EPA Facts about Tritium
What is Tritium?
Tritium is a form of hydrogen that is radioactive,
and like hydrogen it reacts with oxygen to form
water. Tritium is produced naturally in the upper
atmosphere when cosmic rays strike
atmospheric gases. Tritium can also be produced
by man during nuclear weapon explosions, in
reactors intended to produce tritium for nuclear
weapons, and by reactors producing electricity.
What are the uses of tritium?
Tritium has been produced in large quantities by
the nuclear military program. It is also used to
make luminous dials and as a source of light for
safety signs (such as EXIT signs). Tritium is used
as a tracer for biochemical research, animal
metabolism studies, and groundwater transport
measurements.
How does tritium change in the
environment?
Tritium is not a stable element. Tritium decays
by emitting a beta particle and turning into
helium. The release of radiation during this
decay process causes concern about the safety
of tritium and all other radioactive substances.
The radiation from the decay of tritium is in the
form of beta particles, which are of very low
energy. As a result, the particles cannot pass
through the skin surface.
Tritium is the only radioactive isotope of
hydrogen and, like hydrogen, it reacts with
oxygen to form water. The transformation of
tritium to tritiated water is complex and slow.
The time required for a radioactive substance to
lose 50 percent of its radioactivity by decay is
known as the half-life. Tritium is a colorless,
odorless gas with a half-life of 12.3 years.
Tritiated water moves through the environment
like ordinary water.
How are people exposed to tritium?
Although large quantities of tritium have been
released into the environment, the dose to
humans is small. Tritium was disbursed
throughout the world by atmospheric nuclear
weapons tests that took place from the mid-
1950s to the early 1960s. The inventory of
tritium in the atmosphere peaked in 1963 and
has been decreasing rapidly since then. Levels of
naturally occurring tritium in the atmosphere
produced by cosmic rays are constant, and it is
projected that levels of manmade tritium will be
comparable to natural tritium by 2030.
Tritium is currently produced by reactors that
generate electricity. Other sources of tritium
include government plants that have
reprocessed reactor fuels. Individuals can also
be exposed to tritium via broken exit signs and
luminous dial items that contain tritium.
Since tritium reacts similarly to ordinary
hydrogen, it is incorporated into the body easily
in the form of water.
Overall, the risk to the average person from
tritium is typically not significant since current
world-wide levels of tritium in the environment

-------
from man-made and natural sources are low.
Accidental exposure from elevated levels of
tritium from broken exit signs or other
concentrated sources, however, can pose a
health risk to individuals.
How does tritium get into the body?
Most tritium in the environment is in the form of
tritiated water, which is dispersed throughout
the environment in the atmosphere, streams,
lakes, and oceans. Tritium in the environment
can enter the human body as a gas or as a liquid
by ingestion and inhalation and through the skin
by absorption. Once entered into the body,
tritium tends to disperse quickly, so that it is
uniformly distributed throughout the body. The
tritium distribution in tissue depends on the
amount of water contained in the tissues.
Tritium is rapidly excreted over a month or two
after ingestion.
Is there a medical test to determine
exposure to tritium?
Since tritium is distributed throughout the body
within a few hours after ingestion, levels within
the body are measured by collecting a urine
sample and analyzing it for tritium.
How can tritium affect people's health?
With respect to chemical reactions, tritium
reacts similarly to ordinary hydrogen. Therefore,
tritium dilutes through the body as ordinary
water. Tritium concentration in soft tissue and
the associated dose to these tissues is generally
uniform and depends on the water content of
the tissue. Tritium is rapidly cleared from tissues
because the water content in the body turns
over frequently.
What recommendations has the U.S.
Environmental Protection Agency made
to protect human health?
Please note that the information in this section
is limited to recommendations EPA has made to
protect human health from exposure to tritium.
General recommendations EPA has made to
protect human health at Superfund sites (the
10~4 to 10"6 cancer risk range), which cover all
radionuclides including tritium, are summarized
in the fact sheet "Primer on Radionuclides
Commonly Found at Superfund Sites."
EPA has established a Maximum Contaminant
Level (MCL) of 4 millirems per year for beta
particle and photon radioactivity from man-
made radionuclides in drinking water. The
average concentration of tritium that is assumed
to yield 4 millirems per year is 20,000 picoCuries
(pCi/L). If other radionuclides that emit beta
particles and photon radioactivity are present in
addition to tritium, the sum of the annual dose
from all the radionuclides cannot exceed 4
millirems/year.
For more information about how EPA addresses
tritium at Superfund sites
Contact Stuart Walker of EPA:
(703) 603-8748 or walker.stuart@epa.gov,
or visit EPA's Superfund Radiation Webpage:
http://www.epa.gov/superfund/resources/radiation/

-------