100% Tritiated water has a dose factor of 0.000018mSv/kBq. Measurable immediate effects start at 500 mSv and a minimum dose of 8 Sv would be required for a reasonable guarantee of mortality with treatment (note that Tritium is very easy to flush out of the body - the recommended treatment if exposed is to drink as much beer as you can. Seriously.)But if you're the Soviets (or CIA or whoever else) trying to poison a dissident spy or other person of interest, you already have a source of tritium and hopefully an operating budget that can afford the cost of the tritiated water to kill this individual. This thread and some simple research shows that regular heavy water would at best make the target sick and not kill them since you have to replace a huge amount of their liquid intake with heavy water to make things lethal. My question is--is tritiated water more efficient, and to what degree?
That makes a reasonably lethal dose 8000/0.000018 = 4.45 x 10^8 kBq = 445 GBq of Tritium (4.45 x 10^11 Bq)
Now this isn't actually very much by weight - Tritium has a specific activity of 3.57 x 10^14 Bq/g so essentially 1 mg would be a potentially lethal dose. The problem is firstly that Tritium is very hard to get hold of in quantity - my previous job had 20g on site and was subject to regular IAEA audits and safeguards - and secondly that handling it is an absolute pig. In my previous job I was dealing with designs to shift quantities of a few grams of it around a plant and the level of containment required is astonishing - it'll go through pretty much anything, even forged stainless steel given time, and is exceptionally easy to detect. If you thought the Polonium trail left after they killed Litvinenko was obvious, you should see how easy it would be to trace a Tritium trail: it's detectable at 1 part in 10^18 atoms, and would get everywhere (when handling items potentially contaminated with it there would often be a Health Physics technician standing there to check I changed my outer gloves no less than every 10 minutes - any longer and it would go through them and potentially onto my skin).