Comment by jandrewrogers

That is an accurate summary of the literature as I remember it. Arsenic has been replicated in a bunch of animals including non-mammals. It seems to generalize well and the background is substantive. There are also plausible hypotheses for mechanisms of action. The assumption is that a common effect across a sufficiently diverse set of animals applies to humans, which is probably a good heuristic.

The evidence for lead is much more sparse. It is interesting, and plausible, but without more evidence it is more of a curiosity. For better or worse, there has been zero interest in investigating that anomaly further. People should avoid lead exposure regardless.

Thankfully elements like mercury never show up in these studies. Nothing in my chemistry training suggests that mercury by nature could ever be anything but toxic to life and the evidence seems to support that. It would be weird to find out that was wrong, though I would accept it with sufficient evidence.