Re: EPA, risk and dose

[BLHamrick@AOL.COM]

Eric,



Your explanation below makes sense, because that amounts to choosing a

 different set of units to express the limits, but that does not jive with 

the

 EPA written guidance, which states, e.g., "No simple and direct conversion

 between radiation dose and radiogenic cancer risk is available...a given 

dose

 from one radionuclide via a given exposure pathway may present a much

greater cancer risk than the same dose from another radionuclide and/or

 exposure pathway...Therefore, any conversion between dose and risk must be

 performed on a radionuclide-and pathway-specific basis."



It seems to me, they are saying that the energy imparted to a given organ by

 one radionuclide being inhaled will not have the same effect as the same

 total energy imparted to the same organ by a different radionuclide that is

 ingested.  And, that's where they lose me.  The different effects of 

high-LET

 vs. low-LET radiation are built in via the quality factors to dose

 calculations, so that does not help the EPA's argument any.



If, instead, they are meaning to say that a different pathway and/or 

different

 radionuclide will impact different organs, that doesn't help their argument

 either, because that information also goes into the dose calculations.



Finally, they may be saying, without ever saying it, that the NRC's use of 

the

 CEDE does not adequately characterize the overall cancer risk, because the

 ICRP's normalization of the doses and effects is inadequate, but their own

 guidance contradicts that

possibility.



The only thing they can possibly be saying is that 100 rem to the thyroid 

from

 the inhalation of I-131 will not create the same risk of cancer as 100 rem 

to

 the thyroid from the ingestion of I-125, and that means they have some 

other

 idea about just what is causing the damage and/or risk.



Barbara L. Hamrick

BLHamrick@aol.com



In a message dated Thu, 29 Mar 2001 12:54:44 PM Eastern Standard Time,

 "Frohmberg, Eric"

<Eric.Frohmberg@STATE.ME.US> writes:



<< As I understand it, EPA's cancer slope factor has all the dosimetry

assumptions built into it.  There are some differences in the dosimetry

(which version of ICRP is used, etc.), but instead of taking an intake

(pCi/lifetime) and calculating a dose, they are simply calculating risk.

 And, of course, the risk estimates would change over time just as the dose

estimates would.>>









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