I can tell you this more ducks are injured using steel than if we were allowed to use lead in areas where ducks simply pass thru.
I'll second that. In my limited experience, steel shot injures (usually lethal) ducks far more than lead.
I suppose the lead has the potential to injure other game or fish, while steel just wounds the individual duck. Even so, it seems to me injury with steel shot is even more inevitable than ingesting lead.