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Re: Does dioxin toxicity increase in the environment??

  I've always wondered if the more toxic congeners 
  of PCBs, furans and dioxins might be accumulating while 
  the total levels appear to be dropping.
  In the Lake Michigan region, agencies claim progress is 
  being made because PCBs have dropped dramatically 
  since the 1970s.
  But the more toxic PCBs accumulate in the fatty 
  layers of aquatic wildlife in Lake Michigan, and 
  as one organism dies another eats its body.   Is 
  it possible that this cycling and storage 
  mechanism actually protects and preserves the 
  most dangerous chemicals, while the less toxic 
  types are exposed and degraded by the elements?   
  Is it possible that the actual toxicity of the total remaining 
  chemicals in the Lake Michigan food chain is actually 
  much higher now and will continue to grow?
  If this is true, and the other speculation about 
  less toxic congeners degrading into more toxic 
  congeners is true  --- then progress will be even 
  more difficult.
  Does anyone know of research data on this?
  Date:          Sat, 2 Aug 1997 07:35:10 -0400 (EDT)
  Reply-to:      alanwatson@gn.apc.org
  From:          Alan Watson <alanwatson@gn.apc.org>
  To:            Multiple recipients of list <dioxin-l@essential.org>
  Subject:       Re: Does dioxin toxicity increase in the environment??
  My earlier post was incomplete and lacked these references - sorry:
  Some work has been done on photolytic degradation to potentially more 
  toxic congeners by:
  Miller, G.C., Herbert,V.R. Mueller, M., Mitzel, R., Zepp, R.G. (1989).  
  Photolysis of octachlorodibenzo - p- dioxin on soils: Production of 
  2,3,7,8 - TCDD.  Chemosphere, 18,1265
  Bueser, H.R. (1976) Preparation of qualitative standard mixtures of 
  polychlorinated dibenzo-p-dioxins and dibenzofurans by ultraviolet and 
  irradiation of the octachloro compounds. J. Chromatography., 129,303.
  Bueser, H.R. (1979) Formation and Identification of tetra- and 
  pentachlorodibenzo-p-dioxins from photolysis of two isometric 
  hexachlorodibenzo-p-dioxins.  Chemosphere,4,251.
  Whilst these tend to be accelerated lab studies with high UV input it 
  seems plausible that similar reactions could take place in the 
  environment over longer periods of time.
  Could it be possible, for example, that an increase in TEQ in the 
  environment  could explain some of the discrepancies between current 
  emission and deposition inventories?
  If this does happen how can you possibly regulate dioxin emissions on a 
  TEQ basis - the limits would be meaningless in real terms.
  Any comments on this would be greatly appreciated!
  Best wishes
         _\\|//_                Alan Watson C.Eng                  
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