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Does dioxin degrade in the environment??

  At 07:28 PM 7/31/97 -0400, jon@cqs.com  wrote:
  >Hello, folks,
  >There has been some discussion here about "natural"
  >dioxin formation from the burning of coal and oil.
  >There is a great deal of evidence that the burning of
  >does *not* produce any significant amounts of dioxin.
  >The studies
  >of older sediment have essentially ruled out the
  >"natural" production
  >of dioxin. There is essentially no dioxin in sediment
  >previous to 1940 (Czuczwa,  1984, 1985, 1986).
  The above assumes to some extent that  chlorinated dibenzo-dioxins will
  never degrade in the environment. 
  However, according to the articles below, that may
  not be necessarily the case.  This guy discusses
  a half-life of dioxins in soils at Seveso of 9.5 years, although
  photodegradation of chlorinated dioxins/furans would
  be unlikely to be a factor for buried sediments not 
  exposed to light (or contained in someones fat cells)..  
  As near as I can tell from other articles I've read, 
  PCBs are more stable and less susceptible to 
  degradation than chlorinated dibenzo-dioxins.   That is 
  why PCBs have been found to be recycling between
  atmosphere/water interfaces in the Great Lakes.
  In addition, I've heard
  about research at Michigan State University that 
  is examining the ability of naturally occurring
  white rot fungi to dechlorinate
  chlorinated dibenzo-dioxins.....
  On the issue of dioxin formation from the burning of
  coal, it is well known that such compounds can be formed
  in cement kilns that do not burn hazardous waste.  In fact,
  non-waste burning cement kilns are in the list of EPA's
  source catagories ranking dioxin emitters as I recall.
  Dioxins that form in such situations arise from the action
  of hydrogen chloride produced when inorganic chlorine
  in coal is burned, producing hydrogen chloride.  Hydrogen
  chloride in turn reacts with ordinary straight chain hydrocarbons
  commonly found in limestone or shale under the influence
  metallic catalysts to form chlorobenzenes and chlorinated 
  phenols.  These reactions occur downstream from the main
  combustion zone.
  The chlorobenzenes and chlorophenols in turn are available to participate in
  more catalyzed reactions to form chlorinated dibenzo-dioxins/
  Ecotoxicol Environ Saf 1989 Oct;18(2):149-164 
  2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) persistence in the Seveso
  (Milan, Italy) soil.
  Cerlesi S, Di Domenico A, Ratti S
  Department of Nuclear and Theoretical Physics, University of Pavia, Italy. 
  Preliminary results of a new study on TCDD environmental 
  persistence at Seveso (Milan, Italy) are presented. For this study,
  the most contaminated territory, Zone A, was divided into areas 
  to fractionate the available TCDD levels in soil into data sets
  with reduced value spreads. In addition, various time subsets 
  were defined for each area. Selected data were fitted with the
  exponential model y = y0.e-k.1. It was estimated that at least 
  1.2 kg TCDD was present in Zone A shortly after the accident.
  On average, a considerable portion (23%) of this amount lay 
  on vegetation; TCDD which was not photodegraded or
  volatilized before the heavy rains of fall 1976, was later washed 
  off and transferred to ground by water action. From this study,
  mean analytical underestimations affecting January 1977 and 
  March 1978 contamination map data were on the order of 30 and
  24%. All the above figures are considered optimistic. A few 
  years after the accident, mean TCDD half-life in soil appeared to
  be 9.1y (t1/2-95% CLs, 6.2-17y). 
  Science 1977 Mar 25;195(4284):1337-1338 
  Environmental degradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin
  Crosby DG, Wong AS
  Herbicide formulations containing known amounts of
   2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and exposed to natural
  sunlight on leaves, soil, or glass plates lost most or all of the 
  TCDD during a single day, due principally to photochemical
  dechlorination. Despite the known persistence of pure TCDD, 
  it is not stable as a contaminant in thin herbicide films exposed to
  outdoor light. 
  Abstracts with a considerable amount of 
  environmental content like these can be found on Pub Med....
  The price is right....  Free searching!!!
  Alex J. Sagady & Associates        Email:  asagady@sojourn.com
  Environmental Consulting and Database Systems
  PO Box 39  East Lansing, MI  48826-0039  
  (517) 332-6971 (voice); (517) 332-8987 (fax)