37 Because the uptake of strontium-90 is related to dietary calcium, and because the metabolism is complex, it is not possible to state what minimum “ quantity of strontium-90 would be lethal to man. Certuinly the animal studies show that at feeding levels many times higher than the ICRP maximm permissible body burden for humans (strontium-90) effects in animals are . a4fficult to detect. Question 5C Some nuclides have more, and same have less destructive energy per disintegration than strontium-90. Would a curie of tritium, for instance, be lethal? Answer 5C © Tritium, ingested as tritiated water, mixes with the total body water . and is comparatively rapidly excreted in urine, sweat, feces, and via the lungs with an effective half-life of 10-12 days. Although the physical half-life is relatively long, 12.4 years, the short effective half-life means that it does not remain in the body for a long period. The average effective energy of the beta particles per disintegration is 6 x 1073 Mev. Because of these factors, the total dose from a curie of tritium would not be expected to be lethal. Based on calculations published by the United Kingdom (Pub- lication AHSB (RP) R-20, 1962) the dose would be about 200 rems. approximately 90% would be received during the first month. purposes, Of this, For comparative total body gamma doses of 250 rems have been given to humans in cancer therapy. Question 5D Is there any radionuclide which would not be lethal if one curie were absorbed by a man?