EPA HEAST Table (April 2001) question

[SShafer1@AOL.COM]

I am posting this question for a friend.  Thanks for your help.







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Could someone offer an explanation as to why EPA cancer risk slope factors

in the most recent HEAST (April 2001) for external radiation exposure

scenarios (including ground surface deposition, volummetric soil exposure

and submersion) are significantly higher for some common gamma-emitting

radionuclides contained in the uranium and thorium decay chains?  Examples

include Th-232: 1995 HEAST - 2.0 E-11 and 2001 HEAST - 3.4 E-10; U-238+D:

1995 HEAST - 6.6 E-8 and 2001 HEAST - 1.1 E-7 (all units  are 1/yr per

pCi/g).  I've read through supporting documentation and can only guess that

the EPA risk coefficients have somehow been modified (I just can't find any

discussion) as part of the 2001 HEAST tabulation since it appears external

dose rate factors from FGR 12 are still the basis for the overall slope

factor.

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