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

[david bell]

Below is correct; EPA regulates an acceptable daily dose (TDI) as 0.01pg/kg 
of TEQ. However, as Tony says, there is quite a bit of interest in this 
figure and how you arrive there. For example, the WHO says 1-4 pg/kg should 
be the TDI, and the UK government says 10 pg/kg should be the TDI (see 
http://www.doh.gov.uk/pub/docs/doh/pcddfish.pdf for references). All of 
these agencies use the same data, are trying to get the same safety level, 
so it is surprising to see such divergence of TDI figures.

I suspect that part of the difference is due to the long half-life of TCDD 
in humans, at 7 years (2000+ days), versus twenty-one days in rat. This 
introduces a scaling factor of 100.

I think EPA has known for a long time that average intake of dioxin TEQs is 
1 pg/kg/day- about 100 times greater than the set TDI. ( see 
http://www.epa.gov/ncea/docs/food99.wpd). It is not clear that it would be 
possible to reduce TEQ exposure to the EPA recommended guidelines.

cheers
david



> >"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

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com