[Dioxin-l] Re: Dioxin-l digest, Vol 1 #14 - 13 msgs

[Tony Tweedale]

>"A single McDonalds hamburger has 100 picograms of
>dioxin in it, the EPA max dosage is 0.7 picograms for
>an ADULT."
>
>Pretty upsetting if true.  What's the source of this
>number?
>
>Andy

>That figure is in the updated EPA Dioxin Reassessment (not yet published).
>The original data is in the 1994 EPA dioxin reassessment, and summarized in
>the book "Dying From Dioxin" by Lois Gibbs. At the time, the EPA max
>allowable dose was 0.006 picograms per kg of body weight, so a 70 kg person
>was supposed to have a max dose of 0.4 pg. That figure has been pushed up to
>0.01 pg/kg , probably as a result of industry pressure.
>
>Jon Campbell
----

US EPA upped its "acceptable" daily dose of the dioxin-like PCDD/FF/PCBs
from 0.006 to 0.01 pg/kg of  bw/d in its '94 draft risk reassessment, which
was the collaboration of most of the world's dioxin experts and many top
toxicologists.  Several industries had asked then EPA Admin Reilly to
reassess the risk of dioxin.  They believed the cancer risk to be lower
than EPA then did, based on some toxicologists review of the pathology
organ microscope slides of the dioxin cancer in rodents study that EPA used
to set its ambient H2O quality criteria (EPA's 1st and only dioxin risk
assesment and relying on cancer effects only, until the one Reilly agreed
to, the one we're all still waiting to be finalized).

In the reassessment, EPA and many outside experts agreed the basic
dose/cancer risk curve (slope) derived from this rodent assay was
essentially correct..  The acceptable dose was upped a bit based on this
collaborative assessment of the pathoplogy slides--I don't know the details
that decision relies on.  It is certainly possible EPA upped the allowable
cancer dose for political reasons, tho this part of the reassessment was
done purely by scientists, as I understand it.

See _Science_ 1991 p. 624-6 (Feb something) for a news story of these
pre-reassesment thoughts.  The slide review combined w/ the new knowledge
that all dioxin's known effects are mediated by the Ah receptor, so
apparantly the thinking on the part of EPA toxicologist Linda Birnbaum, Don
Barnes (of EPA's Science Advisoy Board, now the SAB's chief staffer),
Michael Gallo of Woods Johnson, and others was that there is a threshold
for ALL dioxin's effects.  I.e., some were using the industry
toxicologist's claim that the slides show there is a dioxin dose cancer
threshold (below which cancer doesn't occur) and the Ah-mediation theory to
claim that there is a threshold for all effects.  Several thousand
receptors were thought to have to be filled to initiate action.  At the
Banbury Conference were much of this occured, prelimanary calculations
showed an acceptable daily dose to be 1-3 pg/kg/d--100 to 300 times more
than what EPA ended up picking (and of course for other effects, the "safe"
dose is indicated o be lowere, tho not enough is known yet).  U. MD's Ellen
Silbergeld was cautioning not to adopt a threshold model so quickly, that
receptor intricacies demand a more cautious approach.  In sum, it'd be more
interesting to know the pathology slide details that led EPA to conclude
0.01, not 1.0 pg/kg/d is right; than to know why  they went from 0.006 to
0.0`1 pg/kg/d.

This is what lead to the request for EPA to reassess dioxin's risk.  As we
know, EPA for the first time ever included cumulative doses in assessing
risk and and used the Ah mediated toxicity concept to develop detailed risk
assessments for as many effects as the existing literature allowed.  Its
draft conclusion, aside from essentilly confirming its orginal cancer risk,
is that we are exposed to much more dioxin-like ccompounds than is safe--ie
roughly in the range that is known to cause effects.  See deVito et all in
an issue (Jan I think) of the '96 _Env Health Perspectives_ for a complete
review of these risks.

Of course, since then, the literature has continues to grow, and more is
known about these various effects risk, and about other effects of dioxins.
No one has yet been able to capture the full risk (all the toxins) of the
new environment we live in.  it's not one we evolved in, which was, e.g., a
creosote-filled one, in which we learned to use the Ah receptor (creosotes
are aryl hydrocorbons) to bind creosotes and hydroxylate (add an -OH group)
to make them more water soluble & excretabale in urine).  But, as someone
posted a couple weeks ago, dioxin--quite indestructable, as most O-halogens
are--uses Ah to travel to the chromosone and sit on genes, modulating god
knows how many genetic functions].  Endocrinologists such a Frederick
vomSaal have shown that some hormones are more potent at vanishingly small
soses than at higher doses--somehow, too many hormones floods and shuts off
the supply of recceptors, it is thought (this effectivly puts paid for now
the claims of some here that we can reduce  levels of dioxin to acceptable
ones.  So, while the effects literature grows, EPA diddles (us), by
refusing for political reasons to update or release the reassessment.
dirty sh*ts.

Tony Tweedale

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

Temperate but endangered planet.  Enjoys weather, northern lights,
continental drift.  Seeks caring relationship with intelligent life form.
      -Friends of the Earth