Tritium

Tritium is a radioactive isotope of hydrogen with 2 neutrons and 1 proton in the nucleus. It decays to form the daughter nuclide helium-3 and emits low-energy beta radiation. Tritium has a physical half-life of 12.3 years. "Tritiated" water (HTO) is a form of water in which the hydrogen atoms are replaced with tritium.

If tritiated water is absorbed by the human body, it undergoes metabolic processes just like normal water and is quickly excreted again. It has a biological half-life of around 10 days. There is no enrichment via the food chain.