This piqued my curiosity and is something well outside of my normal hobbies/interests (conservation of old books or antiques, physical library spaces in general, etc), so I was curious who started it. Turns out the answer is Dr Melissa Tedone - Lab Head for Books & Library Materials Conservation at Winterthur Museum.

She had been reading a book about arsenic-containing wallpapers in Victorian-era England, and connected mental dots while examining a book entered into the museum with a microscope. Pretty fascinating stuff: https://www.youtube.com/watch?v=6jH1niN3NpU the backstory starts around the ~1:40 mark

I once took a course called "poisonous books", a survey of literature throughout history considered "dangerous" due to the ideas presented. This is far more literal!!

No doubt considered quite useful at the time for its naturally insecticidal properties...

Librarians might be exposed more, and the information on the page has a hint of MSDS-like paranoia, but I wonder how toxic it is in practice to the individual who may have a few of these on a shelf somewhere.

"Klaatu Barada Nikto"