> Millions of dollars are spent on determining the lethal doses of
>these compunds (LD-50).

        This is a measure of acute (i.e prompt) toxicity only.  Of greater
concern generally are delayed effects   -  cancer, malformations _in
utero_, mutations, and some mental effects (where applicable).


>there is a
>concentration at which dioxin is not dangerous, just as there is an amount
>of salt which is poisonous to a human being.

        With a few if any exceptions, no threshold (safe dose) has been
shown for any agent causing those types of delayed harm.
        The notorious 'dioxin' is soluble in water to the extent of only
0.2 ppb, but at that "less than one person in China" level in a standard
plant-cell culture causes severe harm e.g bits of chromosome floating free
in the cytoplasm.  We have no evidence of a no-effect dose for mutagens
such as this.
        A good book is S S Epstein  The Politics of Cancer.


>There is also a word for inordinate fear of an item: superstition.
>Perspective is what I am talking about, and to have that, one must be
>informed.

        Political misuse of fear evoked by unwarranted alarms has largely
replaced in the media any duty to present authority, reliable fact, or
informed opinion.  I complained about this in a public debate (about GM)
last Sat, naming some of NZ's main poseuses who have thus usurped expert
status; nobody showed any sign of dispute.

R