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

[Henshel, Diane S.]

I think it behooves everyone to remember, while these numbers are being
thrown around, that these numbers are based on the cancer risk numbers.  As
Tony alluded to, the endocrine and developmental effects are likely to be
(well, appear to be) much more sensitive effects than cancer. 
Diane Henshel

	-----Original Message-----
	From:	Tony Tweedale [SMTP:ttweed@wildrockies.org]
	Sent:	Tuesday, January 04, 2000 2:06 PM
	To:	dioxin-l@venice.essential.org
	Subject:	[Dioxin-l] Re: Dioxin-l digest, Vol 1 #14 - 13 msgs

	>"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




	_______________________________________________
	Dioxin-l mailing list
	Dioxin-l@lists.essential.org
	http://lists.essential.org/mailman/listinfo/dioxin-l