Re: non-combustion oriented volatilization

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

Since this is my nickel, I'll take a crack at an answer.  I apologise up
front for a lack of literature references, I'm composing this Sunday
afternoon.


>I have a couple of nagging questions. Your help would be appreciated.
>
>Louis Shadoff wrote:
>
>>Lastly, it is well established that UV light decomposes dioxins.  They must
>>be exposed to the UV light so that dioxins on the surface of a matrix are
>>destroyed, but those within the matrix are unaffected if it cannot transmit
>>the light (e.g. soil, fly-ash).
>
>What does (do?) the dioxins decompose TO when exposed to UV?
>
>At what rate do they decompose? Do they decompose so effectively that it is
>safe to emit them from power boiler stacks in pulp mills? (This is what a
>Risk Assessment in British Columbia Canada suggested.)
>

If they are decomposed, they are not being emitted.

>Secondarily, what does OCDD decompose to?
>

I don't know, specifically.  Se below.

>Delores Broten
>Delores Broten, Reach for Unbleached! Foundation
>Box 39, Whaletown British Columbia
>Canada, V0P 1Z0
>Ph/fax (604) 935-6992
>e-mail: dbroten@oberon.ark.com

UV light causes free-radical reactions to occur.  Initial attack is at the
carbon-chlorine bond.  If hydroxyl is present, for instance water, it
attaches forming the aryl-hydroxy compounds.  Once a chlorine in the 2,3,7,
or 8 position is substituted with non-halogen the toxicity drops
dramatically.  Alan Pohland, when he was at the University of Rochester
(New York) did screening tests on a multitude of substituted dioxins to
establish this finding.

Exposure long enough, causes complete decomposition to carbon dioxide,
water and HCl.  Phil Kearney of USDA, Beltsville did a micro-ecosystem
study of carbon radio-labelled 2,3,7,8-TCDD and found that as it moved
through the ecosystem it decomposed in the air forming, ultimately,
radio-labelled CO2.

The time for decomposition depends on the matrix, and its ability to expose
the dioxins to the light.  It also depends on the wavelength and intensity
of the light.  The toxic oil which caused all the problems in Missouri was
decontaminated by building a UV reactor on the site and recirculating the
oil through the reactor until the dioxins were no longer detectable.

An early study was done by Crosby on dioxins on the surface of leaves
exposed to sunlight.  He found a half-life on the order of hours, as I
recall.

In the lab, analytical standard solutions must be protected from room light
since, in clear vials, the concentration can drop a factor of two in one
month.  (A personal observation)




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