Re: non-combustion oriented volatilization

[lshadoff@brazosport.cc.tx.us (Lewis A. Shadoff)]

>To the list:
>
>There's more on decomposition of these materials as well.
>
>1)  UV light does decompose dioxin-like materials; an even more powerful
>decomposer is hydroxyl radicals (Hites, ES&T, earlier this year).  The
>mechanism is dechlorination, and the most reactive materials (those that go
>away fastest) are the most toxic (tetra more reactive than penta, etc.)
>

Just as an aside, Ron Hites is one of Klaus Biemann's students (MIT).
Klaus is one of the foremost mass spectroscopists, and pioneered (among
other things) the use and acceptance of GC-mass spectrometry data of body
fluids, in conjunction with Mass. General Hospital, to identify the
possible drugs in patients who arrived unconsious.  I met Ron when he was
there.

>2)  Curiously, the fingerprint of dioxins emitted from various sources does
>not match the fingerprint in soil or in animal fat.  In other words, the mix
>of congeners changes from, say, an incinerator to the grass a cow eats.  The
>EPA's Science Advisory Board recognized this and suggested that EPA modify
>its transport models to reflect the different chemical and physical natures
>of different congeners.  One of those chemical natures is reactivity.
>

Animals selectively retain the 2,3,7,8-isomers.  This is in accordance with
the receptor theory of toxicity.  The stereochemistry of the
2,3,7,8-containing isomers fits in a biological receptor which normally
accepts something else.  Other isomers do not fit and are excreted.

Prof. Otto Hutzinger (Germany) fed fly-ash to fish and demonstrated this
selective retention.  The 2,3,7,8-isomers were not the most prominent in
the fly-ash, but were the most prominent in the fish.  It also demonstrated
that fish could extract the dioxins from a medium to which they are
strongly bound.

The rate of chemical, UV, etc. degradation is also probably isomer
specific, but may not necessarily favor the 2,3,7,8-isomers.  It depends on
the specific degradation process.

>3)  Mike McLachlin at Bayreuth, who knows this stuff pretty well, believes
>that tetras mainly reside in the atmosphere, and octa mainly resides on soil.
> Reactions that remove dioxin take place mainly in air, not on particles, as
>Dr. Shadoff points out.
>

It makes sense that the more volatile isomers would move into the vapor
state much faster than the less volatile.  The vapor pressures are quite
low, though.  When 2,3,7,8-TCDD is put on the direct probe of a mass
spectrometer at 10-6 torr, the spectrum is weak.  OCDD must be heated to be
seen in the spectrometer at all.

>4)  All that said, it means that thinking only of the reactivity for a
>minute, these processes would tend to remove tetras and pentas from the air
>(e.g., environment) and leave mainly the octa and hepta on soil.
>

This doesn't jibe with Barry Commoner's recent statement.

>5)  EPA notes that soil all looks pretty much alike whether you're 1000 yards
>from the Columbus MSW Incinerator (whose reputation is well known) or
>isloated in Nebraska.  Mainly octa with some heptas and less hexa.
>

That is for incineration (combustion) sources of dioxins.  If the source is
2,4,5-T, then the major isomer is 2,3,7,8-TCDD. (There is no OCDD in
2,4,5-T)

>I think this alll kind of hangs together.
>
>Bill Carroll
>Chlorine Chemistry Council



Lewis A. Shadoff BS, PhD, Lake Jackson, Texas