Richard writes:

<<Some plants are known
to aggregate selenium in toxic levels ("locoweed")>>

   I've never seen locoweed in the produce section of my natural food store.
But, there is plenty of kale, with naturally occuring fluorine.

<<Certainly there can be too many of a naturally occurring trace element in
water that can be dangerous. Too much arsenic may be naturally occurring but
toxic, for instance.>>

But the question remains is fluorine dangerous?  The answer is no, not in
normal trace organic mineral amounts.  Is fluoride dangerous?  You bet.

Siobhan