium-241 in Lake Michigan was found in the
hydrous oxides fraction of both the sediment core samples and the suspended
particulate matter(1).
Soil Adsorption/Mobility :
Fallout americium-241 (the low levels found in environmental media worldwide
from atmospheric nuclear weapons tests) is predominantly retained to the upper
few centimeters of soil where it is associated with organic matter and bound to
manganese and iron oxides(1). Leaching studies of surface-deposited
americium-241 in three Indian soils of widely differing characteristics, namely
laterite, medium black, and alluvial, were conducted in soil columns using
simulated rain corresponding to the mean annual precipitation. It was found that
98% of the americium was retained in upper 2 cm of soil; amending the soil with
organic matter only slightly reduced its mobility(1). In a study of the various
soil components in six successive layer of undisturbed grassland in Germany the
attachment of americium to soil component varied considerably with soil layer.
The largest amount of americium-241 was attached to organic matter, 18-74%,
depending on the soil layer. A substantial fraction, 12-64%, was bound to
oxides. In the 5-10 cm layer, the americium-241 in the readily exchangeable
fraction was a minimum, 1.5%, while that attached to soil minerals was a
maximum, 68%(1).
Environmental Water Concentrations :
SEAWATER: Americium-241 concentrations in large volume water samples collected
from the Catalan Sea in the northwestern Mediterranean in 1991 at depths of 2-3
m (surface), 100 m, 500 m, and 1000 m were 1.0, 1.1, 1.9, and 1.5 mBq/cu m,
respectively(1). Americium-241 levels in surface seawater of the North Sea and
North Atlantic Ocean stayed around 10 Bq/cu m (270 pCi/cu m) between 1976 and
1988, but may be considerably higher near discharges from nuclear facilities(2).
Threshold Limit Values :
The Physical Agents TLV Committee accepts the occupational exposure guidance of
the International Commission on Radiological Protection (ICRP). Ionizing
radiation includes particulate radiation (e.g., alpha particles and beta
particles emitted from radioactive materials, and neutrons from nuclear reactors
and accelerators) and electromagnetic radiation (e.g., gamma rays emitted from
radioactive materials and x-rays from electron accelerators and X-ray machines)
with energy greater than 12.4 electron-volts (eV) ... The guiding principle of
radiation protection is to avoid all unnecessary exposures. ICRP has established
principles of radiological protection. There are (1) the justification of a work
practice: No work practice involving exposure to ionizing radiation should be
adopted unless it produces sufficient benefit to the exposed individuals or the
society to offset the detriment it causes. (2) The optimization of a
workpractice: All radiation exposures must be kept as low as reasonably
achievable (ALARA), economic and social factors being taken into account. (3)
The individual dose limits: The radiation dose from all relevant sources should
not exceed the /ICRP/ prescribed dose limits.
Other Occupational Permissible Levels :
The recommendations in the American National Standards Institute standard, ANSI
Z88.2-1992, "American National Standard For Respiratory Protection,"
are endorsed by the U.S. Nuclear Regulatory Commission and may be used by
licensees in establishing a respiratory protection program with the
/several/exceptions /including limitations that do not permit or greatly
restrict the use of quarter-facepiece respirators and supplied air respirators
and self-contained breathing apparatus (SCBA) that operate in the demand mode./
Special Reports :
U.S. Nuclear Regulatory Commission; Regulatory Guide 8.34 - Monitoring Criteria
and Methods to Calculate Occupational Radiation Doses. 1992/ Available at http://www.nrc.gov/reading-rm/doc-collections/reg-guides/occupational-health/active/8-34/index.html
as of September 25, 2006
MORE ABOUT HEALTH EFFECTS
Evidence
for Carcinogenicity:
There is sufficient evidence in experimental animals for the carcinogenicity of
mixed alpha-particle emitters (radium-224, radium-226, thorium-227, thorium-228,
thorium-230, thorium-232, neptunium-237, plutonium-238, plutonium-239 (together
with plutonium- 240), americium-241, curium-244, californium-249 and
californium-252). /Radium, Plutonium, Americium, Curium, Californium/
Internalized radionuclides that emit alpha-particles are carcinogenic to humans
(Group 1). In making this overall evaluation, the Working Group took into
consideration the following: Alpha-particles emitted by radionuclides,
irrespective of their source, produce the same pattern of secondary ionizations
and the same pattern of localized damage to biological molecules, including DNA.
