systematic treatment of the relative internal hazards of the elements
found in radioactive fall-out material.
Consideration of the problem
has led to the conclusion that the bone seeking elements are the ones
most likely to be the major cause of hazard for long-term internal
effects.
The comparison of the various elements produced included the
following parameters in calculating relative effect.
1.
Fission yield
2.
Natural decay constant (A, in Table 7)
3.
Biological elimination constant 0, » in Table 7)
4.
Oral absorption, %
5.
Deposition fraction in bone
6.
Average energy of emitted particles and relative biological
effectiveness.
For comparative purposes, Table 7 has been compiled on the
basis of metabolic data taken primarily from the work of J. G.
Hamilton2l/ to show the approximate relative internal hazards posed by
various radioisotopes found in bomb debris.
This table indicates that within a short time after detonation
strontium-89, strontium-90, and barium-140 are relatively comparable in
their effects.
As time passes, however, strontium-90 becomes increas-
ingly important and by the end of the first year it is the most important element to consider in hazard evaluations.
Maximum Permissible Concentrations of Radioisotopes.
Radio-
active isotopes are damaging agents to humans, apparently without
threshold effect, when one considers genetic damage and possibly without threshold for carcinogenesis except for the fact that low doses
may have a latent period greater than the human life span.
In a true
biological sense, therefore, limits of acceptable damage must be set
and the amounts of material which will not exceed these limits determined.
37/
Hamilton, J.G., The Metabolic Properties of the Fission Products
and the Actinide Elements, Rev. Modern Physics 20:718, 1948.
97