In article ,
The Natural Philosopher writes:
On investigation, you are right. Tritium is both light and radioactive,
It also has a half life measured in days, so poses very little hazard.

12.something years, according to

www.epa.gov/radiation/radionuclides/tritium.htm and

others: 4500+/-8 days.

Perhaps I should have said more exactly that 'any radioactive element
with a sufficient half life to actually be present and represent a risk
to health will be very heavy'

Tritium only occurs naturally AFAICT on account of cosmic ray
bombardment. It decays as fast as it is produced.

This will be a different kind of tritium, then, from the stuff in the Traser
key-tags in my pockets, will it? Ummm...
--
SAm.