39
Question 6
-
Is it accurate to say that, ounce for ounce and gram for gram, radioactive
substances are a million times more harmful to life than any other environ-
v mental pollutants?
If not, what is a reasonable comparison?
Answer 6
Table I shows that for most radioisotopes the mass required to produce
short term toxic effects may be greater than that required for some chemical
toxins .
On the other hand, Table II shows that, for severe long term effects
which eventually result in death, the mass required for the most effective
radiocarcinogens (radiation sources that produce tumors) is much less than
that required for the more effective chemical carcinogens; the radiation
sources would appear to be as much as 100,000 or more times more effective
on e gram basis.
These large ratios do not apply to the more common and
important radioisotopes such as tritium, cesium-137, or strontium-90, which,
as the following discussion points out, may not be more effective ona
|
gran basis than potent chemical agents.
There.is very great interest in determining the body burden levels that
“induce subtle long term effects, although at present there is little experi-
mental data available in mammals.
A simple proportional interpolation of
high level burdens is probably not valid because it appears that many radiatic
effects exhibit threshold properties; that is, radiation doses below a
threshold level produce essentially no detectable effect,
The present
explanation for this response is that cells are capable of repairing many
forms of radiation damage provided the exposure is delivered at a low enough
rate.
The existence of similar repair mechanisms which protect cells from
chemical carcinogens or mutagens (mutation producing agents ) is not well