These effects, observed in vitro, include DNA doublestrand breaks, chromosomal
aberrations, gene mutations and cell transformation. All radionuclides that emit
alpha-particles and that have been adequately studied, including radon-222 and
its decay products, have been shown to cause cancer in humans and in
experimental animals. Alpha-particles emitted by radionuclides, irrespective of
their source, have been shown to cause chromosomal aberrations in circulating
lymphocytes and gene mutations in humans in vivo. The evidence from studies in
humans and experimental animals suggests that similar doses to the same tissues
- for example lung cells or bone surfaces - from alpha- particles emitted during
the decay of different radionuclides produce the same types of non-neoplastic
effects and cancers. /Internalized alpha-emitters/
Human Toxicity Excerpts:
/CASE REPORTS/ /WHOLE BODY IRRADIATION, Acute Effects/ In 1976, a 64-yr-old
operator was injured by a chemical explosion in a glove box used for
americium-241 recovery /USTUR Case 246/. As a result of the accident, he was
heavily contaminated with americium, sustained a substantial internal deposition
of this isotope, was burned with nitric acid, and injured by flying debris about
the face and neck. He was assisted from the accident scene by co-workers. His
contaminated clothing was removed and decontamination begun by flushing his face
and eyes with water. He was transported to an Emergency Decontamination Facility
(EDF) by about 2 hr after the accident. Upon arrival, he was administered 1 g of
calcium diethylenetriamine pentate (CaDTPA) iv and further decontaminated in a
shower. Removal of superficial foreign matter from the face and neck and
irrigation of the eyes with normal saline were carried out. Initial medical
appraisal revealed nitric acid burns of the face, neck, and upper back
permitting internal deposition of americium-241 in addition to the americium-241
inhaled. He had a productive cough associated with the inhaled acid fumes. The
following is a summary of the medical care and evaluation during his stay at the
EDF and transition discharge. Iv administration of DTPA continued with several
daily doses for the first month, although the form was switched to ZnDTPA.
Decontamination was undertaken twice daily for the first week and then once a
day until discharge approximately 5 months after the accident. Fluid intake was
encouraged to promote urinary excretion; all urine and fecal specimens were
collected for radiobioassay. The principal medical problem was the patient's
eyes, which had corneal nitric acid burns with superficial corneal and
conjunctival foreign bodies which were excised or spontaneously extruded over a
period of months. For the first 4 months, daily superficial debridement of the
face and neck was performed without anesthesia to remove scales, crusts, scabs,
and extruding bodies. The frequency of debridement was then decreased. Over
several months, foreign bodies measuring up to 0.5 cm were extruded
spontaneously or removed with forceps. Laboratory studies were conducted daily
for the first 3 months and less frequently thereafter. These included a CBC,
urinalysis, blood chemistry tests, and fecal occult blood. The results were
normal except for a decline in the peripheral lymphocyte count on the day of the
accident. It remained depressed for several months. Chest radiographs, pulmonary
function tests, and electrocardiograms were normal (the patient had a history of
acute myocardial infarction). Special studies included analyses of peripheral
lymphocyte chromosomes, a facial skin biopsy, and a bone marrow aspiration.
Radiation-induced cytogenetic lesions in lymphocytes were observed. The skin
biopsy revealed scattered alpha "gistars". The bone marrow, examined 2
weeks after the accident, was normal, as were all other tests. A staff
psychologist was involved in the care of the patient; after 2 1/2 months, the
patient was transferred to a travel trailer adjacent to the EDF, which provided
a transitional environment before discharge. After discharge, the patient
received daily DTPA iv therapy by local medical professionals. In the summer
after the accident, the patient developed acute iritis. A cataract was removed
about 18 mo after the incident; it contained 0.019 Bq (0.5 pCi) of americium-241
but was thought to be traumatic in origin. A right cataract was extracted
surgically one year later along with five small foreign bodies from the cornea
and conjunctiva. About 6 1/2 yrs after the accident, drainage occurred from his
right forehead. A corneal transplant was performed about 7 1/3 yrs after the
accident. Bilateral glaucoma developed later. Eleven years after the accident,
the man died of congestive heart failure with chronic coronary artery disease.
