more on ATSDR dioxin detoxification

[ttweed@wildrockies.org (Tony Tweedale)]

jon, in the doc. I have on this that I previously referenced, ATSDR states
that their 1 pg/kg/d oral acute & chronic MRL developed in '89, and the
subsequent 50 ppt screening level for PCDD/F in soils, is derived from a
reproductive study in rats (uncited!).  then it says: "Based on a review of
more recent literature, ATSDR scientists concude the MRL of 1 pg/kg/day is
approx. 2 orders of magnitude  below the noncancer health effects observed
in recent studies.  This is also true for cancer efffect studies."  I have
no idea how they reach this conclusion despite EPA's massive literature
review & subsequent "safe" (NOEL has not been established) dose of 0.006
pg/kg/d!!

the 1 ppt action level was derived from a "level of concern" identified in
kimbrough '84, which was based on the kociba  '78 rat cancer study (which I
believe still serves as the LOEL for PCDD/f for cancer, ie was confirmed in
EPA's '94 draft reassesment ... I think).  Somehow, ATSDR reconciles FDA's
10(-6) cancer risk level of 0.0057 pg/kg/d, also derived from kociba, with
their own screening level of 50 ppt (based on 1 pg/kg/d)!!

plus EPA & everyone else says cancer is not the most sensitive effect observed.



Tony Tweedale
Causality is a concept not subject to empirical demonstration.   -David
Hume (1711-'76)