If one were to handpick a career that guaranteed a safe work environment, librarian would seem a reasonable choice. A trio of books found at the University of Southern Denmark may have just upended that assumption as researchers discovered a possible toxic avenger from the Renaissance era. Experts were studying the three 16th- and 17th-century books in the university's library, scrutinizing the books' covers that Gizmodo explains had been pieced together from recycled medieval manuscripts (a common way to strengthen book bindings then). But Jakob Povl Holck and Kaare Lund Rasmussen were having trouble reading the text thanks to a thick layer of green paint, so they ran the books through an X-ray—and found the paint contained arsenic, a highly poisonous compound. "Could something like this happen in reality? Poisoning by books?" the two write for the Conversation.
At first the scientists thought the paint was used to make the book more visually appealing, though they soon ruled that out, as only portions of the covers were painted. Their new theory on the emerald-green coating: It was used to keep bugs and vermin from snacking on the books. Holck tells Gizmodo there was "no real danger" to himself or other researchers, as they'd been handling the books meticulously even before they discovered the arsenic. Still, Rasmussen tells Fox News that librarians should exercise caution when working with old books, making sure to wear gloves and to store tomes with green paint in dry, dark places (arsenic can convert to an airborne gas if exposed to light and humidity). These particular volumes are now stored in well-labeled cardboard boxes in a ventilated cabinet, the scientists say. (There's arsenic in many of the foods we eat, including rice and red wine.)