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processes and food chains.
Some of these, such as strontium
90 have an especial affinity for the skeleton and thus pre~
sent a problem somewhat analogous to that of radium.
Fortunately, we have a growing mass of precise information
concerning the quantitative relations between ingested radium
and thorium and the subsequent development of bone pathology.
The most important result of the presence of excessive amounts of radium in the skeleton is the increase in
frequency of osteogenic sarcoma and it is presumed that the
most important gifect of the ingestion of considerable
amounts of Sr 7% would be tumor production.
The amount
required to produce such an effect is obviously considerable.
I estimate tnat the amount of such material now
present over the United States would have to be increased
by the order of one million times before an increased
frequency of bone sarcoma from this cause could be
recognized.
Genetic Effects:
Radiation may not only damage the somatic
cells but by acting upon certain stages of the germ cells
may give rise to alteration of the genes upon which inheritance depends.
It appears to be well established that
there is no definite threshold for this effect and that there
is a linear relaticnship between the frequency of the gene
changes and the total irradiation.
At the present time, it
seems that the rate at which the radiation is given is a
minor and perhaps negligible factor.
The quantitative studies have necessarily been
made with relatively high exposures varying from a minimum
of 50 roentgens with mice to a maximum of several thousand
roentgens in the case of the more resistant fruit fly.
Each species has its own range of sensitivity.
If one assumes that the linear relationship which
has been experimentally determined holds for all exposures
however small, then the extrapolation of the data leads to
the conelusion that a smali but finite probability exists
for gene mutations at the level of the radioactivity of the
natural environment.
That mutations do occur in all living
things is well established and indeed forms the basis for
all evolution.
At present, however, we do not know to what
extent the normal mutation frequency is caused by the radioactivity of the natural environment and what is due to other
factors.
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