Based on samples collected after his death, the estimated cumulative bone
surface dose ranged from 120 to 510 Gy. The dose rate to the lungs varied from
0.12 Gy per day for the first day of exposure to 0.0001 Gy per day at death. The
liver rate varied from 0.36 Gy per day to 0.0017 Gy per day at death. The bone
dose was initially 0.011 Gy per day, dropping to 0.0038 Gy per day until 900
days post exposure when it gradually increased to 0.0051 Gy per day. During the
years 6 to 10, the skin lost about 93 kBq (2.5 uCi) of americium-241, the bone
gained about 67 Bq (1.8 uCi), the liver gained about 7.4 kBq (0.2 uCi), and
about 30 Bq (0.8 uCi) was excreted. The total americium-241 excreted was 41 MBq
(1.1 uCi) with almost half excreted in the first 3 days and DTPA therapy was
judged to be very effective in preventing the deposition of life threatening
doses of americium-241 to the bone and liver. DTPA was also effective in
reducing the clearance half-time of the liver activity to about 20 days as
compared with a predicted 20 years. The effect of DTPA therapy on lung clearance
was not measurable. Clearance of americium-241 from the bone was not affected by
DTPA except possibly during the first week. /Americium-241/
/CASE REPORTS/ Lifetime follow-up of US Transuranium Registry /USTUR/ Case 246
demonstrated the lack of severe biological effects resulting from his exposure
to americium-241. Deterministic effects observed were limited to hematological
changes, including lymphopenia and thrombocytopenia. These hematological changes
were consistent with those observed in experimental animals following actinide
exposure. Cataracts were removed from the left and right eyes at 547 and 1,030 d
after the accident, respectively, but were considered to be trauma-induced
rather than radiation-induced. No abnormal findings were reported from gross or
histological examinations of tissue samples removed at autopsy, other than those
resulting from the subject's preexisting cardiovascular disease. /Americium-241/
/CASE REPORTS/ /LUNG/ External measurements of internally deposited
americium-241 in the lungs of a man exposed to americium in an occupational
accident /USTUR Case 246/ determined an initial lung burden of 960 kBq (26 uCi)
measured 3 days after the exposure that decreased to 55 kBq (1.5 uCi) after 2
years. However, no pathological changes to the lung attributed to radiation
exposure were identified in the autopsy of this man 11 years later. Exposure was
predominantly dermal via facial lacerations, but included inhalation. /It was/
estimated that the man received a total lung dose of 1.7 Gy (170 rem) based on
the ... estimate of 1.3 Gy (130 rem) for the first 5.7 years plus a dose of 0.4
Gy (40 rem) for the remaining 5.7 years, based on estimated lung burden at
autopsy. /Americium-241/
/CASE REPORTS/ /BONE/ Pathological changes ... were found in the bones of a
worker at the Hanford nuclear weapons plant
who had been extensively contaminated with americium-241 /USTUR Case 246/. When
he died 11 years after his accident from a pre-existing heart condition, his
skeleton contained an estimated 500 kBq of radionuclide - an amount that had
already been much reduced by decorporation therapy from an initial estimated
intake of 185 MBq. The bones examined were the patella, clavicle, sternum, rib,
vertebral body and ossified thyroid cartilage; all showed evidence of radiation
damage. The cellularity of most bones was reduced, and little evidence of recent
active bone remodeling was seen in any bone other than the vertebra, as
concluded from the redistribution of the americium in the vertebral body. In
several bones, the architecture was disrupted, with woven bone, abnormal
appositional bone deposits, bizarre trabecular structures and marked
peritrabecular fibrosis. Growth arrest lines were common. When compared with
trabecular bone modeling, that of cortical bone in the rib appeared less
disrupted. Overall, the results obtained are consistent with those observed in
dogs at a similar level of actinide intake. /Americium-241/
/CASE REPORTS/ /HEMATOPOIETIC SYSTEM/ /Eight yrs after a 64-year old man was
exposed to americium-241 in a chemical explosion/, leukopenia was evaluated by a
hematologist. Diagnosis of a possible hypoproliferative, myeloproliferative, or
myelodysplastic syndrome was considered. /USTUR Case 246/ /Americium-241/
/CASE REPORTS/ /HEMATOPOIETIC SYSTEM/ ... The bone marrow of /USTUR Case 246/
had been substantially damaged by alpha-irradiation from americium, principally
on the bone surfaces. A ... finding was a marked decrease in bone marrow
cellularity associated with dilatation of blood sinusoids. The severity of these
effects varied according to site and was greatest in the vertebral body, where
the marrow was almost acellular, and least in the clavicle. In addition,
extensive peritrabecular marrow fibrosis was present in some bones, including
the rib and clavicle. ... Fibrosis is a common observation in bones irradiated
by bone-seeking radionuclides and has been linked to bone sarcoma induction.
