Re: non-combustion oriented volatilization

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

>i'm learning a good deal from this discussion, but i have a recurring set
>of questions.  dr. shadoff wrote:
>

These are all really good questions, however, you've about reached the
limit of my willingness to speculate.  (It's sort of the difference between
guesstimates and SWAG [silly wild-assed guess]  :>)

>>Date: Sun, 4 Aug 1996 16:02:12 -0500
>>From: lshadoff@brazosport.cc.tx.us (Lewis A. Shadoff)
>>To: dioxin-l@essential.org
>>Subject: Re: non-combustion oriented volatilization
>
>>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
>
>arttaches at what rate, or rather how prferentially (in various environments)?

Since the carbon-chlorine bond is the weakest in the molecule, the rate of
scission of this bond is the fastest (as opposed to carbon-carbon or
carbon-oxygen).  That's as close as I can come to an answer.

>
>
>>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.
>
>how complete is this Rx, how fast, and in what environments doesn't it occur?
>

Dr. Kearney used radiation detectors to follow the movement of the
radio-labelled dioxin through the microecosystem.  All of the
radio-labelled carbon was accounted for as CO2 in his experiments.

>
>>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
>
>do photol. Rx form other pcdd/f's/other Ah-binding compounds
>preferentially?  to what extent do differnt pcdd/f photolize?
>
>>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.
>
>again, at what product did the Rx's terminate?
>

What Crosby studied was the disappearance of TCDD by measuring its
concentration, as I recall.  He didn't determine the products of the
reaction.  At that time, detection limits were low ppm - high ppb, making
the determination of reaction products extremely difficult.  Not many
people were willing to handle high concentrations/quantities of dioxins.

>
>>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)
>
>again, to what compounds?

I don't know.  I found this as part of the QC program for the lab which
checked the integrity of the standard reference materials used in the
determination of dioxins in environmental samples.

>Cold Mountain, Cold Rivers
>Box 7941  Missoula Montana USA 59807
>406-728-0867 phone & fax
>cmcr@ism.net

Lew



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