Philip Poburka on thu 19 oct 00
Was just thinking...'soils' are usually aerobic, and rather
'living'...'clay' deposits are anaerobic and rather inactive/stable...this
may have some bearing on probable or actual 'half life' of Dioxins, or other
compounds.
I am not sure just what is meant by 'half life' in this context- does it
mean volume of measureably presence resulting from 'decay' from 'migration'
or from what mechanism of diminution?
Phil
On my 2nd or 3rd 1/2 life
here 'in'
Las Vegas etc
------Original Message------
From: Cindy Strnad
To: CLAYART@LSV.CERAMICS.ORG
Sent: October 18, 2000 3:25:57 PM GMT
Subject: Re: Dioxins'half-life
You're always so tactful, Bass.
Okay, that makes sense.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Smart girl, Cindi!!!,
You said:
"If the dioxin has a half-life in soil of around 10 years (you said,
"greater" than
10 years, but that doesn't sound like 100,000 years at any rate), then the
dioxins in ball clay are likely to be a fairly recent addition. Not the
result of ancient deposits".
I said:
"In soil TCDD has an extremely long half-life time, greater than 10 years".
This statement was used by Lennart Hardell M.D. PhD. in Carl Zenz's
Occupational Medicine, last edition. This information was published by
italian authors after the Seveso accident in Italy in "Accidental exposure
to dioxin".
Now if we accept Michael Bank's hypothesis on the presence of dioxins
in certain clay deposits, and I think we should (his being quite better than
mine):
"I didn't refrain just to be nice Edouard... :) I was surprised and a
little unsettled to hear that dioxins could occur naturally in kaolinitic
clays. And a little sceptical to be honest. But then geologists once
thought plutonium didn't occur in nature, but now it appears to be there,
quite naturally.
Apart from your forest fire theory, another feasible source of
polychlorinated organic compounds (including dioxins and PCB's) could be
nearby coal beds. These are known to be rich in reactive aromatic compounds
such as phenols which could combine with the chlorine in naturally trapped
brine to produce the super carcinogens. Many fireclays and china clays are
closely associated with coal seams. The close association of coal with
white clay beds is genetic. Kaolinitic clays are often produced in
feldspathic rocks in contact with the coal by the strong acids which are a
by-product of the coalification process. Carcinogenic organic compounds
like the phenols, must migrate away from the coal into clays.
Michael Banks,
Nelson,New Zealand"
then we may think that dioxins are migrating into clay deposits
from neighboring coal seams on a more or less continuous basis.
Later,
Edouard Bastarache
Dans / In "La Belle Province"
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
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pedresel on thu 19 oct 00
Philip is right to wonder about "half life" in this context. It's a
huge approximation wrapped around a bunch of assumptions. Unfortunately
it often reflects the reality that we don't know much and it is the best
we can do.
First: The rate of degradation will depend on environmental conditions
so he is absolutely correct that aerobic vs anaerobic can have a huge
effect. This is obviously true when you are talking about
biodegradation because some bugs thrive under aerobic conditions and
some don't. So you really have to define what degradation mechanism you
are talking about.
Second: A "half life" implies that you are talking about first order
degradation. Simply that means that it is like radioactive decay. Half
the amount present will decay in a certain amount of time. There is no
particular reason to believe this will be the case. There is no reason
to believe that the conditions will stay the same so it would be true.
But the real system is often so complex and the experimental data so
limited that that's the best approximation anyone can make. It could be
hugely in error for conditions other than where it was measured.
In general, listed half-lives only relate to decay, not migration.
Hope this helps.
-- Evan in W. Richland WA who is wondering why he is seeing very few
geese this fall.
Philip Poburka wrote:
>
> Was just thinking...'soils' are usually aerobic, and rather
> 'living'...'clay' deposits are anaerobic and rather inactive/stable...this
> may have some bearing on probable or actual 'half life' of Dioxins, or other
> compounds.
>
> I am not sure just what is meant by 'half life' in this context- does it
> mean volume of measureably presence resulting from 'decay' from 'migration'
> or from what mechanism of diminution?
>
> Phil
>
> On my 2nd or 3rd 1/2 life
> here 'in'
> Las Vegas etc
>
> ------Original Message------
> From: Cindy Strnad
> To: CLAYART@LSV.CERAMICS.ORG
> Sent: October 18, 2000 3:25:57 PM GMT
> Subject: Re: Dioxins'half-life
>
> You're always so tactful, Bass.
>
> Okay, that makes sense.
>
> Cindy Strnad
> Earthen Vessels Pottery
> RR 1, Box 51
> Custer, SD 57730
> USA
> earthenv@gwtc.net
> http://www.earthenvesselssd.com
>
> Smart girl, Cindi!!!,
>
> You said:
>
> "If the dioxin has a half-life in soil of around 10 years (you said,
> "greater" than
> 10 years, but that doesn't sound like 100,000 years at any rate), then the
> dioxins in ball clay are likely to be a fairly recent addition. Not the
> result of ancient deposits".
>
> I said:
>
> "In soil TCDD has an extremely long half-life time, greater than 10 years".
> This statement was used by Lennart Hardell M.D. PhD. in Carl Zenz's
> Occupational Medicine, last edition. This information was published by
> italian authors after the Seveso accident in Italy in "Accidental exposure
> to dioxin".
>
> Now if we accept Michael Bank's hypothesis on the presence of dioxins
> in certain clay deposits, and I think we should (his being quite better than
> mine):
>
> "I didn't refrain just to be nice Edouard... :) I was surprised and a
> little unsettled to hear that dioxins could occur naturally in kaolinitic
> clays. And a little sceptical to be honest. But then geologists once
> thought plutonium didn't occur in nature, but now it appears to be there,
> quite naturally.
> Apart from your forest fire theory, another feasible source of
> polychlorinated organic compounds (including dioxins and PCB's) could be
> nearby coal beds. These are known to be rich in reactive aromatic compounds
> such as phenols which could combine with the chlorine in naturally trapped
> brine to produce the super carcinogens. Many fireclays and china clays are
> closely associated with coal seams. The close association of coal with
> white clay beds is genetic. Kaolinitic clays are often produced in
> feldspathic rocks in contact with the coal by the strong acids which are a
> by-product of the coalification process. Carcinogenic organic compounds
> like the phenols, must migrate away from the coal into clays.
>
> Michael Banks,
> Nelson,New Zealand"
>
> then we may think that dioxins are migrating into clay deposits
> from neighboring coal seams on a more or less continuous basis.
>
> Later,
>
> Edouard Bastarache
> Dans / In "La Belle Province"
> edouardb@sorel-tracy.qc.ca
> http://www.sorel-tracy.qc.ca/~edouardb/
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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