I think the prof should mind his own business.  The decision is up to the
mother.  The nerve of his/her saying "wean or drop", especially the wean
part.  She takes the responsibility and s/he keeps mouth shut.  You get
exposed to as many volatile compounds just walking outside in a city for
goodness sakes.  Like all chemicals and drugs, yes, some will get into the
milk, but since the concentration in the mother's blood is likely to be
quite low, the baby will get only smidgens.

Jack Newman, MD, FRCPC