I was curious about this too. From what I've read, the plastics should be safe - so I did a Google search. So far, I haven't found any links saying otherwise. It would depend on whether the bags were made with PVC or acetate.
I came across the "Scrapbook Preservation Society" Website (didn't know there
was such a place

) and thought this might help:
"What questions should I ask my retailer or supplier to ensure that a product is safe for preservation scrapbooking?
That depends on the product. The answer for adhesives wont be the same as for papers and wont be the same as for eyelets as for pressed flowers.
Papers - lignin-free, neutral sized, buffered, passes PAT
Plastics - PVC free, non cellulose (acetate or nitrate), preferably polypropylene, polyester, or polyethylene, passes PAT
Adhesives - passes PAT, no latex/rubber
Inks - pigment, fade-proof, waterproof, bleed-proof, lightfast, passes PAT
Embellishments - the questions to ask at this time are unknowneveryone must decide for her/himself if they are willing to risk using embellishments that one day may prove harmful to their photos and scrapbook creations"
It's an interesting site. Here's a link to their FAQ:
http://www.scrapbookpreservationsociety.com/faq.htm#16