No question lead is toxic and remains so basically forever as it doesn't decompose. One pellet shot any time in the last century, when injested by a swan, kills it - happening right now up in Watcom county. But that's because the swan grinds it up in their gizzard.

After a century or so of lead broken off in the river, lead that migrated downward as it is heavier than most river rock and gravel, has had time to stew in the hyphoreic zone - basically the underground "river" that flows under the bed and interfaces with ground water, I would bet that we will start to see lead "hits" in adjacent wells. There is already a pretty toxic soup in much of our ground water, and this is just another contributer to it. Given enough time and freedom from environmental regulations, we will eventually foul our nest enough to kill us all. Probably good riddance, but sure wish we wouldn't take the rest of God's innocent creatures with us