STEVE INSKEEP, HOST:

Now, it's not news that some people consider books to be dangerous. They can mean that in a negative way, as when communities try to contain books, get them off the library shelves. They can mean that in an ironic way, that ideas in this book are powerful, dangerous. Researchers at the University of Delaware have an entirely different reason to think that some books are dangerous.

LEILA FADEL, HOST:

The Poison Book Project is working to identify old books that contain toxic pigments like arsenic, which made Victorian-era books in the 1800s more eye-catching. Melissa Tedone is leading the project.

MELISSA TEDONE: In the case of this bright emerald-green pigment, it was the only really bright, intense, colorfast type of green that was available.

INSKEEP: Tedone says she was asked to treat an old book that had lost its front and back covers when she was struck by the book's vibrant binding. She'd been reading a book about 19th-century wallpaper at the time.

TEDONE: It was just one of those little moments where sometimes the thought floats through your mind, oh, this couldn't possibly be an arsenic-based pigment, could it?

FADEL: Turns out, it was. Since the project launched five years ago, Tedone's team has cataloged more than 300 books containing the pigment, a figure that's likely just a drop in the ink pot.

TEDONE: They were being bound in these giant binderies that had lots and lots of staff who were working assembly-line style. Some of the binderies that did produce these emerald-green books were producing thousands of book bindings a week.

INSKEEP: Wow. So what about toxic books that may be in libraries or even bookstores today? At Lipscomb University in Nashville, chemistry student Abigail Herman (ph) is working with university librarians to see if there are any such in their collection.

ABIGAIL HERMAN: The persistence of local book collecting within both public and private institutions is really a concern if they don't know exactly what they're exposing themselves to.

FADEL: Herman says there's not a lot of awareness around the issue. That's what Melissa Tedone at the University of Delaware hopes her efforts can help address.

TEDONE: We want to find ways that we can still give researchers and the public access to these books but do it in a way that we feel confident is going to keep everyone safe.

INSKEEP: Wow. Leila, I mean, this is one of those classic stories. It reminds me of the story about the radium watch dials - I mean, people in a different generation using something they didn't realize quite how hazardous it was at the time.

FADEL: Yeah. So who knows what the future generations will see that we're using that's hazardous?

INSKEEP: Oh. You know - I mean, that makes you humble, doesn't it?

FADEL: Yeah.

INSKEEP: I think about that sometimes, how will future generations view what we do?

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