/Americium-241/
/CASE REPORTS/ /WOUND CONTAMINATION/ Glovebox Accident Involving
Plutonium-Americium Contamination and Hand Amputation. An employee ... in
plutonium fuel fabrication reached for an item in his glovebox and his glove was
caught by a milling machine that tore off his right hand. /An hour later/ ...
patient /arrived at the treatment center. ... The patient was surveyed for
external contamination while in the ambulance. No widespread removable
contamination was found, so the patient was brought in and placed on a
decontamination table /at which time the attending physician/ learned that the
patient had lost his right hand at the wrist. /A half-hr later/ the plant
health physics supervisor arrived with the contaminated hand wrapped in plastic
in an ice bucket. The hand was immediately counted ... and the patient's stump
was counted ... with a ... NaI crystal. An initial estimate ... indicated ... an
amount, if entering bone, /that/ could result in bone dose commitments in the
tens of millions of rem ... Additional measurements /after ... debridements/
indicated that ... remaining contamination on the hand and stump was still more
than 100 times the Maximum Permissible Body Burden (MPBB). .... The difficult
decision was made by the patient and his family, as well as the involved
physicians and health physicists, to reattach the hand despite its excessive
residual radioactivity. Considerations included the youth of the worker, his
right-handedness, location of the radioactivity, the availability of DTPA
chelation therapy, and the likelihood of the patient's availability of multiyear
observation. ... Unfortunately, circulation in the fingers of the reattached
hand did not improve quickly enough for tissue survival, so the hand was
reamputated, ... infused with formaldehyde and recounted ... showing about 4 uCi
(about 100 MPBB) still on the surface. ... Since reamputation of the hand was
done approximately an inch higher than the original accidental amputation, the
reamputated hand turned out to contain practically all of the remaining
contamination. ... The medical management of an injured and contaminated patient
in this case required at least about two person-days of professional dedication
of a medical-health physics team already experienced with accidents involving
external and internal contamination with americium-plutonium mixtures; this
input was in addition to collaboration with a number of other physicians and
medical and health physics technicians. The average medical institution likely
to receive contaminated victims of a terrorist attack will not have such
personnel or equipment resources. Any expectation of a medical capacity for
triage and management of such patients requires prior training and equipping of
personnel in each medical institution for the simplest counting and
spectrometric measurements, and ready-made methods of data interpretation.
/Plutonium-239 and americium-241 nitrates/
/CASE REPORTS/ /WHOLE BODY IRRADIATION/ Another accidental exposure ... involved
a glovebox explosion that released ... plutonium-239 and americium-241
/nitrates/. ... The external contamination was spectacular. Alpha count rates on
the patient ... were up to 10+6 counts per minute, ... as high as we could read.
Removable contamination was all over the body, with maxima of 10,000 alpha cpm
on the face and 20,000 on the legs ... , after /initial decontamination/... .
The contamination was finally reduced very sharply with the use of Schubert's
solution /3.0 g/L tartaric acid, 4.2 g/L citric acid, 8.0 g/L disodium DTPA or
EDTA, 2.2 g/L calcium chloride adjusted to pH 7 with NaOH/ ...This patient had
the additional complication of wounds that ... served as a residual depot of the
radioactive material. ... The scar tissue was subsequently excised because there
was continued high activity in the area /and/ a very diffuse distribution of the
material. Our initial in vivo measurements made one day after the incident ...
/showed a / burden ... projected to produce ... an initial bone dose of about
1,500 rem per year. Thus, DTPA treatment was ... medically indicated, if
effective. The next measurements presented are at 60 days and over the time
period from 70 to 130 days, during which the body content fell gradually.
