The traditional answer of 476 is interesting for things that didn't happen in 476:
* The capital of the Roman Empire wasn't sacked, nor was the capital of the Western Roman Empire sacked.
* The last claimant of Augustus of the Western Roman Empire wasn't killed. (Although the imperial court in the Eastern Roman Empire didn't recognize his claim).
* No vestiges of Roman rule, such as the Roman Senate, ended.
* Contemporary political discussions didn't feel that a major event or break in history had happened.
* Archaeological evidence doesn't point to a major break in the economic conditions or the material record of the era (that would come later, with the Plague of Justinian).
Of course, many pedants will come out saying that the Roman Empire really fell in 1453, because that it is when the Ottomans sacked Constantinople. But again, why 1453?
* Why not 1204, when the Latin Empire sacked Constantinople and ruled from there for 60 years?
* Why not 1461, when the Empire of Trebizond (another rump state of the Byzantine Empire created by the sack in 1204) fell to the Ottomans?
* Or indeed, why not 1475, when the Principality of Theodoro, itself the rump state of the Empire of Trebizond, also gave in to the Ottomans?
* Or 1460, when the Despotate of Morea--the last part of the Byzantine Empire supposedly conquered by the Ottomans--was disestablished as a tributary state by the Ottomans?
* Indeed, it's worth pointing that the last Byzantine Empire had to have his accession to the throne confirmed by the Ottoman Emperor of the time (Murad II)--the Byzantine Empire by the 1440s was itself basically an unruly tributary state of the Ottoman Empire.
So going back to the article's question, if lead poisoning is supposedly one of the reasons for the fall of the Roman Empire, which fall of which Roman Empire are they talking about, and why didn't it contribute to the not-falling of the contemporary not-exactly-the-Roman-Empires running about?