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Re: Background Dioxin Levels?

  Dioxin is not natural in soil and there are still places where soil
  samples can be taken and the analysis will come back all non detects.
  One reference illustrating this is Jay Van Oostdam _Dioxins and Furans
  in the BC Environment_ (BC MoE 1995).  Many samples were taken in this
  study, and mostly around known sources, yet there were still non detects
  for all congeners.
  What is really meant by "background"?  How stable should the background
  be?  When looking at a single primary source, background can include
  all the dioxin slowly but continuously diffusing from all the other
  sources.  This may be used to justify increasing levels, but really,
  does it?
  Another point to watch when interpreting background is how non detects
  contribute to TEQ; nd=0, nd=0.5dl or sometimes a more complex procedure.
  When not much is being detected, and among few samples, this is quite
  significant.  Using nd=0.5dl, a backgound of 1 or 2 pg/g may be
  posited when there was no real detection.
  Philip Fleischer   philip@prcn.org