Brent,
Lead is one of the heaviest elements. When it is shot in a swamp of mud it will most probably sink into the mud. Duck's eat water borne grass, crustaceans, and other vegetation. How are waterfowl going to ingest something that's immersed in the mud whilst in pursuit of water borne food? Furthermore, if they accidently take it into mouth why not spit it out? The idea that waterfowl are ingesting something that is not natural to them seems peculiar.