Other
Chemical/Physical Properties :
DECAY PATHWAY: Neptunium-237, half-life 2,144,000 years, decays via alpha
emission, 4.959 MeV, to protactinium-233, half-life 26.967 days.
Protactinium-233 decays via beta emission, 0.571 MeV, to uranium-233, half-life
159,200 years.
Other Chemical/Physical Properties :
DECAY PATHWAY: Neptunium-239, half-life 2.3565 days, decays via beta(-)
emission, 0.722 MeV, to plutonium-239, half-life 24,110 years. Plutonium-239
decays via alpha emission, 5.245 MeV, to uranium-235, half-life 703,800,000
years.
Radiation Limits & Potential :
DECAY PATHWAY: Neptunium-237, half-life 2,144,000 years, decays via alpha
emission, 4.959 MeV, to protactinium-233, half-life 26.967 days.
Protactinium-233 decays via beta emission, 0.571 MeV, to uranium-233, half-life
159,200 years.
Radiation Limits & Potential :
DECAY PATHWAY: Neptunium-239, half-life 2.3565 days, decays via beta(-)
emission, 0.722 MeV, to plutonium-239, half-life 24,110 years. Plutonium-239
decays via alpha emission, 5.245 MeV, to uranium-235, half-life 703,800,000
years.
Environmental Fate/Exposure
Summary :
Neptunium was the first synthetic transuranium element of the actinide series
discovered. Neptunium-239 (half-life = 2.4 days) was first produced in 1940 at
Berkeley, CA by the bombardment of uranium-238 with cyclotron-produced neutrons.
Seventeen isotopes of neptunium are known and all are radioactive. Neptunium-237
is obtained in gram quantities as the by-product from nuclear reactors in the
production of plutonium. The longest lived isotope is Np-237; it is an
alpha-emitter with a half-life of 2.14 million years. Neptunium is a by-product
of plutonium production activities. Neptunium is present in spent nuclear fuel,
high-level radioactive wastes resulting from the processing of spent nuclear
fuel, and radioactive wastes associated with operations of reactors and fuel
reprocessing plants. A small amount of neptunium would have been generated by
atmospheric nuclear weapon testing, which ceased worldwide by 1980. The amount
of neptunium in soil from past nuclear testing is on the order of 0.0001 pCi/g.
Releases of neptunium from weapons production facilities have cause localized
contamination. There are no major commercial uses of neptunium. Trace quantities
of neptunium are found in nature associated with uranium ores. Neptunium
compounds are ionic and would not be volatile and would exist solely in the
particulate phase in the ambient atmosphere. Particulate-phase neptunium
compounds will be removed from the atmosphere by wet or dry deposition. In soil,
neptunium is generally more mobile than other transuranic elements such as
plutonium, americium, and curium, moving with percolating water to lower soil
layers. Neptunium compounds bind to soil particles, and bind more tightly with
clay soils as compared with sandy soils. Neptunium is readily taken up by
plants, with plant concentrations similar to soil concentrations. Neptunium
compounds are ionic and would not volatilize from moist or dry soil surfaces.
Neptunium has 4 valence states in water: Np3+; Np4+; NpO+; and (NpO)2+.
Neptunium forms tri- and tetrahalide compounds such as NpF3, NpF4, NpCl4, NpBr3,
NpI3, and oxides of various compositions such as Np3O8 and NpO2. Since neptunium
has only been produced in limited quantities and it has few uses outside of
research activities, exposure to neptunium compounds would be limited to
individuals involved in scientific research using neptunium or at plutonium
production or nuclear waste facilities. (SRC)
Artificial Pollution Sources :
Neptunium was the first synthetic transuranium element of the actinide series
discovered(1,2). Neptunium-239 (half-life = 2.4 days) was first produced in 1940
at Berkeley, CA by the bombardment of uranium-238 with cyclotron-produced
neutrons(1,2). Seventeen isotopes of neptunium are known and all are
radioactive(1). Neptunium-237 is obtained in gram quantities as the by-product
from nuclear reactors in the production of plutonium(2). The longest lived
isotope is neptunium-237; it is an alpha-emitter with a half-life of 2.14
million years(3). Neptunium is a by-product of plutonium production
activities(1). Neptunium is present in spent nuclear fuel, high-level
radioactive wastes resulting from the processing of spent nuclear fuel, and
radioactive wastes associated with operations of reactors and fuel reprocessing
plants(1). A small amount of neptunium would have been generated by atmospheric
nuclear weapon testing, which ceased worldwide by 1980(1). The amount of
neptunium in soil from past nuclear testing is on the order of 0.0001 pCi/g(1).
Releases of neptunium from weapons production facilities have caused localized
contamination(1). There are no major commercial uses of neptunium(1). Neptunium
forms tri- and tetrahalide compounds such as NpF3, NpF4, NpCl4, NpBr3, NpI3, and
oxides of various compositions such as Np3O8 and NpO2(2).
