[Dioxin-l] pcdd/f in penta -- clarification

[Tony Tweedale]

dr. schecter and others are correct; hexa-->octo congeners predominate in
pentachlorphenol, due to the degree of chlorination of the penta ring, and
how it di-merizes (forms 2 rings).  Despite thiis congener profile, on a
TEq basis, EPA's comprehensive 4/98 'Inventory of Sources of Dioxin inthe
U.S.' (external review draft) estimates 89.2% of ALL pcdd/f releases to the
env. in '95 are from penta (much to a v. localized soil environmnet, I
imagine)--25 *KG* TEq/yr!  This is what my referenced post months ago
said--possibly some confusion also came from other old posts of mine
repeating that older batches of 2,4,5-T herbicide had up to 1% total
dioxins, and 2,4,5-T is more enriched in TCDD.  (Note many sources are
totally left out of EPA's source assessment due to insuficent data, many
relating to PC production and disposal/incineration).  In sum then, though
not much penta TEq is released to air (or water) (my assumptions), a LOT is
nevertheless being put into the env.

Note that the only cancer assay for dioxins other than TCDD were performed
(by the NTP, v. thorough cancer assays) for the 2 common HxCDD isomers
common in penta.  -->>They turn out to be essentially as potent carcinogens
as TCDD, which resulted in EPA's 'safe " dose estimate of 0.01 pg/kg/d TEq.
This has received little publicity.  I agree w/ Jon or whoever said cancer
is a potent effect of dioxins that seems to be similar in different
species.  Certainly though we need to pay for more cancer asays on other
congeners and in other species!

I disagree cl is needed for drinking water disinfection--perhaps a little
to provide residual disinfection to the point of delivery--but a dose of a
much stronger oxidant like ozone, &/or filtration, is a widely used
technology.  Note that giardia cysts are resistant to Cl, but not O3.
---

>PCP contains higher chlorinated dioxins and dibenzofurans and usually little
>or no tcdd. -Arnold Schecter
>
>This might be found in the ATSDR Tox profile on pentachlorophenol.  Do you
>have access?  Andy

Tony Tweedale

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

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