Repeated DTPA treatments were given during this time /but/ the lung component of
this body burden could still be measured by localized external counting for up
to 1 yr after the accident. Thus, the rapid translocation from the lung expected
from nitrate compounds of plutonium and americium did not materialize. ...
Initial estimates of plutonium uptake into blood were obtained under the
assumption ... that DTPA increased plutonium excretion by about a factor of 50
on the day following treatment. The increase in urinary excretion of americium
was a much lower factor (about 5 to 7); americium was later found to be more
transportable from lung to systemic circulation and into urine than oxides of
plutonium, even without treatment. Management lessons learned from this case ...
are pertinent to the preparation of medical facilities expecting to evaluate and
care for persons severely contaminated by a terrorist attack. There were long
time periods between some of the urinary measurements, due to overloading of
commercial laboratories that were not accustomed to analyzing many samples
containing high amounts of plutonium and americium. This delayed decisions about
DTPA effectiveness to some degree. In addition, the patient developed a paranoid
outlook and ... underwent an episode that required psychiatric treatment. A
suspected contributor to this complication was the fact that a number of
different physicians ... might have presented different versions of his
prognosis and consequent treatment. /Plutonium-239 and americium-241 nitrates/
/CASE REPORTS/ /WHOLE BODY IRRADIATION/ Worker Exposed to Inhalation of 241-AmO2
over a Two- to Three-Year Period. /The glovebox operator prepared foils
containing americium oxide powder and a "small" amount of visible dust
was sometimes released in the pressing operation . The operator also removed the
pellet to another box for sintering at 1,500 deg F./ The annealed compact was
transported to a table where it was sandwiched between two 0.003-inch gold
foils, heated ... to 900 to 1,000 deg F, and rolled. ... The operator wore no
respirator after the initial sintering operation, and the rolling operation was
performed without local exhaust ventilation. ... A special breathing zone sample
/taken/ the last day ... the operator ... work/ed/ with radioactive materials,
showed a concentration of about 1.6x10-10 uCi/mL during a 96-min operation
/using a reduced amount of americium/. ...The initial assessment of /total body
burden was ... 1 or 1.8 uCiof americium-241/(measurements at two separate
facilities)/. Such a deposition was projected to possibly deliver tens of
thousands of rem to bone during the remaining lifetime of the patient (and
somewhat smaller, but also high, doses to kidney and liver). ... In addition to
total body measurements, counts were taken with collimated crystals /which
showed/ that much of the americium had already translocated to bone, liver, and
other soft tissue ... . It became imperative ... to examine the potential
effectiveness of chelation therapy and begin treatments. .. Between June and the
beginning of chelation therapy in September 1967 with the calcium trisodium salt
of diethylenetriamine pentaacetic acid (CaNa3DTPA), baseline urine samples were
evaluated ... . Virtually all urine was collected from September 1967 through
December 1974 while chelation therapy was being carried out. Fecal collection
was halted at week 80. ... In 1979, after cessation of treatments, the remaining
body burden was 0.72 uCi with most of the remaining burden in bone. ... More
than half of the removal of americium-241 from this patient could be attributed
to the effectiveness of the chelation therapy. /Later medical practice used a
DTPA compound incorporating zinc into the complex. DTPA therapy at 1 gm per week
in a single treatment was as efficacious as two 0.5-gm treatments several days
apart per week./ Long-term (years) treatments with 1 gm per wk DTPA apparently
had no ill effect on the patient over a period of many years of observation.
/Americium-241 oxide/
/CASE REPORTS/ The examinees demonstrated definite effects caused by total
influence of americium-241 and plutonium-239: chronic radiation sickness with
diffuse pneumosclerosis, chronic toxic radiation bronchitis and peripheral blood
changes (reactive alterations and stable lower platelets and reticulocytes
count), microfocal hypoplasia, osteodysplasia, and reactive hepatopathy.
