In a message dated 2/2/98 10:17:15 AM, you wrote: >ATSDR states >that their 1 pg/kg/d oral acute & chronic MRL developed in '89, and the >subsequent 50 ppt screening level for PCDD/F in soils, is derived from a >reproductive study in rats Please pardon my ignorance, but what exactly is the importance of a "screening level" of 50 ppt? Also, is that in TEQ or as total PCDD/F?