Re: non-combustion oriented volatilization

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

>HELP!!
>
>I am writing a paper on the various types of medical waste sterilization
>processes, and the biggest roadblock I've hit is this:
>
>Are dioxins (specifically PCDDs, not just any VOCs) volatilized from
>products which may contain PCDD residue (plastics, latex, bleached paper) IF
>THE ITEMS ARE NOT ACTUALLY BURNED?
>
>I am familiar with the formation of dioxins on the fly ash emitted from
>incinerators, but other processes such as microwave treatment and steam
>(autoclave) treatment operate at temps around 100 degrees C or less.
>While these processes seem to be ideal b/c there seem to be no emissions,
>it would be ill-advised to support them catagorically without knowing if
>they, too, pose a danger from dioxin exposure.
>
There are a number of considerations which make an answer difficult.
Consider the following:

Dioxins in the pure state sublime.  I have stored them in sealed vials, and
found them to have re-crystallized all over the inner surface of the vial
over a period of several months.  As the temperature increases, the rate of
sublimation will also increase.

However, if the dioxins are incorporated in a matrix, like plastic, or
fly-ash, they appear to be strongly bound, and are removed with difficulty
(reflux with hexane or methylene chloride only partially successful, reflux
with toluene or chlorobenzene much more successful).

Steam distillation, on the other hand, is an effective method for
extracting polar organics from various matrices, and while I have no
first-hand knowledge of steam distillation of dioxins, I would predict
that, if they are not bound to a matrix, they would be more mobilized by
steam distillation than in the absence of water.

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).

The relative importance of these factors should be weighed for each
situation.  Also, I assume that there are other considerations which did
not occur to me as I formulated this reply.



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