RE: Ancient radiation levels were higher than today's levels

[Bernard L Cohen <blc+@pitt.edu>]

On Mon, 20 Dec 1999, Bradshaw, Keith wrote:

> 	Dear RADSAFERS
> 
> 	Implicit in these arguments about background radiation levels and
> the speed of evolution seems to be that background radiation is a
> significant cause of mutations compared to other mechanisms.  I read
> recently that every cell in our bodies averages 10000 DNA lesions per day
> (can anyone confirm/refute this?), and the cause was put down to free
> radicals as a result of food oxidation.
> 
> 	So my question is, what proportion of DNA lesions are caused by
> background radiation?  You can probably see my argument.  If radiation is
> responsible for 100%, then a doubling of the radiation dose might give a
> doubling of the evolution rate, but if it's responsible for only 0.1%, then
> doubling it might only give a 0.2% increase in the rate, which is surely
> indetectable.

	According to a forthcoming paper by Pollycove and Feinendagen,
chemical and thermal effects cause 150,000 single strand breaks and 200
double strand breaks per cell per day. By comparison, 10 rem of radiation
causes 200 single strand breaks and 4 double strand breaks per cell. If
double strand breaks are the source of cancer initiation, 10 rem of
radiation per year causes 4 double strand breaks per cell per year which
increases the number of cancer initiations by 4/200 = 2%. However,
according to linear-no threshold theory, 10 rem of radiation per year
increases one's cancer risk by 150% -- a very large discrepancy..
	I consider this to be one proof (among many others) that cancer
initiation by DNA damage is not the controlling factor in radiation
induced cancer, which destroys the logical basis for linear-no threshold
theory.


> 
Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


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