Indeed, and for a layman like me it even sounds quite plausible that this could be what is making people go "mad as a hatter": https://en.wikipedia.org/wiki/Erethism
Add to that that the routes of administration preferred by heaver users (smoking and injection) are also those that maximize the harms of mercury exposure.
Thanks! Only about 2-3% of their samples seemed to contain mercury though, so it is not as prevalent as I could fear. As far as I understand the report, the vast majority of P2P syntheses use a Leuckart reaction and so do not depend on a heavy metal containing reducing agent.
Add to that that the routes of administration preferred by heaver users (smoking and injection) are also those that maximize the harms of mercury exposure.