Toxicity of 99tc: Can it represent a risk to man?

The movement through the environment and the toxicity to plants of v c have been studied. However, information is scanty on Tctoxicity to mammals even though this is the decisive criterion for assessing the consequences of releases of Tc. A critical tissue could be the thyroid because of its preferential accumulation of Tc and the developing organism because of its greater radiosensitivity; moreover, this toxicity might be enhanced under conditions of a low iodine (I) diet. These questions were studied in rats given large amounts of 99Tc in either a normal or an I-deficient diet for several months starting 2 wk before mating. Newborns were continued on these diets after weaning. The parameters determined were: Occurrence of pregnancy and litter size, triiodothyronine and thyroxin in serum, uptake of 13’1 by the thyroid 24 h after injection, histology of the thyroid and concentration of Tc in tissues of the mothers and their descendants. Thyroid damage, as well as the effects on pregnancy, could be observed after amounts of 10 pg Tc g-I food. Iodine deficiency only slightly influences the v cto xicity. The chemical and radiological toxicity of v cto rats is small. Consequently, it seems unlikely that contamination levels in the environment would ever reach levels that could lead to serious non-stochastic effects, even in the developing organism.