To answer the question, yes tritium is radioactive. Even from its definition, it clearly states that it is radioactive. So let’s take a look at what tritium really is; tritium is a beta-emitting radioactive isotope of hydrogen. It consists of two neutrons and one proton, which makes it three times as heavy as a hydrogen nucleus. Tritium wouldn’t be in existence in our environment if the cosmic radiation that produces it in the atmosphere is in small amounts. The unstable tritium nucleus has a half-life of 12.3 years, which is shorter if you were to look at it from the radioactive timescale. This comparatively fast disappearance means that only a little tritium can accumulate in a single space at a time.
The fact that tritium has a short life has resulted to it being classified as a highly radioactive element. But fortunately, this high activity is attenuated by some other properties in the decay process. On average, the energy of the emitted electrons tends to be super low, that is 5.7 keV, as opposed to the normal energy emitted during beta decay. And apart from the low energy electron, tritium emits no gamma ray at all.
Just like hydrogen, tritium is mobile in nature. It can combine with oxygen to form tritiated water, giving it the ability to easily get into the human body through the water cycle. Once tritium is inside your body, it leads to internal exposure, even though the element is eliminates from the body very quickly. One fact about tritium is that it has a biological half-life of 10 days which is far shorter when you compare it to the 12.3 years of its radioactive half-life. Only one nucleus of tritium out of the 650 total will decay while still inside the human body. And due to the low emission energy the trajectory of the beta electrons will not exceed a few microns inside the human body.
Tritium has a low radiotoxicity, which to dose factor in other words. And according to the WHO, the acceptability limit of tritium in the water is 10000 Becquereles per litre. The limit is pretty protective, as an individual should only drink 2 litres of such water in one day for a year if they are to be exposed to a dose of 0.1 mSv per in one year. So basically, as you have seen in the article, tritium is pretty much radioactive but it’s not at all dangerous to the body.