US Environmental Protection Agency


What are the properties of tritium?

Tritium is a hydrogen atom that has two neutrons in the nucleus, in addition to its single proton, giving it an atomic weight near three. Although tritium can be a gas, its most common form is in water, because, like non-radioactive hydrogen, radioactive tritium reacts with oxygen to form water. Tritium replaces one of the stable hydrogens in the water molecule, H2O, and is called tritiated water (HTO). Like H2O, tritiated water is colorless and odorless.

Tritium has a half-life of 12.3 years


Tritium is produced commercially in reactors. It is used in various self-luminescent devices, such as exit signs in buildings, aircraft dials, gauges,
luminous paints, and wristwatches. Tritium is also used in life science research, and in studies investigating the metabolism of potential new drugs.


Exposure to Tritium

How does tritium get into the environment?

Tritium occurs naturally in the environment in very low concentrations. Most tritium in the environment is in the form of tritiated water, which easily disburses in the atmosphere, water bodies, soil, and rock.

In the mid-1950s and early 1960s, tritium was widely dispersed during the above-ground testing of nuclear weapons. The quantity of tritium in the atmosphere from weapons testing peaked in 1963 and has been decreasing ever since.

Today, sources of tritium include commercial nuclear reactors and research reactors, and government weapons production plants. Tritium may be released as steam from these facilities or may leak into the underlying soil and ground water. However, such releases are usually small and are required not to exceed federal environmental limits.

A recently documented source of tritium in the environment is tritium exit signs that have been illegally disposed of in municipal landfills. Water, which seeps through the landfill, is contaminated with tritium from broken signs and can pass into water ways, carrying the tritium with it.

Tritium readily forms water when exposed to oxygen. As it undergoes radioactive decay, tritium emits a very low energy beta particle and transforms to stable, nonradioactive helium. Tritium has a half-life of 12.3 years. Current treatment of landfill leachates do not remove tritium.

How are people exposed to tritium?

People are exposed to small amounts of tritium every day, since it is widely dispersed in the environment and in the food chain. People who live near or work in federal weapons facilities or nuclear fuel cycle facilities may have increased exposure. People working in research laboratories may also come in contact
with tritium.

There are both natural and man-made beta emitting radionuclides. Potassium-40 and carbon-14 are weak beta emitters that are found naturally in our bodies.
Some decay products of radon emit beta particles, but its alpha-emitting decay products pose a much greater health risk.

Beta emitters that eject energetic particles can pose a significant health concern. Their use requires special consideration of both benefits and potential, harmful effects.

Key beta emitters used in medical imaging, diagnostic and treatment procedures are phosphorus-32, and iodine-131. For example, people who have taken radioactive iodine will emit beta particles. They must follow strict procedures to protect family members from exposure. Radioactive iodine may enter the environment during a nuclear reactor accident and find its way into the food chain.


How does tritium get into the body?

Tritium primarily enters the body when people swallow tritiated water. People may also inhale tritium as a gas in the air, and absorb it through their skin.


Does the way a person is exposed to beta particles matter?

Yes. Direct exposure to beta particles is a hazard, because emissions from strong sources can redden or even burn the skin. However, emissions from inhaled or ingested beta particle emitters are the greatest concern. Beta particles released directly to living tissue can cause damage at the molecular level, which
can disrupt cell function. Because they are much smaller and have less charge than alpha particles, beta particles generally travel further into tissues. As a result, the cellular damage is more dispersed.


What does tritium do once it gets into the body?

Tritium is almost always found as water, or "tritiated" water. Once tritium enters the body, it disperses quickly and is uniformly distributed throughout the body. Tritium is excreted through the urine within a month or so after ingestion. Organically bound tritium (tritium that is incorporated in organic compounds) can remain in the body for a longer period.

Tritium atoms can exchange with any hydrogen atoms. If the hydrogen atom is part of an organic molecule, the tritium becomes 'organically bound' and is transported with the molecule rather than moving freely like water.


What happens to inhaled radioactive materials?

Radioactive particles can lodge in the lungs and remain for a long time. As long as it remains and continues to decay, the exposure continues. For radionuclides that decay slowly, the exposure continues over a very long time. Inhalation is of most concern for radionuclides that are alpha or beta particle emitters. Alpha and beta particles can transfer large amounts of energy to surrounding tissue, damaging DNA or other cellular material. This damage can eventually lead to cancer or other diseases and mutations.



Exposure by the ingestion pathway occurs when someone swallows radioactive materials. Alpha and beta emitting radionuclides are of most concern for ingested radioactive materials. They release large amounts of energy directly to tissue, causing DNA and other cell damage.


Health Effects of Tritium

How does tritium affect people's health?

As with all ionizing radiation, exposure to tritium increases the risk of developing cancer. However, because it emits very low energy radiation and leaves
the body relatively quickly, for a given amount of activity ingested, tritium is one of the least dangerous radionuclides. Since tritium is almost always
found as water, it goes directly into soft tissues and organs. The associated dose to these tissues are generally uniform and dependent on the tissues' water content.


Are children more sensitive to radiation than adults?

Yes, because children are growing more rapidly, there are more cells dividing and a greater opportunity for radiation to disrupt the process. EPA's radiation protection standards take into account the differences in the sensitivity due to age and gender.

