Re: changing rad levels over time (2)

[Andrew Karam <karam.1@osu.edu>]

>Hello Mr. Karam,
>
>Many years ago (it must have been between 1978 and 81) I saw a review
>about available data on effects of low level radiation. It was published
>in Health Physics and the author came to the conclusion that the
>statistic significance of any single study was weak, but in sum they
>showed that slightly elevated dose rates were beneficial as they
>produced less cancer than normal or even "zero" doses. I had the
>impression that lower organized and older forms of life (algae, insects,
>...) showed higher resistance than newer and highly developed forms like
>mammals. This led me to the hypothesis that the optimum dose rate for an
>organism (equilibrium between harmful and beneficial effects) is that,
>under which it initially developed since this is the environment for
>which this being was constructed by evolution. Will this fit your
>calculations on rad levels in geologic time scales?
>

Mein Lieber Herr Weiss:

The latest UNSCEAR report (1996) gives some information on radiation
resistance of a variety of organisms.  One table in particular (I can't
remember the number, and my copy of the report is at work) shows
graphically the ranges of LD50 doses for differing classes of organisms.
With the exception of molluscs (which may be explained by the shielding
provided by their shells), these doses change according to the time at
which the types of organisms first appeared on earth.  I can only speculate
as to the reason for this because my academic background is in geology, not
biology, but my co-author is a paleontologist and is starting to look into
that a little more.  It is also intriguing to note that some of the more
slowly-evoloving species (such as the horseshoe crab) have low potassium
concentrations.  This is something else we have not had the time to look
into, but hope to in the future.  Unfortunately, we have no way of knowing
if ancient horseshoe crabs had similar K contents, so we can only speculate
about this, too.  Sigh....

Danke fur Ihren Anmerkung!

Andy
The opinions expressed above are well-reasoned and insightful.  Needless to
say, they are not those of my employer.(with apologies to Michael Feldman)


Andrew Karam, CHP				"The mind is not a vessel
karam.1@osu.edu				to be filled but a fire
						to be lighted." (Plutarch)
Ohio State University 
Radiation Safety Section
1314 Kinnear Road
Columbus, OH  43221
(614) 292-1284    	(614) 202-7002 (fax)