I researched this extensively when working for the state health department a
few years ago. Here's what I found:

Lead is a mineral/metal. Mineral levels are stable in milk and are not
affected by mother's diet nor the maternal serum level of the substance.
However, if the mom's level is high, the baby may have more environmental
exposure also. Tap water used to prepare formula may have high lead levels,
especially if boiled.

The IQ difference deficit in lead-poisoned children is about 4 points. The
difference in IQ between premies fed formula and those fed Breastmilk is
TWICE AS MUCH - about 8 points. (Lucas study in Lancet).

Linda Smith, Dayton OH