Tritium is a radioactive isotope of hydrogen. It has the same number of protons and electrons as hydrogen but has 2 neutrons, whereas regular hydrogen does not have any. This makes tritium unstable and radioactive. Tritium is produced naturally from interactions of cosmic rays with gases in the upper atmosphere, and is also a by-product of nuclear reactors. Like all radioactive isotopes, tritium decays. As it decays, it emits beta radiation. The physical half-life of tritium is 12.33 years, meaning that it takes just over 12 years for tritium to decay to half of its original amount. As tritium decays, it changes to helium.
Tritium can be combined with phosphor to create glow-in-the-dark lighting such as exit signs, emergency lighting in buildings, and airport runway lights. It is also used as a tracer in biomedical research to study and diagnose heart disease, cancer and AIDS. In the future, it may also be used to generate electricity in fusion reactors. Where does tritium go? Small amounts of tritium are released to the environment, mostly from reactor operation and maintenance and during the manufacture of tritium light sources.
The most common form of tritium is tritiated water, which is formed when a tritium atom replaces a hydrogen atom in water (H2O) to form HTO. HTO has the same chemical properties as water and is odourless and colourless. Tritiated water has a biological half-life of 10 days, but in the body, a small amount binds to proteins, fat and carbohydrates with an average 40-day half-life.
Some of the tritium released into the environment can get into nutrients such as carbohydrates, fats or proteins. Tritium consumed in food (organically bound tritium) poses a slightly greater health risk, as the body retains it longer than tritiated water. This means the tritium atom is more likely to decay while in the body, possibly damaging cells. The body can repair this type of damage on its own.
Tritium is a relatively weak source of beta radiation, which itself is too weak to penetrate the skin. However, it can increase the risk of cancer if consumed in extremely large quantities. Tritium can enter the body through inhalation, ingestion or absorption through the skin. Most tritium leaves the body as tritiated water in urine, in breath as moisture and through perspiration. Most inhaled tritiated hydrogen gas is exhaled immediately.
The Canadian Nuclear Safety Commission (CNSC) sets limits on the releases of tritium and requires all Canadian nuclear operators to conduct and report on their environmental monitoring. The highest average annual tritium level measured in the drinking water of Canadian communities near nuclear facilities is about 18 becquerels per litre (Bq/L), well below Health Canada’s recommended drinking water limit of 7,000 Bq/L.