Re: non-combustion oriented volatilization

[dbroten@oberon.ark.com (Delores Broten)]

Thank you very much for your answers. Of course, now there are more
questions. I hope there are not too many for your patience. 

Does this breakdown-in-sunlight mean that the dioxin from forest fires is
NOT MAINLY from dioxin deposited on leaves? (My sick mind also immediately
whispers that maybe ozone depletion has an 'UP' side.) 

Would it imply that incineration of dioxin-contaminated wastes should only
occur during bright sunlight? I am thinking that at night the dioxins would
not be exposed to UV and would have time to get buried in soil. (Of course,
you can't turn a pulp mill on-and-off like that, but in theory....) 
 
Would churning up dioxin-contaminated beaches expose the dioxins to
sufficient sunlight to lead to decomposition? 

Could this mean that people with dioxin in their water should have UV
treatment systems attached to their taps? Would it help? 

Does this UV decomposition also apply to PCBs? If yes, what about the
circulation by re-volatilization of PCBs and other POPs to the Arctic? I
think that is an accepted model now. I had thought the model also applied to
dioxins, but perhaps I misunderstood. 

Thank you, Delores 

>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
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