Re: non-combustion oriented volatilization

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

>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.)
>

There have been two rather definitive studies on wood burning indicating
that dioxins are produced from the wood itself.  One by Nestrick and
Lamparski burned wood that Lamparski had growing on his farm in a
wood-burning stove.  (No record of pesticide use).  The other is by Chris
Rappe (Sweden) who gathered wood from a forest far from any human activity
and burned it in the lab.

>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....)
>

Ah, if it were only true.  Unfortunately, the dioxins in fly-ash (soot) are
incorporated internally.  Sunlight cannot penetrate to decompose the
dioxins.  I suppose it wouldn't hurt, though.

>Would churning up dioxin-contaminated beaches expose the dioxins to
>sufficient sunlight to lead to decomposition?
>

Again, the UV light must reach the dioxins; soil is opaque.  If churning up
the soil creates dust, then the people doing the churning may be exposed to
dioxins by breathing the dust.

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

The dioxins in water are all on particulates (opaque to UV).  One can
determine the dioxin content of water by filtering through a 0.3 micron
filter and analyzing the filtered material.  More than 95% of the dioxins
are recovered this way.  If you are now thinking that filtering potable
water is the solution, there are some difficulties to overcome.  The
filters plug after a few gallons of water pass through, and the
back-pressure rises to unworkable levels.  The filters are expensive, as
well.

>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.
>

The vapor pressure of PCBs are much higher than dioxins, and they can
therefore achieve higher air concentrations.  UV light probably does
decompose a significant portion, but some must certainly survive.  Think of
what a half-life means.  If it is, for example, 1 day, then half is gone
the first day.  The next day half the remaining is gone, the next day half
of the remaining, and so on.  The time to get to the last molecule is
rather long.



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