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

["Bjorn Cedervall" <bcradsafers@hotmail.com>]

>	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 think that it may be important to consider the types of DSBs and also how 
they are detected (a DSB detected by some assays may biologically be 
recognized and repaired as 2 SSBs). A DSB handled by the topoisomerase II 
system is well defined whereas DSBs caused by ionizations probably & usually 
are not "clean" and more of ruptures that differ from DSB to DSB (abasic 
sites, at least two SSBs, base damages in different combinations and with 
different spacial relationships).

Bjorn Cedervall  bcradsafers@hotmail.com
PS. My own thoughts only.
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