Watch out for their pretty emerald green cover. This pigment, “Paris green”, also called Schweinfurt green, or even “Vienna” green, was used in the 19th century to tint cardboard, decorations or even the edges of books (a technique called marbling). Problem: it contains arsenic.

In Germany, the University of Düsseldorf closed its doors for several days in March to check the contents of its library, as reported by the daily Süddeutsche Zeitung.

Across the Rhine, several establishments have also closed their doors to check whether 19th century works do not contain arsenic and analyzes are also underway in Alsatian libraries, reports the daily Latest News Alsace.

Books likely to contain arsenic would not really present a risk in themselves “when they are placed on the shelves, but this may be the case if you moisten your fingers with your tongue to turn the pages”, warns the university in a press release. Another possible mode of contamination: inhalation of powder while handling books. In either case, it would be mainly repeated ingestion that would be problematic.

The symptoms of acute arsenic poisoning are listed by the World Health Organization: “vomiting, abdominal pain and diarrhea. Subsequently, numbness and tingling in the extremities, muscle cramps and, in extreme cases, death occur.”

The substance in question, the famous “Schweinfurt green” comes from a copper derivative. It became widespread in the 19th century for its low cost. Pretty and inexpensive, it was a hit and was found in large quantities in books, but also in clothes, paintings and even wallpapers… Already at the time, it was suspected of causing poisoning, such as this academic article details it.

In the United States, since 2019, a research project at the University of Delaware, the “Poison Book Project” (which could be translated as “poisoned book project”) aims to identify works containing arsenic and held in historical libraries around the world. Its database contains works in French.

The head of this project advises “not to throw away potentially poisoned works”, but to send them to conservators, as she explained to National Geographic. For their part, the librarians at the University of Chicago wanted to be reassuring: “all green books do not contain arsenic,” they wrote in a public note in 2023.