So if the mother avoids all possible AL (uses iron or SS pans, no canned goods, not in any products etc) I would say it would be an extremely low transfer rate. The body does not make AL, right? So it's from our environment/food/lifestyles in the world now. A lot of people are informed though and avoid it at all costs/as much as possible.
Even if it has some AL it's still the healthiest thing for our human infants/children. Lord knows what in formula/cow's milk these days (GMO's, hormones, puss, blood, etc?)