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Next step is to warn librarians and readers of old books to wear protective gloves, and to advise libraries to store any green painted old books in a dry, dark environment out of harm’s way of people inhaling the air above the books, the reason for the latter recommendation is that arsenic has a tendency to transform to the airborne arsine (AsH3) given the right conditions of humidity and light. Besides the toxicity, arsenic is also carcinogenic.