Fetuses are also highly sensitive to radiation. The resulting effects depend on which systems are developing at the time of exposure.


Beta Particle:

an electron or positron emitted by certain radioactive nuclei. Beta particles can be stopped by aluminum. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received.They also pose a serious internal radiation threat if inhaled or ingested.


What conditions lead to beta particle emission?

Beta particle emission occurs when the ratio of neutrons to protons in the nucleus is too high. In this case, an excess neutron transforms into a proton and an electron. The proton stays in the nucleus and the electron is ejected energetically.

This process decreases the number of neutrons by one and increases the number of protons by one. Since the number of protons in the nucleus of an atom determines the element, the conversion of a neutron to a proton actually changes the radionuclide to a different element.

Often, gamma ray emission accompanies the emission of a beta particle. When the beta particle ejection doesn't rid the nucleus of the extra energy, the nucleus releases the remaining excess energy in the form of a gamma photon.

The decay of technetium-99, which has too many neutrons to be stable, is an example of beta decay. A neutron in the nucleus converts to a proton and a beta particle. The nucleus ejects the beta particle and some gamma radiation. The new atom retains the same mass number, but the number of protons increases to 44. The atom is now a ruthenium atom.

Other examples of beta emitters are phosphorous-32, tritium (H-3), carbon-14, strontium-90, and lead-210.


GREENPEACE: What is tritium?

Radioactive water or water vapour. It’s not something in the water, but the water molecules themselves that are radioactive.

Tritium is the radioactive isotope of hydrogen. That means tritium is unstable and gives off radiation when it disintegrates. In the environment, the most common kind of tritium is tritiated water - that is, water molecules in which one (or both) of their hydrogen atoms is radioactive.

Is it dangerous?

Yes, tritium is hazardous when you drink it, eat it, breathe it in or you absorb it through your skin.

Tritium is not considered an external hazard, but is an internal one. It has a radioactive half life of about 12 years, which means it stays around in the environment for a long time. It has the unusual properties of extremely rapid transport in the environment, quick uptake by humans, fast exchange mechanisms with other hydrogen atoms, and the ability to bind with organic molecules during cell formation and cell metabolism.

What are the effects of exposure to tritium?

Radiation causes cancers, congenital malformations and genetic defects

Tritium is a radionuclide and all radionuclides when ingested or inhaled give off radiation. Radiation is known to be a carcinogen, teratogen and mutagen, and these effects are thought to occur down to the lowest possible exposures.

Why are tritium standards of specific concern in Canada?

Huge amounts of tritium are pumped into Lake Huron and Lake Ontario every day from Canada’s nuclear power stations. Huge amounts are released into the air, as well.

Tritium discharges from Canadian reactors are by far the largest in the world from civil nuclear power stations. They are 100s to 1000s times greater than tritium discharges from other kinds of nuclear reactors.

Should I be concerned?

The closer you live to a nuclear power station, the more you should inform yourself about tritium. Near them, all rivers, wells, vegetation and animals, including humans, have raised levels of tritium inside them.

Tritium emissions into the air result in all downwind matter containing hydrogen becoming tritiated to ambient levels. This results in people drinking, breathing and absorbing tritium-contaminated water, and eating tritium-contaminated food.

What is the Ontario Drinking Water Advisory Standards Council (ODWASC) asking for input on?

After the release of McGuinty government’s energy plan, which foresees spending over $40 billion on building nuclear reactors, the Toronto medical officer of health asked the Ontario minister of the environment to review provincial drinking water standards for tritium, a radioactive emission from Ontario’s nuclear plants.

After the public consultation, the ODWASC will make a recommendation to the Ministry of the Environment on revising tritium standards in Ontario.

Have Ontario’s tritium standards been reviewed in the past?

Yes, but the province ignored the committee’s recommendations because of pressure from the nuclear industry.

In 1992, the Ontario government requested its Advisory Committee on Environmental Standards (ACES) to enquire into this issue for setting an Ontario drinking water standard for tritium. The 1994 ACES report recommended immediate adoption of a 100 Bq/L standard, reduced to 20 Bq/L within five years.

The former Ontario Hydro alleged, however, that the standard recommended by ACES would cost billions to implement. As a result, the provincial government deferred to Hydro’s views and announced the current standard of 7,000 Bq/L.

Why did the (ACES) committee recommend tightening tritium standards?

The ACES committee reviewed the differences in approach to setting standards for toxins and radiation.

The current tritium standard corresponds to a risk of 350 excess fatal cancers per million people. On the other hand, the Canadian federal drinking water objectives for chemicals are set at levels that provide a lifetime risk of 1–10 excess fatal cancers per million people.

The primary reason for the difference is that the excess cancers predicted from radiation exposure are calculated by assuming one year’s consumption of drinking water: the lifetime risk is calculated as if that year of consumption were the only consumption. With chemicals, the assumption is that people consume the affected drinking water for their whole lifetime— commonly set at a 70-year exposure.

Why such a difference should exist is strange—it’s another example of the apparently favoured status of radiation in Canada.

This report concludes that official attitudes on tritium are unscientific and incorrect, that tritium’s hazardous nature should be fully acknowledged by radiation protection agencies in Canada, and that tritium’s dose coefficient should be increased substantially

<< Back to Previous Page