Re: DIOXIN-L digest 698

[ttweed@wildrockies.org (Tony Tweedale)]

>From: "Jon Campbell" <jon@cqs.com>
>     The ATSDR is in the process of officially downgrading the toxicity of
>dioxin, by upgrading the maximum tolerable dose to
>1 picogram/kg/day. The EPA's dose limit is .006/kg/day.

I recently had the opportunity to bring this up at the draft RI/FS stage of
a penta wood preserving state superfund site here.  MT DEQ had not used
this MTD/MRL based dose but had used some other EPA one (that fell in
between) as a screening level determination (using ATSDR's criteria) for
PCDD/F in residential soils.

this was a confirmation that the old screening & action levels ATSDR was
using are still valid!  ie they reviewed the new literature & reconcluded
their old MRL dose of 1 pg/kg bw/d is safe!  it is based on one cancer
study, whereas the 0.006 dose is f'rom an exhaustive liter. review, and I'm
not sure the dose they seleceted is from tests that established a NOEL!

the draft ATSDR proposal was published in:  de rosa et al. 'Dioxin &
dioxin-like compounds in soil, ...' _J. Clean Techn., Env Tox & Occup Med._
6:2:117-163 (97).  it has a brief fairly frank discussion of EPA's 0.006
dose, but it didn't seem to affect their faculties...


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