I don't have hard data on how many microns or percents of primer heavy metals are ending up in my gas tube or on my clothes or hands. But from what I know it's a nonzero amount and I take precautions accordingly like I would for any nonzero amount of heavy metals. Lead is cumulative, so every tiny bit adds up over the years.

If you don't think that's an issue for you, then rock on my friend. Keep doing it the way you want.