Decaying food and wet paper are very likely to be contaminated with fungi. Many of the fungi found on food and wet paper produce enzymes capable of breaking down cellulose and other strengthening components of paper. Recycled paper is not treated in any way that kills the fungal spores. Any treatments used to destroy fungal spores would be expensive or potentially dangerous for users of the recycled paper products. Any spores that make their way into recycled paper products would ultimately germinate and decay the product or could contaminate anything packaged in the product.