> Show me a causal chain

The article itself says that the theory that Rome fell due to lead poisoning is disputed. In fact they say these then recent findings are contradicting the theory. The exact quote you didn't seem to notice:

"The city's infatuation with lead pipes led to the popular (and disputed) theory that Rome fell due to lead poisoning. Now, a new study reveals that the city's lead plumbing infrastructure was at its biggest and most complicated during the centuries leading up to the empire's peak."

> or this is yet another a puff piece from Ars.

There is something particularly odious about complaining about the lack of intellectual rigour while showing none in the same comment.