Frequency of these effects increased with higher radiation exposure and did not
depend on the age. /Americium-241 and plutonium-239/
/CASE REPORTS/ Histopathology and qualitative autoradiography studies were
undertaken on bone removed at autopsy from USTUR Case 246. The histopathology
examination revealed extensive bone marrow peritrabecular fibrosis and decreased
cellularity in most samples. In addition, histological indicators suggest that
bone cell turnover was suppressed at most sites, although turnover was found to
be essentially normal in a vertebral body sample. The autoradiographic studies
showed that bone turnover that had occurred resulted in the redistribution of
americium within bone. However, surface deposits of americium remained
conspicuous at many sites, particularly those with low bone growth activity. A
few percent of the americium was present in the bone marrow. The dosimetric and
toxicology findings indicate that current assumptions about the metabolic
behavior of bone-seeking radionuclides are likely to be unrealistically
simplistic. /Americium-241/
/BIOMONITORING/ PURPOSE: To evaluate by the fluorescent in-situ hybridization
(FISH) technique the dose-response and intercellular distribution of
alpha-particle-induced chromosome aberrations. In particular, the validity of
using the yield of characteristic types of chromosome abnormalities in stable
cells as quantitative indicators for retrospective dose reconstruction has been
evaluated. Monolayers of human peripheral lymphocytes were exposed at doses from
0.02 to 1 Gy to alpha-particles emitted from a source of americium-241. The most
probable energy of the alpha-particles entering the cells was 2.7 MeV. FISH
painting was performed using DNA probes for chromosomes 2, 4 and 8 in
combination with a pan-centromeric probe. In complete first-division cells,
identified by harlequin staining, aberrations involving painted target
chromosomal material were recorded as well as aberrations involving only
unpainted chromosomal material. In total, the percentage of complex aberrations
was about 35% and no dose dependence was observed. When complex-type exchanges
were reduced to simple base types, the different cell distributions were clearly
over-dispersed, and the linear coefficients of the dose-effect curves for
translocations were significantly higher than for dicentrics. For past dose
reconstruction, only a few complex aberrations were in stable cells. The linear
coefficient obtained for transmissible aberrations in stable cells was more than
seven times lower than that obtained in all analysed cells, i.e. including
unstable cells. /The authors concluded that/ FISH-based analysis of complex
rearrangements allows discrimination between partial-body exposures to
low-linear energy transfer radiation and high-linear energy transfer exposures.
In assessing past or chronic exposure to alpha-particles, the use of a
dose-effect curve obtained by FISH-based translocation data, which had not
excluded data determined in unstable cells, would underestimate the dose.
Insertions are ineffective biomarkers because their frequency is too low.
/Americium-241/
/BIOMONITORING/ A radiation worker and his wife, college-age daughter, and
10-yr-old son ... were exposed for several yrs in their house to elevated levels
of americium-241 that resulted in body burdens of 6.5 to 89 nCi (0.24 to 3.3 kBq)
from a source used by the father for private experiments. Chromosomal
aberrations in isolated leukocytes were noted to be similar to those observed in
other cases of accidental or therapeutic exposure to external radiation sources.
/Americium-241/
/BIOMONITORING/ Chromosomal aberrations (symmetrical translocations and
dicentrics and ring chromosomes) in lymphocyte preparations were elevated for an
entire group of 7 nuclear fuel production workers who were
exposed for 11-22 yrs to external gamma radiation, with an additional internal
exposure for 6 of these workers to americium-241 5 yrs prior to the analysis.
The total effective dose equivalent from exposure to external gamma radiation
and internal contamination with americium-241 /ranged from 29 to 393 mSv./
/Americium-241/
Medical Surveillance:
Americium-241, emits gamma radiation (60 keV) that can be detected with
specially designed ... detectors that are placed over the lungs to determine the
amount of radioactive material in the lungs.
In vivo measurement of americium is available for both americium-241 and
americium-243, though it is not routinely performed for americium-243. Hanford
in vivo measurements for americium include chest counts, skeleton measurements
by head counting, liver counts, and wound counts....An annual urine-sampling
program is recommended for monitoring /worker/ intakes of pure americium-241.