Sediment/Soil Concentrations :
SEDIMENT: The British Nuclear Fuels Ltd nuclear fuel reprocessing plants at
Sellafield in Cumbria, UK discharge low level radioactive waste into the Irish
Sea(1). Neptunium-237 concentrations in sediment cores samples collected in
October 1994 from 9 sites around the intertidal area of the Irish Sea, UK ranged
from 13.1 to 412 mBq/kg(1)
MORE ABOUT HEALTH EFFECTS
Evidence for Carcinogenicity:
Evaluation. There is inadequate evidence in humans for the carcinogenicity of
neutrons. There is sufficient evidence in experimental animals for the
carcinogenicity of neutrons. Overall evaluation. Neutrons are carcinogenic to
humans (Group 1). In making the overall evaluation, the Working Group took into
consideration the following: When interacting with biological material, fission
neutrons generate protons, and the higher-energy neutrons used in therapy
generate protons and alpha particles. Alpha Particle-emitting radionuclides
(e.g. radon) are known to be human carcinogens. The linear energy transfer of
protons overlaps with that of the lower-energy electrons produced by
gamma-radiation. Neutron interactions also generate gamma-radiation, which is a
human carcinogen. Gross chromosomal aberrations (including rings, dicentrics and
acentric fragments) and numerical chromosomal aberrations are induced in the
lymphocytes of people exposed to neutrons. The spectrum of DNA damage induced by
neutrons is similar to that induced by X-radiation but contains relatively more
of the serious (i.e. less readily repairable) types. Every relevant biological
effect of gamma- or X-radiation that has been examined has been found to be
induced by neutrons. Neutrons are several times more effective than X- and
gamma-radiation in inducing neoplastic cell transformation, mutation in vitro,
germ-cell mutation in vivo, chromosomal aberrations in vivo and in vitro and
cancer in experimental animals.
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: (1) 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 double-strand breaks, chromosomal
aberrations, gene mutations and cell transformation. (2) 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. (3) 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. (4) 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.
Human Toxicity Excerpts:
/OTHER TOXICITY INFORMATION/ In the nuclear fuel cycle the transuranic
radionuclides plutonium-239, americium-241 and neptunium-237 would probably
present the most serious hazard to human health if released into the
environment. ... The principal late effects of all three radionuclides are the
induction of cancers of bone, lung or liver. For the latter tumors the induction
risk per unit radiation dose appears similar for the three radionuclides. But in
bone there are indications that, due to microscopic differences in the
distribution of the alpha-particle radiation dose, the efficiency of bone cancer
induction may increase in the order americium-241 less than plutonium-239 less
than neptunium-237. No case of human cancer induced by these radionuclides is
known. /Plutonium-239, americium-241 and neptunium-237/
/OTHER TOXICITY INFORMATION/ LIFETIME CANCER MORTALITY RISK. Risks are for
lifetime cancer mortality per unit intake (pCi) averaged over all ages and both
genders. /Neptunium isotopes/
ISOTOPE
Inhalation (pCi-1)
Ingestion (pCi-1)
Neptunium-235
1.0x10-12
2.8x10-13
Neptunium-236
2.6x10-9
1.5x10-11
Neptunium-237
1.5x10-8
5.8x10-11
Probable Routes of Human Exposure:
Since neptunium has only been produced in limited quantities(1) and it has few
uses outside of research activities(2), exposure to neptunium compounds would be
limited to individuals involved in scientific research using neptunium or at
plutonium production or nuclear waste facilities(SRC).
Evidence for Carcinogenicity:
Evaluation. There is inadequate evidence in humans for the carcinogenicity of
neutrons. There is sufficient evidence in experimental animals for the
carcinogenicity of neutrons. Overall evaluation. Neutrons are carcinogenic to
humans (Group 1). In making the overall evaluation, the Working Group took into
consideration the following: When interacting with biological material, fission
neutrons generate protons, and the higher-energy neutrons used in therapy
generate protons and alpha particles. Alpha Particle-emitting radionuclides
(e.g. radon) are known to be human carcinogens. The linear energy transfer of
protons overlaps with that of the lower-energy electrons produced by
gamma-radiation. Neutron interactions also generate gamma-radiation, which is a
human carcinogen. Gross chromosomal aberrations (including rings, dicentrics and
acentric fragments) and numerical chromosomal aberrations are induced in the
lymphocytes of people exposed to neutrons. The spectrum of DNA damage induced by
neutrons is similar to that induced by X-radiation but contains relatively more
of the serious (i.e. less readily repairable) types. Every relevant biological
effect of gamma- or X-radiation that has been examined has been found to be
induced by neutrons. Neutrons are several times more effective than X- and
gamma-radiation in inducing neoplastic cell transformation, mutation in vitro,
germ-cell mutation in vivo, chromosomal aberrations in vivo and in vitro and
cancer in experimental animals.
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: (1) 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 double-strand breaks, chromosomal
aberrations, gene mutations and cell transformation. (2) 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. (3) 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. (4) 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.
Probable Routes of Human Exposure:
Since neptunium has only been produced in limited quantities(1) and it has few
uses outside of research activities(2), exposure to neptunium compounds would be
limited to individuals involved in scientific research using neptunium or at
plutonium production or nuclear waste facilities(SRC).