What is the CPSIA?

Yes and no. The testing requirement depends on the printing date. Books printed before 1985 may contain lead in the ink. At this point in time, the CPSC has recommended that libraries wait for further guidance on how to handle their pre-1985 collections.
Current testing recommendations would destroy library collections and XRF testing is recommended only [...]

Before 1985, book printers were permitted to use lead in ink.  Some books printed before 1985 therefore might contain lead in the ink (although most do not).  Because CPSIA’s requirements apply to the sale of any children’s item regardless of its date of manufacture, it is now illegal to sell used books unless it can [...]

Until the CPSIA, books have been largely unregulated.  In fact, the inclusion of books in the requirements of the CPSIA shocked the publishing industry. Under the law the way it is currently written, even self-publishers will have to have their books tested and provide test results, just like the books manufactured in the usual manner.
Used [...]