Such a program is capable of demonstrating regulatory compliance with both
stochastic and deterministic dose limits, but is not capable of demonstrating
compliance with administrative control levels of 500-mrem committed effective
dose equivalent or lower. More frequent urinalysis can provide some improvement
in sensitivity, but primary reliance must be placed on prompt detection of
potential intakes by workplace indicators and special bioassay monitoring to
provide low-level dosimetry. Annual chest counting is appropriate as an
augmentation, particularly when americium-241 is used as an indicator for
plutonium. ?Americium-241 and americium-243/
Americium ... can be found as the ingrown 241-Am progeny of plutonium-241... or
as a separated americium-241 isotope that exists singly or in combination with
other separated isotopes in waste mixtures. In the case of plutonium-241, /with
ingrown/ americium-241... assume that behavior is characteristic of plutonium;
i.e., the plutonium biokinetic model is used for americium because the americium
is considered trapped in a plutonium matrix, which limits its behavior to that
of the predominant matrix. /Americium-241 and plutonium-241/
After 2 1/2 months, the patient /who had been accidently exposed to americium.
was transferred to a travel trailer adjacent to the Emergency Decontamination
Facility, which provided a transitional environment before discharge. After
discharge, the patient received daily DTPA iv therapy by local medical
professionals. ... DTPA therapy was judged to be very effective in preventing
the deposition of life threatening doses of americium-241 to the bone and liver.
DTPA was also effective in reducing the clearance half-time of the liver
activity to about 20 days as compared with a predicted 20 years. The effect of
DTPA therapy on lung clearance was not measurable. Clearance of americium-241
from the bone was not affected by DTPA except possibly during the first week.
/Americium-241/
Long-term (years) treatments with DTPA apparently had no ill effect on the
patient over a period of many years of observation. /Americium-241/
Populations at Special Risk:
Infants exposed to levels of americium in food or water similar as adults, or
who ingest similar amounts of americium subsequent to an inhalation exposure,
may absorb more americium and acquire a higher internal burden of americium. The
ICRP assumes age-related differences in intestinal absorption of americium
swallowed following clearance from the lungs. The fractional absorption value
employed for a 3-month-old infant is a factor of 10 higher than for an adult.
Probable Routes of Human Exposure:
The general population may be exposed to elevated levels of americium-241 from nuclear
accidents or from residing in areas in the proximity of hazardous waste sites
where this radionuclide is present. Exposure is generally through the inhalation
and ingestion of dust from these sites. Workers involved in producing ionization
smoke detectors or other devices containing americium-241, workers at nuclear
reactors or Department of Energy (DOE) facilities, and workers who use
americium-containing devices (neutron backscatter sources for checking roof
leaks and road undermining, and well logging equipment) may also be exposed to
higher levels of americium-241(1).
Evidence for Carcinogenicity:
There is sufficient evidence in experimental animals for the carcinogenicity of
mixed alpha-particle emitters (radium-224, radium-226, thorium-227, thorium-228,
thorium-230, thorium-232, neptunium-237, plutonium-238, plutonium-239 (together
with plutonium- 240), americium-241, curium-244, californium-249 and
californium-252). /Radium, Plutonium, Americium, Curium, Californium/
Internalized radionuclides that emit alpha-particles are carcinogenic to humans
(Group 1). In making this overall evaluation, the Working Group took into
consideration the following: Alpha-particles emitted by radionuclides,
irrespective of their source, produce the same pattern of secondary ionizations
and the same pattern of localized damage to biological molecules, including DNA.
These effects, observed in vitro, include DNA doublestrand breaks, chromosomal
aberrations, gene mutations and cell transformation. All radionuclides that emit
alpha-particles and that have been adequately studied, including radon-222 and
its decay products, have been shown to cause cancer in humans and in
experimental animals. Alpha-particles emitted by radionuclides, irrespective of
their source, have been shown to cause chromosomal aberrations in circulating
lymphocytes and gene mutations in humans in vivo. The evidence from studies in
humans and experimental animals suggests that similar doses to the same tissues
- for example lung cells or bone surfaces - from alpha- particles emitted during
the decay of different radionuclides produce the same types of non-neoplastic
effects and cancers. /Internalized alpha-emitters/
Probable Routes of Human Exposure:
The general population may be exposed to elevated levels of americium-241 from nuclear
accidents or from residing in areas in the proximity of hazardous waste sites
where this radionuclide is present. Exposure is generally through the inhalation
and ingestion of dust from these sites. Workers involved in producing ionization
smoke detectors or other devices containing americium-241, workers at nuclear
reactors or Department of Energy (DOE) facilities, and workers who use
americium-containing devices (neutron backscatter sources for checking roof
leaks and road undermining, and well logging equipment) may also be exposed to
higher levels of americium-241(1).
All of the above is
directly from http://toxnet.nlm.nih.gov/