Background Dioxin Levels?

["Rebecca Leighton Katers" <cwac@execpc.com>]

  I was just told by an FDA policy person that 
  recent information shows that dioxin background 
  levels range from 2 to 3 ppt.
  
  This seemed awfully high to me, so I questioned
  him and asked if he meant background 
  in the food supply or natural background in the 
  soil --- and he said natural background in soil.
  
  He said that the 1 ppt limit for the chicken 
  recall and fish farms was simply their limit of detection, 
  not a regulatory number.  
  
  Can anyone recommend key documents which show natural 
  background levels are lower?
  
  Rebecca Leighton Katers
  Clean Water Action Council of N.E. Wisconsin
  2220 Deckner Avenue
  Green Bay, WI 54302
  Phone:  414-468-4243
  Fax:  414-468-1234
  E-mail:  cwac@execpc.com