Actinides in the environment refer to the
sources, environmental behaviour and effects
of actinides in Earth's environment.
Environmental radioactivity is not limited
solely to actinides; non-actinides such as
radon and radium are of note.
== Inhalation versus ingestion ==
Generally, ingested insoluble actinide compounds,
such as high-fired uranium dioxide and mixed
oxide (MOX) fuel, will pass through the digestive
system with little effect since they cannot
dissolve and be absorbed by the body.
Inhaled actinide compounds, however, will
be more damaging as they remain in the lungs
and irradiate the lung tissue.
Ingested low-fired oxides and soluble salts
such as nitrate can be absorbed into the blood
stream.
If they are inhaled then it is possible for
the solid to dissolve and leave the lungs.
Hence, the dose to the lungs will be lower
for the soluble form.
== Thorium in the environment ==
In India, a large amount of thorium ore can
be found in the form of monazite in placer
deposits of the Western and Eastern coastal
dune sands, particularly in the Tamil Nadu
coastal areas.
The residents of this area are exposed to
a naturally occurring radiation dose ten times
higher than the worldwide average.
=== Occurrence ===
Thorium is found at low levels in most rocks
and soils, where it is about three times more
abundant than uranium, and is about as common
as lead.
Soil commonly contains an average of around
6 parts per million (ppm) of thorium.
Thorium occurs in several minerals, the most
common being the rare earth-thorium-phosphate
mineral, monazite, which contains up to about
12% thorium oxide.
There are substantial deposits in several
countries.
232Th decays very slowly (its half-life is
about three times the age of the earth).
Other isotopes of thorium occur in the thorium
and uranium decay chains.
Most of these are short-lived and hence much
more radioactive than 232Th, though on a mass
basis they are negligible.
=== Effects in humans ===
Thorium has been linked to liver cancer.
In the past thoria (thorium dioxide) was used
as a contrast agent for medical X-ray radiography
but its use has been discontinued.
It was sold under the name Thorotrast.
== Uranium in the environment ==
Uranium is a natural metal which is widely
found.
It is present in almost all soils and it is
more plentiful than antimony, beryllium, cadmium,
gold, mercury, silver, or tungsten, and is
about as abundant as arsenic or molybdenum.
Significant concentrations of uranium occur
in some substances such as phosphate rock
deposits, and minerals such as lignite, and
monazite sands in uranium-rich ores (it is
recovered commercially from these sources).
Seawater contains about 3.3 parts per billion
of uranium by weight as uranium (VI) forms
soluble carbonate complexes.
The extraction of uranium from seawater has
been considered as a means of obtaining the
element.
Because of the very low specific activity
of uranium the chemical effects of it upon
living things can often outweigh the effects
of its radioactivity.
Additional uranium has been added to the environment
in some locations as a result of the nuclear
fuel cycle and the use of depleted uranium
in munitions.
== Neptunium in the environment ==
Like plutonium, neptunium has a high affinity
for soil.
However, it is relatively mobile over the
long term, and diffusion of neptunium-237
in groundwater is a major issue in designing
a deep geological repository for permanent
storage of spent nuclear fuel.
237Np has a half-life of 2.144 million years
and is therefore a long-term problem; but
its half-life is still much shorter than those
of uranium-238, uranium-235, or uranium-236,
and 237Np therefore has higher specific activity
than those nuclides.
== Plutonium in the environment ==
=== 
Sources ===
Plutonium in the environment has several sources.
These include:
Atomic batteries
In space
In pacemakers
Bomb detonations
Bomb safety trials
Nuclear accidents (such as Chernobyl)
Nuclear crime
Nuclear fuel cycle
=== 
Environmental chemistry ===
Plutonium, like other actinides, readily forms
a plutonium dioxide (plutonyl) core (PuO2).
In the environment, this plutonyl core readily
complexes with carbonate as well as other
oxygen moieties (OH−, NO2−, NO3−, and
SO42−) to form charged complexes which can
be readily mobile with low affinities 
to soil.
PuO2CO32−
PuO2(CO3)24−
PuO2(CO3)36−PuO2 formed from neutralizing
highly acidic nitric acid solutions tends
to form polymeric PuO2 which is resistant
to complexation.
Plutonium also readily shifts valences between
the +3, +4, +5 and +6 states.
It is common for some fraction of plutonium
in solution to exist in all of these states
in equilibrium.
Plutonium is known to bind to soil particles
very strongly, see above for an X-ray spectroscopic
study of plutonium in soil and concrete.
While caesium has very different chemistry
to the actinides, it is well known that both
caesium and many of the actinides bind strongly
to the minerals in soil.
Hence it has been possible to use 134Cs labeled
soil to study the migration of Pu and Cs is
soils.
It has been shown that colloidal transport
processes control the migration of Cs (and
will control the migration of Pu) in the soil
at the Waste Isolation Pilot Plant.
== Americium in the environment ==
Americium often enters landfills from discarded
smoke detectors.
The rules associated with the disposal of
smoke detectors are very relaxed in most municipalities.
For instance, in the UK it is permissible
to dispose of an americium containing smoke
detector by placing it in the dustbin with
normal household rubbish, but each dustbin
worth of rubbish is limited to only containing
one smoke detector.
The manufacture of products containing americium
(such as smoke detectors) as well as nuclear
reactors and explosions may also release the
americium into the environment.
In 1999, a truck transporting 900 smoke detectors
in France had been reported to have caught
fire; it is claimed that this led to a release
of americium into the environment.
In the U.S., the "Radioactive Boy Scout" David
Hahn was able to buy thousands of smoke detectors
at remainder prices and concentrate the americium
from them.
There have been cases of humans being exposed
to americium.
The worst case was that of Harold McCluskey,
who was exposed to an extremely high dose
of americium-241 after an accident involving
a glove box.
He was subsequently treated with chelation
therapy.
It is likely that the medical care which he
was given saved his life; because of the difference
in the chemistry of americium (the +3 oxidation
state is very stable) to plutonium (where
the +4 state can form in the human body) the
americium has very different biochemistry
to plutonium.The most common isotope americium-241
decays (half-life of 431 years) to neptunium-237
which has a much longer half-life, so in the
long term, the issues discussed above for
neptunium apply.Americium released into the
environment tends to remain in soil and water
at relatively shallow depths and may be taken
up by animals and plants during growth; shellfish
such as shrimp take up americium-241 in their
shells, and parts of grain plants can become
contaminated with exposure.
== See also ==
Uranium in the environment
Radium in the environment
Background radiation
Radioecology
