Re: non-combustion oriented volatilization

[DrBillC@aol.com]

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.)

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.

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.
 
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.

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.

I think this alll kind of hangs together.

Bill Carroll
Chlorine Chemistry Council