The National Library of France has quarantined four 19th-century books believed to contain arsenic.

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"We have quarantined these works and an external laboratory will analyze them to assess how much arsenic is present in each volume," the library said in a statement on Thursday.

The library identified the offending copies after US researchers discovered that chemicals were used to color book bindings in the Victorian era.

The arsenic-containing green pigments were called Paris green, emerald green or Scheele green in honor of a German-born chemist.

Researchers at the University of Delaware, who have tested hundreds of books for heavy metals since 2019, have compiled a list of potentially dangerous volumes as part of the "Poison Book Project".

16 MILLION BOOK COLLECTION

The French library found that its collection of more than 16 million books contained four copies of the books on the list.

These include Edward Hayes' two-volume The Ballads of Ireland, published in 1855, a bilingual anthology of Romanian poetry by Henry Stanley from 1856, and the Royal Horticultural Society's 1862-63 book.

The National Library of France said it would examine other green-covered books outside the Poison Book Project list.

The World Health Organization warns that long-term exposure to inorganic arsenic, especially through drinking water and food, can lead to skin lesions and skin cancer.