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Re: dioxin inventory stored in soil

  Sounds an attractive idea, but is there enough data for any sort of accuracy?
  Also,  presumably dioxin can end up much deeper in the soil, than the
  sampling depth (round here they sample to about 4" or 6" deep, I can't
  remember which it is).  Hence the "background" inventory calculated below
  would perhaps vastly underestimate the actual amount of dioxin stored in the
  soil. I bet the calculated amount would be enormous anyway, but has any work
  been done to see how dioxin levels tail off as you dig deeper, on average?  
  Presumably, this would be very highly dependent on what the land was used
  for - if it is farmland ploughed every year, for example, the dioxin would
  perhaps be evenly distributed to the depth of the ploughing, whereas land
  which is never dug would only have the dioxin buried through worm action?
  And how would you allow for land that has been built on for many years? -
  perhaps that would cancel out the "deeper than sample depth" effect.
  If it were possible to estimate how dioxin levels tail off with depth, you
  could get a better estimate of the real size of the soil dioxin burden
  across the planet.  However, have enough samples been taken, of "ordinary"
  areas, to make any generalisations about "average" soil levels at all
  accurate?  How accurate would the soil inventory actually be?
  At 15:45 27/08/97 -0400, Philip Fleischer wrote:
  >>According to Bill Farland of EPA speaking today at Dioxin '97, soil
  >>background levels across the US are ca. 20+/-6 ppt and that's what it will
  >>say when the reassessment issues.
  >To make this statement definitive, Bill Farland should describe sampling
  >methodology, including for example, 'depth'.  If we take the land surface
  >area of the US and Canada, and multiply by the depth, then using the
  >20 ppt we can arrive at our total background inventory of dioxin stored in
  >soil.  Should be an interesting number, the concept and origins of this
  >inventory are interesting too.  We can divide by population and attribute
  >per capita 'ownership' as well.
  >Philip Fleischer   philip@prcn.org