The National Library of France has pulled four books from its shelves for the most unusual of reasons—they might be poisonous. As the AFP explains, this is not a metaphor. The 18th-century books have green covers believed to be laced with arsenic. It’s not clear how much of a danger the poison would actually pose to people handling the books, but the library is taking a better-safe-than-sorry approach. “We have put these works in quarantine and an external laboratory will analyze them to evaluate how much arsenic is present in each volume,” it says in a statement.

It seems that publishers in the Victorian era sometimes used arsenic to color book bindings, and this is not the first time tainted books have turned up in the world. Researchers at the University of Delaware have an ongoing project to identify books that used arsenic to achieve colors typically called Paris Green, Emerald Green, or Scheele’s Green (the latter for a chemist). For the record, the books now out of circulation in Paris are two volumes of The Ballads of Ireland by Edward Hayes, an anthology of Romanian poetry by Henry Stanley, and the 1862-1863 book of the Royal Horticultural Society. (More strange stuff stories.)